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This is to certify that the
dissertation entitled

CHARACTERIZATION OF ARSENIC, CHROMIUM, AND
COPPER RELEASED FROM CHROMATED COPPER
ARSENATE TYPE C (CCA-C) - TREATED SOUTHERN PINE

presented by
Weining Cui

has been accepted towards fulfillment
of the requirements for the

Doctoral degree in Forestry

MM

Major Professor’s Signature
7 / I 6/ 04
Date

 

 

MSU is an Affirmative Action/Equal Opportunity Institution

 

 

 

 

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PLACE IN RETURN BOX to remove this checkout from your record.
TO AVOID FINES return on or before date due.
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DATE DUE DATE DUE DATE DUE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

2/05 c:/ClRC/Dato0m.lndd-n15

 

CHARACTERIZATION OF ARSENIC, CHROMIUM, AND COPPER RELEASED
FROM CHROMATED COPPER ARSENATE TYPE C (CCA-C) - TREATED
SOUTHERN PINE
By

Weining Cui

A DISSERTATION
Submitted to
Michigan State University
in partial fiJlfillment of the requirements
for the degree of
DOCTOR OF PHILOSOPHY
Department of Forestry

2004

 

ABSTRACT
CHARACTERIZATION OF ARSENIC, CHROMIUM, AND COPPER RELEASED
FROM CHROMATED COPPER ARSENATE TYPE C (CCA-C) — TREATED
SOUTHERN PINE
By

Weining Cui

Toxicological review of arsenic, chromium, and copper indicated that the toxicity
of arsenic (As), chromium (Cr), and copper (Cu) is strongly affected by both the exposure
level and their oxidation states. Arsenic and the hexavalent form of chromium are known
human carcinogen. Trivalent chromium is essential to human health. In a short term low
dose exposure, trivalent inorganic arsenic is more potent than pentavalent arsenic.

Commercial chromated copper arsenate type C (CCA), and CCA with water
repellent (WR) treated southern pine boards were exposed in the field and the
dislodgeable solids were collected on a monthly basis. A method using test tube brush
wiping accompanied with water spraying was selected to collect the dislodgeable solids
for characterization. Using atomic absorption spectroscopy, As, Cr, and Cu were detected
in the solids collected from both CCA and CCA/WR treated wood after an acid digestion.
The composition of elemental As, Cr, and Cu in the solids were less than 4 wt.%. Higher
amounts of As, Cr, and Cu was collected from the wood surface at the initial stage of
field exposure and decreased rapidly after three months. The addition of the water
repellent reduced chemical loss from wood at the initiation of field exposure. After 15
months similar levels of As and Cu loss were found in CCA and CCA/WR treated wood.
The loss of Cr from CCA/WR treated wood remained lower than that from CCA treated

wood.

Environmental scanning electron microscope (ESEM) study indicated that the
solids mainly consisted of wood splinters with small chemical deposits. The particle Sizes
of the chemical deposits were mostly less than 10 um, the size of wood splinters were
between 10 and 100 um. Energy dispersive x-ray analysis (EDXA) found similar
elemental compositions in dislodgeable solids collected from CCA and CCA/WR treated
wood. Arsenic, chromium, copper, iron, calcium, potassium, chloride, sulfur, silicon,
magnesium, sodium, carbon, and oxygen were detected in the solids. After 7 months of
field exposure, contamination by sand or soil in the field was observed in the solids by
comparing their x-ray diffractograms before and after a field exposure.

As, Cr, and Cu from the dislodgeable solids partially solubilized in water (pH 3,
4, 5, and 6) during a 168-hour test. The solubilization of As, Cr, and Cu was increased
with time, and presented to be pH dependent at various time frame. The addition of a
water repellent to CCA wood treatment significantly increased the proportions of As, Cr,
and Cu solubilized from the dislodgeable solids. Both AsV (H2ASO4') and As‘" (H3AsO3)
were solubilized from the dislodgeable solids. Asv was the dominant form in water
during the first 24 hours. A significant decrease in the proportion of Asv and increase in
As!" were found after 168 hours. Larger amounts of soluble CrVI was found with the
solids from CCA/WR treated wood than those in solids from CCA treated wood.

Both Asv and As"I were detected in the leachate of CCA-treated wood in a 558-
hour leaching. About 70-90% of total arsenic was found as AsV and 10-30% as As'" in
the first 270 hours. The concentrations of total arsenic, Asv, and Asm presented to be

time dependent.

To mum, dad, and my husband Jianguo, for their love, support, and understanding

iv

ACKNOWLEDGEMENTS

I would like to express my sincerely appreciation for Dr. D. Pascal Kamdem, my
advisor, for inspiring guidance, encouragement and supporting me through my graduate
study at MSU. A publication such as this would not be possible without his advisory and
assistance.

Thanks to Dr. Karen Chou, for helping me to make the great transition from a
student to a scientist. I am greatly impressed by her professional, ethical, and scientific
characteristics. 1 would not have been so confident in presenting what I have learned and
what I have thought in front of public without the encouragement from her. Dr. Chou has
not only been a great mentor, but a friend with whom I could personally talk with. I
appreciate all I have learned from her.

I am much obliged to Dr. Eugene A. Pasek, for his resourceful knowledge in
wood preservation, his intelligent insights into this study, and his valuable suggestions
and comments, which makes this dissertation greatly improved from the draft.

Thanks to Dr. Mel Koelling for his invaluable suggestions in this study, and his
kindness support to young scientists.

Special thanks to Dr. Thomas C. Voice and Dr. Lisveth Flores del Pino, for
proving their newly developed arsenic speciation method while the patent process
pending, and providing the graphite furnace atomic absorption spectroscopy for arsenic
analysis, which is critical in fulfill the objectives of this study.

Thanks to my colleagues Pascal Nzokou, Haihong Jiang, Kyle Wehner, Joe

Pennock, for their help in the lab.

The USDA 2002-34158-2697 CSREES, under the Michigan State University
Eastern Hardwood Utilization program provided funding for this research. The continued

financial support throughout my research program is gratefiilly acknowledged.

vi

TABLE OF CONTENTS

List of tables ...................................................................................................................... x
List of figures .................................................................................................................. xii
Chapter 1 Introduction ..................................................................................................... 1
1.1 Overview .......................................................................................................... 1
1.2 CCA preservatives ........................................................................................... 1
1.3 Statistical data on CCA-treated wood .............................................................. 4
1.4 CCA-treated wood and the environment ......................................................... 4
1.5 Current status of CCA-treated wood ................................................................ 5
1.6 Toxicity of arsenic, chromium, and copper ..................................................... 6
1 .7 Objectives ......................................................................................................... 7
Chapter 2 Literature review - arsenic, chromium, and copper in the environment
and their toxicity .......................................................................................... 10
2.1 Arsenic ........................................................................................................... 10
2.1.1 Arsenic exposure ....................................................................................... 10
2.1.2 Arsenic toxicity .......................................................................................... 13
2.2 Chromitun ...................................................................................................... 16
2.2.1 Chromium exposure .................................................................................. 17
2.2.2 Chromium toxicity ..................................................................................... 20
2.3 Copper ............................................................................................................ 22
2.3.1 Copper exposure ........................................................................................ 23
2.3.2 Copper deficiency in human ...................................................................... 25
2.3.3 Copper toxicity .......................................................................................... 26
2.4 Environmental regulation of arsenic, chromium, and copper ........................ 27
2.4.1 National wide ............................................................................................. 27
2.4.2 Michigan .................................................................................................... 28
Chapter 3 Collection of the Dislodgeable Solids from Chromated Copper Arsenate
Treated Southern Pine ................................................................................. 31
3.1 Introduction ................................................................................................... 3 1
3.2 Material and Methods .................................................................................... 35
3.2.1 Dislodgeable solids collection for collection methods comparisons ......... 35
3.2.2 Dislodgeable solids collection for characterization ................................... 38
3.2.3 Analysis ..................................................................................................... 43
3.3 Results and Discussion ................................................................................... 46
3.3.1 Instrumental detection limits of elemental arsenic, chromium, and copper
by using FAA and GFAA .......................................................................... 46
3.3.2 Comparisons of the dislodgeable solids collecting methods ..................... 47
3.3.3 Dislodgeable solids collected from CCA and CCA/WR-treated southern
pine ............................................................................................................ 52

vii

3.3.4 Arsenic, chromium, and copper in CCA and CCA/WR-treated southern

pine ............................................................................................................ 56
3.3.5 Chemical redistribution of arsenic, chromium, and copper after 15 months
of field exposure ........................................................................................ 60
3.3.6 Arsenic, chromium, and copper redistribution in CCA and CCA/WR-
treated southern pine in field exposure ..................................................... 62
3.4 Conclusions .................................................................................................... 67

Chapter 4 Environmental Scanning Electron Microscope and X-ray Diffractometry

Characterization of the Dislodgeable Solids .............................................. 69

4. 1 Introduction .................................................................................................... 69
4.2 Instrumental analysis ...................................................................................... 71
4.2.1 ESEM-EDS ................................................................................................ 71
4.2.2 XRD ........................................................................................................... 72
4.3 Results and Discussion ................................................................................... 74
4.3.1 ESEM-EDS ................................................................................................ 74
4.3.2 XRD ........................................................................................................... 80
4.4 Conclusions .................................................................................................... 87

Chapter 5 Solubilization of Arsenic, chromium, and Copper from the Dislodgeable

Solids ............................................................................................................. 90
5.1 Introduction .................................................................................................... 90
5.2 Arsenic speciation .......................................................................................... 91
5.3 Chromium speciation ..................................................................................... 94
5.4 Material and Methods .................................................................................... 94
5.4.1 Dislodgeable solids solubility study protocol ............................................ 96
5.4.2 Total arsenic, chromium, and copper solubilized from the dislodgeable
solids .......................................................................................................... 98
5.4.3 Speciation of arsenic solubilized from the dislodgeable solids - selective
ion-exchange measurement of AsV and Asm .......................................... 100
5.4.4 Ultraviolet visible (UV-vis) spectroscopy analysis of hexavalent chromium
(Crw) in water ......................................................................................... 103
5.4.5 Statistic analysis ...................................................................................... 104
5.5 Results and discussion ................................................................................. 104
5.5.1 Speciation of chromium solubilized from the dislodgeable solids .......... 104
5.5.2 Water soluble arsenic, chromium, and copper in the dislodgeable solids
................................................................................................................ .108
5.5.3 Proportions of water soluble arsenic, chromium, and copper in the
dislodgeable solids .................................................................................. 119
5.5.4 Speciation of arsenic solubilized from the dislodgeable solids ............... 122
5.6 Conclusions .................................................................................................. 13 1

Chapter 6 Speciation of Arsenic in the Leachate of Chromated Copper Arsenate

(CCA) Treated Southern Pine .................................................................. 133
6.1 Introduction .................................................................................................. 133
6.2 Material and Methods .................................................................................. 134

viii

 

6.2.1 Commercially prepared CCA-treated southern pine ............................... 134
6.2.2 Laboratory prepared CCA-treated southern pine .................................... 134
6.2.3 CCA treating solution and wood treatment ............................................. 135
6.2.4 Chemical retentions in CCA-treated wood .............................................. 135
6.2.5 Laboratory accelerated leaching test .......................................... 135
6.2.6 Atomic absorption spectroscopy (AA) measurement of arsenic, chromium,
and copper ........................................................................ 136
6.2.7 Speciation of Cr‘" in the leachate ............................................................ 137
6.2.8 Speciation of arsenic in the leachate ........................................................ 137
6.2.9 Statistic analysis ...................................................................................... 138
6.3 Results and discussion ................................................................................. 138
6.3.1 Elemental arsenic, chromium, and copper in the treating solutions and
treated wood ............................................................................................ 138
6.3.2 CrVl and elemental arsenic, chromium, and copper in the leachate of CCA-
treated wood ............................................................................................ 139
6.3.3 Speciation of arsenic in the leachate ........................................................ 145
6.4 Conclusions .................................................................................................. 153
Chapter 7 Conclusions ................................................................................................. 155
Appendices .................................................................................................................... 160
Bibliography ....................................................................................... 201

ix

Table 1-1.

Table 2-1.

Table 2-2.

Table 2-3.

Table 2-4.

Table 3-1.

Table 3-2.

Table 3-3.

Table 3-4.

Table 3-5.

Table 3-6.

Table 3-7.

Table 3-8.

Table 3-9.

Table 5-1.

LIST OF TABLES

The weight percentage composition of CCA preservatives type A, B and C

....................................................................................................................... 3
LD50 values of arsenic, chromium, and copper compounds ....................... 15
Toxicity values of arsenic, chromium, and copper ..................................... 18
National wide environmental regulation of As, Cr, and Cu ........................ 29
General cleanup criteria and screening levels of As, Cr, and Cu in soil and
groundwater, Michigan ............................................................................... 30
Weather condition on the day of the dislodgeable solid collection ............. 40

Determination of the detection limits of As, Cr, and Cu by using FAA ..... 48
Determination of the detection limit of As by using GFAA ....................... 49

Arsenic, chromium, and copper collected from CCA treated southern pine
by using the glove-on-hand wiping, the paper wiping, and the test tube
brush wiping methods ................................................................................. 50

Arsenic, chromium, and copper collected from CCA treated wood surface
using various methods ................................................................................. 53

Dislodgeable solids collected fiom CCA or CCA/WR treated southern pine
during the field exposure ............................................................................. 54

Comparison of elemental As, Cr, and Cu contents in the l-mm surface layer
of CCA treated wood and in the dislodgeable solids .................................. 59

Arsenic, chromium, and copper contents (%) in CCA and CCA/WR treated
southern pine before and after 15 months of field exposure ....................... 61

Arsenic, chromium, and copper losses after field exposure - comparisons of
values from this study and J in and Preston (1993) ...................................... 63

Concentration of Cr“ in dissolving water (pH 3, 4, 5, and 6) and the
corresponded percentage (%) of CrVI in total chromium from the
dislodgeable solids .................................................................................... 106

Table 5-2.

Table 5-3.

Table 5-4.

Table 5-5.

Table 5-6.

Table 6-1.

Table 6-2.

Table 6-3.

Table 6-4.

Table 6-5.

Table 6-6.

Table 6-7.

Percentage (%) of soluble arsenic, chromium, and copper in total arsenic,
chromium, and copper form the dislodgeable solids ............................... 112

Weight percentage of soluble As, Cr, and Cu in the dislodgeable solids and

the corresponded atomic ration of As: Cr: Cu ......................................... 120
Arsenic speciation of standard Asv and Asm solutions ........................... 123
Speciation of arsenic solubilized from the dislodgeable solids ............... 125

Distribution of arsenic species solubilized from the dislodgeable solids 127

Weight gain of southern pine blocks after CCA treatment and the selection
of treated blocks for the leaching test ...................................................... 140

Arsenic, chromium, and copper in CCA-treated wood ........................... 141

Percentage of leached element in CCA-treated cubes in a 558-hour
leaching ................................................................................................... 145

Percentage of Asv and Asm in the leachate from CCA-treated cubes 149

One-wa ANOVA analysis of significant difference of total arsenic, ASV,
and As in leachate of commercially CCA-treated wood collected at
various time interval ................................................................................ 150

One-wa AN OVA analysis of significant difference of total arsenic, ASV,
and As1 in leachate of laboratory CCA-treated wood collected at various
time interval ............................................................................................. 151

Comparison of arsenic speciation in CCA treated wood ........................ 153

xi

Figure 1-1.
Figure 3-1.
Figure 3-2.

Figure 3-3.

Figure 3-4.

Figure 3-5.

Figure 3-6.

Figure 4-1.

Figure 4-2.

Figure 4-3.

Figure 4-4.

Figure 4-5.

LIST OF FIGURES

CCA exposure through residential use of CCA-treated wood .................. 8
Deck built with CCA treated wood ......................................................... 41
Seasonal weathering report of Lansing, Michigan, USA ........................ 42

The sectioning scheme of CCA and CCA/WR treated southern pine for
the chemical redistribution study ............................................................ 44

Arsenic, chromium, and copper collected from (A) CCA, (B) CCA/WR
treated southern pine using DI water during field exposure ................... 57

(A) As, (B) Cr, (C) Cu distribution in CCA treated southern pine with no
field exposure and after 15-month of field exposure, and (D) the
earlywood and latewood distributions in wood sections ......................... 64

(A) As, (B) Cr, (C) Cu distribution in CCA/WR treated southern pine
with no field exposure and after 15-month of field exposure, and (D) the
earlywood and latewood distributions in wood sections ......................... 65

ESEM images of dislodgeable solids collected from CCA-C treated
southern pine, (A) before field exposure at (1) 300><, (2) 1000><
magnifications; and (B) after field exposure at (l) 300><, (2) 1000><
magnifications ......................................................................................... 75

ESEM images of dislodgeable solids collected from CCA-C/WR treated
southern pine, (A) before field exposure at (1) 300X, (2) 1000><
magnifications; and (B) after field exposure at (1) 300><, (2) 1000><
magnifications ......................................................................................... 76

EDS spectrum of the dislodgeable solids collected from CCA-C treated
southern pine, (a) before the filed exposure, (b) after 7 months of field
exposure .................................................................................................. 77

EDS spectrum of the dislodgeable solids collected from CCA-C/WR
treated southern pine, (a) before the filed exposure, (b) after 7 months of
field exposure .......................................................................................... 78

XRD diagrams, (A) CCA-C treated southern pine before field exposure,
(B) CCA-C treated southern pine after field exposure, (C) untreated
southern pine ........................................................................................... 81

xii

Figure 4-6.

Figure 4-7.

Figure 4-8.

Figure 4-9.

Figure 4-10.

Figure 5-1.

Figure 5-2.

Figure 5-3.

Figure 5-4.

Figure 5-5.

Figure 5-6.

Figure 5-7.

Figure 5-8.

Figure 5-9.

Figure 5-10.

XRD diagrams, (A) CCA-C/WR treated southern pine before field
exposure, (B) CCA-C/WR treated southern pine after field exposure, (C)
untreated southern pine ........................................................................... 82

XRD diagram of the dislodgeable solids collected from the surface of
CCA-C treated southern pine: (a) before field exposure, (b) after 7
months of field exposure, (c) sand .......................................................... 84

XRD diagram of the dislodgeable solids collected from the surface of
CCA-C/WR treated southern pine: (A) before field exposure, (B) after 7
months of field exposure, (C) sand ......................................................... 85

XRD diagrams, (A) solids from CCA-C treated southern pine leachate,
(B) solids from CCA-C/WR treated southern pine leachate, (C) CCA
preservative ............................................................................................. 86

XRD diagrams of CCA main ingredients, (A) CuO, (B) CrO3, (C)
A8205 .............................................................................. 88

Structures of arsenate and arsenite .......................................................... 93

pE-pH diagram for the As-HzO system at 25°C with total As species of
50 ppb ...................................................................................................... 95

Protocol of the dislodgeable solids solubilization study ......................... 97

Determination of total arsenic, chromium, copper solubilized from the
dislodgeable solids and the speciation of arsenic and chromium in water

................................................................................................................. 99
Cartridges used for arsenic speciation: (A) pre-column, (B) modified

chromosorb cartridge ............................................................................ 101
Working curve for CrVI analysis by using UV-vis spectrometry .......... 105

Soluble CrVI and total chromium in dissolving water at different pH from
dislodgeable solids CCA ....................................................................... 109

Soluble CrVI and total chromium in dissolving water at different pH from
dislodgeable solids CCA/WR ............................................................... 110

Working curve of elemental arsenic determination by using GFAA.... 111

Percentages of total arsenic solubilized from the dislodgeable solids 114

xiii

Figure 5-11.
Figure 5-12.

Figure 5-13.

Figure 5-14.

Figure 6-1.

Figure 6-2.

Figure 6-3.

Percentages of chromium solubilized from the dislodgeable solids ....... 115
Percentages of total copper solubilized from the dislodgeable solids ..... 116

Soluble Asm, Asv, total As, and the sum of AsIII and AsV from
dislodgeable solids CCA ......................................................................... 128

Soluble Asm, Asv, total As, and the sum of AsIn and AsV from
dislodgeable solids CCA/WR .................................................................. 129

Cumulative CrVI in the leachate of commercially and laboratory treated
wood ........................................................................................................ 142

Cumulative element fiom commercially and laboratory CCA-treated
southern pine cubes in a 558-hour leaching test ......... 144

ASV, Asm and total As in the leachate fi'om (A) commercially, and (B)
laboratory treated wood ........................................................................... 147

xiv

-.~_..__.__.____.__ -4

Chapter 1.

Introduction

1.1 Overview

Wood has been used in construction for thousands of years. It is susceptible to
decay and insect damage in exterior and interior applications. Wood density and
mechanical properties are the mostly affected aspects. The average service life of virgin
southern yellow pine in above ground application has been estimated at about 13 years in
Wisconsin (Highley 1995), and about 10 years in Mississippi (Eslyn and Highley 1976).
The extent of damage can be reduced if wood is used in a non-hazardous environment or
if appropriate chemicals are used (Smith and Shiau 1998). The introduction of chemicals
in wood is called wood preservation. Preserved wood has prolonged service life. Among
several types of wood preservatives, chromated copper arsenate (CCA) is one of the most

extensively used materials with a track record of more than 60 years (Hingston et a1.

2001).

1.2 CCA preservatives

CCA preservative called ‘Ascu’ was first patented in India in 1933 (Eaton and
Hale 1993). Trials carried out during the 1930’s and 1940’s in India for the treatment of
railway sleepers and in the United States for the treatment of poles gave excellent results.
CCA wood treatment was first used in Europe in the 1950’s. Presently, CCA-treated
wood has been widely used for landscape timbers, decks, fences, and fabricated outdoor

structures to protect against fungi, insects and marine borers (Eaton and Hale 1993).

CCA mainly consists of arsenic (As), chromium (Cr), and copper (Cu). There are
different types of CCA formulations available in market. In Europe, Boliden Mining Co.
developed Boliden K33 based on metal oxide, salt-free components in Sweden. Britain’s
Hickson and Welch Ltd. and Celcure Co. devised salt-type formulations in Britain known
as Tanalith C and Celcure A (Eaton and Hale 1993). In the US, American Wood
Preservers’ Association (AWPA 2003) defines CCA types A, B and C based on the
relative amounts of oxides (CuO, 003 and A3205) present in the formulation. CCA type
C (CCA-C) is the most widely used formulation among the three types of CCA
preservatives in the states.

Table 1-1 lists the formulation of CCA type A, B, and C preservatives (AWPA
2003). Potassium dichromate, sodium dichromate, or chromium tiroxide are the major
sources of hexavalent chromium; the diavalent copper is prepared from either copper
sulfate, basic copper carbonate, cupric oxide or cupric hydroxide. Arsenic pentoxide,
arsenic acid, sodium arsenate or pyroarsenate are sources of pentavalent arsenic in the
formulation of CCA type C preservatives (AWPA 2003).

The function of copper in wood preservative is to protect against wood decay
fungi (Sisler and Cox 1960; Somers 1963). Copper toxicity is mostly attributed to the
cupric ion (Cu2+) decomposing hydrogen peroxide (H202) /oxygen free radical (02") to
oxygen gas and formation of hydroxyl radical (OH'), and results in uncontrolled
oxidation process (Hartmann and Weser 1977; Simpson et a1. 1988). The fungicidal
property of copper is reported to be dependent on the affinity of Cu2+ for different
chemical groups in the fungal proteins, particularly thiol groups, which results in the

denaturation of ftmgal proteins and enzymes (Eaton and Hale 1993). Arsenic in CCA acts

 

 

 

 

 

 

 

 

 

 

 

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as inhibitors of respiratory pathways for insects and fungi. Arsenate anions can substitute
phosphate anions during the formation of high-energy intermediates, adenosine
triphosphate (ATP) (Corbett et a1. 1984). Chromium in CCA is reduced by wood
components thereby causing the copper and arsenic to become insoluble. Chromium (III)
arsenate (CrAsO4), chromium (III) hydroxide (Cr(OH)3), and copper (II) - wood
carboxylate complexes are the most plausible products of CCA preservative with wood
(Bull 2001).

The retention level of CCA preservative in wood with good performance for
ground contact application is 6.4 kg/m3, which is equivalent to 0.40 pound per cubic foot

(pct) CCA oxides, and 4.0 kg/m3 (0.25 pot) for above ground usage (AWPA 2003).

1.3 Statistical data on CCA-treated wood

In the past two decades wood treated with CCA has dominated the market of
wood preservation, accounting for more than 75% of the total amount of treated wood.
The total amount of CCA yearly consumed is estimated at 1.0><108 kg compared to the
other water-home preservatives of 1.5><106 kg (Connell et a1. 1990). According to
American Wood Preservers Institute (AWPI 1997), about 79.1% of preserved wood was
treated with waterborne preservatives in USA, 1996 (1.3><107 m3 out of 1.7><107 m3).
About 6.5X106 kg of CCA (oxides, dry basis) was used compared to 1.9><106 kg of other

waterborne preservatives.

1.4 CCA-treated wood and the environment

 

The sound performance, relatively low cost, and clean surface of CCA-treated
wood distinguish itself from a large variety of other treated wood. However, the potential
leaching of arsenic, chromium, and copper from wood in service to the surrounding
environment have been monitored from both laboratory accelerated leaching tests
(Cooper 1993; Van Eetvelde et a1. 1995; Waldron et a1. 2003), and in-service treated
wood (Jin and Preston 1993; Solo-Gabriele et al. 2003a; Waldron et al. 2003). Elevated
levels of arsenic, chromium, and copper in soil have been related to the presence of CCA-
treated wood (Suzuki and Sonobe 1993).

Another important issue is the presence of some solid deposits, which might
contain arsenic, chromium, and copper on the surface of CCA-treated wood in service.
The formation of the dislodgeable solid include an initial loss of surface deposits; the
migration of CCA components; the loss of CCA components during wood degradation;
mechanic depletion of wood fiber; and the accumulation of dirt and sand etc. during

outdoor exposure (Gradient Corporation 2001).

1.5 Current status of CCA-treated wood

Due to the public concerns about potential human exposure to the hazards from
CCA-treated wood, especially arsenic and chromium, CCA-treated wood manufactures in
the US. have made a voluntary decision to withdraw CCA-treated wood from the market
available to consumers. This decision was announced by US. Environmental Protection
Agency (USEPA) on February 12, 2002. Since December 31, 2003, no CCA-treated

wood has been manufactured for residential use (U SEPA 2002). Public health

 

information regarding arsenic is provided to consumers for each single piece of CCA-
treated wood produced before December 31“, 2003, which is currently sold to consumers.

The Canadian Pest Management Regulatory Agency (PMRA) is in collaboration
with USEPA to have a re-registration review of CCA. There is no CCA-treated wood
available for residential use, similar voluntary label changes has been made in Canada
(PMRA 2002).

In Europe, the use of CCA-treated wood has been restricted in Germany, Sweden,
Austria, Finland, the Netherlands and Denmark. Labeling with consumer safety
information is required. The sale of CCA-treated wood for residential use will be banned
by June 30, 2004 in the above mentioned 6 European countries. In the United Kingdom,
the Health and Safety Executive recommended continuing use of CCA-treated wood
because of the environmental situation, especially the presence of termites (Dang et al.
2003).

Australian Pesticides and Veterinary Medicine Authority (APVMA) has initiated
a reconsideration of the registration and associated labeling in CCA-treated wood. A draft
report is anticipated by mid-2004 for public comments (Dang et a1. 2003).

Additional research on public health risks related to exposure to CCA-treated
wood is being carried out in New Zealand. However, the Environmental Risk
Management Authority (EMRA) is against a reassessment of registration of CCA (Dang

et a1. 2003).

1.6 Toxicity of arsenic, chromium, and copper

 

Humans, especially children may be exposed through direct dermal contact with
CCA-treated wood, or through oral ingestion of chemical residues from the touching of
the wood surface (McMahon and Chen 2001). The major routes of arsenic, chromium,
and copper exposure through the residential use of CCA-treated wood are summarized in
Figure 1-1, which include oral ingestion of the dislodgeable solids or the soil
contaminated by the leachate of CCA-treated wood, inhalation of small particles in the
air, such as contaminated soil, dislodgeable solids/wood sawdust, or dermal contact with
the leachate, dislodgeable solids, or the contaminated soil.

Animal studies of some arsenic, chromium and copper compounds have indicated
the acute toxicity of arsenic, chromium, and copper is influenced by their oxidation
states. In an acute exposure, inorganic trivalent arsenic (Asm) is more potent than
pentavalent arsenic (Asv), hexavalent chromium (CrVI) is more potent than trivalent
chromium (Crm), and cupric copper (Cu") is more potent than cuprous copper (Cu')
(Frank and Moxon 1936; Gaines 1960; Tatken and Lewis 1983). Chronic study suggested
that CrVI is “most appropriately designated a known human carcinogen by the inhalation
route of exposure” (USEPA 1998a); and Cr"1 is “essential for lipid, protein, and fat
metabolism in animals and humans” (USEPA 1998b). Copper is essential to life, but
elevated amount of copper exposure may be associated with the development of diseases

such as Wilson’s disease (Clarkson 1991).

1.7 Objectives
The potential risk of using CCA-treated wood in residential deck and playsets has

been proposed (McMahon and Chen 2001). However, limited information is available on

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the nature of the chemicals leached or dislodged from CCA-treated wood. Several risk
assessments have been performed based on the hypothesis that the nature of As, Cr, and
Cu leaching or dislodging on treated wood surface is similar to that in treated wood
(U SEPA 2001a; Gradient Corporation 2001; Dang et a1. 2003). Such assumptions may
under or over estimate the risk associated with CCA-treated wood and its impact on the
environment and human health.

The objective of this study was to characterize and identify the chemical nature of
solids and liquid that may migrate from CCA-treated wood in service to the surrounding

environment. This information is greatly needed to carry out an accurate risk assessment.

Chapter 2

Literature review
- arsenic, chromium, and copper in the environment and their toxicity

2.1 Arsenic

The name arsenic is derived from Greek “arsenikon”, which means powerful,
strong and potent. Arsenic sulfides were used for medical purpose, such as treatment of
ulcers by Hippocrates around 2500 years ago.

Arsenic naturally exists in minerals with more than 60% as inorganic pentavalent
arsenic (Onishi 1969). The average value of arsenic concentrations in rocks is reported at
2 mg/kg (O’Neil 1990). Up to 200 mg/kg in phosphate rocks and 900 mg/kg in
argillaceous sedimentary rocks have been reported (O’Neil 1990). The presence of
arsenic in ground water has been related to arsenic in rocks but the correlation is not
clearly established. Two major environmental conditions have been used to explain the
solubilization of arsenic in ground water. One is the oxidation of the relatively insoluble
arsenic in rock by the introduction of air and aerated water (Mallick and Pajagopal 1995);
the other is arsenic eroding from mineral deposits in river and adsorbed onto iron

hydroxides to go to the groundwater (N ickson et a1. 1998).

2.1.1 Arsenic exposure

Unlike man-made toxicants, arsenic exposure is unavoidable in daily life because
of its ubiquitous presence. Major routes of arsenic exposure include inhalation of
contaminated soil and dust floating in the air, and oral ingestion of contaminated soil or

water.

10

 

2.1.1.1 Arsenic in the air

Arsenic concentrations in the air vary with the geological region. Other factors
such as land use, and industrial contamination may also affect air quality. Based on the
report fiom the Directorate General for Environment (2000), background arsenic levels
are 0.2-1.5 ng/m3 in rural areas, 0.5-3 ng/m3 in urban areas, and about 50 ng/m3 in
industrial areas. Up to 1483 ng/m3 has been reported in Caletones, Chile, near a copper

smelter (Romo-KrOger and Llona 1993).

2.1.1.2 Arsenic in water

Arsenic is generally present in inorganic pentavalent form (ASV) in surface water,
and inorganic trivalent arsenic (Asm) in groundwater (Cherry et al. 1979). In both surface
and ground water, the background concentration of arsenic ranges from 1 to 10 ug/l.
Elevated concentrations of arsenic in drinking water have been reported in Taiwan, West
Bengal, India, Bangladesh, Chile, North Mexico, Argentina, China, USA, Finland,
Hungary, Greece and Romania (National Research Council 2001). In the United States,
based on USEPA’s estimation, about 3.5><105 people are exposed to drinking water with
more than 50 ug/l of arsenic and about 2.5><106 people are consuming drinking water

with arsenic level ranges from 25ug/l to 50ug/l (IARC 1987).

2.1.1.3 Arsenic in soil

Arsenic tends to be adsorbed to soil particles (Gomez-Caminero et a1. 2001). Less
movement of arsenic is observed in clay compared to that in sandy soil (Hiltbold et al.
1974; Elfving et al. 1994). Arsenic concentrations in soils from a non-orchard area in

Annapolis valley, USA were reported as ranging from trace level to 7.9 mg/kg (dry

11

weight), while arsenic levels ranged from 9.8-124.4 mg/kg in orchard soil treated with
arsenicals (Bishop and Chisholm 1962). In Zimbabwe, up to 9,500 mg/kg of arsenic has
been reported in some gold / arsenic mine dumps (Jonnalagadda and Nenzou 1996).
Oxidation, reduction, adsorption, dissolution, precipitation and volatilization of
arsenic exist in soil (maana and Keefer 1994). Arsenate is the dominant form in the
porewater of aerobic soils, with small amount of arsenite and monomethylarsonous acid
(MMA) (Gomez-Caminero et a1. 2001). Arsenate exists as H2AsO4' in an acidic soil
condition and HASO42' in an alkaline soil condition. Arsenate and arsenite can be
methylated by soil organisms resulting in the production of volatile methylated arsines. It
has been reported that about 12% of the arsenic in soil is lost through volatilization

(Woolson 1977).

2.1.1.4 Arsenic in food

The average daily dietary ingestion of arsenic varied from 17 to 291 pg depending
on the geological region, human age, and dietary habit (Gomez-Caminero et a1. 2001),
with approximately 25% in inorganic and 75% in organic form (WHO 1996). Fish and
meat are the major arsenic sources of human dietary exposure besides drinking water. In
Canada, the mean arsenic contents have been reported at 1,600 ng As/g in fish samples,
and 24 ng As/g (wet weight) in meat and poultry (Gomez-Caminero et al. 2001). Arsenic
may accumulate in some fish species. In a Swedish study, the total arsenic concentrations
in brackish-water fish were 200-2,600 ng As/g from an area near a smelter polluted by
arsenic, compared with 50-240 ng AS/g in the reference fish from an non-contaminated

area. About 5-12% of the arsenic was in inorganic form (Norin et a1. 1985).

12

2.1.1.5 Arsenic in plants

Variations in uptake of arsenic, chromium, and copper have been observed with
different plants. Study of plants in adjacent to CCA contaminated soil found that the
above ground portion of rye grass did not absorb significant amount of arsenic,
chromium, or copper; elevated concentrations of the three elements were found in the
root portion of rye grass. Radish (analyzed as the complete plants) selectively absorbed
more arsenic, but not the other two elements. It was noticed that horsetails (Equisetum)
could accumulate all the three elements, but no accumulation was observed with cattails
(T ypha) (Cooper et al. 1995). A four-year study found that no significant difference
existed in the arsenic uptake by banana plants when using CCA-treated eucalypts as the
supporting stakes compared to those using untreated wood stakes (Li et al. 2003).

The presence and function of arsenic species in plants is not fully understood.
After uptake by cell cultures of the Madagascan periwinkle, methylarsenicals could not
be detected by using Nuclear Magnetic Resonance (NMR) (Cullen et al. 1994). Gomez-
Caminero et al. (2001) proposed that organic arsenic could be bound to large molecules, .

possibly to a lipid-soluble species located in plant cell membrane.

2.1.2 Arsenic toxicity
The toxicity of a chemical reagent could be described based on acute exposure

(less than 24 hours) or chronic exposure (more than 3 months) (Klaassen and Watkins 111

2003).

2.1.2.1 Acute toxicity

13

 

Symptoms of arsenic acute toxicity include nausea, vomiting, abdominal pain,
watery diarrhea, hypotension, shock, and death (Williams 1999). Medium lethal dose
(LDso) is the dosage of chemicals needed to produce death in 50% of treated animals
(Klaassen and Watkins 2003). Variations in LDso exist among different chemical forms
of arsenic (Table 2-1). Arsenic toxicity is affected by its chemical species. The LDso of
sodium arsenite in man is reported at 10 mg/kg, while arsenic trioxide in man is more
potent compared to sodium arsenite, which is 1.43 mg/kg (Tatken and Lewis 1983).
Inorganic pentavalent arsenic (Asv) is less toxic than inorganic trivalent arsenic (As"').
The LDso of sodium arsenate is 70 mg/kg compared to that of sodium arsenite at 41

mg/kg in rats (Smyth et al. 1969; Tatken and Lewis 1983).

2.1.2.2 Chronic toxicity

Signs of arsenic chronic toxicity include fatigue, rash, fluid retention
gastroenteritis, leukopenia and anemia, sensorimotor peripheral neuropathy, noncirrhotic
portal hypertension, and peripheral vascular insufficiency (Novick and Warrell 2000;
Abernathy et a1. 2003). Chronic exposure to excess amount of inorganic arsenic has been
reported in the development of blackfoot disease, hyperpigrnentation, keratosis, anemia,
leukopenia, diabetes (Chen et al. 1986; Cuzick et al. 1992; Guo et al. 1997; Ferreccio et
al. 2000; Chen and Chen 2002; Nakadaira et a1. 2002; Chen et al. 2003a, b, c; Guha-
Mazumder 2003). However, there is no sufficient data to establish a reliable dose-
response relationship of long term - low dose arsenic toxicity mainly because of

concomitant exposure to other toxicants, variations in individual human susceptibility,

14

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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and limited case-specific exposure data in epidemiological study (Wildfang et al. 2001).
The lack of animal models limits the understanding of the mechanisms of arsenic
toxicity. Reference dose (Rfl3) is a numerical estimate of a daily oral exposure to the
human population that is not likely to cause harmful effects during a lifetime (Klaassen
and Watkins 2003). The oral RID of arsenic is established at 3><10‘4 mg/kg-day using the
thresholds of cellular necrosis (U SEPA 1998c) (Table 2-2).

Arsenic is an established human carcinogen. Cancers in skin, lung, and the urinary
system, including kidney, bladder, ureter and urethra have been observed upon arsenic
exposure (Tseng et a1. 1968; Tseng 1977; Morton et al. 1976; Southvvick et al. 1981;
Chen et al. 1986; Cuzick et al. 1992; Guo et al. 1997; Ferreccio et al. 2000; Chen and
Chen 2002; Nakadaira et a1. 2002; Chen et al. 2003a, b, c; Guha-Mazumder 2003).
Arsenic exposure has also been associated with disease in other internal organs, such as
liver cancer but with less convincing evidence (Liu et al. 2002). An increase in the rate of
cancer in lung has been observed with occupational exposure to arsenic of smelter
workers in Tacoma, WA, Magma, UT, Anaconda, MT, Ronnskar, Sweden, and
Saganoseki-Machii, Japan (Enterline and Marsh 1982; Lee-Feldstein 1983; Axelson et al.
1978; Tokudome and Kuratsune 1976; Rencher et al. 1977).

The cancer slope factor via oral exposure to arsenic is determined at 1.5 (mg/kg-
day)’l (USEPA 1998c). An updated value at 3.67 (mg/kg-day)'l has been applied in a
recent risk assessment for children exposure to CCA-C treated playset decks prepared by

USEPA (Dang et al. 2003) (Table 2-2).

2.2 Chromium

l6

The name chromium is derived from Greek "chroma", and means "color".

Chromium is a metal found in natural deposits. There are two commonly existing
oxidation states of chromium in the environment: trivalent chromium (Crm) and
hexavalent chromium (0“), which persist in sediments and with high potential of
accumulation in biota (Gomez-Caminero et al. 2001). Crm commonly exists as stable
complexes with both organic and inorganic ligands (Hartford 1979). CrVI exists as oxo
species, i.e. CrO3 and CrO42', which are strong oxidizers (Cotton and Wilkinson 1988).
The most common species of CrVI in solution are hydrogenchromate (HCrO4'), chromate
(CrO42'), and dichromate (CrzO72'). In basic or neutral solution (pHZ7), chromate is the

principle species; while at low pH, dichromate species predominate (U SEPA 1998a).

2.2.1 Chromium exposure

Maj or routes of chromium exposure are through inhalation, oral ingestion and
dermal absorption. Humans are subjected to chromium exposure both environmentally
and occupationally. The environmental sources mainly include airborne emissions from
chemical plants and incineration facilities, road dust from catalytic converter erosion,
asbestos brake lining erosion, topsoil, rocks, cement dust, contaminated landfills, and
tobacco. Occupational chromium exposure is mainly from leather tanning and textile
manufacturing, chrome electroplating, alloy production, welding of alloys or steel, paints,
pigments, photoengraving, copier servicing, antifreeze, production of magnetic audio
tapes, tattooing, wood preservatives, agricultural fimgicides, anti-algae agents, and

porcelain / ceramics / glass manufacturing (ATSDR 1993).

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2.2.1.1 Chromium in the air
Chromium concentration in ambient air generally ranges from 0.01 to 0.03 ug/m3
(EAD 2001). Little information is available regarding the nature of chromium species in
the air. It is recognized that Cr0 and CrIII are stable in the environment and do not undergo

any interactions intensively (Tovvill et al. 1978). Cer in the air interacts with dust

III

particles to form Cr (NAS 1974). Chromium in the air may precipitate to the ground.

However, particle size smaller than 10 um may remain in the air and travel with the wind

(U SEPA 1998a).

2.2.1.2 Chromium in soil and plants

Based on the report from Environmental Assessment Division (EAD 2001), the
concentration of naturally occurring chromium in the soil in the United States is reported
in the range of 1 to 2,000 ppm, with an average concentration of 54 ppm. It is generally

estimated that about 10% to 17% of chromium in soil is Crv'. Chromium tends to

accumulate in clay soil.

2.2.1.3 Chromium in water

Major sources of chromium in aquatic system are from the surface runoff,
precipitation fiom the air, and the release of industrial wastes. Most Crm end up in the
sediments as Cr203°nH20, and Cr’" can be dissolved in aquatic media as a water-soluble
complex and persist for a long period (USEPA 1998a). Chromium concentration in

drinking water is usually less than 2 ug/l (EAD 2001). Most of the chromium in

groundwater is Crv’ (EAD 2001).

19

2.2.1.4 Chromium in food
Not much information is available on the chemical forms of chromium in food.
Based on the data provided by Healthy Eating Club (2003), chromium contents are
relatively high in egg yolk (183 ug/ 100g food) and Brewer’s yeast (112 pg/ 100g food).
Chromium concentrations range from 42 to 57 ug/ 100g food in beef, cheese, liver and
vvine. Chromium contents in some vegetables are reported between 10 ug/ 100g food

(spinach) and 35 ug/ 100g food (black pepper).

2.2.2 Chromium toxicity

2.2.2.1 Cr‘“

Since the 1950’s, Crm has been known as a trace mineral required by human body
for insulin to use glucose properly. “Crm potentiates insulin action in peripheral tissue
and is essential for lipid, protein, and fat metabolism in animals and humans” (USEPA
1 998b). Chromium deficiency may result in changes in glucose and lipid metabolism, and
be associated with maturity-onset diabetes, cardiovascular diseases, and nervous system
disorders (Anderson 1993, 1995).

National Research Council (NRC 1989) recommended an estimated safe and

adequate daily dietary intake for Crm of 50-200 ug/day.

2.2.2.2 Cr"

III

In vivo reduction of CrVI to Cr has been observed in humans and laboratory

animals. The reduction agents include gastric juices, ascorbate, and glutathione.

20

Chromium can be localized in proximal renal tubules within the lysosomes (Suzuki and

Fukuda 1990).

2.2.2.2.1 Acute toxicity

Skin irritation, ulceration, and problems in respiration are common symptom of
chromium acute toxicity (USEPA 1998a, b). Accidental ingestion of CrVI may result in
metabolic acidosis, acute tubular necrosis, kidney failure, and death (Saryan and Reedy
1 988). Liver and other organs may also be damaged (Clarkson 1991).

The lethal dose of sodium dichromate through intravenous injection of several
laboratory animals ranges from 37 to 417 mg/kg (animal species not specified). The
lethal dose of sodium dichromate to mice is reported at 32 mg/kg (Clarkson 1991). The
LDso of chromium (III) chloride in mice is observed at 140 mg/kg (Smyth et al. 1969)
(Table 2-1).

2.2.2.2.2 Chronic toxicity
Chronic exposure to CrVI may result in damage to liver, kidney, lung, circulatory
and nerve system. Skin irritation is also frequently observed (Dayal et al. 1995; Bradshaw
et al. 1998). The amount of bioavailable chromium through inhalation is affected by the
particle size, oxidation states, solubility, activity of alveolar macrophages, and the
interaction of chromium with body tissue (U SEPA 1998a). Epidemiological studies
found there is an increased rate of human lung cancer upon chromium exposure (Davies
1984). Injuries to the skin, nasal and respiration mucous membrane have been noted upon

human occupational exposure to hexavalent chromium (Clarkson 1991). Elevated rate of

21

bronchiogenic cancer have been reported with heavy occupational exposure to hexavalent
chromium compounds through respiration in Germany, USA, Norway, and the United
Kingdom (USEPA 1998a). Development of oral ulcers, diarrhea, abdominal pain,
indigestion, vomiting, leukocytosis, and immature neutrophils have been reported with
chronic consumption of CrVI contaminated well water (CrVI concentration at 20 mg/l)
adjacent to a chromium alloy plant (Zhang and Li 1987). Based on the urinary data,
intake of CrVI at more than 0.02 mg/kg-day may result in serious illness; liver damage has
been observed of CrVI intake at 0.04 mg/kg-day (Clarkson 1991).
Table 2-2 summarizes the toxicity values of Cr” and Cer provided by
Environmental Assessment Division (BAD 2001). The oral RfD of CrIII is 1.5 mg/kg-day,
the inhalation Rfl) of CrVI is 2.9><10'5 mg/kg-day. The slope factor to determine the

cancer risk of CrVI exposure through inhalation is 42 (mg/kg-day)".

2.3 Copper

Copper is a natural element found in the earth’s cnrst with an average
concentration at 50 jig/kg. The actual quantity of copper varies with geologic region,
depending on the amount present in the earth. Copper is found in most plants, animals,
surface and ground water.

Copper is involved in the formation of hemoglobin, bones, carbohydrate
metabolism, catecholamine biosynthesis, and the cross-linking of collagen, elastin, hair

keratin, and balancing the biological environment of the nervous system (Clarkson 1991).
It is important for some enzymes such as cytochrome oxidase, tyrosinase, ascorbic acid

oxidase, uricase, catalase, and peroxidase to function normally (Clarkson 1991).

22

Copper is primarily used as metal or alloy in manufacture of wire, pipes, and
other metal products; and commonly used in agriculture to treat plants for pest control; in
water treatment for algae; as preservatives for wood, leather, and fabrics. Copper is also

used in antifouling paints (marine coatings for ships), and a potential replacement for

organotins.

2.3.1 Copper exposure

The'major human exposure to copper is through inhalation, ingestion of food and
water, and dermal contact with copper containing water and soil. Copper fiom water

pipes may be one of the important sources of copper in drinking water.

According to the data from Toxics Release Inventory (TRI 2002), the amount of
copper release to the environment in year 2000 was about 4.2><106 kg. Among which
12.8% was released to the air, about 0.4% to the water, 0.8% to the ground, and 86.0% to
the land. Domestic waste water, combustion process, wood production, phosphate

fertilizer production are also important sources of copper release to the environment.

2.3.1.1 Copper in the air
Copper can be emitted into the air mainly from windblown dust. The

concentration of copper in the air ranges from 5 to 200 ng/m3, and up to 5,000 ng/m3 near

copper smelters (ATSDR 2002).

2.3.1.2 Copper in food

23

Copper contents are high in liver (around 150 ug/g wet in sheep and pork livers),
lobster (36.60 ug/g wet), syrup (43.36 ug/g wet), crab and clams (6.08-7.39 ug/g wet),
walnuts (6.51 ug/g wet), peas (2.38 ug/g wet) and beans (1.09-3.95 ug/g wet), chili (1.82

pig/g wet), and whole wheat (1.07 ug/g wet) (Brewer 1992).

2.3.1.3 Copper in plants
Copper concentrations in plant tissues are reported in the range of 5 to 20 mg/kg
on dry weight basis (Patsikka et al. 1998). The bioavailability of copper to plants depends
on the presence of ionic copper. Copper based compounds with low water solubility or
complexes with substrates in soil or the environment such as humic acid and fulvic acids,
or Cu-OH-lignin of peat soils reduce copper availability for “uptake” by plants (Owen
1982). The copper content of wheat increases as it is grown from the north to the south in
the U.S., this has been documented at 4.2 ug/g when planted in Oregon, 6.2 ug/g in
Oklahoma, 7.8 ug/g in Texas, and 8.7 ug/g in California (Owen 1982). Copper can be
stored in the roots of pines and delivered to the shoots when it reaches a certain

concentration. Copper concentration is high in cabbage leaves, peony buds, young oat

plants and roots of rice plants (Owen 1982).

2.3.1.4 Copper in water
Copper exists in oceans, rivers, lakes and wells with the predominate form being
the bivalent oxidation state (Cun) (ATSDR 2002). The average copper concentration in

oceans is reported at 1.2 ug/l. The copper concentration increases with the depth. Copper

contents in river water are often higher than that in seawater, which has been reported up

24

to 10 ug/l (Owen 1982). Copper concentrations in tap water vary with the scenario of
water exposure to copper tubing and tanks. The copper content is reported at 0.26 ug/ml

in the morning and 0.11ug/ml in the evening because of the solubilization of copper from

the tubes to water overnight (Owen 1982).

2.3.1.5 Copper in soil
It has been well recognized that copper contents in soil vary and affect the copper

content in plants. The copper content in soil has been reported to range from 1 to 4000
lag/g (Owen 1982; IRIS 2003). Soil samples from Wisconsin (USA), African, Ghana,

India, and USSR are reported at 20, 68, 21-77, 11-175, and 1-980 ug/g respectively

(Brewer 1992).

2.3.2 Copper deficiency in human
Copper deficiency in humans may result in anemia, neutropenia (Montorsi et al.

1975), osteoporosis, pallor, dermatitis, anorexia, diarrhea, hepatomegaly, and slow

growth (Hambidge 1977).
The US. National Academy of Sciences’ Food and Nutrition Board (2003)

recommends a daily allowance (RDA) of copper at 0.2 to 0.22 mg for infants, 0.34 to

0.44 mg for children, 0.7-0.9 mg for adults, 1.0 mg for women in pregnancy, and 1.3 mg

for women in lactation.

25

2.3.3 Copper toxicity

Accidental ingestion of samphire, “strongly impregnated with copper” by a 17-

year-old girl, was reported to cause abdominal pain, skin rash, followed by severe
diarrhea, retching, and green vomitus, and an eventually death (Percival 1785). Symptom
of headaches, hypoglycemia, increased heart rate, nausea, inhibition of urine production,
anemia, hair loss in women, and. damage in brain, liver and kidneys have been observed
with high copper exposure. Copper interferes with zinc, which is essential in producing
digestive enzymes. Excessive copper in children is associated with hyperactive behavior,
ear infections, and learning disorders such as dyslexia (Owen 1981).

Symptoms of violent retching, muscular spams, and collapse are usually observed
in copper poisoned animals (Owen 1981). Rats fed with copper sulfate at a dietary level
of 25 Cu mg/kg-day for a continuous 4 weeks presented slightly decrease in food intake
and growth rate (Clarkson 1991). The food intake and body weight of rats decreased with
the increased copper sulfate (CuSO4) content in diet. At dose level of 200 Cu mg/kg-day,
rats were observed to eat less than 1/5 of the regular amount of food and die within one
week (Clarkson 1991). Pigs fed with CuSO4 in diets at 12.5-21.25 mg Cu/kg-day for 48-
79 days showed a gradual development of anemia, jaundice, hepatic necrosis,
gastrointestinal hemorrhage, and decreased weight gain (Clarkson 1991).

Lehmann (1897) summarized that the lethal dose of CuSO4 in humans is 7.5g or
higher with oral ingestion. Table 2-1 lists the lethal dose values of some copper
compounds. The oral LDso of CuSO4 for rats is reported at 960 mg/kg (Smyth et a1.
1969), and 87 mg/kg in mice (Jones et al., 1980). The oral LDso of copper (II) chloride in

rats is 140 mg/kg and 265 mg/kg for copper (I) chloride (Tatken and Lewis, 1983).

26

Epidemiological study found that a genetic disorder called Wilson’s disease was
associated with excess level of copper exposure. Low serum and hair copper levels were
found in patients, but high copper levels were present in the liver and brain (Lal and
Sourkes 1971; Owen 1974). A remarkable symptom of over exposure to copper resulting
in Wilson’s disease is blue and brown at the fingernails (Owen 1974). One of the other
reported diseases associated with excess level of copper exposure is Parkinson’s disease,
which affects about 1% of the population over the age of 60 years in the United States
(Gorell et al. 1997; Wechsler et al. 1991). The main symptom of Parkinson’s disease is a
pronounced tremor of the extremities - notably the hands, chin or lips, stiffness or
slowness of movement, a shuffling walk, stooped posture, and difficulties in performing
simple tasks.

USEPA has not provided specific data on the RID of copper exposure (IRIS
2003). Copper has not been classified as human carcinogen due to the lack of human data

and inadequate of animal data (IRIS 2003).

2.4 Environmental regulation of arsenic, chromium, and copper
2.4.1 National wide

Table 2-3 lists the environmental regulation levels of arsenic, chromium, and
copper in the US. USEPA set the National Primary Drinking Water Regulations for
arsenic, chromium, and copper at 10 ug/l, 100 ug/l, and 1.3 mg/l, respectively.

WHO published the latest edition of arsenic in drinking water regulation level at
10 pg/l with an estimated excess lifetime skin cancer risk at 6><10‘4 associated with

arsenic exposure at this level (WHO 1963).

27

American Conference of Governmental Industrial Hygienists (ACGIH), National
Institute for Occupational Safety and Health (N IOSH), and Occupational Safety and
Health Administration (OSHA) also provide occupational regulation levels of arsenic,

chromium, and copper in the air (Table 2-3).

2.4.2 Michigan

Table 2-4 summarizes the general cleanup and screening levels of arsenic,
chromium, and copper in Michigan (DEQ 2004). The statewide default background
levels in soil are 5.8 mg As /kg, 18 Crm /kg, and 32 mg Cu/kg on dry weight base. The
drinking water protection criteria of the three elements in soil are 23 mg As/kg, 1,000,000
mg Crm/kg, 30 mg CrVI/kg, and 5,800 mg Cu/kg (dry weight). The direct contact criteria
are set at 7.6 mg As/kg, 790,000 mg Crm/kg, 2,500 mg CrVI/kg, and 20,000 mg Cu/kg
(dry weight). The residential and commercial drinking water criteria are set at 50 ug As/l,

100 pg CHIN/1, and 1,000 11g Cu/l.

28

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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30

Chapter 3
Collection of the Dislodgeable Solids
from Chromated Copper Arsenate Treated Southern Pine
3.1 Introduction

The presence of arsenic, chromium, and copper on the surface of chromated
copper arsenate (CCA) treated wood has been reported. The amount of arsenic,
chromium, and copper present varied with CCA retention in treated wood, the wood
species, the method of wood treatment (full cell or empty cell), and the seasoning afier
the wood treatment (Coggins and Hiscocks 1978, Murphy and Dickinson 1990, and
Cooper et al. 1997). CCA components on the wood surface may represent a potential risk
to humans and the environment. It is hypothesized that children at playground or decks
built up with CCA-treated wood may come in contact with the dislodgeable solids from
wood surface. Contamination may occur through skin contact (dermal absorption), hand—
to-mouth behavior (oral ingestion) with wood sawdust, soil contaminated with CCA
components, and / or water runoff on rainy days.

“Dislodgeable solids” is defined as material that can be removed or may come
loose from the surface of CCA-treated wood. The formation of dislodgeable solids
involves a series of processes, which include the migration of CCA components from the
inner to the outer zone of wood; sludge deposits during CCA wood treatment; sand and
dirt introduced during wood handling; the loss of CCA components during wood
degradation; and the mechanical depletion of wood splinters, accompanied with the

accumulation of dirt, sand, etc. during exterior exposure.

31

CCA sludges may come from the reduction of hexavalent chromium by
interaction with soluble wood extractives or additives such as water repellents during the
wood treatment process (Sonti et al. 1987; Pasek and McIntyre 1993; Bull 2000;
Stevanovic-Janezic et al. 2001a). The formation of dislodgeable solids on CCA-treated
wood surface may also be attributed to wood weathering, which is caused by sunlight,
temperature and moisture (Kalnins and Feist 1991), and influenced by wood species (Cui
et al. 2004). Studies of CCA fixation in wood revealed that most of the interactions
between CCA components and wood are through lignin (Dahlgren and Hartford 1972a, b,
c; Pizzi 1982a, b, c). Lignin is photo-degraded and water-soluble quinone-like
compounds are formed during wood weathering (Fengel and Wegener 1984). CCA
components may come loose from treated wood during the photodegradation of lignin. In
formation of dislodgeable solids on the surface of CCA-treated wood may also be caused
by the biological activity.

The addition of water repellents (WR) into CCA wood treatment has been applied
industrially for years to help improve the dimensional stability of wood. In general,
commercial WR used for CCA treatment contains oil, a solvent to reduce the viscosity of
the oil, and a surfactant to keep the WR compatible with CCA treating solution (Williams
and F eist 1999). WR treatment may reduce the rate of water absorption and desorption by
wood, and consequently decrease the changes of moisture content in wood, which
reduces wood swelling, shrinking, cracking, and peeling (Zahora 1995).

Several risk assessments associated with contacting CCA-treated wood in
playground, deck or other residential use have been conducted (U SEAP 2001b; Gradient

Corporation 2001; Dang et al. 2003). The cancer risk of arsenic exposure through oral

32

ingestion of the dislodgeable solids and CCA contaminated soil was estimated at 2><104
by USEPA (2001b), and 1.4><10'4 in a recent risk assessment of children exposed to
CCA-treated wood in playsets (Dang et al. 2003). However, the cancer risk at 3><10'6
provided by Gradient Corporation (2001) is far less than USEPA’s estimation. The
toxicity of an element is influenced by the route and the amount of exposure. The levels
of CCA components that can be dislodged and available on the surface of CCA-treated
wood are sources of debate. Several numbers on the amount of arsenic, and chromium
that could be collected from the surface of CCA-treated wood were proposed (Stilwell
1999; Maas et al. 2002). These numbers were obtained using several methods to collect
and quantify. Little information was given on wood species, the age in service, chemical
retention, and details on the method of collection.

In this study we proposed to qualify and quantify the dislodgeable solids that can
be removed from the surface of commercial CCA type C (CCA) and CCA/WR southern
pine treated at a retention of 6.4 kg/m3 total oxides. To achieve this goal, the first step
was to collect the dislodgeable solids. No standard protocol is available to collect
dislodgeable solids from CCA-treated wood. Several methods to collect the dislodgeable
solids have been applied and reported: hand wiping, cloth wiping, and paper wiping
(Gradient Corporation 2001). We proposed to use three methods to compare the amount
of arsenic, chromium, and copper collected: the first method was a glove-on-hand
wiping, which consisted of wearing a latex-free nitrile glove on both hands and use the
palms to wipe the surface of CCA-treated wood; the second method was to use cellulose
filter paper to wipe the board surface; and the third method used a test tube brush to brush

wipe a wet board surface. The most appropriate method which was capable of obtaining

33

m. Cal-c... n.5- r 05.5 I. to: 15:1

the largest amount of arsenic, chromium, and copper from the wood surface without
changing the chemical nature was selected for further study in order to facilitate
characterization of the dislodgeable solids.

CCA and CCA/WR-treated southern pine boards were exposed in the field (above
ground). The dislodgeable solids were collected on a monthly basis, to determine the
amount of arsenic, chromium, and copper that could be obtained at different stage of
exterior exposure. To illustrate the mi gration/redistribution of arsenic, chromium, and
copper in treated wood during the field exposure, and the potential impact on the amount
of the three elements collected in the dislodgeable solids, chemical distributions in wood
samples with no field exposure and after 15 months of field exposure were analyzed.

Atomic absorption spectroscopy (AA) was used to quantify the amount of arsenic,
chromium, and copper in solid samples after an acid digestion. AA analysis is based on
the absorption of electromagnetic radiation by atoms or ions. When a sample is atomized
at high temperature (e.g. 2100~2400°C for acetylene/air mixture for flame atomic
absorption spectroscopy; and 1500-2600°C for samples in a pyrolitically coated graphite
tube for graphite furnace atomic absorption spectroscopy), a substantial fi'action of the
metallic constituents are reduced to gaseous atoms and ionized. The electronic transitions
of the outermost electrons yield ultraviolet or visible radiation, which serves as the basis
for AA analysis. AA is sensitive means for the quantitative determination of more than
60 metals or metalloid elements.

A flame atomic absorption spectroscopy (FAA) was applied to analyze elemental
arsenic, chromium, and copper at parts per million levels (ppm), and a graphite furnace

atomic absorption spectroscopy (GFAA) was used to analyze elemental arsenic at parts

34

 

per billion levels (ppb). The detection limits of arsenic, chromium, and copper by using
FAA and the detection limit of arsenic by using GFAA were determined by following a
procedure described by Perkin-Elmer (1982). The instrumental detection limit is defined
by Delahay (1957) as the lowest concentration of the element that can be clearly

differentiated from zero by the instrument at a signal to noise ratio of 2.

3.2 Material and Methods
3.2.1 Dislodgeable solids collection for collection methods comparisons
3.2.1.1 CCA-treated southern pine

CCA-treated southern pine boards used for comparing the dislodgeable solids
collection methods were obtained from Osmose, Inc. The boards were removed from an
artificial deck built aboveground by Osmose, Inc. in F ayetteville, GA after a 16-month
exterior exposure. The initial chemical retention in the wood was labeled at 6.4 kg/m3.
The dimension of each board was 2.5cm x 14cm x 60cm. The weathered surface of the
board was used to collect the dislodgeable solids. All the boards had been subjected to an

initial test-tube brush wiping before used for the collection method comparisons.

3.2.1.2 Dislodgeable solids collection methods

The collection of dislodgeable solids was performed in the lab at a room
temperature of 20°C and relative humidity of 655%. Three dislodgeable solids
collecting methods were used: a glove-on-hand wiping, a paper wiping, and a test-tube

brush wiping. The protocol of each collection method is described as following.

35

mm»a:. I? a “inn“? .2?!

3.2.1.2.1 Glove-on-hand wiping method

The dislodgeable solids were collected by using hand with glove on. Powder and
latex free Nitrile-Blue medical examination gloves purchased from Maxxirn Medical Inc.
MA were used (Item # 484501). The surface area of the hand conducted for the
dislodgeable solids collection was about 100 cmZ/hand. The load applied for the wiping
(both hands) was measured by using a balance (ACCU-2101, Fisher Scientific). A load of
1000:t200 g, which corresponded to a pressure of 5.0il.0 g/cm2 was applied for the
glove-on-hand wiping. Dry board surface was wiped once along the longest edge starting
from one end to the other. It took about 15 seconds to wipe a single board. The gloves
were rinsed after each single board wiping with 150 ml deionized (DI) water (pH of
5.6i0.1), and a new pair of gloves was used for each single board. A total of 10 boards
with a total surface area of 0.85 m2 were used for the glove-on-hand wiping. The wash
was collected and concentrated. FAA was used to determine the amount of arsenic,

chromium, and copper collected.

3.2.1.2.2 Paper wiping method

Dry Whatrnan #1 filter paper (Whatrnan International Limited, England) with a
surface area of 176 cmZ/piece was used to wipe the wood surface. A total of 10 boards
with surface area of 0.85 m2 were subjected to the paper wiping. One piece of filter paper
was used to wipe a single board. Both hands were loaded on the filter paper for the
wiping. Each board surface (dry) was wiped once along the longest edge starting from
one end to the other. The load applied was 1000:|:200 g, which corresponded to a pressure

of 5.0:b1.0 g/cmz. It took about 15 seconds to wipe a single board. The filter paper was

36

 

collected and acid digested. Blank filter paper was also digested as the control. The

digested samples were analyzed for arsenic, chromium, and copper contents using FAA.

3.2.1.2.3 Test-tube brush wiping method

About 150 ml of deionized (DI) water (pH of 5.63:0.1) was used for each board
with a surface area of 0.085 m2. The board was placed at a 45-degree angle with one end
in a polyethylene tray (Rubbermaid). The dimension of the tray was 56 cm X 41 cm X 14
cm. An initial DI water spraying (about 30 ml) was applied to wet the board surface by
using a washing bottle (Polyethylene 250ml, VWR 16651-573). The wetted surface was
then wiped with a test tube brush (white bristles, fan style tip, 13 cm in length x 3 cm in
diameter, VWR 17212-028) from the top to the bottom end along the longest edge of the
board. About 30-50 ml of DI water was sprayed on the board surface followed by a test
tube brush wiping. Each board was wiped 3-5 times until all the 150 ml DI water was
consumed. About 40-60 seconds was used to wipe a single board. The wash from the
wiping was collected in the polyethylene tray. The load applied for the brush wiping was
250i30 g. The contacting area between the brush and the board was about 39 cm2. The

pressure applied for the wiping was about 6.4i0.7 g/cmz.

3.2.1.2.4 Wash concentrating and drying

The wash collected from the glove-on-hand wiping or the test tube brush wiping
was filtered through a thin layer of glass wool (Pyrex brand filtering fibers, Owens-
Coming Fiberglass Corporation. Catalog No. 3950) placed on a Biichner funnel (glass, 17

cm in diameter) to remove particles larger than 0.5 mm. The wash filtered through the

37

 

glass wool was collected in a 4-liter Erlenmeyer flask (Pyrex 4L, heavy duty) and stored
at 4°C in a refrigerator before further concentration. The wash was concentrated using
roto-evaporation (RE 120 & Buchi Rotovapor R-200, Brinkmann Instruments, Inc.). The
rota-evaporation was carried out within 24 hours afier the wash collection. The roto-
evaporation was set at a temperature of 45°C and a vacuum level of 28-30 inch Hg.
About 95% of the water was evaporated during the rote-evaporation. The concentrated
wash was transferred into a beaker (Griffin glass w/spout, 150 ml capacity, 57 mm X 82
mm, VWR 13912-182) and exposed to the air at a temperature of 20°C and relative
humidity of 65i5%. It took approximately 2 days for the concentrated wash to dry. After
air drying, solids were collected in a glass bottle (round glass, 60 ml wide mouth, black
screw cap w/flat, disc-type polyvinyl liners, VWR 16194-020) tighten with a cap and

stored in freezer until further analysis.

3.2.2 Dislodgeable solids collection for characterization
3.2.2.1 CCA and CCA/WR-treated southern pine

Commercial CCA type C (CCA) and CCA with water repellent (CCA/WR)
treated southern pine lumbers were purchased from Lowe’s in Lansing, Michigan in
November, 2001. The lumber was labeled with Georgia-Pacific Co., Atlanta, GA at a
chemical retention of 6.4 kg/m3. According to Georgia-Pacific Co}, Chemical
Specialties, Inc. is their provider of the WR. The dimensions of the boards were 2.6cm X
15cm X 244cm. Each board was cut into 4 samples of identical size (2.6cm X 15cm X

61cm) to facilitate the handling during the dislodgeable solids collection.

 

1 lnfonnation obtained from a telephone conversion with Georgia-Pacific Corporation

38

 

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An artificial deck was constructed using these CCA or CCA/WR-treated southern
pine boards. The deck was loaded at Tree Research Center (TRC), Department of
Forestry, Michigan State University, East Lansing, Michigan (Figure 3-1). CCA-treated
southern pine boards were isolated from CCA/WR treated boards to prevent possible
contamination from each other. The deck was 0.6 m above ground with a total decking
area of 7.3 m2. The seasonal weather report of Lansing, Michigan, USA (42°N 84°W) is

illustrated in Figure 3-2.

3.2.2.2 Dislodgeable solids collection from wood exposed in the field

CCA and CCA/WR-treated southern pine boards were collected from TRC once
every month during the field exposure trials for the dislodgeable solids collection.
Dislodgeable solids were collected from the weathered surface of wood and the collection
was performed in the same day when boards were harvested, and returned to the field in
the following day. The board surface subjected to dislodgeable solids collection was
placed facing the sunshine consistently in the field. The collection schedule was set on
the 8th of every month with the exception of rainfalls, the collection schedule was
postponed to the next earliest clear day. The collection in the following month followed
the regular schedule. Table 3-1 lists the weather information on the day of the solids
collection, provided by the database in www.wunderground.com. An initial dislodgeable

solids collection was performed in November, 2001 before the field exposure.

3.2.2.3 Arsenic, chromium, and copper distribution in CCA and CCA/WR-treated
southern pine with no field exposure and after 15 months of field exposure

39

 

 

 

 

 

 

 

 

 

 

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Figure 3-2.

The chemical distributions in CCA and CCA/WR-treated southern pine were
analyzed after 15 months of field exposure in TRC, and compared to chemical
distributions in wood cut from the same parent board and stored in lab with no field
exposure. Wood samples were sectioned into thin layers parallel to the exposed surface.
The sectioning schemes are illustrated in Figure 3-3. Arsenic, chromium, and copper in

each section were measured individually using FAA after an acid digestion.

3.2.3 Analysis
3.2.3.1 Acid digestion of solid samples

An acid digestion was applied to solid samples such as the treated wood and the
dislodgeable solids by following the protocols described in American Wood-Preservers’
Association Standard (AWPA 2003): Wet Ashing Procedure for Preparing Wood for
Chemical Analysis (A7-93); and Analysis of Treated Wood and Treating Solutions by
Atomic Absorption Spectroscopy (Al 1-93). The reagents used for the acid digestion were
nitric acid (A.C.S. Reagent, 68-70%, EM Science) and perchloric acid (A.C.S. Reagent,

70%, Aldrich).

3.2.3.2 Atomic absorption spectroscopy measurement of elemental arsenic,
chromium, and copper - FAA and GFAA

Quantification of elemental arsenic, chromium, and copper at parts per million
(ppm) level was completed by using Flame Atomic Absorption Spectrophotometer (FAA,
Model: Perking Elmer 3110), equipped with an electrodeless discharge lamp (EDL) for
arsenic, and hollow cathode lamps for chromium and copper (Perkin E1mer).A graphite

fumace atomic absorption spectroscopy (GFAA, AAnalyst 800, Perkin Elmer

43

 

 

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Co., CT, USA) equipped with an EDL arsenic lamp was used to quantify arsenic in parts
per billion (ppb) level.

The atomic absorption standard solutions of arsenic, chromium, and copper were
purchased from Aldrich Chemical Co. The concentrations of elemental arsenic,
chromium (V I) and elemental copper in the standard solutions were 990 ug/ml in 2 wt.%
potassium hydroxide (KOH), 1005 rig/ml in 1 wt.% hydrochloric acid (HCl), and 1007
rig/ml in 1 wt.% nitric acid (HN03), respectively. The solutions used to build the working
curve for AA measurement were diluted from the atomic absorption standard solutions by
using 2 wt.% KOH for arsenic, 1 wt.% HCl for chromium, and 1 wt.% HNO3 for copper.
Solutions at elemental arsenic concentrations of 0 ppm, 10 ppm, 25 ppm, 50 ppm, and
100 ppm were used to establish the working curve for arsenic analysis. Solutions at 0
ppm, 0.1 ppm, 0.5 ppm, 5 ppm, and 10 ppm of chromium were used to build the working
curve for chromium analysis. Concentrations of the solutions used to construct the
working curve for copper analysis were 0 ppm, 0.5 ppm, 5 ppm, and 10 ppm.

The concentrations of the solutions used to construct the working curve for
arsenic analysis by using GFAA were 0 ppb, 2.5 ppb, 5 ppb, 10 ppb, 25 ppb, 50 ppb, 100
ppb, 150 ppb, and 200 ppb. A matrix modifier was used to reduce the interferences,
particularly matrix effects in GFAA analysis. The matrix modifier was prepared by
dissolving 0.1g palladium (II) chloride (PdClz, 99.999%, Aldrich), 10 g citric acid
((HOC(C02H)(CH2C02H)2, 99.5%, A.C.S. Reagent, Aldrich), and 0.05 g ammonium
ttmgstate (99.99%, Aldrich) in 10ml hydrochloric acid (HCl, 6N, double distilled,
Caledon Laboratory Chemicals), and diluted to 1000 ml using DI water (Flores del Pino

2003)

45

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To determine the detection limits of arsenic, chromium, and copper by using FAA
and arsenic by using GFAA, two concentrations of solutions were prepared for each
element from the atomic absorption standard solutions according to Perkin-Elmer (1982).
The lower concentration standard was approximately 5 x the expected detection limit, and
the second standard was made twice this concentration: arsenic solution at concentrations
of 2.7 ppm and 4.8 ppm, chromium solutions at 0.6 ppm and 1.3 ppm, and copper
solutions at 2.6 ppm and 5.2 ppm were prepared to determine the detection limits of
arsenic, chromium, and copper, respectively by using FAA. Two arsenic solutions at the
concentrations of 2.5 ppb and 5.0 ppb were prepared to determine the detection limits of
arsenic by using GFAA. The concentrations of the two solutions of each element were
measured by using AA in the sequence of blank, low-concentration solution, blank, high-
concentration solution, and repeated the sequence for at least 20 times.

The detection limits of arsenic, chromium, and copper by using FAA, and the
detection limit of arsenic by using GFAA were calculated according to Perkin-Elmer
(1982) by using Equation 1.

. . . concentration of the solution x 2 standard deviation
detection limit = (1)

mean

 

3.2 Results and Discussion

3.3.1 Instrumental detection limits of elemental arsenic, chromium, and copper by
using FAA and GFAA

Tables 3-2 and 3-3 list the derivations of the detection limits. The detection limits
of arsenic, chromium, and copper by using FAA were determined at 0.6 ppm, 0.02 ppm,

and 0.3 ppm, respectively. The detection limit of arsenic by using GFAA was 0.3 ppb.

46

 

3.3.2 Comparisons of the dislodgeable solids collecting methods

Table 3-4 lists the FAA analysis results of elemental arsenic, chromium, and
copper contents in the dislodgeable solids collected by using the glove-on-hand wiping,
the paper wiping, and the test tube brush wiping methods. One-way ANOVA analysis
indicated that significant difference existed in the amount of arsenic, chromium, or
copper collected by using different collecting method (Appendix 1, 2, and 3).

From a total surface area of 0.85 m2 of CCA-treated southern pine (Osmose Inc.
samples, collected from an artificial deck afier field exposure), about 0.13i0.02 mg,
0.24i0.04 mg, and 0.13i0.09 mg of elemental arsenic, chromium, and copper were
collected by using the glove-on-hand wiping method. Relatively larger amounts of
arsenic, chromium, and copper, at 0.33:1:0.02 mg, l.49:k0.16 mg, and 0.57:1:0.05 mg,
respectively, were obtained from the same board surface area by using the paper wiping
method compared with the glove-on-hand wiping method. The largest quantities of
arsenic, chromium, and copper were obtained by using the test tube brush wiping method.
About 1.82:1:0.09 mg of arsenic, 2.45:1:0.06 mg of chromium, and 0.98d:0.12 mg of copper
were collected from 0.85 m2 of board surface.

Similar pressure at 5.0i1.0 g/cm2 was applied on the board surface by using the
glove-on-hand wiping method and the paper wiping method. The surface area of both
hands was about 200 cm2, which was close to the surface area of the filter paper used
(176 cmz). A single wiping was applied by using both collecting methods. The wiping
behavior could be described as an “abrasion” of the residuals from the wood surface. The
residuals abraded from the wood surface could transfer back to board during the wiping

process. The significant difference in the amount of arsenic, chromium, or copper

47

 

 

 

 

 

 

 

 

 

 

 

 

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collected by using the glove-on-hand wiping, and the filter paper wiping could be
attributed to the “transfer efficient” - the ratio between the amount of residuals presence
on the wood surface and those transferred to the Nitrile-Blue glove or the filter paper.
The filter paper tended to “pick up” more residuals compared to the glove. Therefore, the
material used for the wiping could affect the amount of chemicals collected.

Compared with the glove-on—hand wiping and the filter paper wiping, a 3-4 times
repeated wiping behavior was applied to each single board by using the test tube brush
wiping method with a slightly higher pressure applied at 6.7i0.7 g/cmz. The test tube
brush wiping accompanied with water spraying consisted of relatively more activities,
which included water absorption by wood, chemicals solubilization and leaching, and an
abrasion with the brush bristles. Besides, the running water on the board surface from the
water spraying facilitated the collection of the abraded residuals. These were possibilities
as to larger amount of residuals were obtained from the board surface compared to the
other two methods.

By using a moist polyester wiping, Stilwell (1999) collected about 6.9 mg/m2 of
arsenic from CCA-treated wood (new, sold for playground construction), and 3.5 mg/m2
of arsenic by using the same collecting method from a in-service playground. Maas et al.
(2002) reported the collection of arsenic at 2.3-10.9 mg/m2 and 2.4-20.3 mg/m2 of
chromium from new boards at chemical retention of 6.4 kg/m3, and 1.6-4.5 mg/m2 of
arsenic and 2.0-5.0 mg/m2 of chromium from boards afier 6 months of outdoor exposure
(Table 3-5). No detailed information on the wiping behavior, such as the pressure applied
or the wiping speed was provided from either of these studies. The amounts of arsenic

and chromium collected by using the glove-on-hand wiping and the paper wiping were

51

 

WW“ -

relatively lower compared with Stilwell (1999) and Maas et al. (2002). One of the factors
that caused the lower values of arsenic and chromium collected could be attributed to the
relatively longer duration of wood exterior exposure (16 months). The amount of arsenic
and chromium collected using the test tube brush wiping method was comparable with
what has been reported by Stilwell (1999) and Maas et a1. (2002).

In order to study the properties of the dislodgeable solids collected, it is critical to
avoid altering the nature of the chemicals in the dislodgeable solids. Therefore, the
selection of the wiping material, and the collection of the residuals from the wiping
material are important to obtain accurate information. In order to collect a relatively
larger amount of dislodgeable solids to facilitate further analysis, the test tube brush

wiping method was selected in this study.

3.3.3 Dislodgeable solids collected from CCA and CCA/WR-treated southern pine
Table 3-6 presents the elemental arsenic, chromium, and copper contents in the
dislodgeable solids collected from CCA or CCA/WR-treated southern pine at different
stage in the field study. From a total board surface area of 1.83 m2, similar mass of
dislodgeable solids were obtained from these two types of boards before field exposure.
About 0.56 g and 0.62 g of solids were collected from CCA and CCA/WR-treated wood,
respectively. FAA analysis found that, the contribution from arsenic, chromium, and
copper to the dislodgeable solids was less than 4% in weight. The dislodgeable solids
were mainly composed of wood fibers and soil/dust collected from the board surface. The

dislodgeable solids collected from CCA-treated wood consisted 1.2% of arsenic, 1.6% of

52

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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54

chromium, and 0.73% of copper. About 50% decrease in the contents of both arsenic and
chromium were noticed from dislodgeable solids collected from CCA/WR-treated wood
compared to those from CCA-treated wood. About 25% decrease in copper content was
found, which was not proportional to the decrease of arsenic or chromium in the solids.
With similar mass of dislodgeable solids collected, the decreased arsenic, chromium, and
copper contents in dislodgeable solids fi'om CCA/WR-treated wood suggested that water
repellent treatment retard the leaching of CCA components instead of the loss of wood
fibers.

After one month of field exposure, an 8% increase in arsenic content and an 18%
increase in chromium in the dislodgeable solids collected from CCA-treated wood
compared with the initial collection were observed. About 300% increase in copper
content in the dislodgeable solids after one month of field exposure suggested that the
reaction sites of copper in wood could be independent of arsenic or chromium. The
addition of WR decreased the depletion of the three elements from wood surface
compared with that from wood with no WR treatment. However, there was still a 100%
increase in copper content in the dislodgeable solids compared with the initial collection
(Table 3-6). These findings are in consistent with the theories of CCA interactions with
wood proposed by Pizzi (1982a, b) and Bull (2000, 2001): copper interacts / complexes
with wood carboxylate independent of arsenic or chromium, the complex formed is
relatively more soluble compared to the fixation product of arsenic and chromium, such
as chromium (III) arsenate and chromium (III) hydroxide.

Figure 3-4 illustrates the elemental arsenic, chromium, and copper contents in the

dislodgeable solids collected from CCA and CCA/WR-treated southern pine during the

55

field exposure. The largest depletion of arsenic, chromium, and copper was observed at
the initial stage of the field exposure. A general decrease of the three elements collected
was observed through out the first three months and became stable thereafter. The
amount of arsenic, chromium, or copper collected from board surface expressed in mg/m2
are calculated and listed in Table 3-6. About 3.7 mg/mz, 5.0 mg/mz, and 2.2 mg/m2 of
arsenic, chromium, and copper, respectively were collected from CCA-treated wood
before the field exposure. About 2.0 mg/mz, 2.3 mg/mz, and 1.9 mg/mz, respectively were
collected from CCA-C/WR treated wood before the field exposure. The amount of
arsenic, chromium, and copper collected decreased to 0.11 mg/mz, 0.12 mg/mz, 0.25
mg/mz, respectively from CCA-treated southern pine, and 0.16 mg/mz, 0.19 mg/mz, and
0.22 mg/m2 from CCA/WR-treated wood afier 6 months of field exposure in TRC.

In Figure 3-4, relatively larger amount of arsenic, chromium, and copper were
depleted from CCA-treated wood compared with CCA/WR-treated wood during the first
two months of field exposure, minimum difference in the depletion of the three elements
was observed thereafter, which suggested the addition of WR to CCA wood treatment
reduced the leaching of the three element at the initial stage of field exposure. However,
with a prolonged duration of field exposure, WR could be depleted from treated wood or
modified caused by the environmental factors such as rainfalls, snow, UV, ect., and
resulted in a relatively less significant performance in retarding the leaching of arsenic,

chromium, and copper.

3.3.4 Arsenic, chromium, and copper in CCA and CCA/WR-treated southern pine

56

 

3.9.5 '

 

5.00 an: (A)

 

 

 

 

Field exposure, months

 

Element collected from board surface, mg/m2

6.00
5.00 - (B)
4.00 ~ As
we" Cr
3.00 ~ —£:—Cu

 

 

 

 

F'eld exposure, months

Figure 3—4. Arsenic, chromium, and copper collected from (A) CCA, (B) CCA/WR
treated southern pine using DI water during field exposure

57

 

3.3.4.1 Arsenic, chromium, and copper in the l-mm surface layer of CCA and
CCA/WR-treated southern pine

Since the dislodgeable solids collection using test tube brush wiping was most
related to chemical leaching and “abrasion” of wood fibers on the wood surface layer,
arsenic, chromium, and copper retentions in the l-mm surface layer of the treated wood
were analyzed and compared with the three elemental contents in the dislodgeable solids
(Table 3-7). Arsenic, chromium, and copper contents in the surface layer of CCA-treated
wood were 3.38 mg/g, 6.26 mg/g, and 1.56 mg/g, respectively, and 4.59 mg/g, 9.19 mg/g,
and 2.02 mg/g, respectively in the surface layer of CCA/WR-treated wood. The
corresponded percentage compositions expressed in oxides were calculated according to
the equations listed in Appendix 2 and presented in Table 3-7. The percentage
composition of A3205, Cr03, and CuO was 32.0 : 52.7 : 15.3 in CCA dislodgeable solids
and 31.5 : 43.5 : 25.0 in CCA/WR dislodgeable solids. Compared with their percentage
composition in the l-mm surface layer at 27.0 : 62.6 : 10.4 from CCA-treated wood and
25.8 : 64.7 : 9.5 from CCA/WR-treated wood, the percentage composition of arsenic and
copper increased while chromium decreased in the dislodgeable solids. The increase in
arsenic and copper and decrease in chromium also indicated that the test tube brush
wiping collection method was composed of both “abrasion” of fibers on wood surface
and the leaching of CCA components. Should the dislodgeable solids have contained
only “abraded” wood fibers, similar composition of arsenic, chromium, and copper as
those in the surface layer of treated wood would have been expected. The decreased
composition of chromium could be attributed to the decreased leaching of chromium after
CCA fixation in wood (Cooper 1993; Murphy and Dickinson 1990; Cooper et a1. 1997;

Kennedy and Palmer 1994; Lahiry 2001; Crawford et al. 2002).

58

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59

3.3.5 Chemical redistribution of arsenic, chromium, and copper after 15 months of
field exposure

Table 3—8 summarizes arsenic, chromium, and copper contents in CCA or
CCA/WR-treated southern pine before and after 15 months of field exposure and the
corresponding elemental losses in percentage.

CCA-treated wood consisted of 0.35% of arsenic, 0.76% of chromium, and 0.17%
of copper before the field exposure. After 15 months, arsenic, chromium, and copper
contents in CCA-treated wood were 0.26%, 0.52%, and 0.13%, respectively. About
24.5% loss in arsenic, 31.9% loss in chromium, and 23.9% loss in copper were observed
(Table 3-8).

The initial content of the three elements in CCA/WR-treated wood were 0.42%,
0.81%, and 0.20% for arsenic, chromium, and copper, respectively. Afier 15 months of
field exposure, about 22.3% loss in arsenic, 22.6% loss in chromium, and 22.0% loss in
copper were detected (Table 3-8).

The chemical retentions in wood were calculated by using the wood density value
at 500 kg/m3 according to AWPA standard A12 (AWPA 2003) and listed in Table 3-8.
The chemical retentions in CCA and CCA/WR-treated wood before the field exposure
were at 7.1 kg/m3 and 8.5 kg/m3, respectively, and 5.3 kg/m3 and 6.6 kg/m3 afier 15
months of field exposure. The total chemical losses were 25.3% in CCA-treated southern
pine and 22.2% in CCA/WR-treated southern pine.

Similar percentages of arsenic and copper loss at 22.0-24.5% were observed fiom
CCA and CCA/WR-treated southern pine, suggested that the addition of WR to CCA

wood treatment did not retard the depletion of arsenic or copper throughout the

60

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61

15 months of field exposure. However, a decrease of chromium loss from 31.9% in CCA-
treated southern pine to 22.6% in CCA/WR-treated southern pine was observed, which
indicated that the addition of WR was effective in reducing the loss of chromium within
15 months.

Table 3-9 lists the chemical losses of wood afier 15 months of field (TRC)
exposure and a study conducted by Jin and Preston (1993). A broad range of chemical
loss, at 18.8-72.8% of arsenic, 13.6-23.6% of chromium, and 7.8-27.0% of copper from
CCA-treated wood was reported by Jin and Preston (1993) after 12 months of field
exposure in Hilo, H1. The wood chemical retentions, wood dimension, and the geological
region of the field exposure, and the exposure duration may have affected the results. The
levels of arsenic and chromium lost fi'om both CCA and CCA/WR-treated wood were
relatively close to wood at chemical retention of 4.0 kg/m3 observation by J in and Preston
(1993). A 22.0-23.9% of copper loss afier TRC exposure was relatively larger than the

7.8% of copper loss at chemical retention of 4.0 kg/m3 by Jin and Preston (1993).

3.3.6 Arsenic, chromium, and copper redistribution in CCA and CCA/WR-treated
southern pine in field exposure

The redistribution of a chemical in wood is defined as the changes in chemical
distribution pattern in wood. The chemical redistribution of arsenic, chromium, and
copper in CCA and CCA/WR treated southern pine in a lS-month field exposure is
plotted in Figures 3-5 and 3-6. The distributions of earlywood and latewood in wood
samples used to study the redistribution pattern are marked in the legend in each figure.

Afier 15 months of field exposure, arsenic, chromium, and copper contents

decreased in the weathered face of CCA-treated southern pine. The largest decreases in

62

 

 

 

 

 

 

 

 

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Figure 3-5. (A) As, (B) Cr, (C) Cu distribution in CCA treated southern pine with no field
exposure and after 15-month of field exposure, and (D) the earlywood and
latewood distributions in wood sections, ' ' ' earlywood, _ latewood

(A) As
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Figure 3-6. (A) As, (B) Cr, (C) Cu distribution in CCA/WR treated southern pine with no

month of field exposure, and (D) the earlywood
65

and latewood distributions in wood sections, ' ' ' earlywood, —

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0

arsenic, chromium, and copper were observed in the top l-mm section of the weathered
surface, with about 75% decrease in arsenic and about 60% decrease in both chromium
and copper, which was partially attributed to the chemical leaching and the collection of
the dislodgeable solids. The metallic components of CCA could migrate from the top
toward the bottom side. This was demonstrated by larger depletions of arsenic,
chromium, and copper from the weathered side of wood, the gradually less depletion
from the bottom (unweathered) side, and the increased arsenic, chromium and copper
content in the 20-23 mm section. The migration of the metallic components in wood may
be caused by the weather conditions. During rainfalls or during the melting of snow, large
amount of water was absorbed by the wood. The mobile arsenic, chromium, and copper
could move with the water flow following an “up-to-down” pattern caused by gravity.
The 5-8-mm wood section was mostly latewood, higher in density and more
hydrophobic. Therefore, a “jammed” water movement resulted in a relatively less
chemical depletion.

The redistribution patterns of arsenic, chromium, and copper in CCA/WR-treated
southern pine after 15 months of field exposure were different from those in CCA-treated
wood (Figure 3-6). The chemical loss of arsenic, chromium, and copper in the top 3-mm
sections of CCA/WR-treated southern pine was not as severe as those in CCA-treated
wood. Increases of arsenic, chromium, and copper in the 1-2 mm section were observed.
The highest chemical depletion was found in the 3-8 mm and the 14-20 mm sections. The
chemical retentions in the unweathered side remained close to those with no field
exposure. The chemical redistribution pattern in CCA/WR-treated wood could be

described as a depletion “from inner to peripheral zone” pattern. The chemical

66

redistribution pattern in CCA/WR-treated wood could be attributed the introduction of
water repellent, which consisted of paraffin wax and increased the hydrophobisity of
wood. Less water was absorbed during the period of rainfall, but once absorbed, the
water stayed longer in wood. The migration of arsenic, chromium, and copper with the
water evaporation from the inner sections to the peripheral zone became important, and

resulted in larger depletion of arsenic, chromium, and copper in the core.

3.4 Conclusions

The amount of arsenic, chromium, and copper collected from the board surface of
CCA-treated wood was significantly influenced by the collection methods such as a
glove-on-hand wiping, a paper wiping, or a test tube brush wiping method. Largest
quantities of arsenic, chromium, and copper were obtained by using the test tube brush
wiping method.

The compositions of elemental arsenic, chromium, and copper in the dislodgeable
solids collected from CCA and CCA/WR-treated southern pine were less than 4%. Larger
amounts of arsenic, chromium, and copper were collected from the board surface at the
initial stage of field exposure and decreased rapidly after three months.

The addition of water repellent reduced the chemical losses at the initial stage of
wood exterior exposure. After 15 months, similar levels of arsenic and copper loss were
found in CCA and CCA/WR-treated wood. The loss of chromium from CCA/WR-treated
southern pine remained lower than that from CCA-treated wood.

Different chemical redistribution patterns were observed with CCA or CCA/WR-

treated southern pine after 15 months of field exposure. The largest depletion of arsenic,

67

chromium, and copper was noticed on the weathered surface of CCA-treated wood, while
the largest chemical depletion was noticed in the inner zone rather than the peripheral
region of CCA/WR-treated wood. Arsenic, chromium, and copper level in the unexposed

side of CCA and CCA/WR-treated wood remained stable.

68

Chapter 4

Environmental Scanning Electron Microscope and X-ray Diffractometry
Characterization of the Dislodgeable Solids

4.1 Introduction

Data from atomic absorption spectroscopy analysis of the dislodgeable solids
collected from chromated copper arsenate type C (CCA) and chromated copper arsenate
type C with water repellent (CCA/WR) treated southern pine indicated that less than 4%
of the solids consist of arsenic, chromium, and copper. The nature of the remaining 96%
was unknown.

Environmental scanning electron microscope (ESEM) is a useful technique to
collect information on the topography, morphology, microstructure, and elemental
composition of a specimen (Schalek and Drzal 2000). The advantage of ESEM compared
to traditional scanning electron microscope (SEM) is that ESEM works under controlled
environmental conditions and requires no conductive coating on the specimen. This
makes it possible to examine specimens in their natural state under a vacuum of less than

50 Torr (6650 Pa).

X-ray energy dispersive spectrosc0py (EDS) uses silicon doped with lithium as a
detector. The interaction between the energetic monochromatic electrons from an
impinging electron beam and the electrons in the atoms of the specimen results in the
generation of X-rays. The generated X-rays impinge on the silicon detector surface. The
penetration depth of the X-ray into the silicon is directly related to the energy of the X-
rays. EDS permits detection of elements ranging from carbon (Z=6) to bismuth (Z=83)

at chamber pressures of 2-10 Torr (665-1330 Pa) of water vapor.

69

Environmental scanning electron microscope equipped with X—ray energy
dispersive spectrosc0py (ESEM-EDS) has been previously used to reveal the
macrodistribution of preservative in treated wood (Dawson-Andoh and Kamdem 1998;
Kamdem et al. 1998; Rosenqvist 1999). However, little information on crystalline
properties could be provided by ESEM.

X-ray diffractometry (XRD) is a useful technique to study compounds with
ordered structures. When X-ray beam traverses the crystallite, the beam light was
reflected from interplanar spacing of the particles at a certain direction. The identification
of chemical compounds is based upon the position of the reflected lines (in terms of 9 or
20) (Skoog 1984; Klug and Alexander 1954). The uniqueness of an X-ray diffraction
pattern for each crystalline substance makes XRD a convenient and practical means for
the qualitative identification of crystalline compounds. However, the XRD peak intensity
of the crystalline component in a given sample is influenced by percentage composition
and the density of the crystallite in its matrix, and its particle size. The XRD peak may
not be identifiable if the composition of the crystallite is too low in its matrix or the
particle size is smaller than the instrument detection limit.

XRD technique has been used to elucidate the nature of crystallite in treated
wood. Gallacher et al. (1995) identified the crystal formation of copper
dimethyldithiocarbamate (CDDC) in CDDC treated wood using XRD. Sutter et al. (1983)
confirmed the formation of copper oxalate in copper treated wood by copper tolerant
fungi. Kamdem et al. (1998) identified the formation of cuprous oxide (Cu20) in copper

naphthenate treated southern pine afier a post-treatment steaming.

7O

ESEM-EDS analysis was employed in this study to examine the topography and
chemical composition of the disoldgeable solids. XRD was used to investigate any
possible crystalline information presented in the dislodgeable solids collected from CCA

and CCA/WR treated southern pine.

4.2 Instrumental analysis
4.2.1 ESEM-EDS

The dislodgeable solids collected before and after 7 months of field exposure
from both CCA and CCA/WR treated southern pine were used for ESEM-EDS analysis
to reveal the topography and the particle size, as well as the chemical composition of the
dislodgeable solids.

The ESEM-EDS analysis was performed using an ElectroScan 2020 outfitted with
a LaB6 filament. The ESEM was equipped with a Link ISIS system that had an energy
resolution of 130 eV and an image resolution of 5-7 nm. An Oxford Si(Li) detector
utilizes an Atmospheric Thin Window (ATW) that X-ray mapping allowed the
determination of imaging the chemical composition of a specimen.

All the dislodgeable solids were imaged at an accelerating energy of 20 Torr, a
water-vapor pressure of 2.0 Torr, at magnifications of 300)( and IOOOX. The EDS
measurements were completed using the bullet detector with a working distance of 19

mm at a 30° takeoff angle.

71

4.2.2 XRD
The XRD patterns of the dislodgeable solids were collected and compared with
their parent boards, the corresponded water leachate, and the main ingredients of CCA

preservatives, to investigate any crystalline correlation among these samples.

4.2.2.1 Sample preparation

XRD diffractograms of the dislodgeable solids were collected directly with no
further preparation. The dislodgeable solids were obtained from CCA and CCA/WR
treated southern pine boards before and after 7 months of field exposure (Tree Research
Center, Michigan State University, East Lansing, Michigan). The collection of the
dislodgeable solids has been described in Chapter 3.

Commercial CCA and CCA/WR treated southern pine lumbers (Georgia-Pacific
Corporation, Atlanta, GA) were purchased from Lowe’s. The chemical retention of the
lumber was 6.4 kg/m3 on the label. The dimension of the boards was 2.6cm x 15cm ><
244cm. The surface of wood with no field exposure, and the weathered surface of wood
exposed in the field were used to obtain the XRD patterns. Wood samples were
microtomed into thin slices (about 200 um).

Untreated southern pine powder was prepared from defect free sapwood of kiln
dried southern pine with no field exposure. Wood was ground and passed through a sieve
at a size of 40 mesh.

Solids from the leachates were prepared from commercial CCA and CCA/WR
treated southern pine. The treated wood was ground into powder using a hammer mill.

About 100 ml of Deionized (DI) water was mixed with 20 g of CCA or CCA/WR treated

72

southern pine powder and stirred for 6 hours at room temperature. The leachate was then
filtered through a 0.45-um filter unit (Millex-HA, Millipore Corporation, MA, USA)
driven with a 20-ml syringe (Becton Dickinson & Co., part No. 301625) to remove the
wood powder. The leachate after the filtration was concentrated by using roto-
evaporation (RE 120 & Bilchi Rotovapor R-200, Brinkmann Instruments, Inc.). The
concentrated leachate was air dried and used to collect XRD diffractogram.

CCA preservative was prepared by using fieeze-drying of CCA stock solution
obtained from Osmose, Inc. at a concentration of 9.4% total oxides.

The XRD patterns of CCA main ingredients including arsenic (V) oxide (A5205,
99.99+%, Aldrich), chromium (V I) oxide (003, 98%, ACS Reagent, Aldrich), copper
(II) oxide (CuO, ACS Reagent, 99+%, Aldrich) were collected with no further
preparation.

The XRD diagram of sand (SiOz, 50-70 mesh, Aldrich) was also collected

directly.

4.2.2.2 XRD diffractogram collection

During the XRD diffractogram collection, samples were mounted to a sample
holder using double sided tape. The diffractogram was obtained by running a Rigaku
XRD diffractometer using Cu Kn radiation of 9. equal to 1.5418 A, and a voltage of 45
kV at 100 mA. Diffraction patterns were collected using DD and DS slot widths of 05°.
The diffraction angle (20) was measured from 5" to 65° at a speed of 2°/minute. The
detection limit with a typical background at 200 counts was approximately 0.2% in

weight composition and 100 A in particle size.

73

4.3 Results and Discussion
4.3.1 ESEM-EDS

Figures 4-1 and 4-2 present the ESEM images of the dislodgeable solids collected
from CCA or CCA/WR treated southern pine before and after 7 months of field exposure,
respectively. A typical pattern of small particles randomly distributed was observed with
all the dislodgeable solids examined. Particles with length ranging from 10 to 100 um
were labeled “large”, and “small” for those with length less than 10 pm.

In Figures 4-1A, the small particles were attributed to chemical deposits from
CCA treatment, and the large particles were wood splinters collected from the surface of
CCA-treated wood.

After 7 months of field exposure, the small particles were still observable at 300x
or higher magnifications (Figures 4-1B). However, unlike the typical long, narrow shaped
larger particles in the dislodgeable solids before the field exposure (Figures 4-1A), the
pattern of the large particles was not uniform after the field exposure. The disappearance
of the characteristic pattern of wood splinters was attributed to the photodegradation of
wood during exterior exposure (Kalnins and Feist 1991).

Figures 4-2A and 4-2B are the images of the dislodgeable solids collected from
CCA/WR treated southern pine before and after the field exposure, respectively. The
disappearance of the characteristic pattern of wood splinters in the dislodgeable solids
from CCA/WR treated wood after the field exposure was also observed.

EDS spectrum of the dislodgeable solids collected from CCA or CCA/WR treated
southern pine at 300x magnification are illustrated in Figures 4-3 and 4-4. The elemental

compositions of the dislodgeable solids from CCA and CCA/WR treated southern pine

74

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cps W: ~ I
15‘.’ 20 ;
i; (A)
Si ca
10 1 K
t i .
Cl!
M ‘8‘ 'l Cf
Si 1W9 A
u " [Fa " Fe
1 .' Vii s I C t
H N Fe Cu AsAs ;
01,,
0 5 10 15 20
Energy(keV)
cps“;
Si
15J
.z (B)

 

 

 

 

0 5 10 15 20
Energy (keV)

Figure 4-3. EDS spectrum of the dislodgeable solids collected from CCA treated
southern pine, (A) before the filed exposure, (B) after 7 months of field
exposure

77

 

 

    

 

 

 

 

 

 

 

cps «7S0
r
|
l C
10 .V; (A)
‘1 . Ca
NI SI ‘
t.
I. If?
1 t
5—i “for“!
. Cr
We.
‘ (fibwikja Cr 2’
V ‘. UFCFCU 1
M5 Cu AS J
0~—- . ~ ‘*"—r‘*“""""'*"1" w
0 5 10 15 20
Energy(keV)
we 1
15% .
I Ca (B)
‘ O
10“
S
I .‘ 9
5—4 1 I ‘
1W i
:2 Cu
1U Mg M Fe CUAS AS
0....,,...}rTfiT..r.
0 5I 10 15 20
Energy(keV)

Figure 4-4.

EDS spectrum of the dislodgeable solids collected from CCA/WR treated
southern pine, (A) before the filed exposure, (B) after 7 months of field
exposure

were qualitatively similar. The EDS peaks of arsenic, chromium, and copper were
identified in the entire spectrum collected. This consistent presence of arsenic, chromium,
and copper in the dislodgeable solids was attributed to CCA wood treatment. Besides
these three elements, iron, calcium, potassium, chloride, sulfur, silicon, magnesium,
sodium, carbon, and oxygen were also found in dislodgeable solids collected from both
CCA and CCA/WR treated wood. Calcium, potassium, magnesium, sodium, carbon, and
oxygen may come from the wood components (Fengel and Wegener 1984). Calcium,
magnesium, silicon and aluminum may also come from airborne soil. Sulfur could come
from the air pollution, such as the release of sulfur dioxide (S02) during coal burning and
come done out of the atmosphere by rain. Iron and chloride may come from the
contamination during wood industrial treatment.

The relatively strong signal of both carbon and oxygen suggested the presence of
organic material. Since CCA preservatives are composed of non-carbon based inorganic
chemicals (AWPA 2003), this organic material present in the dislodgeable solids could
be attributed to the collection of wood material. This hypothesis was supported by
observations from ESEM study.

After 7 months of field exposure, an addition of aluminum was found in the
dislodgeable solids collected from both CCA and CCA/WR treated wood (Figures 4-3B
and 4-43). Significant increase in the peak intensities of silicon, sulfur, and decrease in
the peak intensity of chromium were also observed after the field exposure. The presence
of aluminum in field (TRC) soil has been demonstrated in a previous soil analysis by
Crawford et a1. (2002). This addition of aluminum and the increment of silicon could be

attributed to the accumulation of soil on wood surface during the field exposure and

79

consequently collected in the dislodgeable solids. Another alternative for the silicon
source could come from the glassware used during the dislodgeable solids collection. The
increased peak intensity of sulfur could be attributed to the air pollution, or the presence
of biological organisms on the wood surface. The decreased peak intensity of chromium
is in consistent with atomic absorption spectroscopy analysis (Chapter 3), which
indicated that chromium content in the dislodgeable solids decreased after the field

exposure.

4.3.2 XRD
4.3.2.1 Wood

XRD patterns of untreated southern pine powder and CCA-treated southern pine
before and after field exposure are illustrated in Figure 4-5. Two broad peaks from

cellulose exist in the 20 angle between 10° and 25° (Kamdem et al. 1998). This typical

cellulose pattern is attributed to the 101,101, 002 and 040 reflections of cellulose I
(Fengel and Wegener 1983). Cellulose I patterns presented in untreated southern pine
(Figure 4-5C), CCA-treated southern pine before and after the field exposure (Figure 4-
5A, B). No significant modification in the XRD patterns was observed after CCA
treatment and the field exposure compared with untreated southern pine.

This characteristic pattern from cellulose I was also observed with CCA/WR
treated southern pine before the field exposure (Figure 4-6A, B). No other significant
peak information was observed throughout the rest of the diffraction angle (20 at 25° to

65 °).

80

 
   

 

 

 

 

   
     

 

 

 

 

  

 

 

 

002 ‘
400 1
1 (A) CCA treated southern pine
300 1 before field exposure
200. J
100 H 1
0 i i I‘ ‘ I'A " 7' “u“ A Q
5 15 25 35 45 55 65
1000
002
800 7 (B) CCA treated southern pine
600 101’ 1 01 after field exposure
400 A 040
200 ~
0 v , , f
5 15 25 35 45 55 65
2500
002
2000 _
101, 101 ,
1500 , (C) untreated southern pine
1000 r
500 r
0 r r A
5 1 5 2 5 3 5 4 5 5 5 6 5

Figure 4-5.

Diffraction angle 2-theta, degree

XRD diagrams, (A) CCA treated southern pine before field exposure, (B)
CCA-C treated southern pine after field exposure, (C) untreated southern
pine

81

3000
2500 -
2000 ~
1500 a 101, 101
1000
500

 

002

(A) CCA/WR treated southern
pine before field exposure

 

 

 

 

700
600 — 002 (B) CCA/WR treated southern pine
500 _ after field exposure

 

101,10i

200-
100*

 

 

 

2500

 

002

i

2000

101,10i

L

1500 (C) untreated southern pine

  

1

1000

500 :

 

 

 

5 15 25 35 45 55 65
Diffraction angle 2-theta, degree

Figure 4-6. XRD diagrams, (A) CCA/WR treated southern pine before field exposure,

(B) CCA/WR treated southern pine after field exposure, (C) untreated
southern pine

82

4.3.2.2 Dislodgeable solids
The diffractograms of the dislodgeable solids collected from CCA and CCA/WR
treated southern pine before the field exposure are presented in Figures 4-7A and 4-8A.

Two broad peaks between 10° and 25° were identifiable, which are attributed to the

101,101, and 002 reflection fi'om cellulose I. This was an indication of the presence of
wood material in the dislodgeable solids, which was also evidenced in the ESEM
observation. Afier 7 months of field exposure, this cellulose pattern disappeared in the
dislodgeable solids (Figures 4-7B and 4-8B). This could be attributed to the decrease of
wood material in the dislodgeable solids or the deformation of cellulose I lattice during
wood weathering (Kalnins and Feist 1991).

Two peaks at 20 angle of 205° and 262° consistently presented in the
dislodgeable solids from wood before and after the field exposure (Figures 4-7A, B and
4-8A, B). These two peaks are attributed to the presence of sand (SiOz) (Figures 4-7C
and 4-8C), which may come from contamination during industrial wood treatment and /

or the surrounding environment during the field exposure.

4.3.2.3 Solids from the leachate and CCA main ingredients

XRD diffractograrns of the solids dried up fi'om CCA and CCA/WR treated
southern pine leachates are illustrated in Figure 4-9. No identifiable crystalline
information was obtained, which suggested that the solids from leachates were either

amorphous or the crystallite size formed afier a roto-evaporation were smaller than the

detection limit at 100 A.

83

5000
4000
3000
2000
1000

Figure 4-7.

 

 

 

 

(A) dislodgeable solids collected
26.2 ° from CCA treated wood
20.5 ° before field exposure
101, mi 002
5 l 5 2 5 3 5 4 5 5 5 6 5

 

 

(B) dislodgeable solids collected
from CCA treated wood after 7-
month field exposure

26.3 °

    

 

 

 

 

 

 

 

 

 

5 15 25 35 45 55 65
26.7“
21.0° (C) sand
46.0°
55.2°
39.7°
36.8°
“T i {Jr HJAAJ
15 25 35 45 55 65

Diffraction 2-theta angle, degree

XRD diagram of the dislodgeable solids collected from the surface of
CCA treated southern pine: (a) before field exposure, (b) after 7 months of
field exposure, (c) sand

84

800
700
600
500
400
300
200
100

1400
1200
1000

800

200

5000
4000
3000
2000
1000

Figure 4-8.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

" 20 5 9 26.2 o
_ ‘ .. I (A) dislodgeable solids from
A '1'? 002 CCA treated wood before
_ field exposure
‘ 101, 101
5 1 5 2 5 3 5 4 5 5 5 6 5
26.3 °
(B) dislodgeable solids from
A . CCA/WR treated wood after 7-
r 20-6 month field exposure
A 11.4 °
5 15 25 35 45 55 65
26.7°
(C) sand
21 .0°
460°
55.2 °
39.7 °
36 8°
-11 “J 11L -Ilirlul ---
5 15 25 35 45 55 65
Diffraction 2-theta angle, degree
XRD diagram of the dislodgeable solids collected from the surface of

CCA/WR treated southern pine: (A) before field exposure, (B) after 7
months of field exposure, (C) sand

85

500

 

 

 

 

 

 

 

 

 

 

4 00
(A) lechate from CCA
3 00 treated southern pine
2 00
100 W
0 l . A . , ‘
5 1 5 2 5 3 5 4 5 5 5 6 5
500
400
(B) lechate from CCA/WR
300 treated southern pine
200
100
0 t .
5 15 25 35 45 55 65
7 00
600 A .
500 I» (C) CCA preservative
4 0 0 Er i
3 00 l l
200 L
I
O t l r l J_
5 l 5 25 3 5 45 5 5 6 5

Diffraction angle 2-theta, degree

Figure 4-9. XRD diagrams, (A) solids from CCA treated southern pine leachate, (B)
solids from CCA/WR treated southern pine leachate, (C) CCA
preservative

86

Industrially, CCA preservative is prepared by adding chromium (VI) trioxide to
water to form chromic or dichromic acid, and solid copper oxide to form a copper
dichromate solution; arsenic pentoxide is added as solution of arsenic acid. The
preservative is a mixture of ions that could form a mixture of copper dichromate, copper
arsenate, etc. After CCA wood treatment, a series of interactions could be carried out
between CCA components and wood, results in the reduction of Cr“, and the formation
of chromium (III) arsenate / hydroxide, and complex between chromium, copper and
wood (Bull 2001). Figure 4-10 illustrates the XRD patterns of the main ingredients of
CCA preservative: CuO, Cr03, and A320; No crystalline information could be
observed with Asz05 (Figure 4-10C). Peaks at 325°, 353°, 388°, and 488° from CuO
(Figure 4-10A), peak at 591° from 003 (Figure 4-10B) could not be identified from
either CCA-treated wood (Figures 4-5 and 4-6) or the dislodgeable solids (Figures 4-7
and 4-8), which suggested that afier CCA wood treatment, there is no presence of CuO,

Cr03, and /or A5205 in treated wood.

4.4 Conclusions

The dislodgeable solids mainly consisted of wood splinters with small chemical
deposits distributed in wood matrix. The particle sizes of the chemical deposits were
mostly less than 10 um, and the wood splinters between 10 and 100 um. After the field
GXposure, the crystalline lattice of cellulose l in wood was destroyed.

Similar elemental compositions were found in the dislodgeable solids collected

from CCA and CCA/WR treated southern pine. Arsenic, chromium, copper, iron,

87

9000
8000 ,
7ooo «
6000 , (A) CuO

 

353°
3&8"

4000 4
3000 T
2000 1 32.5 48.8°
1000 < . - - L m: . l _

 

 

 

 

5 10 15 20 25 30 35 4O 45 50 55 60 65

250

 

2°“ (B) 003

150

so~ A " it,

 

 

 

 

600 ~ (C) AS205

 

 

 

5101520253035404550556065
Diffraction 2-theta angle, degree

Figure 4-10. XRD diagrams of CCA main ingredients, (A) CuO, (B) 003, (C) Asz05

88

potassium, chloride, sulfur, silicon, magnesium, sodium, carbon, and oxygen were
detected in the dislodgeable solids from wood before the field exposure. After 7
months of field exposure, contamination of sand or soil from the surrounding

environment was observed with the dislodgeable solids.

89

Chapter 5

Solubilization of Arsenic, chromium, and Copper from the Dislodgeable Solids

5.1 Introduction

Human exposure to arsenic and chromium through the use of chromated copper
arsenate (CCA) treated wood is considered a potential risk of human health (McMahon
and Chen 2001). Study of the dislodgeable solids collected from the surface of CCA-
treated southern pine boards found that, the dislodgeable solids mainly consisted of wood
splinters with less than 4 wt.% of total arsenic, chromium, and copper. In residential
exposure to CCA-treated wood, oral ingestion of the dislodgeable solids through a hand-
to-mouth behavior, typically found in children, can be one of the main routes of exposure
to arsenic, chromium, and copper. In an exterior exposure, chemicals dislodged from
CCA-treated wood could partially solubilize during a rainfall. A direct dermal contact
with the contaminated rainfalls can be another important route of exposure to arsenic,
chromium, and copper.

The toxicity of arsenic, chromium, and copper varies with the chemical forms
(Tatken and Lewis 1983). Simple hydrated metal ions are considered to be the most toxic,
while strong complexes and species associated with colloidal particles are usually
assumed to be less toxic (Russeva 1995). The water solubility of arsenic compounds
influences their bioavailability. The absorption of arsenic in a water-soluble form through
the gastrointestinal tract is generally assumed to be nearly complete (Campbell 1995).
Arsenic in water-insoluble forms may be incompletely absorbed (McMahon and Chen

2001). The toxicity of arsenic and chromium is strongly affected by their oxidation states.

90

In a short term and large dose exposure, inorganic pentavalent arsenic (Asv) is less potent

111

than inorganic trivalent arsenic (As ); hexavalent chromium (Crv') has been recognized

I") is human essential (Schroeder and

as a carcinogen while trivalent chromium (Cr
Balassa 1966; Hughes et al. 1994; Healy et al. 1998).

The objective of this study is to characterize the solubilization of arsenic,
chromium, and copper from the dislodgeable solids collected on the surface of CCA type
C (CCA) and CCA type C with water repellent (CCA/WR) treated southern pine boards,

and to speciate the chromium and arsenic solubilzed.

5.2 Arsenic speciation

In documented studies, arsenic leaching of CCA-treated wood is generally
reported in total amount with little information on the species. No standard method of
arsenic speciation in CCA-treated wood is available from American Wood Preservers’
Association (AWPA 2003). In recent years, there are several studies conducted to
speciate arsenic from CCA-treated wood. Nygren and Nilsson (1993) used a selective
solvent extraction coupled with atomic absorption spectroscopy (AA) to study arsenic
species in CCA-treated wood, and found more than 99.5% of total arsenic was Asv, with
less than 0.5% of total arsenic as Asm. Information on the extraction efficiency and
stability of arsenic species during the extraction was not provided. Hingston (2003)
published a paper describing the use of differential pulse polarography to speciate the
species of arsenic in leachate of CCA-treated wood, and found less than 10% of total

III

arsenic was As . Solo-Gabriele et al. (2003b) reported the speciation of arsenic in the

leachate of CCA-treated wood removed from service by using high performance liquid

91

chromatography coupled with hydride generation atomic fluorescence spectrometry
(HPLC-HG-AF S). It was reported that As"I ranged fi'om 0 to 51% of total arsenic in the
leachate from various treated wood samples.

Most of the studies associated with arsenic speciation are conducted with liquid
or aqueous phase solution. The history of arsenic speciation in water could be traced back
to year 1775. The reduction of arsenic to volatile arsine (AsH3) was classified as a
“hydride generation” analytical method (Partington 1962). AsV and As‘11 were determined
using hydride generation reactions by varying the pH of the solution (Cullen et al. 1994).
The documented speciation methods of arsenic in water and biological samples include:

sequential spectrophotometric determination of Asv and Asm

by controlling the pH of the
reduction solution, which is appropriate for determination of 240 ug of each arsenic
species (Howard and Arab-Zavar 1980); solvent extraction combined with neutron
activation with a detection limit of 10'2 ug/l described by several authors (Yasui et al.
1978; Mok et al. 1986); colorimetric detection of the colored complex formed between
arsine and silver diethyldithiocarbamate with a detection limit of 40 ug/l used by Irgolic
(1994); high-performance liquid chromatography equipped with inductively coupled
plasma and atomic emission spectrometry O-IPLC-ICP-AES) and / or mass spectrometry
(HPLC-ICP-MS) were also used to speciate arsenic and the detection limits were at
subnanogram level (Monplaisir et al. 1994).

An ion-exchange chromatography method of arsenic speciation in water was
developed and reported by Flores del Pino (2003). This method was employed in this

study to speciate arsenic solubilzed from the dislodgeable solids. The chemical structures

of AsV and AsIll are presented in Figure 5-1. The conversion between As"1 and AsV is

92

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93

influenced by the redox potential (Eh) and pH of the matrix. The Eh—pH diagram of
different arsenic species at 25°C and at pressure of one atmosphere is illustrated in Figure
5-2 (Ferguson and Gavis 1972). The Eh-pH correlation between various arsenic species
suggests that pH modification of a matrix can be used to change the ionized and neutral
forms of arsenic without altering their oxidation states. This principle was used to

m from Asv using pH and ion-exchange chromatograPhY-

separate As
5.3 Chromium speciation

After CCA treatment, a series of interactions may carry out, mainly between
arsenic, chromium, copper, and wood components. Chromium in CCA-treated wood is
mainly Crm, due to the reduction of CrVI after fixation (Cooper and Ung 1993). Bull
(2000, 2001) pointed out that three major fixation products could exist in CCA-treated
wood: chromium (III) arsenate (CrAsO4), chromium (III) hydroxide (Cr(OH)3), and
copper complexing with wood components. Crw could also be reduced to Crm through
the interaction with some functional groups of lignin or the lignin fraction. The reduction
of CrV1 is used as an indication of CCA fixation in wood. If fixation is not complete,
relatively large amount of CrVI would be present in treated wood and ready to leach
(Chen et a1. 1994; Cooper et al. 1994).

A colorimetric method using the complexing between CrVI and 1, 5
diphenylcarbazide was employed to determine the amount of CrVI solubilized from the

dislodgeable solids.

94

 

 

 

 

20 ‘\ H3A304 H20
(unstable) 1 0
16 "‘ / - .
3.
12 - H2ASO4- \ASO4 ' '75
3 _\ - 50
HAsO42‘

4 -r H3A503 ”-25
PE 0 _, '0 Eh (V)
-4 _ --.25

As
-3 - --.50
"2(9) \
-12 _ .-
H20 H2A503' 75
—16 (unstable) HAsOaz‘ 1 0

 

 

 

Figure 5—2. pE-pH diagram for the As-HZO system at 25°C with total As species of 50
ppb

95

5.4 Material and Methods
5.4.1 Dislodgeable solids solubility study protocol

A laboratory method was developed to characterize the solubilization of arsenic,
chromium, and copper from the dislodgeable solids at various test durations and pH of
the water matrix. The dislodgeable solids collected from CCA-treated southern pine
(dislodgeable solids CCA), or CCA/WR-treated southern pine (dislodgeable solids
CCA/WR) before the field exposure were used in this study. The collection of the
dislodgeable solids has been described in Chapter 3. Arsenic, chromium, and copper
contents in dislodgeable solids CCA were 1.2%, 1.6%, and 0.73% in weight,
respectively; and 0.59%, 0.67%, and 0.73%, respectively in dislodgeable solids
CCA/WR.

Figure 5-3 presents the protocol of the solubilization study. About 10 mg of the
dislodgeable solids were weighed using a digital balance (accuracy: 0.001 g, Mettler
AE200, Mettler Instrument AG, Switzerland) and mixed with 13.0 ml of dissolving water
in a 15-ml centrifuge tube (Polypropylene, Sterile, VWR 21008-678). About 360 mg of
dislodgeable solids were used to prepare 36 centrifuge tubes. A total of 72 tubes were
prepared: 36 from dislodgeable solids CCA and 36 from dislodgeable solids CCA/WR.
The 36 tubes containing each type of dislodgeable solids were divided into four groups.
In each of the 9 tubes 13.0 ml of deionized (DI) water at pH 3, 4, 5, or 6 was added. The
pH of the DI water was adjusted using sulfuric acid and measured by a pH meter
(Consort P601 from Scientific Instrument, Inc.) equipped with a pH electrode (Cole-
Parmer Instrument Co. Catalog number 5990-65). The centrifuge tubes were fitted with

screw caps, to limit water evaporation and air exposure. The suspension in the centrifuge

96

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tube was shaken using a mechanical mixer (Thermolyne Model 37615, Barnstead /
Thermolyne, Iowa, USA) at room temperature. Three tubes at each pH were collected
after 1, 24, and 168 hours.

The suspension was filtered through a 0.45-um filter unit (Millex-HA, Millipore
Co., Cat. No. SLHA0250S) driven with a 20-ml syringe (Becton Dickinson & Co., Part
No. 301625). The filtered liquid was collected in a clean 15-ml centrifuge tube for further
analysis. About 8 m1 of the filtered liquid was used to determine the total chromium and
copper, about 4 ml used for chromium speciation, and another 1.0 ml for total arsenic
determination and arsenic speciation.

Figure 5-4 illustrates the procedure of total arsenic, chromium, copper analysis,

and the speciation of arsenic and chromium.

5.4.2 Total arsenic, chromium, and copper solubilized from the dislodgeable solids

Total arsenic, chromium, and copper solubilized from the dislodgeable solids in
water were measured using atomic absorption spectrometry (AA). A graphite furnace
atomic absorption spectroscopy (GFAA, AAnalyst 800, Perkin Elmer Co.) equipped with
an EDL arsenic lamp was employed to determine arsenic concentration at parts per
billion level (ppb). A flame atomic absorption spectrophotometer (FAA, Model: Perking
Ehner 3110), equipped with an EDL arsenic lamp, and hollow cathode lamps for
chromium and copper (from Perkin Elmer) was used to determine arsenic, chromium and
copper concentrations in parts per million level (ppm). The preparation of the standard
solutions to obtain the working curve of each element for AA analysis has been described

in the experimental section of Chapter 3.

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Samples subjected to GFAA determination of arsenic were prepared after 25-fold
dilution from the initial filtered liquid. About 1 ml of the diluted solution was used to

determine the total arsenic, and 20.0 ml of the diluted solution for arsenic speciation.

5.4.3 Speciation of arsenic solubilized from the dislodgeable solids - selective ion-
exchange measurement of Asv and Asm

5.4.3.1 Procedure of Asv and As"1 speciation

Arsenic speciation was performed immediately afier the sampling to limit
possible oxidation or reduction of arsenic. Figure 5-5 illustrates the pre-column and the
modified chromosorb cartridge used for arsenic speciation. Cation exchange resins with
mesh size ranging from 50 to 100 were packed in a l-ml syringe (Becton Dickinson
309602 NH 17530). The cation exchange capacity of this pre-column was 2 meq/g. The
resin was pre-wetted with DI water before use. The pre-column was connected to a
vacuum pump under a vacuum level of 10 in Hg (3.4><104 Pa). The 20.0 ml diluted
solution passed through the pre-column (cation-exchange) at a flow rate of l ml/minute.
The function of the pre-column was to eliminate the potential interference of cations
before arsenic speciation, such as copper (Cup) from CCA.

The pH of the solution passing through the pre-column was adjusted to 2.5-3.5 by
using 1.0N of hydrochloric acid (HCl) and / or 0.1N of aqueous ammonium hydroxide
(NH40H) before the separation of AsV and Asm. The pH of the solution was measured by
using a pH meter (Consort P601 from Scientific Instrument, Inc.). The separation of Asv
and AsIn was performed by passing the solution through a modified chromosorb
cartridge, which was a silanized diatomaceous earth with dioctyltin dichloride

((CngthnClz) that preferentially absorb Asv. AsV in an ionized form was absorbed on

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the modified chromosorb in the cartridge and As"1 in its neutral form was found in the

effluent. The Asv trapped in the modified chromosorb cartridge was desorbed by using

0.5N of HCl. The solution passing through the cartridge contained AsIII

, the elution
washed out from the cartridge consisted of Asv, and the initial liquid collected were
analyzed by using GFAA to determine the contents of Asm, Asv, and total arsenic,

respectively.

5.4.3.2. Asv and As"! recovery rate - arsenic speciation of standard Asv and AsIll
solutions using the selective ion-exchange method

The standard AsV solutions were prepared from arsenic pentoxide (AS205,
99.999%, ACROS). About 0.05 g of A5205 was weighed and solubilized in 2 ml of
perchloric acid (HC104) and 5 ml of nitric acid (HN03, double distilled, Caledon
Laboratory Chemicals), and set for 2 hours for the solubilization before diluted to 500 ml
using 0.1N HN03. The arsenic concentration was measured at 65.2 ppm (mg/l) using
FAA. The standard Asv solutions at concentrations of 5 ppb (pg/l), 10 ppb, 50 ppb, 100
ppb, 300 ppb, and 500 ppb were diluted from the initial solution using 0.1N HN03
accordingly.

The standard Asm solution was prepared according to Chen et al. (2002). Arsenic
trioxide (0.0660 g, AS203, 99.995%, Aldrich) was weighed using a digital balance
(accuracy: 0.001 g, Mettler AE200, Mettler Instrument AG, Switzerland). This 0.0660 g
of A8203 was dissolved in 1000 ml of NaOH solution (0.1N) and acidified to pH between
2.5-3.5 by using 0.1N HCl (6N, double distilled, Caledon Laboratory Chemicals)

titration. The arsenic concentration was measured at 49.98 ppm using FAA. The standard

102

As"l solutions at the concentrations of 5 ppb, 10 ppb, 50 ppb, 100 ppb, 300 ppb, and 500
ppb were diluted from the initial solution accordingly using 0.1N HCl.

The concentrations of both Asv and Asm standard solutions prepared were
measured by using GF AA. These standard solutions were analyzed using the selective

III

ion—exchange arsenic speciation method. The recovery rate of Asv or As was defined as

[I]

the ratio between the amount of Asv (or As ) detected afier the speciation to the known

I") in the standard solution. The recovery rate of Asv or AsIn was

amount of Asv (or As
used as an indicator of the efficiency of Asv or Asm that could be detected by using this

selective ion-exchange method.

5.4.4 Ultraviolet visible (UV -vis) spectroscopy analysis of hexavalent chromium
(Cr") in water

CrVI in water was determined by using a colorimetric method described by
Cooper and Ung (1993). The standard solutions were prepared by diluting CrVI standard
solution (1000 ppm, Atomic absorption standard, Aldrich) using 0.5N sulfiiric acid
(H2804) (A.C.S. Reagent, 98%, J .T. Baker). The concentrations of the standard solutions
were 0 ppm, 0.2 ppm, 0.4 ppm, 0.6 ppm, 0.8 ppm, and 1.0 ppm. A 2.5 wt.% 1, 5-
diphenylcarbazide solution was used as an indicator. The 1, 5-diphenylcarbazide solution
was prepared by dissolving 2.5 g of 1, S-diphenylcarbazide (A.C.S. Reagent, Aldrich) in
100 ml mixture of acetone (A.C.S. Reagent, J .T. Baker) and DI water (v/v: 1:1). The UV-
vis absorbance of the colored complex formed between CrVI and 1, S-diphenylcarbazide
was measured at 540 nm by using UV-visible (UV -vis) spectrophotometer (DU 6403,

Beckman Co.). The CrVI working curve was obtained by plotting the visible absorbance

103

of CrVI-diphenylcarbazide complex against the corresponding chromium (Crv')

concentrations determined by using FAA.

5.4.5 Statistic analysis

One-way ANOVA analysis (Jandel SigmaStat Version 2.0, Jandel Co.) using all
pairwise multiple comparison tests (Tukey Test) at the significant level of 0.05 was
performed, to analyze significant difference between the percentage of arsenic,
chromium, or copper solubilized from the dislodgeable solids influenced by the pH (pH
3, 4, 5 or 6) of water, the test duration (1, 24, or 168 hours), or the addition of water

repellent to CCA wood treatment.

5.5 Results and discussion
5.5.1 Speciation of chromium solubilized from the dislodgeable solids

The working curve for Crv' analysis using the 1, 5-diphenylcarbazide method is
plotted in Figure 5-6. A linear correlation (R2 = 0.99) was found between the UV
absorbance of CrVI-diphenylcarbazide complex and the concentration of CrVI between 0
to 1 ppm.

Table 5-1 lists the concentrations of CrVI solubilized from 0.010 g of
dislodgeable solids CCA or dislodgeable solids CCA/WR in the 13.0 ml water. The
corresponded percentages of CrVI solubilized from the dislodgeable solids are calculated
using Equation 1 and also reported in Table 5-1. These percentage values were obtained
afier dividing the amount of CrVI present in water by the total chromium in the

dislodgeable solids.

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element solubilized (%)

_ concentration of elemental species in water (mg/1) x 0.0131
— 0.010g dislodgeable solids x total element in dislodgeable solids (%)

 

x100% (1)

In dislodgeable solids CCA, by varying the pH of the water fi'om 6 to 3, about
0.09 ppm to 0.16 ppm of CrVl was found in water during the first hour, which
corresponded to 0.7-1.3% of total chromium in the solids. Afier 24 hours, about 1.1-2.5%
of total chromium in the solids was detected as Cr‘" in water. A maximum value of 4.2%
was found in water at pH 3 after 168 hours.

In dislodgeable solids CCA/WR, by decreasing the pH of water from 6 to 3, the
concentrations of CrVI increased from 0.14 ppm to 0.35 ppm in the first hour, fi'om 0.37
ppm to 0.48 ppm after 24 hours, and from 0.42 ppm to 0.70 ppm after 168 hours.

One-way ANOVA analysis suggested that significant difference existed in the
percentage of CrVI solubilized from dislodgeable solids CCA and dislodgeable solids
CCA/WR throughout the 168-hour test duration (Appendix 3 Tables 1-3). Relatively
larger percentage of CrVI was found with dislodgeable solids CCA/WK (Table 5-1)
resulted from a relatively incomplete CCA fixation in CCA/WR-treated wood, which
could mainly be attributed to the presence of water repellent. The UltraWood water
repellent used in this commercial CCA/WR-treated wood was a paraffm wax and
surfactant based emulsionz. The main fimction of water repellent is to reduce the water
absorption and desorption, and therefore improve the dimensional stability of wood

products (Williams and Feist 1999; Zahora 1995).

 

2 Information obtained from CS], 1nc., provider of Ultrawood WR used for this commercial CCA wood
treatment

107

After CCA treatment, CCA components penetrate into the cell wall of tracheids,
and preferentially react with guaiacyl lignin (Petty and Preston 1968; Newman and
Murphy 1996). With the presence of water repellent it takes longer period for water to
evaporate from wood, thus interferes the interactions between CCA components and
wood, e.g. the precipitation and / or complexing between copper and lignin, and

reduction of CrVI to CrIII

by the primary alcohol groups in lignin (Pizzi 1982a, b, c; Bull
2001). A lagged CCA fixation resulted in relatively large amounts of unfixed CCA
components in wood ready to leach out (Cooper et al. 1994).

Statistical analysis also suggested that the solubilization of or“ from both
dislodgeable solids CCA and dislodgeable solids CCA/WR are time and pH dependent
(Appendix 3 Tables 4-7). An increased amount of soluble CrVI was observed with the

increased test duration and water acidity (Figures 5-7 and 5-8).

5.5.2 Water soluble arsenic, chromium, and copper in the dislodgeable solids

The working curve used for GFAA arsenic analysis is illustrated in Figure 5-9,
which is the plot of the signal from GFAA versus the concentration of arsenic in the
standard solution. A linear correlationship with a R2 of 0.99 was found at arsenic
concentration from 0 to 200 ppb.

Table 5-2 lists the percentage of total arsenic, chromium, and copper solubilized

in water (pH 3-6) from dislodgeable solids CCA or dislodgeable solids CCA/WR at test

durations of 1, 24, and 168 hours.

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5.5.2.1 Influence of water repellent on the solubilization of total arsenic, chromium,
and copper

Throughout the 168-hour test duration, about 4% to 10% of total arsenic and 4%
to 19% of total copper in dislodgeable solids CCA was solubilized. The percentage of
chromium solubilized was the least of the three elements, ranging fi'om 1.4% to 4.4% of
total chromium in the dislodgeable solids (Table 5-2).

About 14% to 27% of total arsenic and 13% to 34% of total copper were
solubilized from dislodgeable solids CCA/WR. Unlike what was observed with
dislodgeable solids CCA, the proportion of chromium solubilized from dislodgeable
solids CCA/WR was the highest of the three elements. About 26% to 37% of the total
chromium was found in water.

One-way ANOVA analysis suggested that, the percentage of total arsenic,
chromium, and copper solubilized from dislodgeable solids CCA/WR were significantly
larger than those from dislodgeable solids CCA (Appendix 3 Tables 8 to 16). The
interference of water repellent with CCA fixation was demonstrated by the increased
levels of soluble total arsenic, chromium, and c0pper from dislodgeable solids CCA/WR

compared with those from dislodgeable solids CCA (Figures 5-10, 5-11, and 5-12).

5.5.2.2 Influence of test duration on the solubilization of total arsenic, chromium,
and copper

In dislodgeable solids CCA, about 3.5:t0.5%, 7.0:t1.0%, and 9.0i1.0% of total
arsenic was solubilized after 1 hour, 24 hours, and 168 hours, respectively. Similar levels

of chromium at 3.0i1.5% were solubilized throughout the 168-hour test. The percentage

113

 

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Figure 5-10. Percentages of total arsenic solubilized from the dislodgeable solids,
(A) dislodgeable solids from CCA treated wood,
(B) dislodgeable solids from CCA/WR treated wood

114

 

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15 88 8 8 8 8 88 8 8

10 - 8

 

 

 

 

% soluble Cr in total Cr from dislodgeable solids

4 (B)

 

 

 

 

 

Figure 5—11. Percentages of chromium solubilized from the dislodgeable solids,
(A) dislodgeable solids from CCA treated wood,
(B) dislodgeable solids from CCA/WR treated wood

115

% soluble Cu in total Cu from dislodgeable solids

Figure 5—12.

 

 

 

 

 

 

   
    

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(A) dislodgeable solids from CCA treated wood,
(B) dislodgeable solids from CCA/WR treated wood

116

of copper solubilized increased from 4% to 19% from 1 hour to 168 hours (Table 5-2).
One-way AN OVA analysis found that, the solubilization of arsenic was significantly
influenced by the test duration at pH 6 (Appendix 3 Table 17). An increase in the
percentage of arsenic solubilized was observed with increased test duration (Figure 5-
10A). Data groups at pH 3, 4, and 5 failed to pass the normality test. No statistical report
was further performed. The solubilization of chromium presented to be less time
dependent at pH 4, 5, and 6. At pH 3, the solubilization of chromium was significantly
influenced by time (Appendix 3 Table 18). An increase of chromium solubilized was
observed with increased test duration (Figure 5-1 1A). The percentage of copper
solubilized was time dependent at pH 5 and 6 (Appendix 3 Table 19), and increased with
test duration (Figure 5-12A). Data groups at pH 3 and 4 failed to pass the normality test.
No statistical evaluation was reported.

In dislodgeable solids CCA/WR, about 15.0i1.0% of total arsenic was found in
water during the first hour. The amount of water soluble arsenic increased to 19.5i1.5%
afier 24 hours, and 25.5:l:1.5% after 168 hours. About 28.013.0%, 32.5i1.5%, and
35.0:tl.0% of water soluble chromium were found at l-hour, 24-hour, and 168-hour test
durations, respectively. The percentage of copper solubilized from dislodgeable solids
CCA/WR was 15.0:1:3.0%, 27.0:t6.0%, and 31.0:|:3.0% after 1 hour, 24 hours, and 168
hours, respectively (Table 5-2). One-way ANOVA analysis suggested that, the
solubilization of the three elements in dislodgeable solids CCA/WR was time sensitive
(Appendix 3 Tables 20, 21 and 22). The percentage of arsenic, chromium, and copper
solubilized from dislodgeable solids CCA/WR generally increased with the test duration

(Figures 5-IOB, 5-11B, and 5-12B).

117

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This solubilization-time relationship suggested that the dissolving of arsenic,
chromium, and copper from the dislodgeable solids was not equilibrated in most test

conditions by varying the duration fi'om 1 to 168 hours and pH from 6 to 3.

5.5.2.3 Influence of pH on the solubilization of total arsenic, chromium, and copper

Significant difference in the percentage of chromium solubilized from
dislodgeable solids CCA was found in the 1-hour Water matrix at various pH (Appendix 3
Tables 23). The increased amount of water soluble chromium at lower pH could possibly
be attributed to the dissociation of chromium fixation products, such as chromium
arsenate (CrAsO4) and/or chromium hydroxide (Cr(OH)3) as proposed in Equations 2 and
3. The ionized form of chromium is relatively higher in water solubility.

CrAsO4 + 2H+ -> Cr3+ + HzAsO4' (2)

Cr(OH)3 + 3H+ -> Cr3+ + 31120 (3)

No pH dependency was found in the solubilization of chromium afier 24 hours,
which suggested the dissociation of CrAsO4 or Cr(OH)3 was less to negligible after 24
hours.

The percentage of copper solubilized from dislodgeable solids CCA was
influenced by pH at l-hour and 24-hour test durations (Appendix 3 Table 24), which
could also be attributed to the interaction between H+ and copper compounds or copper
complex with wood components proposed by Bull (2000, 2001), resulted in the release of
copper ions in water.

The solubilization of arsenic, chromium, and copper from dislodgeable solids

CCA/WR was also influenced by pH, which increased with the decreasing pH values.

118

The impact from pH was observed with arsenic at all the three time intervals (Appendix 3
Table 25). Chromium was found to be pH dependent during the first hour. No significant
difference was found after 24 hours (Appendix 3 Table 26). The percentage of copper
solubilized was not significantly affected by the pH during the first hour. Significant
difference existed after 24 hours (Appendix 3 Table 27). These observations may also be
explained by the dissociation of CCA fixation products at low pH, and resulted in the
release of soluble arsenic, chromium, and copper in water. The pH dependency of
chromium within l—hour test duration, and after 24 hours for copper from both
dislodgeable solids CCA and dislodgeable solids CCA/WR suggested that the
dissociation of copper and chromium could be carried out individually. Chromium
fixation products could be dissociated during the first hour, which was demonstrated by
the pH dependency of chromium within one hour test duration. The physical dissolving
of unfixed copper in wood dominated during the first hour, which was found to be less
pH dependent. In prolonged test duration, this physical dissolving became less
significant. The dissociation of copper fixation products became important. This
observation was in agreement with Pizzi (1982a,b,c) and Bull (2001), who proposed

copper could be fixed in CCA-treated wood independent from chromium or arsenic.

5.5.3 Proportions of water soluble arsenic, chromium, and copper in the
dislodgeable solids

Table 5-3 lists the weight percentage of water soluble arsenic, chromium, and
copper in the dislodgeable solids, which was derived from Table 5-2. By varying the pH
of the water matrix in the first hour of the test, the proportions of water soluble arsenic,

chromium, and copper corresponded to about 0.05%, 0.03i0.01% , and 0.031001% in

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120

weight of the total dislodgeable solids CCA, respectively. After 24 hours, the proportions
of soluble arsenic, chromium, and copper corresponded to 0.09:1:0.01%, 0.03zt0.01%, and
0.05zt0.01% % of the dislodgeable solids CCA, respectively. These values increased to
about 0.11%, 0.052t0.02%, and 0.03% to 0.14% for soluble arsenic, chromium, and
copper, respectively after 168 hours. The atomic ratio of As : Cr : Cu was in the range of
0.7-2.9 : 0.5-1.2 : 1.0. Compared with the atomic ratio of As : Cr : Cu at 1.27 : 2.04 : 1.00
in CCA-C preservative (AWPA 2003), the decrease in the proportion of chromium was
noticed, which suggested the formation of chromium fixation products with low water
solubility.

Relatively larger proportion of soluble arsenic, chromium, and copper was found
in dislodgeable solids CCA/WR. During the first hour, the amounts of water soluble
arsenic, chromium, and copper corresponded to about 0.09%, 0.19zt0.02%, and
0.081002% of the total dislodgeable solids. After 24 hours, the percentages of soluble
arsenic, chromium, and copper increased to 0.12%, 0.22%, and 0.161003%, respectively.
About 0.16% of the solids was found as soluble arsenic, about 0.24% as soluble
chromium, and 0.18:1:0.02% as soluble copper after 168 hours. The atomic ratio of
soluble As : Cr : Cu in dislodgeable solids CCA/WR was in the range 0.59-1.10 : 1.5-4.0
: 1.0. Compared with the ratios of soluble As : Cr : Cu in dislodgeable solids CCA, an
increase in the proportion of soluble chromium was observed, which suggested that,
relatively larger proportion of chromium was not fixed in CCA/WR-treated wood. This
also explained the increased percentage of soluble arsenic, chromium, and copper in total
arsenic, chromium, and copper from dislodgeable solids CCA/WR compared with those

fi'om dislodgeable solids CCA.

121

5.5.4 Speciation of arsenic solubilized from the dislodgeable solids

5.5.3.1 Asv and As'" recovery rate - arsenic speciation of standard Asv and AsIll

solutions

Ill

The recovery rates after arsenic speciation of AsV and As standard solutions are

listed in Table 5-4. More than 94% of AsV was recovered after the speciation of AsV
standard solutions from 5 ppb to 500 ppb. The concentration of As'11 found in Asv

standard solutions was below the detection limit of 0.3 ppb by using GFAA. The

III III

recovery rate of As after the speciation of As standard solutions at the concentrations

from 5 ppb to 100 ppb was between 74% and 85%. With increased AsIn concentration
from 100 ppb to 500 ppb, Asm recovery rate increased from 85% to 99%. This increased
As"I recovery rate was attributed to the increased stability of Asm at higher

concentrations. Manning and Goldberg (1997) and Gallagher et al. (2001) reported that

[I]

more As could be oxidized to AsV in open air at lower concentrations, and this tendency

[11

decreases with the increase of As concentrations. This phenomenon could be explained

by the thermodynamic principles using actual reversible potential of arsenic. At 298.15 K
(25°C), the half reaction of arsenic in water and its standard electrode potential (E0) are

listed as following (Wilson 1974):

H3Aso4 +2H+ +2e- = 1130.5303 + H20 E A303- , A3033- = 0.559 volt

The actual reversible potential E [1303- M3033— could be expressed by using Nemst
equation (Equation 4).

0.059 [H,Aso,]
_10 _

E 3- 3— =EOAso3‘/Aso3‘ —
Asa, /Aso, 4 3 2 g[H3AsO,]

(4)

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. . . 0 _ _ . .
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III

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5.5.3.2 Speciation of arsenic solubilized from the dislodgeable solids

Results from the speciation of arsenic solubilized from the dislodgeable solids in
the water matrix are listed in Table 5-5. In the first hour samples from dislodgeable solids
CCA, the concentration of Asv was 365i15 ppb in water at pH 6 to 3. Asv concentrations
ranged from 473 ppb to 483 ppb in the 24-hour samples, and from 410 ppb to 564 ppb
after 168 hours. One-way ANOVA analysis indicated that the solubilization of AsV in
dislodgeable solids CCA appeared to be pH dependent after 24 hours (Appendix 3 Table
28). This suggested that Asv solubilized in the first hour could mostly be attributed to
large volume of physical dissolving of unfixed arsenic rather than the fixed products,
which are low in water solubility and sensitive to low pH.

The concentration of Asm from dislodgeable solids CCA was less than 50 ppb
within the first 24 hours. After 168 hours, Asm increased to 360i40 ppb. AsIII
concentration was significantly influenced by the pH in the 1-hour samples, which
increased with the acidity of water. No significant difference was observed with As111 in
the 24-hour samples (Appendix 3 Table 28). Data of As"I after 168 hours failed to pass

the normality test.

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For dislodgeable solids CCA/WR, AsV concentration in water was 455i25 ppb in
the first hour, and 710280 ppb afier 24 hours. AsV concentrations after 168 hours were
similar to those at the 24-hour test duration. Unlike the pH dependency of Asv
solubilized from dislodgeable solids CCA, Asv from dislodgeable solids CCA/WR did
not appear to be pH sensitive (Appendix 3 Table 29). This suggested that large
proportions of AsV solubilized from dislodgeable solids CCA/WR could be attributed to
the physical dissolving of unfixed Asv, with less proportion of arsenic fixation products
such as CrAsO4. This also indicated an incomplete CCA fixation in CCA/WR-treated
wood.

During the first 24 hours, AsIll concentrations in water fell between 120 ppb to
170 ppb from dislodgeable solids CCA/WR, which was higher that those from
dislodgeable solids CCA. Afier 168 hours, AsIll concentrations increased to 400:}:40 ppb,
which was significantly higher than those in the 1-hour and the 24-hour samples
(Appendix 3 Table 30).

One-way AN OVA analysis also found that the addition of water repellent to CCA
wood treatment significantly influenced the concentrations of AsV (or Asm) solubilized
(Appendix 3 Tables 31 to 36). The amount of Asv or As"I solubilized from dislodgeable
solids CCA/WR was generally larger than those from dislodgeable solids CCA and
suggested an incomplete CCA fixation in wood with the presence of water repellent.

The distribution of Asv and AsIll as well as the arsenic recovery rate in terms of
the amount of Asv and Asm detected as a proportion of total arsenic in water are derived

from Table 5—5 and listed in Table 5-6. About 76% to 95% of total arsenic present in

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water was found as Asv in the 1St hour and the 24th hour, and 6% to 9% as Asm from
dislodgeable solids CCA. The proportion of AsIII increased to 41i6% after 168 hours.
Similar phenomenon was observed with dislodgeable solids CCA/WR. About 77:|:7% of
arsenic in water was Asv, and 22i6% was As"I during the first 24 hours. AsV decreased
to 64i6%, and A51" increased to 34i2% after 168 hours. Figures 5-13 and 5-14 illustrate
the concentrations of Asv, Asm, the sum of Asv and A51", and total arsenic in water from
dislodgeable solids CCA and dislodgeable solids CCA/WR. A consistent increase in the
concentration of total arsenic was observed throughout the 168-hour test duration. Asv
concentration increased during the first 24 hours and became stable or even some
decrease in water matrix at pH 4 and 5 from 24 to 168 hours. On the other hand, AsIII
concentrations remained constant in the first 24 hours and increased from 24 hours to 168

hours. The curve of the sum of AsV and As"1

were close to the curve of total arsenic,
which suggested that AsV and As‘" were the major arsenic species solubilized from

dislodgeable solids CCA and dislodgeable solids CCA/WR.

5.5.3.3 Questions raised and future work recommended

The water solubility of Asm compounds is about 4 to 10 folds higher than that of
Asv compounds (Federal Remediation Technologies Roundtable 2004). As"1 has a
greater potential to leach than AsV (Mok and Wai 1994). Therefore, larger proportions of
Asm would be expected at the initial stage of the solubilization test if present in the

dislodgeable solids. The increased amount of As'11

from 24 to 168 hours is suspected to
come from the reduction of AsV during the solubilization process, rather than a release of

AsIn from the dislodgeable solids. The mechanism of Asv reduction in this situation is

130

not clear. The involvement of microbiological activity is highly suspected (Ahmann et
al. 1994; Laverrnan et al. 1995; Newman et al. 1998; Cénovas et al. 2003).

I" to total arsenic in water ranged from

The percentage of the sum of Asv and As
83% to 103% (Table 5-6). This 20% variation between the sum of As" and Asm, and the
total arsenic in water indicated the presence of errors during arsenic speciation, possibly
an incomplete elution of AsV from the modified chromosorb cartridge or the present of

arsenic species other than AsV or As'".

5.6 Conclusions

Arsenic, chromium, and copper partially solubilized from dislodgeable solids
CCA and dislodgeable solids CCA/WR in a 168-hour test. The amount of arsenic,
chromium, and copper solubilized generally increased with the test duration from 1 hour
to 168 hours. The solubilization of chromium was influenced by pH during the first hour
of the test. Copper showed pH dependency in the first 24 hours from dislodgeable solids
CCA and after 24 hours in dislodgeable solids CCA/WR. Arsenic in dislodgeable solids
CCA/WR was pH dependent throughout the 168-hour test duration.

The addition of water repellent to CCA wood treatment significantly increased the
proportions of arsenic, chromium, and copper solubilized from the dislodgeable solids.
Larger amount of soluble Cr‘" were found with dislodgeable solids CCA/WR than
dislodgeable solids CCA.

Both Asv and AsIn were found in the water matrix. Asv was the dominant form

during the first 24 hours. Significant decrease in the proportions of AsV and increase in

131

As'" were found after 168 hours from both dislodgeable solids CCA and dislodgeable
solids CCA/WR.

- h“.

 

132

 

Chapter 6

Speciation of Arsenic in the Leachate of Chromated Copper Arsenate
(CCA) Treated Southern Pine

6.1 Introduction

Toxicity of arsenic and chromium is strongly influenced by their oxidation states.
Inorganic trivalent arsenic (Asm) is more potent than inorganic pentavalent arsenic (Asv)
in an acute exposure; hexavalent chromium (Crw) has been recognized as a carcinogen
while trivalent chromium (Crm) is essential to human health (Schroeder and Balassa
1966; Hughes et al. 1994; Healy et al. 1998).

Copper, chromium, and arsenic have been frequently reported to leach from
chromated copper arsenate (CCA) treated wood. A general finding is that arsenic leaches
the most while chromium tends to be fixed in wood (J in and Preston 1993; Kennedy and
Palmer 1994; Cooper et al. 1997; Yamarnoto et al. 2000; Venkatasamy 2002). Trivalent
chromium is the major chromium species found in the leachate of CCA-treated wood
after the fixation (Cooper and Ung 1993; Kennedy and Palmer 1994; Cooper et al 1994
1997)

Information on arsenic speciation related to CCA-treated wood is limited. There
are several studies carried out to speciate arsenic from CCA-treated wood in recent years.
By using a selective solvent extraction coupled with atomic absorption spectroscopy
(AA), Nygren and Nilsson (1993) reported that less than 0.5% of the total arsenic was
As'" in commercially CCA-treated wood. Hingston et al. (2003) reported that less than
10% of total arsenic in leachate of CCA-treated wood was As‘" by using differential

pulse polarography for arsenic speciation. Using high performance liquid

133

chromatography coupled with hydride generation atomic fluorescence spectrometry
(HPLC-HG-AF S), Solo-Gabriele et al. (2003) found up to 50% of total arsenic in CCA

"1. Various studies using different arsenic speciation methods have

leachate was As
generated a larger variety of data.
The objective of this study is to apply a newly developed selective ion-exchange

chromatography method to speciate arsenic, and to gain insight of arsenic species in the

leachate of CCA-treated wood.

6.2 Material and Methods
6.2.1 Commercially prepared CCA-treated southern pine

Commercially CCA-treated southern pine boards were purchased from a
hardware store located in Lansing, Michigan. The board was labeled at a chemical
retention of 6.4 kg/m3. Defect free cubes measuring 19 mm in edges were cut from these
boards and stored in a conditioning room maintained at 20°C and 65% relative humidity
(RH) for one week before the leaching test. Cubes with similar weight were selected for

further testing.

6.2.2 Laboratory prepared CCA-treated southern pine
Cubes measuring 19 mm in edges were cut from defect-free kiln-dried sapwood
boards of southern pine and stored in a conditioning room maintained at 65% relative

humidity (RH) and 20°C (68°F) until the blocks reached a constant moisture content of

10.50 :1: 0.75%.

134

6.2.3 CCA treating solution and wood treatment

A 1% CCA treating solutions were prepared by diluting 9.4% CCA type C stock
solution received from Osmose, Inc. using deionized (DI) water. The concentrations of
CCA treating solutions were expressed in weight percentage of total oxides for copper,
chromium, and arsenic, as CuO, A5205, and 003, respectively. The elemental copper,
chromium, and arsenic concentrations in the solutions were analyzed using Flame Atomic
absorption spectrometry.

A l-liter stainless steel treating tank was used for wood treatment. A total of 20
southern pine blocks were full cell pressure treated. The treating process included an
84.6—kPa (30" Hg) vacuum for 30 minutes followed by a 1240-kPa (180-psi) pressure for
1 hour with no final vacuum applied. Wood samples were wrapped in plastic bags and
stored in the dark at 20°C (68°F) for 7 days after removed from the treating tank. The
treated blocks were then set unwrapped in a conditioning room at 65% relative humidity

(RH) and 20°C (68°F) for another 3 weeks before further test.

6.2.4 Chemical retentions in CCA-treated wood

The retention of arsenic, chromium, and copper in treated cubes were evaluated
by using chemical analysis protocols A7-93 and A1 1-93 described in American Wood-

Preservers’ Association Standard (AWPA 2003).
6.2.5 Laboratory accelerated leaching test
The laboratory accelerated leaching test of both commercially and laboratory

CCA-treated wood was conducted according to AWPA standard El 1-97 (AWPA 2003)

135

with some modification as described below: six cubes from each treatment were
submerged in 300 ml of deionized (DI) water in an Erlenmeyer flask and magnetic stirred
with magnetic stirring at room temperature. The flask was covered with parafilm to
prevent possible evaporation. The leachate was removed and replaced with fresh DI

water after 6, 24, and every 48 hours thereafter up to a total of 558 hours.

6.2.6 Atomic absorption spectroscopy (AA) measurement of arsenic, chromium,
and copper

Quantification of elemental arsenic, chromium, and copper was completed by
using flame atomic absorption spectrophotometer (FAA, Perking Elmer 3110), equipped
with an electrodeless discharge lamp (EDL) for arsenic, and hollow cathode lamps for
chromium and copper (Perkin Elmer) at parts per million (ppm) level. A graphite fumace
atomic absorption spectroscopy (GFAA, Perkin Elmer AAnalyst 800) equipped with an
EDL arsenic lamp was used to quantify arsenic at parts per billion (ppb) level. Arsenic,
chromium, or copper solutions used to construct the working curves for AA
measurements were diluted from atomic absorption standard solutions purchased from
Aldrich Chemical Co. The preparation of the standard solutions to obtain the working
curve of each element has been described in the experimental section of Chapter 3. A
matrix modifier was used to reduce the interferences from matrix effects during GFAA
measurement of arsenic. The preparation of the modifier was previously described
(Flores del Pino 2003). The instrumental detection limits were 0.6 ppm for arsenic, 0.02
ppm for chromimn, and 0.3 ppm for copper with FAA, and 0.3 ppb for arsenic with

GFAA.

136

6.2.7 Speciation of CrVI in the leachate

Cr"1 in water was determined by using a colorimetric method described by
Cooper and Ung (1993). Chromium solutions with concentrations from 0 to 1.0 ppm
were prepared by diluting CrVI standard solution (lOOOppm, Atomic absorption standard,
Aldrich) using 0.5N sulfuric acid. Diphenylcarbazide solution was used as an indicator,
and was prepared by dissolving 2.5 g of l, S-diphenylcarbazide (A.C.S. Reagent,
Aldrich) in 100 ml mixture of acetone and DI water (v/v: 1:1). The visible absorbance of
the complex formed between CrVI and l, 5-diphenylcarbazide at room temperature was
measured at 540 nm using ultraviolet-visible (UV-vis) spectrophotometer (DU 6403,
Beckman Co.). The CrVI working curve was obtained by plotting a linear regression
between the absorbance of Crw-diphenylcarbazide complex and the corresponding Cr“
concentrations as determined by AA. CrV1 in the leachate was measured directly with no

further preparation.

6.2.8 Speciation of arsenic in the leachate

m could be oxidized to

Asv and AsIn have been reported as time dependent, As
Asv in an open air (Manning and Goldberg 1997; Cénovas 2003). The isolation of Asv
and As111 was performed within 10 minutes after each leachate collection in order to limit
possible changes in arsenic oxidation states. A cation exchange pre-column and a
modified chromosorb column were used to speciate arsenic. The pre-column was
prepared by packing 0.6 g of cation exchange resin with capacity of 2 meq/g into a l-ml

syringe from Becton Dickinson. The modified chromosorb in the column consisted of a

silanized diatomaceous earth with dioctyltin dichloride ((CanhSnClz). The leachate was

137

 

'f‘i“ _ A- "

 

diluted 50 folds to satisfy the ion-exchange capacity of the columns based on preliminary
test. A total of 20.0 ml of the diluted leachate was passed through the pre-column at a
flow rate of 1 ml/min. The pre-column was used to eliminate or reduce potential
interference of cations such as copper (Cu2+) present in the leachate during arsenic
speciation. The pH of the solution eluted from the pre-column was adjusted to 2.5-3.5
using 1.0N hydrochloric acid (HCl). Asv and Asm was separated by passing the pH-
adjusted solution through modified chromosorb column capable of retaining ionized Asv.
AsIll in its neutral form was not retained and present in the eluant. AsV trapped in the
modified chromosorb column was desorbed by using 0.5N HCl. The solution passing

through the column containing As"I

, the elution washed out from the column consisting
of Asv, and the initial leachate after 50-fold dilution were analyzed by using GFAA to

quantify Asm, Asv, and total arsenic, respectively.

6.2.9 Statistic analysis

One-way ANOVA analysis (Jandel SigmaStat Version 2.0, Jandel Co.) using all
pairwise multiple comparison tests (Tukey Test) at the significant level of 0.05 was
performed, to determine if significant difference existed in the concentration of total

Ill

arsenic, Asv or As leached at various leaching durations (0-6 hours, 6-30 hours, 30-78

hours, 78-126 hours, 126-174 hours, 174-222 hours, 222-270 hours, and 270-318 hours).

6.3 Results and discussion

6.3.1 Elemental arsenic, chromium, and copper in the treating solutions and
treated wood

138

Table 6-1 lists the weight of the southern pine blocks before (Wi) and after (Wa)
CCA treatments. The weight gain of each block after CCA treatment was calculated
using Equation 1. Blocks with similar values of weight gain (about 150%) were selected
for the leaching test.

Mxlom (1)
W1

weight gain, % =

The percentage of elemental arsenic, chromium, and copper in CCA-treated wood
are listed in Table 6-2. Arsenic, chromium, and copper retentions in wood were found at
0.23%, 0.46% and 0.13%, respectively in commercially CCA-treated wood, and 0.32%,
0.62%, and 0.17%, respectively in laboratory treated wood. Retentions of the
corresponding oxides in kg/m3 were calculated by using a density of 500 kg/m3 for
southern pine. The chemical retentions expressed in total oxides were 4.8 kg/m’3 in

commercially CCA-treated wood and 6.6 kg/m'3 in laboratory treated wood.

6.3.2 CrVI and elemental arsenic, chromium, and copper in the leachate of CCA-
treated wood

It is reported that in CCA treated wood, a series of interactions may occur
between arsenic, chromium, copper, and wood components, resulting in the formation of
chromium (III) arsenate, chromimn (III) hydroxide, and complex between copper,
chromium and wood components (Bull 2001). The reduction of CrVI to CrIII has been
widely used as indication of CCA fixation in wood (Cooper and Ung 1993; Cooper et al
1994). Figure 6-1 illustrates the cumulative concentrations of total chromium and CrVI in
the leachate from commercially or laboratory CCA-treated wood. The reduced amount of

CrVI present in CCA treated wood after fixation is assumed to be converted to Crm. After

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30 hours of leaching, less than 10% of the total chromium was found as CrV'; this
relatively low level of CrVI suggests a nearly complete CCA fixation in commercially and
in laboratory CCA-treated wood.

The cumulative amounts of arsenic, chromium, and copper in leachate were
calculated and illustrated in Figure 6-2. Arsenic was the element with the highest amount
in the leachate followed by copper and chromium. This is in agreement with the findings
by Jin and Preston (1993) and Kennedy and Collins (2001). A plateau was reached for
chromium after 174 hours and for copper after 366 hours, indicating that the leaching of
chromium and copper was nearly completed after 174 hours and 366 hours, respectively.
Additional leaching of arsenic continued throughout the test. After 558 hours, similar
amount of arsenic was leached from commercially and laboratory treated wood, at 13.15
mg and 13.17 mg, respectively. A total of 0.49 mg of chromium and 1.76 mg of copper
were leached from commercially treated wood; about 0.89 mg of chromium and 2.38 mg
of copper from laboratory treated cubes. Relatively larger amount of chromium and
copper were leached from laboratory treated wood than commercially treated, which was
attributed to the higher chemical retention resulted from a better penetration of CCA
treating solution into small cubes during the laboratory wood treatment.

Table 6-3 lists the percentages of arsenic, chromium, and copper leached from
both commercially and laboratory CCA-treated cubes at each time interval during the
leaching test. After 558 hours, a total of 6.31% and 6.77% of copper were lost through
leaching from commercially and laboratory CCA-treated cubes, respectively. Relatively
less proportions of chromium were leached. About 0.51% of chromium was lost from

commercially treated cubes, and about 0.69% from laboratory treated cubes. The largest

143

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proportion of leaching was found with arsenic at 28.59% and 20.56%, respectively from
commercially and laboratory CCA-treated cubes.

The reduction of CrVI to Crm in CCA-treated wood is generally used as an
indication of CCA fixation (Cooper and Ung 1993; Kennedy and Palmer 1994; Cooper et
al 1994 1997). However, the continuous release of arsenic from CCA-treated cubes
during the 558-hour test suggested that arsenic should also be considered in the
evaluation of CCA fixation in treated wood. Since arsenic toxicity is influenced by its
oxidation states, monitoring its species in the leachate is paramount information in human

health and environmental risk assessment.

6.3.3 Speciation of arsenic in the leachate

The leaching rates of Asv, As'", and total arsenic (pg/h) were plotted as functions
of time in Figure 6-3. The highest leaching rate was found at the initial stage of the test
and decreased with prolonged test duration. In the first 6 hours, the average leaching rate
of total arsenic was 177.8 ug/h from commercially CCA-treated cubes, among which,
110.5 ug/h was attributed to AsV and 53.6 ug/h to Asm. The leaching rate of total arsenic,
Asv, and Asm in the leachate collected from laboratory treated cubes were 205.9 ug/h,
176.9 ug/h, and 28.8 pg/h, respectively. About 12.3 ug/h of total arsenic, 9.4 ug/h of
Asv, and 2.9 ug/h of AsIll were detected in the leachate of commercially treated cubes
from the last collection (510-558 hours interval); about 13.5 ug/h, 9.9 ug/h of Asv, and
3.2 ug/h of Asm were leached from laboratory treated cubes. Similar amount of arsenic

was leached from commercially and laboratory treated wood.

146

 

 

 

 

 

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Tum (h)

Leaching rate of Asv, AsIII and total As from (A) commercially, and (B)
laboratory treated wood

147

 

 

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111

The proportions of Asv and As in total arsenic presented in each leachate are

listed in Table 6-4. The proportions of AsV were relatively larger than those of Asm
during the first 270 hours: about 62.2-99.5% of total arsenic in the leachate of
commercially CCA-treated cubes was found as Asv, and l3.1-30.2% was Asm; about
69.5-86.0% of the total arsenic in the leachate of laboratory treated cubes was found as
Asv, and 109-198% was Asm. The sum of Asv and Asm as a proportion of total arsenic
in each leachate are also listed in Table 6-4. About 102:1:13% of total arsenic in
leachate from the first 270 hours was found as AsV and As'", which suggested that
Asv and As"! were the major arsenic species in the leachate of CCA-treated southern
pine. After 270 hours, relatively larger standard deviations in data groups were noticed.
Tables 6-5 and 6-6 list the result from one-way ANOVA analysis of arsenic
concentrations in leachate collected at various time interval. Statistical analysis suggested

that the concentrations of total arsenic, Asv, and As‘"

were significantly influence by the
leaching duration in the first 270 hours leaching. Significant difference was observed
within most of the treatment groups. Exceptions were found in total arsenic between the
6-30 hours and the 78-126 hours from commercially CCA-treated wood (Table 6-5), the
6-30 hours and the 30-78 hours from laboratory treated wood (Table 6-6). No statistical
difference was found in the concentration of Asv between the 78-126 hours and the 6-30
hours / the 126-174 hours, the 126-174 hours and the 174-222 hours leachates of
commercially treated wood (Table 6-5); the 0-6 hours and the 78-126 hours, the 6-30
hours and the 30-78 hours / the 78-126 hours, the 126-174 hours and the 78-126 hours /
the 174-222 hours, the 174-222 hours and the 222-270 hours leachates of laboratory

treated wood (Table 6-6). Exceptions were also observed in Asm between the 174-222

148

 

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hours and the 222-270 hours leachates of commercially treated wood (Table 6-5), and the
0-6 hours and the 6—30 hours / the 222-270 hours, the 6-30 hours and the 174-222 hours /
the 222-270 hours, the 30-78 hours and the 126-174 hours, the 78-126 hours and the 126-
174 hours, and the 174-222 hours and the 222-270 hours (Table 6-6).

Relatively larger standard deviation existed in the results of arsenic speciation of
the leachate collected after 270 hours. No statistic conclusion was drawn.

The detection of Asv and As"1 in leachate of CCA-treated wood has been reported
by several researchers (Table 6-7). By using a sequential solvent extraction with HCl and
toluene, Nygren and Nilsson (1993) reported that more than 99.5% of total arsenic was
AsV and less than 0.5% was Asm in commercially CCA type B treated wood. Hingston et
al. (2003) leached CCA-treated southern pine cubes with artificial sea water and found

2.9-8.6% of total arsenic in the leachate was Asm

by using a differential pulse
polarography. Unlike the consistent low level of A31" reported by Hingston et al. (2003),
Solo-Gabriele et al. (2003) reported a broad range of A51" in the leachate collected with
CCA-treated wood removed from a playground after 14 years of service. By varying the

pH of leaching water from 1.3 to 12.8, up to 51% of total arsenic was found as Asm

using
HPLC-HG-AF S. However, the time issue involved in arsenic speciation was not
specified in these studies.

AsIII in the leachate was attributed to the reduction of Asv. The mechanism of
AsV reduction in CCA-treated wood is not clear. The involvement of microorganism is

highly suspected (Ahmann et al. 1994; Canovas 2003). Factors such as chemical retention

in wood, the environmental condition, and wood species may possibly influence the

152

 

 

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microbial activity. Further investigations in Asv reduction in leachate of CCA-treated

wood is highly expected.

6.4 Conclusions

Both arsenic and chromium were used to indicate CCA fixation in commercially
and laboratory CCA-treated southern pine in a 558-hour leaching. The largest amount of
leaching was found with arsenic followed by copper. The leaching of chromium and
copper was nearly complete after 174 hours and 366 hours, respectively. Consistent
leaching of arsenic was observed throughout the 558-hour test from both commercially
and laboratory CCA-treated southern pine. A total of 24.6i4.0% of arsenic, 0.6iO.I% of
chromium, and 6.5i0.2% of copper were leached from commercially and laboratory
CCA-treated wood. Less than 10% of total chromium in the leachate was found as CrV'.
Both Asv and As'" were detected in the leachate. In the first 270 hours, about 70-90% of
total arsenic in the leachate was found as AsV and 10-30% as A51". The concentrations of

total arsenic, Asv, and Asm were influenced by the leaching duration.

154

Chapter 7

Conclusions

Arsenic, chromium, and copper could dislodge on the surface of commercial
chromated copper arsenate type C (CCA), and CCA with water repellent (CCA/WR)
treated southern pine boards.

The amounts of arsenic, chromium, and copper obtained in the dislodgeable solids
from the board surface of CCA-treated wood are influenced by the collection methods.
Largest amount of arsenic, chromium, and copper could be collected by using a test tube
brush wiping method, compared with those collected using a glove-on-hand wiping
method, or a paper wiping method. The amount of arsenic, chromium, and copper
collected from CCA-treated wood surface by using the test tube brush wiping method
was about 10 folds higher than those collected by using the glove-on-hand wiping
method.

The amount of arsenic, chromium, and copper collected from CCA-treated wood
surface before a field exposure was higher than those collected from board surface after a
field exposure; the addition of water repellent to CCA wood treatment reduced the
amount of arsenic, chromium, and copper collected from boards in the first 2 months of
field exposure, similar amounts of arsenic, chromium, or copper were collected from
CCA and CCA/WR-treated wood afier 3-4 months.

The dislodgeable solids collected from CCA and CCA/WR-treated southern pine
mainly consisted of wood splinters with small chemical deposits randomly distributed in

the wood matrix. The amount of arsenic, chromium, and copper formed less than 4 wt.%

155

of the dislodgeable solids. The particle sizes of the chemical deposits were mostly less
than 10 um, and between 10 and 100 um for the wood splinters. The elemental
compositions in dislodgeable solids collected from CCA and CCA/WR-treated wood
include arsenic, chromium, copper, iron, calcium, potassium, chloride, sulfur, silicon,
magnesium, sodium, carbon, and oxygen were detected in the solids. After 7 months of
field exposure, the deformation of cellulose in the dislodgeable solids caused by wood
weathering was observed using environmental scanning electron microscope (ESEM) and
X-ray diffractometry (XRD). The accumulation of sand or soil from the surrounding
environment on the board sm'face and consequently collected in the dislodgeable solids
by comparing their x-ray diffractograms before and after the field exposure.

Study of the solubilization of dislodgeable solids collected from CCA and
CCA/WR-treated wood before the field exposure found that arsenic, chromium, and
copper partially solubilized from the dislodgeable solids in water at pH 3, 4, 5, and 6. The
amount of arsenic, chromium, and copper solubilized generally increased with time. The
solubilization of chromium was influenced by pH during the first hour of the test. Copper
presented pH dependency in the first 24 hours from dislodgeable solids collected with
CCA-treated wood and after 24 hours from solids collected with CCA/WR-treated wood.
Arsenic in the solids collected with CCA/WR-treated wood appeared to be pH dependent
throughout the 168-hour test duration. The addition of a water repellent to CCA wood
treatment significantly increased the proportions of arsenic, chromium, and copper
solubilized from the dislodgeable solids.

Both AsV (H2A304') and Asm (H3AsO3) were solubilized from the dislodgeable

solids. AsV was the dominant form in water during the first 24 hours. A significant

156

 

decrease in the proportion of AsV and increase in As'" were found after 168 hours. A
significant increase in the proportion of AsIn in total arsenic was observed in a prolonged
test duration from 24 hours to 168 hours. Larger proportions of soluble Cer was found
with the solids from CCA/WR-treated wood than those from solids collected with CCA-
treated wood.

Speciation of arsenic in the leachate of CCA-treated wood found the presence of
both AsV and As"I during a 558-hour leaching. In the first 270 hours, about 70-90% of
total arsenic in the leachate was found as AsV and 10-30% as Asm. The concentrations of

total arsenic, Asv, and As"1 presented to be time dependent in leachate collected at some

time intervals.

157

APPENDICES

158

 

ACRONYMS in Appendices

SD standard deviation

SEM standard error of the mean
DF degree of freedom

SS sum of squares

MS mean squares

F F statistic

P P value

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