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LIBRARY
Michigan State
University

This is to certify that the

dissertation entitled

Development of an Arsenic Speciation Method for
Drinking Water and its Application to Human
Health and Risk Assessment

presented by

Lisveth V. Flores del Pino

has been accepted towards fulfillment
of the requirements for

Ph.D. Environmental Engineering/

Environmental Toxicology

Thomas C. Voice

Major professor

degreein

 

 

 

Date 11/28/03

 

MS U is an Affirmative Action/Equal Opportunity Institution 0-12771

PLACE IN RETURN BOX to remove this checkout from your record.
To AVOID FINES return on or before date due.
MAY BE RECALLED with earlier due date if requested.

 

DATE DUE DATE DUE DATE DUE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

6/01 cJCIRC/DateDue.p65-p.15

 

DEVELOPMENT OF AN ARSENIC SPECIATION METHOD FOR
DRINKING WATER AND ITS APPLICATION TO HUMAN HEALTH
AND RISK ASSESSMENT

By

Lisveth V. Flores del Pino

A DISSERTATION

Submitted to
Michigan Sate University
in partial fulfillment of the requirements
for the degree of

DOCTOR OF PHILOSOPHY
Department of Civil and Environmental Engineering

2003

ABSTRACT

DEVELOPMENT OF AN ARSENIC SPECIATION METHOD FOR DRINKING
WATER AND ITS APPLICATION TO HUMAN HEALTH AND RISK ASSESSMENT
By

Lisveth V. Flores del Pino

Chemical Speciation is essential in order to understand the toxic and carcinogenic nature
of elemental contaminats found in environmental and biological systems. For example,
the measurement of total arsenic content does not indicate the levels of the individual
species. Analytical data on the individual Species of an element present in a sample
provides useful information for studying its toxicity, bioavailability, metabolism, or
transport. The risk assessment of the human health associated with the ingestion of such
elements via drinking water and food should therefore be based on analytical data of the

individual species.

The aim of the research described in this thesis was to develop a simple, rapid, sensitive,
accurate, and inexpensive on-site Speciation method of the most toxic dissolved arsenic
species: As (III), AS (V), monomethylarsonic acid (MMA) and dimethylarsenic acid
(DMA). Development criteria included ease of use under field conditions, applicable at
levels of concern for drinking water, and analytical performance. The approach is based
on selective retention of arsenic species on specific ion-exchange chromatography
cartridges followed by selective elution and quantification using graphite furnace atomic

absorption spectroscopy. Water samples can be delivered to a set of three cartridges

using either syringes or peristaltic pumps. Species distribution is stable at this point, and
the cartridges can be transported to the laboratory for elution and quantitative analysis.
These results suggest that this method can be used for analysis of the four primary arsenic
species of concern in drinking water supplies. The method developed was used to
evaluate the stability of arsenic species in groundwater sample over time. It was tested at
different temperatures, pH and dissolved oxygen concentrations. To estimate potential
health risks of inorganic arsenic the analysis of the sources of inorganic arsenic is critical.
Our analysis found that food is the greatest source of inorganic arsenic intake, especially

when the arsenic concentration in drinking water is low.

Copyright by
LISVETH V. FLORES DEL PINO
2003

Acknowledgments

I wish to Show my appreciation and give due credit to the people that made the
completion of this research and dissertation possible

First, I would like to thank to my advisor Dr. Voice for his guidance, support and
give the opportunity to develop my own experimental design and to take the project in a
direction I felt was best. However, he always places me back to earth if I fell off target
from the proper task at hand. I feel very rewarded for having to opportunity to work with
Dr. Voice. A Special thanks to Dr. Long, Dr. Chou and Dr. Davis for always being
willing to discuss my results and for their valuable comments and suggestions.

I would like to thank all my colleagues in Environmental Engineering, Maria,
Chris, Shawn, Stephanie, Masanori, Sajaad and many others. I also thank Dr. Laconto,
Dr. Zhao, Mrs. Hasse, Mr. Joseph and Pan for their assistance during my studies.

I wish to Show my appreciation to my colleagues at “Universidad Nacional
Agraria La Molina” in Peru for their support. I also thank my friends of the Latin
American Association in East Lansing, Romelia, Irvin, David, Karen , Miguel and many
others for helping me during my years here.

Finally, I would like to thank my family in Peru, especially my parents who
always love me and worry me. Asa’s help was, no doubt the reason, that I have arrived at

this point.

Table of Contents

List of figures
List of Tables

Chapter 1 Introduction

1. Background
1.1 Sources and Distribution of Arsenic in the Environment
1.2 Chemistry and Geochemistry of Arsenic
1.3 Uses and Production of Arsenic
1.4 Toxicity and Health Effects of Arsenic
1.5 Why Speciation is needed
1.6 Methods of Arsenic Speciation
1.6.1 Separation Techniques
1.6.2 Detection systems
1.7 Arsenic Regulations
1.8 Human Exposure Assessment
1.9 Risk Assessment
1.10 References

l

l
5
14
15
19
21
21
28
29
32

38
42

Chapter 2 On-Site Method for Arsenic Speciation in Drinking Water

2.1 Introduction

2.2 Experimental Procedure
2.3 Results and Discussion
2.4 References

Chapter 3 Stability of Arsenic Species in Groundwater
3.1 Introduction

3.2 Experimental Procedure

3.3 Results and Discussion

3.4 References

Chapter 4 Human Exposure and Risk Assessment of Inorganic
Arsenic from Food and Drinking Water

4.1 Introduction

4.2 Review of Analytical Data and Analytical Methods

4.3 Evaluation of Analytical Methods

4.4 Human Exposure and Risk Assessment Estimation

4.5 References

Chapter 5 General Conclusions and Engineering Significance

vi

63

66
70
76

80
83
86
101

104
106
109
115
125

130

List of Figures

Figure 1.1 ps-pH diagram for the system AS-S-Fe-HZO
Figure 1.2 Distribution of the published works on Speciation in waters
Figure 1.3 Proposed pathway for arsenic methylation
Figure 2.1 Arsenic Speciation scheme
Figure 2.2 Elution curves for As (V)-MMA separation
Figure 3.1 Stability of AS (111) concentration at different temperatures and pH
Oxygen = 0 mg/L
Figure 3.2 Stability of As (HI) concentration at different temperatures and pH
Oxygen: 2-3 mg/
Figure 3.3 Stability of As (III) concentration at different temperatures and pH
Oxygen: 5-6 mg/L
Figure 3.4 Stability of AS (111) concentration at different temperatures and pH
Oxygen: saturation
Figure 3.5 Stability of Total As and AS (111) concentration at pH=6.98-7.40
Oxygen: 0 mg/L
Figure 3.6 Stability of total As and As (HI) concentration at pH=6.98-7.40
Oxygen: 2-3 mg/L
Figure 3.7 Stability of total As and As (III) concentration at pH=6.98-7.4O
Oxygen: 5-6 mg/L
Figure 3.8 Stability of total As and AS (111) concentration at pH=6.98-7.4O
Oxygen: saturation
Figure 3.9 Fe (II) and total Fe concentration at different temperatures and
Oxygen = 0 mg/L
Figure 3.10 Fe (II) and total Fe concentration at different temperatures and
Oxygen = 2-3 mg/L
Figure 3.11 Fe (H) and total Fe concentration at different temperatures and
Oxygen = 0 mg/L
Figure 3.12 Fe (H) and total Fe concentration at different temperatures and
Oxygen = saturation
Figure 4.1 Contribution of minimum food and water consumption to total
daily intake of inorganic AS
Figure 4.2 Contribution of average food and water consumption to total
daily intake of inorganic As
Figure 4.3 Contribution of maximum food and water consumption to total
daily intake of inorganic As
Figure 4.4 Risk calculated based on skin cancer (1) and bladder-lung cancer (2)
for minimum total intake of inorganic arsenic
Figure 4.5 Risk calculated based on Skin cancer (1) and bladder-lung cancer (2)
for average total intake of inorganic arsenic
Figure 4.6 Risk calculated based on skin cancer (1) and bladder-lung cancer (2)
for maximum total intake of inorganic arsenic

vii

13
20
37
68
71
88
89
9o
91
92
93
94
95
97
98
99
100
117
118
119
121
122

123

List of Tables

Table 1.1 Most common arsenic minerals in nature

Table 1.2 Physical and chemical properties of arsenic

Table 1.3 Some arsenic species

Table 1.4 Arsenic occurrence in groundwater in some countries
Table 1.5 Current and past arsenic uses

Table 1.6 Standards for arsenic in drinking water

Table 1.7 Global arsenic contamination in groundwater

Table 1.8 Arsenic distribution in groundwater samples in Michigan by county
Table 2.1 Furnace temperature program for arsenic analysis

Table 2.2 Interference among four arsenic species

Table 2.3 Arsenic Speciation in spiked samples

Table 2.4 Results of the arsenic Speciation in groundwater samples
Table 3.1 Literature review for the stability of arsenic species

Table 4.1 Analytical methods for determining arsenic in food

Table 4.2 Arsenic Speciation in food

Table 4.3 Dietary intake and water consumption of inorganic arsenic

viii

12
15
31
33
35
69
72
74
75
81
110
112
115

Chapter 1

INTRODUCTION

1. Background

1.1 Sources and Distribution of Arsenic in the Environment

1.1.1 Natural Sources

Arsenic is a metalloid with a name derived from the Greek word “ arsenikon” meaning
"yellow orpiment”. In nature, arsenic exists in the metallic state in 3 allotropic forms
(alpha or yellow, beta or black, gamma or gray) and several ionic forms. Arsenic is
broadly distributed in the environment. It is the twentieth most abundant element in the
earth’s crust with the total amount estimated to be 4.01x1016 kg based on concentrations
in rock material with an average concentration of 1.8 mg/kg (1-6) or 3 mg/kg (7). Arsenic
occurs free in nature in more than 245 minerals, ranging from a few parts per million to
percentage quantities. These are categorized as arsenates (60%), sulphides and sulfosalts
(20%) and arsenides, arsenites, oxides, silicates and elemental arsenic the remaining 20%
(8). The most important arsenic minerals are mixed sulphides of the M (II) ASS type
(arsenopyrite, realgar and orpiment), where M can be Fe, Ni, Co and other two valent

metals. Some common arsenicals are shown in Table 1.1. (9-11)

Arsenic concentration in various types of igneous rocks ranges from <1-15 mg As/kg and
values of < 1-20 mg As/kg have been reported for sedimentary materials. Higher As

concentrations, up to 900 mg As/kg have been found in argillaceous sedimentary rocks

(1,11-14). It is also present in coal, petroleum and especially in oil shales (3,15-17). In
Texas lignite samples, an arsenic range of 1—5.5 mg Ale was reported (15) but the US.

National Committee for geochemistry reported 11 mg As/L as an average of around 800

different coals and 44.3 mg As/L for an oil shale (16,17).

Table 1.1 Most common arsenic minerals in nature

 

 

 

 

 

 

Mineral Composition Occurrence

Native arsenic As Hydrothermal veins

Proustite Ag3ASS3 Generally one of the late Ag minerals in the sequence
of the primary deposition

Rammelsbergite NiAsz Mesothermal vein deposits

Salflorite (Co, Fe) As; Mesothermal vein deposits

Seligmannite PbCuAsS; Hydrothermal veins

Smaltite CoAsz

Niccolite NiAs Vein deposits and norites

Realgar ASS Vein deposits, often associated with orpiment, clays,
limestone, also deposits from hot springs

Orpiment A52S3 Hidrothermal veins, hot springs, volcanic sublimation
product

Cobaltite CoAsS High-temperature deposits, metamorphic rocks

Arsenopyrite FeAsS The most abundant As mineral, dominantly mineral
veIns

Tenannite (Cu, Fe) 121154513 Hydrothermal veins

Enargite CU3ASS4 Hydrothermal veins

Arsenolite A8203 Secondary mineral formed by oxidation of
arsenopyrite, native As and other As minerals

Claudite A5203 Secondary mineral formed by oxidation of
arsenopyrite, native As and other As minerals

Scorodite FeAsO4-2H20 Secondary mineral

Annabergite (Ni,Co)3(AsO4)2~8H20 Secondary mineral

Hoemesite Mg3(AsO4)2-8H20 Secondary mineral, smelter wastes

Haemotolite (Mn.Mg)4Al(AsO4)(OH)3

Conichalcite CaCu(AsO4)(OH) Secondary mineral

Adamite Zn2(OH)(ASO4) Secondary mineral

Domeykite Cu3S Found in vein and replacement deposits formed at
moderate temperatures

Loellingite FeAsz Found in mesothermal vein deposits

Pharmacosiderite Fe3(AsO4)2(OH)3-SH20 Oxidation product of arsenopyrite and other As
minerals

 

 

Arsenic is released to the atmosphere from wind, erosion, and volcanic emissions. The
largest natural source of arsenic emissions to the atmosphere seems to be volcanic
activity with estimates ranging from 1,100-44,100 metric tons (18,19). The atmosphere

accumulates an average of 1.74x106 kg As. This amount is roughly distributed with

1.48x106 kg As in the northern hemisphere and 0.26x106 kg AS in the southern
hemisphere. Arsenic retention time in the atmosphere is between 7—10 days and 89-986

% is present as particulate arsenic (20,21).

Arsenic is also the tenth most abundant element in seawater with a relatively constant
value of about 2 rig/L. However, in estuarine waters arsenic concentrations are more
variable due to river inputs, salinity or redox gradients (7,11,22-25). In most seawater
samples arsenate is the major arsenic species but arsenite can be found at considerable

levels as result of reduction by marine phytoplankton and bacteria (26).

Soils contain a broad range of arsenic concentrations. The principal factors affecting the
arsenic concentration in soils are the parent rock, climate, redox potential status, organic
matter, other inorganic compounds, etc. Typical natural arsenic concentrations in soils
range from 0.1 to 40 mg/kg. The estimated global average arsenic concentration is 5
mg/kg (1,21,27). This varies significantly among geographic regions. For example in
China the average arsenic concentration in soils is 12 mg/kg (001-626 mg As/kg), in
Japan 11 mg As/kg (04-70 mg AS/kg) and USA 7.5 mg As/kg (4.5-13 mg As/kg)
(28,29). However, soils near sulfide ore deposits are reported to contain an average of
126 mg As/kg (2-8,000 mg As/kg) (30). In moderate climates retention times for arsenic
in soils are from LOGO-3,000 years (27). The arsenic species in soils depend on the type
and amounts of sorbing components of the soil, pH and redox potential. Generally,

arsenate is present under oxidizing conditions and arsenite under reducing conditions.

Arsenic concentrations in fresh water are highly variable. Rainfall and snow in rural areas
may contain less than 0.03 ug/L of arsenic (31). Arsenic concentration in unpolluted fresh
waters ranges from 1-10 rig/L but in areas of sulfide mineralization, arsenic levels from
lOO-5,000 rig/L can be found. At moderate or high redox potential, arsenic can be found
pentavalent arsenic oxyanions such as: H3ASO4, HzAs4', HASO42' and As043'. On the
other hand, under acid, mildly alkaline and lower redox potential the trivalent arsenite
specie (H3ASO3) predominates. High levels of arsenic were found in geothermal waters
with concentrations ranging from 80-15,000 rig/L (32). Background concentrations in
groundwater in most countries are less than 10 ug/L (32,33). However, arsenic levels
reported in the literature Show a very large range from 0.5 to 5,000 rig/L in different parts
of the world. Countries with naturally occurring arsenic problems in groundwater are

discussed in detail in Section 1.8.

1.1.2 Anthropogenic Sources

Anthropogenic sources of arsenic release to the soil, aquatic environments and to the
atmosphere, are reported to exceed natural sources by ratio of 3:1 (3). The anthropogenic
inputs vary widely depending on the intensity of human activity, proximity to the source
of contamination, pollutant dispersion patterns, and the time Since deposition and fate of
the arsenic released (34,35). Anthropogenic inputs are estimated to contribute from

28,230 to 54,270 t/yr to the atmosphere (20, 21).

The major current and past anthropogenic sources of arsenic pollution are: mining

activities, smelting, copper production, wood preservatives, agricultures uses, animal

wastes and coal combustion. Levels as high as 9,300 mg As/kg were found in soil
samples collected from gold smelters in Canada (36). Also, levels from 70 to 220 mg/L
of arsenic have been found in soil residues in sites contaminated with arsenic from wood
treated with chromated copper arsenate (CCA) preservative (12,34). Median
concentrations of 130 mg As/kg (range 7-970 mg As/kg) were found in soils near Harz
mountains, Germany with long history of mining and smelting activities (37) and average
of 10,500 mg As/kg (range 300-21,000 mg As/kg) were reported in sludge from

hydrothermal gold processing in Mina Gerais, Brazil (38).

1.2 Chemistry and Geochemistry of Arsenic

1.2.1 Chemistry of Arsenic

Arsenic appears in Group 15 on the periodic table in the third period. Albertus Magnus
first identified the element in 1250 AD. after obtaining it by heating soap together with
orpiment (AS283) (39). Arsenic has an atomic weight of 74.92160 and an atomic number
of 33. Silver-gray arsenic has a specific gravity of 5.73; a melting point of 817 °C (28
atm) and sublimes at 613°C. The yellow amorphous form of arsenic has a specific gravity
of 1.97. Elemental arsenic can be present as a metalloid, but has an elemental structure
similar to non-metals. In the vapor state, arsenic occurs as a tetrameric molecule (AS4). In
high oxidation States arsenic displays covalent tendencies, while in low oxidation states it
shows ionic tendencies (40). Table 1.2 summarizes the physical and chemical properties

of arsenic.

Table 1.2 Physical and Chemical Properties of Arsenic

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Symbol As

Atomic Number 33

Atomic Weight 74.92l6(2)
Natural Isotope 75As (100 %)
Electron Configuration [Ar]4523dm4p3
Valency 3, 5
Oxidation States -3, 0, +3, +5
Coordination number 2, 3.4.5.6
Electronegativity 2.18 (Pauling)
Density (at 14 °C) 5.727 g/Ml
Melting Point at 28 atm 817 °C
Boiling Point 613 °C

Heat of Vaporization 34.76 kJ/mol
Heat of Fusion 27.7 kJ/mol
Specific Heat 0.33 J/g-K
Critical Temperature 1,427 °C
Critical Pressure 22.3 Mpa
Atomic Radius 1.14 °A
Covalent Radius 1.19 °A

Ionic Radius 2.22 °A
Vapor Pressure 1 mm (375 °C)

 

 

 

The oxidation states of arsenic are: -3, 0, +1, +3, and +5. Elemental arsenic (valence 0) is
rarely found under natural conditions. The +3 and +5 states are found in a variety of
minerals and in natural waters. Many of the chemical behaviors of arsenic are linked to
the ease of conversion between +3 and +5 valence states. The chemical structures of
arsenic Species that are relevant in this work are summarized in Table 1.3 (41).

1.2.2 Geochemistry of Arsenic

High concentrations of naturally occurring arsenic are commonly found in groundwater
in Bangladesh, China, India, Taiwan, Argentina, Chile, Mexico, Bolivia, Germany.
Spain, Greece, Ghana, Nepal, Japan, New Zealand, Hungary, Romania, France, Thailand

Canada and USA (1 l). Arsenic in aquatic systems has an unusually complex and

Table 1.3 Some Arsenic Species

 

Name

Abbreviation

Chemical Structure

 

Arsenous acic

AS (111)

OH

I
HO—As—OH

 

Arsenic Acid

As (V)

OH
I
O=As—OH
|
OH

 

Monomethylarsonic acid

MMAA

CH3
|
O = As —— OH
I
OH

 

Monomethylarsonous acid

MMAA (III)

OH

I
CH3 — AS — OH

 

Dimethylarsinic acid

DMAA

CH3
l
O = As — OH

|
CH3

 

Dimethyarsinous acid

DMAA (III)

OH

I
CH3 — AS — CH3

 

Trimethylarsine

TMA

CH3
I
CH3 —— As —— CH3

 

Trimethylarsine oxide

TMAO

C11;
|
O = A8 — CH3
I
CH3

 

Arsenobetaine

ASB

CH3
|
CH3— As*—CH2COO'
|
CH3

 

Arsenocholine

ASC

CH3
I

CH3— As+—CH,_CH20H,X'
l
CH3

 

 

Tetramethylarsonium ion

 

MeAS+

 

CH3
I
CH3 —' AS+ — CH3
|
CH3

 

 

interesting chemistry due to its multi-oxidation states, oxidation-reduction, ligand-
exchange, precipitation, dissolution, adsorption and biological reactions all potentially
taking place in the environment. The mechanisms controlling arsenic release is still not
fully understood because of arsenic minerals containing in the aquifer sediments, and the
associated water chemistry. In aquatic systems arsenic is present in ionic forms of AS all)
and As (V) or methylated forms. In groundwaters the methylated forms are not important
except when anthropogenic contamination is involved. Arsenic mobility in groundwaters is
not fully understood at this time. However, in general arsenic mobilization at a given site
could be influenced by variables such as pH, redox conditions (Eh), clay content, presence
of other metal ions, salinity, presence of non-metal ions, grain size and composition of the
soil and sediment, presence of the anions and complexing ions, groundwater flow rate,

nature of aquifer and temporal variations.

Arsenic Mobility Processes
Arsenic mobility in groundwater is mainly controlled by two types of processes:

adsorption/desorption reactions and solid-phase precipitation/dissolution reactions.

Adsorption/desorption processes are controlled by changes in pH, occurrence of redox
reactions, the presence of competing ions and solid-phase structural changes at the atomic
level. Arsenate and arsenite adsorb to surfaces of a variety of minerals, including iron
oxides, aluminum and clay minerals (42). Adsorption/desorption reactions between
arsenate and iron oxide surfaces are very important because of the abundance of iron

oxides on solid particles in the hydrologic environment (43). The adsorption of arsenate

to iron oxides is very strong and occurs in acidic to neutral water but desorption becomes
preferred as pH values become alkaline (44). The pH dependence of this adsorption is
related to the change in net surface charge of the iron oxide from positive to negative as
pH increases. Iron oxide surfaces also adsorb arsenite, however the reaction is much
weaker than arsenate adsorption. The weaker adsorption reactions are also between both
arsenate and arsenite with aluminum oxide and clay mineral surfaces (43).
Adsorption/desorption reactions of arsenate and arsenite with other surfaces seem to be
more complex than with iron oxides and are not well characterized. (45). Arsenic
adsorption can be affected by the presence of competing ions. Phosphates and silicates
can compete, in particular, with arsenic for the surface sites, thus increasing the mobility
of arsenate and arsenite (46,47). It has been reported that the formation of arseno-
carbonate complexes could increase the release of arsenic from sulfide minerals (48).

Structural changes in solid phases at the atomic level influence arsenic
adsorption/desoprtion. Conversion of phases may happen gradually over time, changing
the density of arsenic adsorption sites. A decrease in the density of adsorption sites can

result in desorption of adsorbed arsenic (45).

The other processes that control arsenic mobility are solid-phase precipitation/dissolution
reactions. These reactions are controlled by solution chemistry, pH, redox state and
chemical composition. Usually aquifers are composed of various solid phases such as
minerals, amorphous oxides, and volcanic glass, organic carbon that exits in a variety of
thermodynamic states. Some solid phases in the aquifers will be dissolved and other

precipitated from solution. Arsenic contained within solid phases as primary component

or as impurity in any of the solid phases is released to groundwater when those solid
phases dissolve. Similarly, arsenic is removed from water when solid phases containing
arsenic precipitate from aqueous solution (45). For example, arsenic often precipitates
with iron oxide (49) so iron oxides act as an arsenic source (case of dissolution) or a sink
(case of precipitation for groundwater). Moreover, solid-phase dissolution will contribute
not only with arsenic contained in that phase but also any arsenic adsorbed to the solid-
phase surface. The release of adsorbed arsenic as a result of solid phase dissolution is
different from the process of desorption from stable solid phase (50). The interplay of
redox reactions and solid-phase precipitation/dissolution may be particularly important in
respect to aqueous arsenic and solid-phase iron oxides and sulfide minerals. High arsenic
concentrations often are associated with iron oxides and sulfides minerals. Iron oxides
usually dissolve under reducing conditions but often precipitate under oxidizing
conditions. On the other hand, sulfide minerals are unstable under oxidizing conditions
but may precipitate under reducing conditions.

Arsenic Mobilization Mechanisms

Several mechanisms are reported in the literature to explain the high arsenic

concentration and mobility in groundwaters around the world. Thus, the most common

processes that control arsenic concentration and mobility in groundwaters are:

a) Oxidation of arsenic-bearing pyrite minerals particularly arsenopyrite (51-55), this
takes place in the aquifer sediments as atmospheric oxygen enters the aquifers in
response to a lowering of the water level according to the following reactions: (56).
FeSz + 15/4 02 + 7/2 H20 2 Fe (OH)3 + 2 3042‘ + 4 Ir

FeAsS +13 Fe3+ + 8 H20 "*4— 14 Fe2+ + 8042‘ +13 H+ + H3Aso.(..,,

10

The stoichiometry of the pyrite oxidation reaction gives iron and sulfate in a molar
ratio of 1:2. Thus, in groundwaters where this mechanism is predominant a
relationship between dissolved arsenic, iron, sulfate and a decrease in pH exists. The
concentration of the released arsenic depends on the arsenic contained in the

arsenopyrite and arsenic bearing pyrite minerals.

b) Reduction of arsenic rich iron oxyhydroxides (57-62), this takes place in anoxic
conditions and the reduction is driven by microbial degradation of sedimentary
organic matter:

8FeOOH + CH3COOH + 14H2C03 —» 8Fe2+ + 16HCO3' + 12H20

The reduction of FeOOH is very common in aquifers where high concentration of

dissolved iron is found and occurs with reduction of arsenate to arsenite and this is shown

because dissolved arsenic is mainly present as arsenite (63,64).

Table 1.4 shows a summary of the occurrences, concentrations and probable mechanism

for the arsenic release in groundwater in different countries.

Thermodynamics of Arsenic Species

Thermodynamic data allows us to describe equilibrium conditions in environmental
sytems and also indicates the direction the non-equilibrium system will move. Thus, it
provides useful information about the occurrence, absence, and predominance of
dissolved and solid arsenic Species under different environmental conditions. Several Eh-

pH or pe-pH diagrams have been reported in the literature (7,22,67). Since arsenic is

11

generally correlated with pyrite minerals Eh-pH or ps-pH diagrams that include arsenic,

sulfide and iron are the most complete way to present this information.

A pe-pH diagram (Figure1.1) for arsenic-sulfur-iron system including oxygen and water
and was constructed based on the thermodynamic data (22,25,66-68). The total arsenic
concentration was 10'5 M equivalent to 550 ug/L, which represents similar concentrations
observed in natural occurring arsenic in groundwater (33,62). Total concentration of
sulfur and iron in the system were 10'5 M.

Table 1.4 Arsenic occurrences in groundwater in some countries

 

 

 

 

 

 

 

 

 

 

 

 

Country/ Well depth, In As, rig/L Mechanism of contamination

regron

Bangladesh 8-260 <2 to >900 Fe-oxyhydroxides reduction, sulfide
oxidation in alluvial sediments

West Bengal 14-132 <1-1300 Fe-oxyhydroxides reduction, sulfide
oxidation in alluvial sediments

China Shallow/deep <100-18600 Reducing environment in alluvial

(Huhhot sediments

Basin)

Taiwan Deep Up to 1800 Strongly reducing environment

Thailand Shallow 120-6700 Oxidation of arsenopyrite in mine
wastes

Ghana 70-100 2-175 Oxidation of arsenopyrite in mine
tailings

Argentina Shallow 100-4800 Volcanic ash with 90% rhyolitic glass

Chile Shallow/deep 100-1000 Volcanic ash

Mexico Shallow/deep 300-1100 Sulfide oxidation in mine wastes

USA 53-56 100-500 Fe-oxyhydroxides reduction, sulfide
oxidation

Canada 8-53 18-146 Sulfides oxidation

 

 

 

 

 

 

At high Eh values in oxygenated waters, arsenic acid species (H3ASO4, H2ASO4',
HAsO42' and A8043”) are stable. At pH less than 1.5 arsenate can precipitates with Fe (III)

to form scorodite (FeAsO4-H20). At high Fe (IH) concentration, scorodite precipitate can

12

be formed at a near neutral pH. Scorodite is commonly found associated with arsenic-

bearing minerals as a weathering product of arsenopyrite (FeAsS) (69).

At an Eh value characteristic of mildly reducing conditions, arsenious acid species
(H3ASO3, HzAsO3‘ and HASO32‘) become stable with H3ASO3 being predominant when
pH is less than 9. Neither of the arsenic oxides A8205 and A8203 is insoluble enough to
show on Figure 1.2. Arsenite is generally present in anoxic environment such as

groundwater, sediment porewater and geothermal water (46.70.71).

 

 

 

 

 

 

 

 

 

 

 

I
I
0 2 4 6 8 10 12 14

 

 

 

Figure 1.1 pe-pH diagram for the system of AS-S-Fe-HZO

13

Under conditions where sulfides are stable, ASS and As2S3 occur as stable solids at pH
below 5.5 and p8 approximately 0. Arsenopyrite is stable under more reducing
conditions. The dominant Oxidation State in FeAsS is As (-1) and its part of the A832'
unit (72). Arsenopyrite and arsenian pyrites are commonly found in arsenic-rich aquifers
and natural deposits (48,73). Arsenic content in arsenian pyrite ranges from less than 0.5
to 10 wt% (73). Most of the arsenic content in arsenian pyrite is probably in a structural
position similar to that in arsenopyrite, where it substitutes for sulfur in the 822' units
yielding ASSZ'. The release of arsenic from arsenian pyrite may be responsible for the
contamination of groundwater in some regions of USA (48). At very low p8 values arsine
(AsH3) may be formed. Arsine is only slightly soluble in water and is very toxic. The pa-
pH diagrams are very useful for predicting many of the complex reactions that involves
arsenic but does not take in account a number of important factors such as organic

arsenicals, effects of solid surfaces and biological reactions.

1.3 Uses and Production of Arsenic

Arsenic was widely used in the nineteenth century as a pigment as particularly for
wallpaper and also was extensively used as a homicidal poison in medieval times until
middle of the nineteenth century (74). Some of the past and current agricultural uses of
arsenic compounds include pesticides, herbicides, insecticides, defoliants, soil sterilants

and animal dips (75). Table 1.5 summarizes the current and past arsenic uses (41,74,75).

14

Table 1.5 Current and past arsenic uses

 

 

 

 

 

 

 

 

Sector Uses

Agriculture Pesticides, insecticides, herbicides, defoliants, desiccants, soil sterilant

Electronics Semiconductors, solar cells, optoelectronic devices, light-emiting
diodes in digital watches, lasers, integrated circuits

Livestock Feed additives, diseases preventatives, animal dips, growth promoters
for poultry and swine, algaecides

Lumber Wood preservatives

Medicine Antisyphilitic drugs, sleeping sickness, psoriasis, asthma, amebiasis,
leukemia, spirochetal and protozoa] disease

Industry Glassware, electrophotography, catalysts, pyrotechnics, antifoulants
paints, dye, soaps, ceramics, pharmaceutical substances, alloys, battery
plates

 

 

Arsenic is generally obtained as a byproduct of the smelting of cooper, lead, cobalt and
gold ores. More than 95% consumed is estimated to be arsenic trioxide. The principal
arsenic producers are China, Russia, France, Mexico, Germany, Peru, Namibia, Sweden
and USA. These countries produce about 90% of the world production (75). The United
States is believed to be the world largest arsenic consumer (25,000 metric tons in 2001) and
about 90 % of the arsenic is used to produce CCA. High purity arsenic metal (99.9999%) is
used in producing gallium arsenide, which is used as a semiconductor in various electronic

devices such as wireless telephones and high-Speed computers (74.75).

1.4 Toxicity and Health Effects of Arsenic
Arsenic toxicity is a complex phenomenon, which affects humans, animals and plants
(76,77). The toxicity of arsenic depends mainly on the concentration of soluble arsenic in

the environment and its oxidation states. Other factors that influence the arsenic toxicity

15

 

are physical state, rate of absorption in the cells, rate of elimination, nature of chemical

substituents, etc.

The toxicity of arsenic is associated with its oxidation state. It is reported that As (III) is
25 to 60 times more toxic than As (V) and several hundred times more toxic than
methylated arsenicals (78). AS (HI) is found to be more water soluble and more mobile in
the environment than As (V) (79). The degree of acute toxicity of arsenic species
decreases in the following order: arsine > AS (111) >AS (V) >MMA (V)>DMA (V) (80).
Recently, it was reported that the LDso for MMA (HI) found in urine was 29.3 mong.
This is 3.8 fold lower than the mm for As (HI) of 112 mol/kg in male Golden Syrian
hamster, suggesting that the methylation of arsenic is not entirely a detoxification

mechanism (81)

1.4.1 Noncarcinogenic effects for humans

Oral exposure acute toxicity. The most common symptoms of acute toxicity via oral
exposure to inorganic arsenic poisoning are nausea, anorexia, vomiting, epigastric and
abdominal pain, diarrhea, dermatitis, muscle cramps, cardiac abnormalities, hepatotoxicity,
bone marrow suppression and hematologic anomalies, vascular lesions, and peripheral
neuropathy. It has been reported that oral doses as low as 20-60 ug/kg/day have toxic
effects in some individuals (82,83). Severe exposures can result in acute encephalOpathy,
congestive heart failure, Stupor, convulsions, paralysis, coma, and death. The acute lethal

dose to humans has been estimated to be around 0.6 mg As/kg/day (82). The ingestion of 3

16

mg As/day for a 1-2 month period was fatal to 1% of a group of infants receiving milk
contaminated with arsenic (83, 84).

Oral exposure sub-chronic toxicity, due to exposure to inorganic arsenic may cause toxic
effects similar to those caused by acute or chronic exposures depending on the dose and
duration. Skin and vascular disorders, neuropathy. gastroenteritis, hepatotoxicity, and
hematological abnormalities have been reported in individuals exposed for time periods
ranging from less than 6 months to 13 years (83). Central nervous system damage (hearing
loss, eye damage, mental retardation, epilepsy), skin abnormalities (melanosis,
desquamation, rashes, and hyperkeratosis) occurred in infants who had been fed arsenic
contaminated milk for 1-2 months with an estimated daily arsenic intake of about 3 mg/day
(84).

Oral exposure chronic toxicity, exhibits symptoms such as weakness, general debility and
lassitude, loss of appetite and energy, loss of hair, hoarseness of the voice, loss of weight,
and mental abnormalities. The most common effects due to long-term exposure are skin,
neurological, and vascular disorders. For example skin abnormalities. particularly
hyperpigmentation and hyperkeratosis has been reported in populations exposed to arsenic
in drinking water (85). For example studies, in Taiwan clearly Shown that arsenic exposure
in drinking water was related to Blackfoot disease which is characterized by a progressive
circulation loss in the hands and the feet and ultimately leads to severely painful gangrene
of the extremities, often requiring amputation of the limb (86,87). The high prevalence and
extreme form of Blackfoot disease reported in Taiwan was not observed in other regions
with Similar arsenic concentrations. Therefore, other factors in addition to arsenic

concentration should be considered to explain this fact (88).

17

Inhalation exposure acute toxicity. Inorganic arsenic dusts can affect respiratory irritation
and mucous membrane damage leading to rhinitis, tracheae bronchitis, laryngitis, shortness
of breath, nasal congestion and perforation of the septum (87-89).

Inhalation exposure chronic toxicity, inhalation toxicity data on inorganic arsenic has
mainly been obtained from occupational exposure studies, identifying chronic respiratory
diseases such as rhinitis, laryngitis, tracheobronchitis, pulmonary insufficiency and blood
disorders in the exposed workers. Arsenic concentration of S 0.5 mg As/m3 has produced
neurological disorders in smelter workers (83). Some researchers reported that babies born
to women exposed to arsenic dusts during pregnancy have had higher incidence in

congenital malformations and below average birth weight (90-92).

1.4.2 Carcinogenicity in Humans

Oral exposure, epidemiological studies have shown a relationship between arsenic
concentrations in drinking water and increased incidences of skin cancers, which include
squamous cell carcinomas and multiple basal cell carcinomas (83.84). More carcinogenic
effects will be discussed in detail in Section 1.8.

Inhalation exposure, studies of smelter and pesticide workers have Shown a close
association between exposure to arsenic and lung cancer mortality (93). The most
important studies of arsenic exposure through inhalation are based on studies of three
copper smelters [Tacoma (Washington), Anaconda, (Montana) and ROnnsk'ar (Sweden)].
These studies demonstrated a statistically significant increase in the lung cancer risk with

increasing exposure.

18

1.5 Why Speciation is needed

The concept of speciation dates back to 1954 introduced by Goldberg to improve the
understanding of biogeochemical cycling of trace elements in seawater (94). This concept
was debated in the scientific community for more than 20 years before the idea was
firmly established (95-98). It is important to emphasize that the ecological and
toxicological effects like essentiality, bioavailability, toxicity, assessment of health
hazards, persistence in the environment and technological properties strongly depend on
the form in which the element occurs in the medium under Study rather than on its total
concentration. In the literature various meanings of speciation can be found. Florence
(99) has defined the term speciation analysis as the determination of the individual
physicochemical forms of the element, which together make up its total concentration in
the sample. According to Lund (94) speciation analysis involves the use of analytical
methods that can provide information about the physicochemical forms of the elements.
Schroeder (100) distinguishes physical Speciation, as differentiation of the physical size
or the physical properties of the element, and chemical speciation, as the differentiation
among the various chemical forms. According to Templenton (101) speciation analysis is
“ the analytical activities of identifying and/or measuring the quantities of one or more
individual chemical species in a sample “, and the speciation of an element as “ the
distribution of an element amongst defined chemical species in a system”. These
activities must be clearly distinguished from the activities “of classification of an analyte
or a group of analytes from a certain sample according to physical (e. g. size, solubility)
or chemical (e.g. bonding, reactivity) properties”. The essential requirement in element

speciation is the need to quantify each of the forms of a given element independently

19

without interference from the other forms. Therefore, an ideal element speciation method
is one that can provide the desired information without altering the distribution of the
different species on the original sample. Thus, speciation can be defined as the
occurrence of different forms (chemical and/or physical) of an element in the original

samples.

The majority of speciation studies have been carried out in water and, this is the most
studied environmental sample. Speciation of samples with low concentrations of arsenic
has obstacles such as sample handling, species separation methods, detection techniques,
losses or nature exchanges of the species present, contamination, etc. Figure 1.2 shows
the distribution of the published papers arranged by elementwe (102). It is important to
note that the majority of the separation methods and detection techniques have been

concentrated on the elemental analysis.

 

Figure 1.2 Distribution of the published works on speciation in waters

20

For the purpose of this study. we focused on the speciation and quantification of As (HI),

As (V), MMA (V) and DMA (V) in water samples. Why Speciation is needed and other

related questions are summarized below:

 

Why?

Environmental risk assessment
Food Industry

Clinical chemistry and medicine
Ecotoxicology

Occupational health and hygiene
Pharmaceutical industry
Petrochemical industry

 

What?

Redox states: As (Hl)/As (V), Cr (III)/Cr(V), Se(IV)/Se(VI), Co(H)/Co(III)
Alkylelement species: MezHg, EtzMg, MeHg+, methylarsenic acids
Compound with c-heteroelement bond: selenoamiacids, organoarsenicals,
arsenosugars

Metalopeptides: metalloenzimes, metallotioneins

Metallodrugs: carboplatin, aurothioglucose

Others: cobalarrrines, metalloporphirines

 

 

Where?

 

Air
Water
Soil and sediments

Biological tissues
Food

 

Question of how to speculate will be discussed in detail in Section 1.6

1.6 Methods of Arsenic Speciation

Most speciation techniques (schemes) rely on the use of one or more separation steps,

followed by element specific detection.

1.6.1 Separation Techniques

The separation techniques usually employed are selective chemical oxidation or reduction,

size fractionation by filtration or dialysis, liquid-liquid extraction, and ion-exchange

chromatography.

21

 

1.6.1.1 Liquid-Liquid Extraction

This technique is mainly used in the inorganic arsenic speciation [separation of inorganic
As (III) from inorganic As (V)] and depends on the pH of the solution and the type of
extractant. Occasionally, this technique is also used to differentiate between inorganic and
organic arsenic. Many extraction procedures have been published to speciate inorganic
arsenic. The most common procedure to extract AS (111) uses ammonium pyrrolidine
dithiocarbamate (APDC)-organic solvent (103-109). In the APDC system only AS (111) is
extracted at pH 4-6.0. Total arsenic is independently determined by extraction with 1M
acid or a neutral medium after reduction of As (V) by using KI to As (III). As (V) is
obtained by subtracting As (III) from total arsenic. The literature reports similar procedures
under varying pH ranges for As (III) extraction, different organic solvents and detection
systems. AS (111) extraction has been carried out at pH 4 to 5.6 (103), pH 3.5 to 5.0 using
citrate buffer (104), pH 5.0 with acetate buffer (106), pH 4.0 to 4.5 (107), pH 1 to 1.5 with
nitric acid (108). With this technique the most popular solvent was chloroform (105,107-
110). Methyl iso-butyl ketone (103,104), chloroform-carbon tetrachloride (106) and
nitrobenzene (103) have also been used. Arsenic quantification has been done by direct
analysis of the organic extract by graphite furnace atomic absorption spectroscopy
(GFAAS) (103-106), neutron activation analysis (NNA) (108,109), after back extraction
(105,109), or rrrineralization of the organic extract (109) by GFAAS (105) and hydride
generation atomic absorption spectroscopy HGAAS (107). Ethylene diamine tetra-acetic

acid (EDTA) was used to prevent metal ion interference in all the cases.

22

A similar extraction procedure for AS (111) uses diethylammonium diethylcarbamate
(DDDC) with carbon tetrachloride, however its application is limited because of the narrow
range of pH, which can be used for the extraction (110). At pH range of 2 to 6 in aqueous
solution As (III) has been reported to form a complex with sodium bis (trifluoroethyl)
dithiocarbamate (As-(FDDC)3). The precipitate was extracted with chloroform. The extract
was evaporated to dryness and redissolved in a minimal amount of chloroform for arsenic

determination by gas chromatographic analysis (111).

Another extraction procedure has been reported for the sequential determination of AS (111)
and As (V) in waters based on the extraction of As (11]) with ammonium sec-butyl
dithiophosphate (ABDP) with hexane (112,113) and chloroform (114). Arsenic
quantification in the organic phase was determined using GFAAS directly (113) or by
hydride generation of the correspondent arsine resulting from the reduction of the extract
from the back extraction of the aqueous phase (112,114). The detection limit was 0.6 —6
ng/L in the three cases was reported. As (III) was extracted as As-thionalide complex in di-

isopropil ether (DIPE) using atomic absorption Spectroscopy for detection (AAS) (115).

The main advantages of these procedures are: preliminary separation can be done at
sampling site avoiding storage, and preservation problems, while acomplising
preconcentration. The main disadvantage of these procedures is that only one specie can be

directly determined and the other is calculated by difference.

23

1.6.1.2 Selective Hydride Generation

This technique has been studied by many researchers (116-129) to isolate arsenic species in
different matrixes. It is based on the reduction of the arsenic compounds to the
corresponding arsines, depending on pH and changing arsines boiling points. Arsine
volatilization was used as one of the earliest techniques in the arsenic test of Marsh (118).
This procedure has been continuously improved and still used to determine total arsenic in
water. The first procedure for speciation and quantification of As ([11), As (V), MMA (V)
and DMA (V) in aqueous samples was published by Braman and Foreback (116). It
consisted of reduction of the arsenic compounds to the corresponding gaseous arsines with
sodium tetraborohydride (NaBH4) and then collected them, using helium as a carrier gas in
liquid nitrogen cooled U-trap hal packed with glass beads. The trapped arsines are
separated by slowly warrrring the trap and selective volatilization according to their boiling
points and then swept by the carrier gas to the detector. As (H1) is the only species, that can
be reduced to arsine by NaBI-l4 at pH 4-9. As (V) must be first reduced to AS (111) before
NaBH4 reduction at pH 1-2. The method has been subsequently improved (117) and the
authors have successfully determined the four species with detection limit for arsenic of

approximately of 0.004-0.02 rig/L.

Further improvement of the arsine generation method for arsenic speciation has been
carried out by optimization of the reducing process, improved cold traps [such as a dry ice
cooled water trap placed between the reaction vessel and nitrogen trap (118-120)], gas
collectors, gas-liquid separators and more sensitive detection systems. Particular

consideration has been given to the selection of buffer systems, reducing, and masking

24

agents (121). Arsenic species are reduced using different acids and buffers such as citrate
buffer pH 5 to avoid interferences form various ions [Co (IH), Fe (IH), Ni (H), etc.] (122),
tris buffer at pH 6-7.5 (118,120,123), acetate buffer at pH 5 (124,125), potassium hydrogen
phthalate at pH 3.5-4 (126), HCl 6M (127), sodium chloride in sulfuric acid media (128)
for arsine generation for As (IH). For the arsines generation of the other arsenic species or
total arsenic HCl at pH S 1 (118-120,122-125,127) and oxalic acid at pH 1.3 (126) is
commonly used. Determination of the released arsines can then be done by measuring
atomic errrission (116,117), gas chromatography with electron capture detector (118), flame
atomic absorption spectrometry (FAAS) (119,122,126,127), AAS and inductively coupled
plasma atomic emission spectrometry (ICP-AES) (121), atomic absorption Spectrometry
with heated quartz atomizer tube (120,123,125), GFAAS (134) and ICP-AES (128). An
interesting approach has also been developed (129) based on the selective hydride
generation of arsine from As (IH) using the old Fleitman reaction (A1 with NaOH), which
is appropriate to be used on-line and applied to direct determination of As (HI) and As (V)
after on-line reduction with KI. The advantage of this procedure is the use of low cost,
stable and easy to handle reagents, differing from the classical sodium tetraborohydride
procedure. Arsenic speciation by selective hydride generation combined with a suitable
detection system seems to be a good method. But may have disadvantages when pH ranges
are wide and under various buffer systems. MMA and DMA can also interfere with As (IH)
determination under this technique. Speciation cannot be carried out at the sampling site

with this approach.

25

1.6.1.3 Chromatographic Methods

Several chromatographic techniques have been published for arsenic Speciation in
environmental samples, such as paper-chromatography (130), gas chromatography
(131,132), thin-layer chromatography and electrophoresis (76,133-135). The most popular
methods are ion exchange chromatography and high performance liquid chromatography.

The last two techniques are discussed below.

Ion exchange chromatography has been applied in arsenic speciation of both inorganic and
organic Species. This method is based on the dissociation constants (pKa) of As (HI), As
(V), MMA and DMA acids since they are weak acids (24). The earliest papers on ion
exchange chromatography for arsenic speciation in water were based on using cation
exchange resins (136,137). As (V), MMA and DMA were separated using a cation
exchange column (Dowex 50 W-X8) and the three fractions then analyzed by the arsine
method (136). More reproducible results were later achieved by modifying this technique
and using FGAAS with a matrix modifier as the detection system (137). However, the
mechanism for the separation is not yet known. The attempt to use cation exchange
chromatography for the separation of As (IH) and AS (V) has not been successful (138).
All four arsenic species have been determined by combining cation and anion exchange
chromatography (139-147). Several stationary phases (resins) used, have been cation
Dowex-50-X8, anion AGl-X8, strong cation exchange resin, silica based anion exchange

resin and others. Mobile phases (eluents) used, have been acetate buffer, phosphate,

26

perchloric acid, trichloroacetic acid, ammonium hydroxide, acetic acid, and hydrochloric

acid. The detection techniques were differential pulse polarography, GFAAS and HGAAS.

As (HI) and As (V) separation has been accomplished by using strong anion exchange
chromatography (148-160) with stationary phases such as Dowex 1-8 anion exchange,
strong anion exchange QMA, silanized diatomite, hydrochloric acid as a mobile phase, and
FGAAS and HPLC-ICP-MS detection. This technique was originally reported for
separating As (IH) and As (V) in groundwater using a strong anion exchange resin (acetate
form). AS (V) was retained in the column, while As (HI) passed trough and As (V) was
eluted using hydrochloric acid 0.12 M. Arsenic in each portion was determined by FGAAS
(148). The main advantage of these techniques is that arsenic speciation can be performed

at the sampling site avoiding any chemical changes in the arsenic species distribution.

With the development of HPLC techniques, a variety of separation modes have been
published for arsenic speciation coupled with selective detection systems such as ICP-MS,
FGAAS and HGAAS (160-182). The HPLC technique is carried out using different
commercial columns such as: C13 reversed-phase, BAX-10, Hamilton PRP-X 100,
Hamilton PRP-l, Dionex IonPAc AS11, reversed-phase Dionex, C18 bonded silica
modified by dioctyldimethylamonium bromide and, various mobile phases such as
ethyltrimethylarnmonium bromide-propanol-borate buffer, methanol-water, sulfuric acid
0.1M, phosphate buffer, tetramethylamonium phosphate, methanol-phosphate buffer. The
main advantage of this technique is that separation of at least eight of the arsenic species

can be accomplished, but this technique is not usable at sampling site.

27

1.6.2 Detection Techniques

Trace levels of arsenic speciation in environmental samples require a high-sensitivity of
detection. A variety of detection techniques are available for arsenic speciation including
AAS (FAAS, HGAAS, GFAAS), ICP (AES, MS), atomic fluorescence spectrometry
(AFS), anodic stripping voltametry (ASV), spectrophotometry, and neutron activation

analysis. This section briefly describes AAS, ICP- MS techniques.

AAS is a highly sensitive and specific single element technique, ideally appropriate for
speciation analysis. The most sensitive techniques utilize GFAAS and HGAAS. FAAS has
not been found to be satisfactory due to its low sensitivity and matrix interferences
(150,183). However, improvement of FAAS has been reported (150,181) by using quartz
adapters. The use of electrothermal atomic absorption spectrometry (ETAAS) or GFAA
has been used for a long time to determine arsenic in environmental samples and is the
most sensitive technique. The performance of this technique depends on the characteristic
of the graphite and other parts of the atomizer system. For these reasons a set of conditions
must exist which provide reduction or elimination of interferences include: a) fast rise in
the atomization temperature (fast thermal equilibrium): b) sample atomization needs to be
delayed until the wall and gas phase have reached their final temperature (atomization from
platform), integrated platform atomizers control this process better than the old platform
types; c) powerful methods of background correction such as Zeeman-effect corrections
and d) the use of mixed chemical modifiers. GFAAS needs only small volumes of the

sample usually 10 to 50 uL and its detection limits are in rig/L range.

28

The ICP-MS technique combines the atomization and ionization generated in an ICP with
MS detection. The advantages of this technique are: high sensitivity (detection limits in
ng/L range), multi-element detection capability and the ability to measure isotopes.
However, arsenic determination in water samples containing chloride is difficult with this
technique because the 75As+ ion (arsenic is monoisotope, 75As) interferes with the
molecular ion 40Ar 35Cl+ formed by the combination of the plasma gas and chloride ion.
Consequently, sample pretreatment may be necessary to separate out the chloride or the
chloride level needs to be monitored simultaneously with the arsenic. Additionally, other
factors need be considered in coupling HPLC with ICP-MS are: a) the use of organic
solvents as mobile phase can destabilize or may extinguish the plasma resulting in poor
precision and accuracy (182), b) organic solvents, carbonates, phosphates can produce
many interferences. A desolvation system can be used to reduce the solvent load to the
plasma and minirrrize polyatomic interferences, but it requires a special instrumental set-up
that can be very complicated for routine analysis (177, 182). On the other hand, using a
hexapole collision cell ICP-MS can reduce this problem. Therefore, ICP-MS is the most
powerful detector for arsenic speciation when the highest sensitivity is needed or several
species have to be determined Simultaneously. But it is very expensive and analysis time

can be too long.

1.7 Arsenic Regulations
The main goal of guidelines for Drinking Water Quality is to protect public health. It has
taken a long time to establish the maximum contaminant level (MCL) in United States for

regulating arsenic concentration in public water supplies. In 1942, the US. Public Health

29

Service GJSPHS) established an arsenic drinking water standard for interstate water
carriers of 50 [Lg/L. In 1962, USPSH identified 10 rig/L as the goal concentration and sets
50 rig/L as the floor for rejecting a water supply. On December 24, 1975 the United
States Environmental Protection Agency (EPA) set National Interim Primary Drinking
Water Regulation for arsenic at 50 jig/L under the authority of the Safe Drinking Water
Act (SDWA) of 1974. In 1980 the International Agency for Research on Cancer (IARC)
determined that arsenic and its compounds are lung and Skin carcinogens in humans on
the basis of sufficient evidence for carcinogenecity in humans and limited evidence for
carcinogenecity in animals. Scientific studies linked arsenic in drinking water to skin
cancer in humans as early as 1898. The first studies reporting dose-dependent effects
came from studies published in 1968 and 1977. EPA’s arsenic work has reflected
scientific uncertainties about health effects of low concentrations of carcinogens and

animal studies suggesting that arsenic may be an essential nutrient.

In 1985, EPA proposed a maximum contaminant level goal (MCGL) for arsenic of 50
rig/L. In 1986, United States Congress passes the SDWA, which included arsenic in
drinking water among 83 contaminants for which EPA must issue new standards by 1989.
In 1988, EPA estimated that arsenic ingestion of 50 jig/L might result in a skin cancer of
l in 400 (184). EPA misses the 1989 deadline in the SDWA for issuing a revised
National Interim Primary Drinking Water Regulation for Arsenic. In 1993, EPA’S
Scientific Advisory Board concluded that available data shows a connection between

high levels of arsenic and internal cancers in humans. At that time the World Health

30

Organization (WHO) recommended 10 rig/L as provisional guideline for arsenic in

drinking water (185).

In 1996, Safe Drinking Water Act Amendments were approved by the US. Congress and
signed into law. Congress mandated that EPA must propose a new arsenic regulation
based on the current scientific evidence by January 2000 and establish a final rule by
January 1, 2002. In 2000, EPA proposed a MCL for arsenic at 5 jig/L in drinking water
and asked on comments on levels at 3, 10 and 20 rig/L. In January 2001, a new US
standard of 10 rig/L for arsenic was established based on the arsenic level recommended
by EPA. Two month later, the Bush administration delayed the implementation of the
new arsenic standard challenging the scientific evidence for the regulation and the
estimated cost for its implementation. Nevertheless, in October 2001, EPA adopted the
10 pg As/L standard to be effective in February 2002 and January 23, 2006 as the
compliance date. The new arsenic standard is intended to protect the consumers against
long-term exposure to arsenic in drinking water (186). Some countries have adopted as
their standard the WHO provisional guideline of 10 rig/L for arsenic in drinking water.

However, many countries have different values as is shown in Table 1.6 (185).

Table 1.6 Standards for arsenic in drinking water

 

Standard, [Lg/L Countries

7 Australia (1996)

10 European Union (1998), Japan (1993), Jordan (1991), Laos (1999),
Mongolia (1998), Namibia, Syria (1994), United States (2002)

25 Canada

50 Bangladesh, Bolivia (1997), China, Egypt (1995), India, Indonesia
(1990), Philippines (1978)

 

 

 

 

 

 

 

 

31

Efforts to revise the arsenic standard have been controversial and the debate continues as
to what level best reduces health risks at a justifiable cost, particularly in small systems
where most violations are expected. The National Research Council (NRC) concluded
that studies essential for improving the accuracy of arsenic risk assessment are still
needed. The majority of EPA’S Science Advisory Board Panel concluded that, there are
uncertainties in the risk estimates, technology (analytical methods and water treatment)
and significant implementation costs. The rule and its delay have created a range of
policy responses. Whatever the out come, water suppliers and communities are urging
Congress to provide more funding to help them comply the arsenic standard and other

SDWA mandates.

1.8 Human Exposure Assessment

Exposure to arsenic occurs in several forms and from different sources. The general
population is exposed to arsenic through water, food, air and soils. People are mainly
exposed via ingestion of food and drinking water. The typical Canadian intake of the total
arsenic from all sources for adults was estimated at 38.5 jig/day (187,188). The intake of
inorganic arsenic from food was estimated to be 12.5 ug/day for males and 8.1ug/day for
females in Canada (189). Intake of arsenic via inhalation is negligible. Exposure to
arsenic in drinking water presents the greatest risk to public health Since the most toxic
arsenic species are inorganic As (IH) and AS (V), and. these two species are found
predominantly in groundwater. Arsenic has been found to occur naturally in drinking

water supplies at numerous locations around the world (11,190) as Shown in Table 1.7.

32

Table 1.7 Global Arsenic Contamination in Groundwater

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Country/region Potential Concentra- Environmental conditions
exposed tion
pulation (pg/L)

Bangladesh 30,000,000 <1 - 2,500 Natural; alluvial/deltaic sediments
with high phosphate, organics

West Bengal, 6,000,000 <10 —3,200 Similar to Bangladesh

India

Vietnam >1,000,000 1 -3,050 Natural; alluvial sediments

Thailand 15,000 lto —5,000 Anthropogenic; mining and dredged
alluvium

Taiwan 100,000- 10 - 1,820 Natural; coastal zones, black shales

200,000

Inner 100,000 <1 - 2,400 Natural; alluvial and lake sediments;

Mongolia 600,000 high alkalinigL

Xinjiang, >500 40 —750 Natural; alluvial sediments

Shanxi

Argentina 2,000,000 >1 - 9,900 Natural; loess and volcanic rocks,
thermal springs; high alkalinity

Chile 400,000 100 - 1,000 Natural and anthropogenic
volcanogenic sediments; closed
basin; lakes, thermal springs, mining

Bolivia 50,000 - Natural; similar to Chile and parts of
Argentina

Brazil - 0.4 —350 Gold mining

Mexico 400,000 8 —620 Natural and anthropogenic; volcanic
sediments, mining

Germany <10 —150 Natural: mineralized sandstone

Hungary, 400,000 <2 —176 N atural; alluvial sediments; organics

Romania

Spain >50,000 <1 —100 Natural; alluvial sediments

Greece 150,000 Natural and anthropogenic; thermal
springs and mining

United <1 —80 Mining; southwest England

Kingdom

Ghana <100,000 <1 - Anthropogenic and natural; gold

175 mining
USA and <1- Natural and anthropogenic; nrining,
Canada >100,000 pesticides, As203 stockpiles, thermal

 

 

 

springs, alluvial, closed basin lakes,
various rocks

 

33

 

Arsenic levels vary among different geographic areas. The majority of Canadian ground
waters have less than 50 ug/L. But natural arsenic concentration was found to range up to
9,100 rig/L in regions of Ontario, Quebec, New Brunswick and Nova Scotia and up to
11,000 rig/L in groundwater in the proximity of an abandoned arsenical wood
preservative facility (191). High arsenic concentrations have also found in groundwater in
Southwestern regions of California, Nevada and Arizona and Midwestern regions of
Utah, South Dakota, Oklahoma, Minnesota, Wisconsin, and Michigan in the United
States. Arsenic concentrations of up to 2,600 rig/L were found in the groundwater in
Joaquin Valley of California, in the C080 Hot Springs of California of up to 7,500 ug/L
and in Imperial Valley of California of up to 15,000 ug/L (192,193). EPA data have
reported that an estimated 5.7 millions of Americans may be exposed to drinking water

with arsenic levels above 10 ug/L (194).

In the case of Michigan the EPA data indicates that 367,000 citizens may be drinking
water with arsenic levels that exceed the 10 ug/L standard and 169,000 citizens may be
drinking water with arsenic concentration of 20 ug/L or more. Since 1981, high arsenic
levels have been reported in 11 counties in Michigan as shown in Table 1.8. Total arsenic
concentrations in groundwater samples in nine counties in Southeast Michigan (Huron,
Tuscola, Sanilac, Lapeer, Genesee, Shiwassee, Livingston, Oakland and Washtenaw)
were found to vary between 0.5 and 278 rig/L. As (HI) specie makes up 53-98% of the

total arsenic (195).

34

Table 1.8 Arsenic distribution in groundwater samples of Michigan by countya

 

 

 

 

 

 

 

 

 

 

 

 

County Samples As As As As
(<10 lug/L) ( “-20 ug/L) (21-50 lug/L) (>50 rig/L)
Genesee 363 43 % 21% 29% 7%
Huron 180 71 % 9% 12% 9%
In gham 120 87% 8% 5% 0%
Jackson 104 86% 9% 1% 5%
Lapeer 340 45% 22% 20% 12%
Livingston 289 85% 12% 3% 0%
Oakland 492 71% 14% 13% 1%
Sanilac 53 77% 13% 8% 2%
Shiawassee 246 79% 1 1% 10% 0%
Tuscola 68 74% 18% 7% 1%
Washtenaw 79 87% 6% 4% 3%

 

 

 

 

 

 

 

 

aMichigan Department of Environmental Quality (MDEQ, Arsenic Database, 2001).

Samples analyzed from 1983-1996.

Numerous studies have reported adverse human health effects associated with arsenic
ingested from groundwater sources (196-216). Further, many studies carried out in
countries outside of USA have shown a relationship between skin and internal cancers
and high concentrations of arsenic in drinking water (several hundred rig/L) (196,
201,205,215). These epidemiological studies establish a strong case that exposure to high
levels of arsenic in drinking water contributes to an increased risk of skin and bladder
cancer. However, no epidemiological studies have been done to assess cancer risks at low

arsenic exposure levels (215,216).

Chronic arsenic ingestion usually produces Skin lesions such as hyperpigmentation and
hyperkeratoses. Hyperpigmentation has been observed at exposure levels of 10 ug As/kg

body weight per day. This dose that would correspond to about 500 ug As/L in drinking

35

water at average consumption levels (216). Adverse effects on the gastrointestinal
system, cardiovascular, and nervous systems have been observed in humans as a result of
acute or sub-acute exposure to inorganic arsenic in the range of several milligrams to
grams per day. Even though, there is general agreement about the health risk posed by
arsenic in drinking water at the very high levels, there is no direct evidence to base risk
estimation for levels of arsenic at or below current drinking water guidelines or standards.
This is an area of a great interest in the scientific community and research is ongoing to

better understand the risks at lower levels of arsenic exposure.

Methylation is the main human metabolic pathway for inorganic arsenic (216, 217-232).
The inorganic arsenic AS (111) and As (V) is metabolized to DMA" and MMAV which are
less acutely toxic and more readily excreted in the urine than the inorganic species. It has
been suggested by many researchers that methylation of arsenic in the body is a
detoxification pathway (217,221). However, recent studies suggest that MMA‘" and
DMA"1 may be more toxic than inorganic arsenic As (IH) and As (V) (221, 225-232).
The proposed reduction and oxidative addition sequence of arsenic methylation is
summarized in Figure 1.3 (217, 233-238). Recent studies indicate that methylation
intermediates are more toxic to mammalian specie cells in vitro than are inorganic
species (228,229,231,238,239). It has been found that the methylated trivalent arsenic
Species are approximately 77-386 times more DNA-damaging agents in the Single-cell
Gel Assay than inorganic As (HI) and As (V) (240). Monomethylarsenous acid and
dimethylarsinous have been found in human urine along with the metabolites of inorganic

arsenic (235,238).

36

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37

l. 9 Risk Assessment

Human health risk assessment is a procedure that is used to predict to what degree,
exposures to a particular agent may adversely affect people. Risk assessment analysis
estimates past exposures to a particular agent and the adverse health effects, which may
or may not have already occurred. It also involves prediction of the possible future
exposure (241). The fundamental objective of risk assessment is to provide scientific
information for risk management, especially for regulation policies. Risk assessment
consists of four major aspects: hazard identification, dose-response assessment, human
exposure assessment, and risk characterization (242). Hazard identification and dose-
response assessment (toxicity of the agent) are combined with the exposure to that agent

(exposure assessment) in order to characterize the risk to human health.

Hazard identification is the process of establishing whether or not a particular chemical
exposure exhibits the potential for adverse health effects. It is accomplished either
through the observation of increased morbidity/mortality after documented human
exposure, or, in the absence of good human health data, through experiments carried out
on laboratory animals. Exposure may take place through three pathways: ingestion (food
or drink), inhalation and contact with the skin (dermal). Once inside the body, the
chemical may be stored, eliminated by excretion, or transformed in more or less toxic
compounds. If a chemical produces a negative effect to the organism, that effect may
either be carcinogenic or non-carcinogenic. The effect to the organism is evaluated by a
test called a "bioassay." The bioassay is able to identify risks of about 1 in 100, but

regulators extrapolate risk in humans to 1 in 1,000,000. As a result, extrapolation is

38

needed from data taken from animals exposed to high chemical doses to humans who will
be exposed to doses that are several orders of magnitude lower. This poses a major

limitation in risk assessment technique.

Dose-Response Assessment is the process in which a mathematical relationship between
the amount of a particular chemical to which a human is exposed (dose) and the risk that
there will be an unhealthy response to that dose. For carcinogens, it is assumed that any
exposure will create some likelihood of cancer. For non-carcinogens, it is assumed that
there is some threshold dose below which there is no adverse effect. The relationship
between dose and response is shown by a "dose-response curve." The Slope of the dose-
response curve in the range of health interest is called the "slope factor" (SF). The slope

factor is in units of (mg/kg/day)".

The dose-response equation for carcinogenic risk is:

Excess Lifetime Cancer Risk (ELCR) =Chronic daily intake (CDI) (mg/kg/day) x SF

The basic equation for calculating system toxicity (noncarcinogenic):
Noncancer Hazard Quotient (HQ) = CDI/chronic reference dose (RfD)(mg/kg-day)
CDI, sometimes called average daily dose is estimated for ingestion via drinking water

using the following relationship with the standard values recommended by EPA.

CDI = C(DI x %A)(ED x %T). mg/kg-day

BWxAT

39

C = concentration, mg/L

D1 = daily intake (from EPA exposure factors)

%A = % absorbed (100% is most conservative)

ED = exposed duration (30 to 40 years maximum)

%T = % of the time actually exposed (100% is most conservative)
BW = body weight (from EPA exposure factors)

AT = Averaging time (from EPA, 70 years).

Exposure Assessment determines the portion of the population that may be exposed to a
specific chemical, specifying how the exposure may occur and determining the
magnitude, duration, pathways of dosage to which people may be exposed using EPA
exposure factors such as human body weights, drinking water consumption, activity

patterns, etc.

Risk Characterization is the process of bringing all the previous steps together. It involves
a qualitative or quantitative estimate of the probability for adverse effects in humans
based in epidemiological and/or animal studies. This step also includes the evaluation of
the overall quality of the data, the specific assumptions and uncertainties, and the level of
confidence in the resulting estimates. For example: usually, if the cancer risk is less than
1 in 1,000,000 the risk is considered acceptable; greater than 1 in 1,000,000, but less than
1 in 10,000 the risk is questionable and greater than 1 in 10,000 the risk is considered
unacceptable. The final estimates of risk derived in this process are used by regulators to

balance health risks against costs and benefits to society, and by the public to evaluate the

40

appropriateness of measures taken to protect their health. The risk characterization is a
complex process with a number of challenges that need to provide adequate and

reasonable protection to the general population (243).

Health risk assessment from ingested arsenic in drinking water has been previously
focused on Skin cancer risk alone. There is now enough scientific evidence to consider
other internal and more fatal cancers produced by ingested arsenic. Different
organizations (e.g.USEPA, WHO) have performed arsenic risk assessments but have
arrived at substantially different conclusions as to where regulatory levels should be set.
The current standard in drinking water of 10 ug/L total arsenic was set by US. EPA in
2002 (same as WHO standard); while in Australia and Canada is 7 and 25 rig/L are the
standards respectively. Extrapolation for cancer from a Taiwanese epidemiology study
estimates a risk of 10“4 at drinking water concentrations of 2 rig/L (244). Of course, such
total arsenic standards ignore the understanding that toxicity between species may vary
by factors of a thousand or more. One reason for such differences is that the arsenic risk
assessment must rely on epidemiological studies, because a suitable animal model has not
been identified for toxicity studies. Epidemiology studies are limited by the assumption
that exposure occurs only through drinking water and by the lack of information on the
chemical form of the arsenic exposure. Current regulatory practice does not distinguish

between arsenic species.

41

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Tsuda, T., Babazono,A., Yamamoto,E., Kurumatani,N., Mino,Y., Ogawa,T.,
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Chiou, H.Y., Hsueh,Y.M., Liaw,K.F., Homg,S.F., Chiang,M.H., Pu.Y.S.,
Huang,C.H., Chen,C.J., Incidence of Internal Cancer and Ingested Inorganic

Arsenic: A Seven-Year Follow-up Study in Taiwan. Cancer Research, 1995. 55: p.
1296-1300.

Chiou, H.Y., Chiou, S.T., Hsu, Y.H., Chou,Y.L., Tseng,C.H., Wei,M.L., Chen,C.J.,
Incidence of Transitional Cell Carcinoma and Arsenic in Drinking Water: A

F allow-up Study of 8,102 Residents in an Arseniasis-endemic Area in Northeastern
Taiwan. American Journal of Epidenrilogy, 2001. 153(5): p. 41-418.

Bates, M.N., Smith,A.H., Cantor,K.P., Case-Control Study of Bladder Cancer and
Arsenic in Drinking Water. American Journal of Epidemilogy, 1995. 141(6): p.
523-530.

Tseng, W.P., Effects and Dose-Response Relationships of Skin Cancer and

Blackfoot Disease with Arsenic. Environmental Health Perpectives, 1977. 19: p.
109-119.

58

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Hopenhayn-Rich, C., Browning,S.R., Hertz-Piccioto,l., Ferreccio,C., Peralta,C.,
Gibb,H., Chronic Arsenic Exposure of Infant Mortaility in Two Areas of Chile.
Environmental Health Perspectives, 2000. 108(7).

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Drinking Water in Utah: A Cohort Mortality Study. Environmental Health
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Chen, S.L., Dzeng,S.R., Yang,M.H., Arsenic Species in Groundwater of the
Blackfoot Disease Area, Taiwan. Environmental Science & Technology, 1994.
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Smith, A.H., Arroyo,A.P., Mazumder,D.N., Kosnett,M.J., Hemandez,A.L.,
Beeris,M., Smith,M.M., Moore,L.E., Arsenic-Induced Skin Lesion Among
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Exposure. Environmental Health Perspectives, 2000. 108(7).

Tseng, C.H., Tai,T.Y., Chong,C.K., Tseng,C.P., Lai,M.S., Lin,B.J., Chiou,H.Y.,
Hsueh,Y.M., Hsu,K.H., Chen,C.J., Long-Tenn Arsenic Exposure and Incidence of
Non-Insulin Dependent Diabetes Mellitus: A Cohort Study in Arseniasis-

Hyperendemic Villages in Taiwan. Environmental Health Perspectives, 2000.
108(9).

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Environmental Levels in New Hampshire. International Journal Hygene
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Ferreccio, C., Gonzalez,C., Milosavjlevic,V., Lung Cancer and Arsenic
Concentration in Drinking Water in Chile. Epidemiology, 2001. 11(6): p. 673-679.

Guo, H.R., Tseng,Y.C., Arsenic in drinking Water and Bladder Cancer:
Comparison Between Studies Based on Cancer Registry and death Certificates.
Environmental Geochemistry and Health, 2000. 22: p. 83-91.

Chiou, H.Y., Huang,W.J., Su,C.L., Chang,S.F., Hsu,Y.H., Chen,C.J., Dose-
Response Between Prevalence of Cerebrovascular Disease and Ingested Inorganic
Arsenic. Stroke, 1997. 28: p. 1717-1723.

NRC (National Research Council). 2001, Washington: National Academy Press.
Buchet, J.P., Roels,L.R., Comparison of the Urinary Excretion of Arsenic
Metabolism After a Single Dose of Sodium Arseinte, Monomethylarsonate or

Dimethylarsinate in Man. International Archives Occupational Environmental
Health, 1981. 48: p. 71-79.

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Vahter, M., Metabolism of Arsenic, in Biological and Environmental Effects of
Arsenic, F. B.A., Editor. 1983, Elsevier: Amsterdam. p. 171-198.

Aposhian, H.V., Biochemical Toxicology of Arsenic. Review Biochemical
Toxicology, 1983. 10: p. 265-299.

Goyer, R.A., Toxic Effects of Metals, in Casarett and Doull's Toxicology: The Basic
Science of Poison, C.D. Klaassen, Editor. 1996, McGraw Hill: New York. p. 696-
698.

Aposhian, H.V., Enzimatic Methylation of Arsenic Species and other New
Approaches to Arsenic Toxicity. Annual Review Pharmacology and Toxicology,
1997. 37: p. 397-419.

Hughes, M.F., Arsenic Toxicity and Potential Mechanism of Action. Toxicology
Letters, 2002. 133(1): p. 1-16.

Roy, R, Saha,A., Metabolism and Toxicity of Arsenic: A Human Carcinogen.
Current Science, 2002. 82(1): p. 38-45.

Yamanaka, M., Okada,S.;, Induction of Lung-Specific DNA Damage by
Metabolically Methylated Arsenics Via the Production of Free Radicals.
Environmental Health Perpectives, 1994. 102(Suppl. 3): p. 37-40.

Wanibuchi, H., Yamamoto,S., Chen,H.,Yoshida,K., Endo,G., Hori,T.,
Fukushima,S., Promoting Effects of Dimethylarsinic Acid on N-butyl-N-(4-
hydroxybutyl)nitrosamine-induced Urinary Bladder Carcinogenesis in Rats.
Carcinogenesis, 1996. 17: p. 2435-2439.

Brown, J.L., Kitchin,K.T., George,M., Dymethylarsinic Acid Treatment Alters Six
Different Rat Biochemical Parameters: Relevance to Arsenic Carcinogenesis.
Teratogenesis, Carcinogenesis and Mutagenesis, 1997 . 17: p. 71-84.

Delnomdediew, M., Basti,M.M., Styblo,M., Otvos,J.D., Thomas,D.J.,
Complexation of Arsenic Species in Rabbit Erythrocites. Chemical Research
Toxicology, 1994. 7: p. 621-627.

Styblo, M., Serves,S.V., Cullen,W.R., Thomas,D.J., Comparative Inhibition of
Yeast Glutathione Reductase by Arsenicals and Arsenothiols. Chemical Research
Toxicology, 1997. 10: p. 27-33.

Lin, 8., Cullen,W.R., Thomas,D.J., Methylarsenicals and Arsinothiols Are Potent

Inhibitors of Mouse Liver Thioredoxin Reductase. Chemical Research Toxicology,
1999. 12: p. 924-930.

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230.

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Zakharyan, R.A., Aposhian,H.V., Enzimatic Reduction of Arsenic Compounds in
Mammalian Systems: The Rate-Limiting Enzime of Rabbit Liver Arsenic
Biotransformation Is MMA( V) Reductase. Chemical Research Toxicology. 1999.
12: p. 1278-1283.

Petrick, J.S., Ayala-Fierro,F., Cullen,W.R., Aposhian,H.V., Monomethylarsonous
Acid (MMA(III)) is more toxic than Arsenite in Chang Human Hepatocytes.
Toxicology Applied Pharmacology, 2000. 163: p. 203-207.

Zakharyan, R.A., Ayala-Fierro,F., Cullen,W.R., Aposhian, H.V., Enzimatic
Methylation of Arsenic Compounds, MonomethylarsonousAcid (MMAIII) is the
Substrate for MMA Methytransferase of rabbit Liver and Human Hepatocytes.
Toxicology Applied Pharmacology. 1999. 158: p. 9-15.

Peng, B., Sharma,R., Mass,M.J., Kligerman,A.D., Induction of Genotoxic Damage
is Not Correlated with the Ability to Methylate Arsenite In Vitro in the Leokocytes
of Four Mammalian Species. Environmental and Molecular Mutagenesis, 2002. 39:
p. 323-332.

Thompson, D.J., A Chemical Hypothesis for Arsenic Methylation in Mammals.
Chemico-Biological Intearctions, 1993. 88(2-3): p. 89-114.

Aposhian, H.V., Gurzau,E.S., Chris,X.; Gurzau,A., Healy,S.M., Lu,X., Ma,M.,
Yip,L., Zakraryan,R., Malorino,R., Dart,R., Tircus,M., Gonzales-Ramirez,D.,
Morgan,D., Avram,D., Aposhian,M., Occurrence of Monomethylarsonous Acid in
Urine of Human Exposed to Inorganic Arsenic. Chemical Research Toxicology,

2000. 13: p. 693-697.

Cullen, W., McBride,B.C., Manji,H., Pickett,M., Reglinsky,A.W., The Metabolism
of Methylarsine Oxide and Sulfide. Applied Organometallic Chemistry, 1989. 3: p.
71-79.

Le, X., Ma,M., Lu,X., Cullen,W.R., Aposhian,H.V.; Zheng,B., Determination of
Monomethylarsonous Acid, a Key Arsenic Methylation Intermediate in Human
Urine. Environmental Health Perpectives, 2000. 108(11).

Le, X., Lu,X., Ma,M., Cullen,W.R., Aposhian,H.V., Zheng,B., Speciation of Key
Arsenic Metabolic Intermediates in Human Urine. Analytical Chemistry, 2000.
72(21): p. 5172-5177.

Styblo, M., Del Razo,L.M., Vega,L., LeCluyse,G., Hamilton,G., Reed,W.,
Wang,C., Cullen,W.R., Thomas,D.J., Comparative Toxicity of Trivalent and

Pentavalent Inorganic Methylated Arsenicales in Rat and Human Cells. Archives of
Toxicology, 2000. 74: p. 289-299.

61

240.

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Kligerman,A., Methylated Trivalent Arsenic Species Are Genotoxic. Chemical
Research Toxicology, 2001. 14: p. 355-351.

EPA, Risk Management and Communication of Drinking Water Contamination.
Office of Drinking Water, 1990: p. 29-54.

NRC, Risk Assessment in the Federal Goverment: Managing the Process. 1983,
Washington: National Academy Press.

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1994, New York: McGraw Hill. 1103.

EPA, Drinking Water Health Criteria Document. Office of Science and
Technology, 1993.

62

Chapter 2

On-site Method for Arsenic Speciation in Drinking Water
2.1 Introduction

Arsenic contamination in natural waters is a worldwide problem that has become the
subject of considerable international attention. Long-term ingestion of drinking water
contaminated with arsenic as been associated with health problems including skin,
bladder and lung cancers, skin lesions, cardiovascular effects, and anemia (1-5).
Widespread health problems, including what is termed “blackfoot disease”, have been
observed in Bangladesh following a program to replace contaminated surface water
supplies with shallow wells. Arsenic levels as high as 1820ug/L have been reported in
some wells in Southwest, Taiwan (1). Drinking water regulations for maximum allowable
levels of arsenic vary by country across the range of 7 ug/L to 50 jig/L, the US. having
recently lowered the standard to 10 rig/L (6). In most cases, the source of the arsenic is

natural, resulting from the dissolution of arsenic-containing minerals in the aquifer (7,8)

Investigations to date have focused largely on total arsenic levels in water supplies, but it
is now understood that toxicity varies with the chemical form of the arsenic (9,10). The
common inorganic arsenic species in water include As (HI) forms ( H3ASO3, HzAsO3',
HASO32') and As (V) forms (H3As04, HZASO4'. HAsof', A8043) (11,12). In addition,
dissolved arsenic can occur as the organic forms dimethylarsinic acid/dimethylarsinate

((CH3)2ASO(OH)) (DMAA/DMA), and monomethylarsonic acid/monomethylarsonate

63

((CH3)ASO(OH)2) (MMAA/MMA). As (IH) is reported to be 25 to 60 times as toxic as
As (V) and several hundred times as toxic as methylated arsenicals (13). A number of

other organic forms can be found, but these are generally considered to be non-toxic

(14,15).

Total arsenic measurement in environmental matrices is relatively straightforward, with
the principal methodologies based on flame (FAAS), hydride generation (HAAS) or
graphite furnace atomic absorption (GFAAS). Arsenic speciation has been more
problematic, however, and a number of separation techniques have been employed to
resolve the various species. Separation approaches reported in the literature include
methods based on sequential volatilization (16-25), liquid-liquid extraction (26-29),
arsine generation (30-36), ion exchange (37-45), ion-pair high-perforrnance liquid
chromatography (46-51), and reverse-phase hi gh-performance liquid chromatography

(52-59).

The problem with using most of the above techniques to assess exposure to various
arsenic species is that they are laboratory based and the distribution of species in a
collected sample is not necessarily stable. For example, it has been shown that As (HI)
can be oxidized to As (V) during storage even when water samples preserved with
hydrochloric acid and other chemicals (60,61). The arsenic separation methods reported
in the literature that might be carried out on-site are limited to separation of As (HI) and

As (V) (39,42,45,62). Thus, there remains a need for method capable of determining the

distribution of the most toxic arsenic species (AS (HI), As (V), MMA and DMA) at the

point of exposure, at concentration levels of interest in drinking water.

The aim of this study was to develop a simple, field-deployable, As-species separation
technique that could be easily coupled to laboratory analysis methods for the four species
of primary interest. Such a method would be useful in both routine monitoring and
exposure assessment studies. Our approach was to utilize or develop solid-phase
extraction materials to selectively retain As species, develop a sequential extraction
approach based on these materials to isolate all four species, implement this approach in a
simple cartridge system that can be used in the field, optimize a methodology for field
extraction, laboratory elution and GFAAS analysis of the extracts, to produce accurate

and precise As species concentration data.

The basic strategy involves three columns and a selective elution procedure. The first
cartridge uses a cation exchange resin to remove interfering cations. The pH of the
sample is then reduced to less than 1.5, which results in formation of the protonated
cation of DMA. This can then be extracted with a second cation exchange resin, and later
eluted with acid. The pH of the effluent is increased to the range 2.5 to 3.5. The third
column is silanized diatomaceous earth containing dioctyltin dichloride to retain As (V)
and MMA. These are later eluted with different strength acids. The mechanism for these
separations has not been verified, but it is thought that As (V) is retained as HzAsO4' by a

combination of anion exchange the formation of tin-oxygen bonds, while MMA is held as

65

by the diatomaceous earth (63-65). As (H1) is found in the effluent from the third

cartridge as it remains in the neutral form and is not retained.

2.2. Experimental Procedure

Cartridges were prepared using a slurry method. A small plug of glass wool was placed
in the bottom of the cartridges to provide a support for the media. A small volume of an
appropriate solvent was mixed with the extraction media to form a homogeneous paste
that would flow. This paste was poured into the cartridges, taking care to prevent cracks,
channels and air bubbles. Glass wool was placed on the top to hold the media in place.
Three cartridges were used, the first removes interferences; the second one retained DMA
and third retains AS (V) and MMA. Cartridge 1 was packed with 0.6g Chelex 100 in
sodium form, as purchased, using deionized water as a solvent. It was then converted to
the ammonia form by passing 20 mL of 1.0 M NH..OH through the cartridge. The
cartridge was then flushed with about 50 mL deionized water to remove the residual
NH40H. A plastic cartridge was used. Cartridge 2 was packed with 0.3 g Dowex 50w
(50-100 mesh, 8% crosslinkage) in the hydrogen form as purchased using 0.1 M HCl as a
solvent. A plastic cartridge was used. Cartridge 3 was packed with a custom sorbent
prepared as follows. Dioctyl tin dichloride was dissolved in n-decanol and rrrixed with
chloroform as a carrier solvent. This solution was shaken with Chromosorb W for 2
hours and dried at room temperature. The suspension was dried using a rotary evaporator
at room temperature, and the dry material is used to pack glass cartridges using 0.001 M

hydrochloric acid as a solvent.

66

After initial development of the procedure, optimization studies were performed to
evaluate the effects of variations in pH adjustment between cartridges, and flow rates for
both extraction and elution. The capacities of cartridges 2 and 3 were evaluated for the
three species retained. The optimized extraction/elution procedure is shown schematically
in Figure 2.1. A water sample was first passed through cartridge 1 using either a syringe
or peristaltic pump. The effluent was adjusted to pH 1-1.5 with 1M HCl and passed
through Cartridge 2 at a rate of 3-4 mljmin. The effluent was adjusted to pH 2.5-3.5
using NH40H and passed through Cartridge 3 at a rate of 0.5-1 mIJmin. Cartridge 2 was
eluted with 5 mL 1 M HCl to produce the DMA fraction. Cartridge 3 was first eluted
with 8 mL 0.2 M HCl and then with 5 mL of 1.0 M HCl to produce As (V) and MMA

fractions, respectively. The effluent of Cartridge 3 contained the As (HI) fraction.

An arsenate standard solution (Inorganic Ventures, Inc.) containing 100.00 ug as As /mL
in 0.7 % perchloric acid was used as the As (V) stock solution and as an analytical
standard. An As (HI) stock solution was prepared by dissolving high purity arseniuos
oxide (GFS Chemical) in a minimal volume of 1M NaOH, neutralizing with 1M HCl
using a methyl orange indicator, and diluting with dionized water to achieve a
concentration of 1,000 mg as As/L. Stock solutions containing 1.000 mg as Ale of
monomethyl arsonate (Chem Service) and dimethyl arsinate (GFS Chemical) were
prepared by direct dissolution in dionized water. Standard solutions, which were used for
the calibration and spiked samples were prepared daily by dilution of the stock solutions.

All chemicals were trace analysis grade.

67

 

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68

The four fractions were analyzed using graphite furnace atomic absorption spectroscopy
(GFAAS). A matrix modifier solution containing palladium chloride. bidistilled
hydrochloric acid, ammonium paratungstate, and citric acid was employed. An
electrodeless discharge lamp (EDL) was used with Zeeman-effect background correction.
Ultra-clean graphite tubes with integrated platforms tube were with the furnace
temperature program shown in Table 2.1.

Table 2.1 Furnace temperature program for As analysis.

 

 

Step Temp, ° C Ramp, 8 Hold, s Read Flow, milan
1 1 10 1 30 250

2 130 15 30 250

3 1200 10 20 250

4 2000 0 5 x 0

5 2400 1 3 250

 

 

 

 

 

 

 

 

To evaluate the method, water samples were spiked with various concentrations and
combinations of the four arsenic species by adding the appropriate stock solution to water
and immediately passing the solution through the series of cartridges. Solutions
containing the four compounds individually were analyzed over the concentration range
10 — 100 ug as As/L. Ten replicates of twelve different combinations of the four species
at levels up to 100 ug as total AS were also analyzed. Finally, a comparison between

spiked samples using deionized water and very hard groundwater was performed.

69

2.3 Results and Discussion

Seven-point calibration curves for the each of the four arsenic species were established
for the concentration range of 1 to 10 rig/L and 5-100 [Lg/L using peak areas. Correlation
coefficients were higher than 0.998 for all species and the relative standard deviations for
the points of the calibration graphs were between 5-10 % for 1-10 ppb and 1-6% from 5-
100 rig/L. Previous studies have reported different response factors, or slopes of the
calibration curves, for different As species (32,66). We found no significant differences.
Three replicates of the calibration procedure were performed on each of three different
days. The relative standard deviation did not exceed 8 % for 1-10 rig/L and 5 % for the
concentration range of 5-100 rig/L. A detection limit of 0.37 rig/L was determined using
the criterion 3 x O'/ S, where O' is the standard deviation of the ten replicates of

background signal and S is the slope of the calibration curve (67,68).

Optimization studies for extraction pH indicated that complete retention of DMA
occurred in the pH range 1.0-1.5. Similarly, complete retention of As (V) and MMA was
achieved in the pH range 2.5-3.5. The effect of the flow rate for extraction by cartridges
2 and 3 was evaluated over the range 0.5-4 mL/min using peristaltic pumps in place of
syringes that would normally be employed under field conditions. The best results were
obtained in the range 3-4 mL/min for cartridge 2 and 0.5- 1 mL/min for cartridge 3.
Elution flow rate was evaluated over the same range with the result that 0.5-1 mUmin
was best for cartridge 2 and lmL/min for cartridge 3. The elution curve for cartridge 3

shown in Figure 2.2 demonstrates excellent resolution of As (V) and MA.

70

 

 

81
7
l r
6 e I I I,“ :‘e
c I
I
E 5 _ 1’ 'll\\\\ 'I
g. ' \‘n l"‘ \
E 4 I .l/ ‘\\ "' ‘ I
E n 0" \‘ I'll. \" \
8 3 - ' / E I" " \
o n ,/ ‘ , , .
U , , \ I. \ \
, Asw) k \ ‘I .-
2 ' I ~ ~ ‘I \
.1 ~ 5‘ 5' MMA \. ‘
1- "1' ‘ ~ \1 - \ 5 '.‘ .
C \ . §
O--——l . . . . fl . -. -¥i=h-,"l f . kt-LE'L.
l 2 3 4 5 6 7 8 9 10 ll 12 13

Volume. mL

Figure 2.2 Elution curves for As (V)-MMA separation
Table 2.2 shows the results obtained using deionized water spiked with each of the four
arsenic Species individually at concentrations from 10 to 100 rig/L. It can be seen that in
all cases except for the higher levels of As (V), recovery is essentially complete (98 —
102%). Recovery of As (V) drops to 82% and 67% in the 80 and 100 ug/L samples,
respectively. An amount of As similar to that not recovered appears as a “false positive”
amount of AS (HI). This suggests that the capacity of cartridge 3 for As (V) is between
50 and 80 rig/L (1.25-2 ug) such that the As (V) introduced to the column above this
amount is not retained, and appears in the column effluent, which is where we would
expect to find As (IH). This could be easily addressed by using a smaller volume of
sample, or in future designs, by either using more sorbent material or higher loading of

dioctyltindichloride on the sorbent.

71

Table 2.2 Interference among four arsenic species (concentration in rig/L)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

As (HI) As (V) MMA DMA
Spiked 10 - -. -
% recovery 99.5
% SD. 6.4
Spiked 50 - -
% recovery 98.6
% SD. 1.4
Spiked 80
% recovery 100.9
% SD. 1.8
Spiked 100
% recovery 101.9
% SD. 2.5
Spiked - 10 -
% recovery 102.5
% SD. 6.1
Spiked - 50 -
% recovery 1.83 98.16
SD. 5.4 2.4
Spiked - 80
% recovery 15.8 81.7
% SD. 4.8 2.6
Spiked - 100
% recovery 39.5 67
% SD. 2.7 1.8
Spiked - - 10 -
% recovery 1.9 98.0
% SD. 3.4 6.0
Spiked 50
% recovery 100.1
% SD. 3.4
Spiked - 80
% recovery 1.8 98.7
% SD. 2.4 2.2
Spiked - 100
% recovery 0.76 100.4
% SD. 6.8 1.5
Spiked 10
% recovery 1.7 98.5
% SD. 5 .6 4.9
Spiked 50
% recovery 103.3
% SD. 1.1
Spiked 80
% recovery 0.96 98.9
% SD. 5.6 2.4
Spiked 100
% recovery 2.4 97.9
% SD. 4.5 1.9

 

 

 

 

 

 

72

It was of interest to evaluate whether the cartridges could be reused after elution.
Cartridges 1 and 2 utilize commercial materials that are designed to be regenerated so this
was not tested further. Cartridge 3 was subjected to 50 extraction/elution cycles.
Analytical performance remained constant over this period of use. The stability of
extracted materials on the cartridge 3 was also evaluated by comparison of cartridges
eluted immediately and after one month of storage at room temperature covered with

aluminum foil. No differences were found.

The performance of the method for samples containing multiple As species is shown in
Table 2.3. Ten replicated of various combinations and concentrations of the four species
ranging from 1 to 60 rig/L were prepared in deionized water. It can be seen that
recoveries were all greater than 80%. Precision is seen to be very good, with relative
standard deviations generally less than 5% except for when concentrations were less than

10 rig/L, where slightly higher values were found.

Two groundwater samples with different hardness levels were spiked with different
concentrations of the four arsenic species to evaluate whether the presence of other ions
that would normally be present affect recovery. The results from 5 replicates of each
water sample are shown in Table 2.4. It can be seen that acceptable recoveries and

comparable precision was found for the groundwater samples.

73

Table 2.3 Arsenic speciation in Spiked samples

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

As(HI) As(V) MMA DMA
Spiked (pg/L) I0 40 10 0
% recovery 86.45 92.34
% RSD* 1.2 2.1
Spiked 0 40 10 10
% recovery 89.45 94.35 105.45
% RSD 1.8 4.9 6.4
Spiked 40 40 10 10
% recovery 98.56 84.89 93.56 101.45
% RSD 2.0 1.4 3.8 5.2
Spiked 40 0 10 10
% recovery 112.34 98.89 99.78
% RSD 2.1 3.8 2.9
Spiked 40 40 10 10
% recovery 108.32 90.45 110.23
% RSD 2.1 1.9 4.6
Spiked 40 20 0 0
% recovery 97.34 83.57
% RSD 3.9 2.6
Spiked 40 40 0 10
% recovery 106.34 82.45 95.64
% RSD 3.0 2.1 5.3
Spiked 5 5 l 1
% recovery 87.45 78.68 0.86 108.25
% RSD 9.1 9.4 11.3 10.6
Spiked 20 10 5 5
% recovery 91.32 77.45 92.6 96.74
% RSD 3.7 6.7 6.9 6.6
Spiked 60 30 5 5
% recovery 93.83 84.42 93.42 97.50
% RSD 1.3 4.4 5.4 5.1
Spiked 30 60 5 5
% recovery 91.50 84.43 89.95 102.35
% RSD 3.5 6.4 7.4 5.6
Spiked 60 40 0 0
% recovery 90.34 88.54
% RSD 3.6 4.5

 

 

 

74

 

Table 2.4 Results of the Arsenic Speciation in groundwater samples

 

 

 

 

Sample Total Hardness As (IH) As (V) MMA DMA
as CaCO3, mg/L

Well 250 0.22 0.67

Spiked 50 30 10 10

% recovery 98.45 86.85 97.42 105.23

% RSD 1.3 2.4 5.1 6.4

MSU tapwater 450 0.3 1.9

Spiked 50 30 10 10

% recovery 95.45 84.35 98.87 101.45

% RSD 1.6 2.2 7.2 8.2

 

 

 

 

 

 

75

 

2.4 References

(1) Tseng, W.P., Chu,H.M., How,S.W., Fong,J.M., Lin,C.S., Yeh,S., J. Nat. Cancer
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(2).Wu, M., Kuo,T.L., Hwang,Y.H., Chen,C.J., Am. J. Epidem, 1989, 130,1123-1132.
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(4) Guo, H.R., Chiang,H.S., Hu,H., Lipsitz,S.R., Monson,R.R.Epidemiology, 1997, 8,
545-550.

(5) Hopenhayn-Rich, C., Biggs,M.L., Smith,A.H. International Journal of
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(6) World Health Organization (WHO), Drinking Water Guidelines and Standard, 1996.
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(8) Simon,G., Huang,H., Penner-Hann,J.E., Kesler,S.E., Kao,L.S., Am. Mineralogis,
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(9) National Research Council (NRC), Arsenic in drinking water. Washington: National
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(10) Jain, C., Ali,l., Water Research, 2000, 34,4304-4312.

(11) Pumedu,B., Sharma,A., Water Research 2002, 36,4916-4926.

(12) Jeckel, M. In Arsenic in the Environment Part I; Nriagu,J., ED. John Wiley & Sons,
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(13) Korte, N., Femando,Q. Critical Reviews in Environmental Control 1991, 21, 1-39.

(14) Shiomi,K. In Arsenic in the Environment Part I; Nriagu,J., ED. John Wiley & Sons,
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(15) Philips, D.J.,Aquat. Toxicol, 1990, 16,151-186.

(16) Braman, R., Johnson,D., Foreback,C., Ammons,J., Bricker,J. Anal. Chem, 1977,
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(17) Carvalho, M., Hercules,D. Anal. Chem. 1978, 50, 2030-2034.

(18) Heinrichs, H., Keltsch,H. Anal. Chem. 1982, 54, 1211-1214.

76

(19) Tesfalidet, S., Irgum, K. Anal. Chem. 1988, 60, 2031-2035.

(20) Galban, J ., Marcos, E., Lamana,J., Castillo,J. Spectr. Acta PartB-Atomic
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(21) Moller, A., Scholz,F. Anal. Proceedings 1995, 32, 495-497.
(22) Frankenberger, W. Soil Biol. Biochem. 1998, 30, 269-274.
(23) Anderson, K., Thompson.M., Culbard,E. Analyst 1986, 111, 1443.

(24) Lopez-Molinero, A., Villareal,A., Aznar,Y.,Benito,M., Castillo,J. App. Spectr.
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(25) Lopez-Molinero, A., Castillo,J.Chamorro,P., Callizo,A. Mikrochimica Acta 1999,
131, 225-230.

(26) Kalyanaraman, S., Khopkar,S. Talanta 1977, 24, 63-65.

(27) Chakraborti, D., De Jonche,W., Adams,F. Anal. Chim. Acta 1980, 120, 121-
127.

(28) Puttermans, F., Vandenwinkel,P., Massart, D. Anal. Chim. Acta 1983, 149,
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(29) Bohr, U., Meckel,L. F res. J. Anal. Chem. 1992, 342, 370-375.
(30) Narsito, H., Agterdenbos,J. Anal. Chim. Acta 1987, 197, 315-321.

(31) Masscheleyn, P., Delaune,R., Patrick,W. Environ. Sci. Technol. 1991, 25, 1414-
1419.

(32) Masscheleyn, P., Delaune,R., Patrick,W. Environ. Sci. Technol.1991, 20, 96-100.
(33) Michel, P., Averty,B., Colandini,V. Mikrochimica Acta 1992, 109, 35-38.
(34) Howard, A., Comber,S. Mikrochimica Acta 1992, 109, 27-33.

(35) Cabreros Pinillos, S., Sanz Asensio,J., Galban Bemal,J. Anal. Chim. Acta 1995, 300,
321-327.

(36) Burguera, M., Burguera,]. Talanta 1997, 44, 1581-1604.

(37) Henry, F., Thorpe,T. Anal. Chem. 1980, 52, 80-83.

77

(38) Pacey, G., Ford,J. Talanta 1981, 28, 935-938.

(39) Ficklin, W. Talanta 1983, 30, 371-373.

(40) Aggett, J ., Kadwani,R. Analyst 1983, 108, 1495-1499.

(41) Gomez, M., Camara,C., PAlacios,M. F res. J. Anal. Chem.1997, 357, 844-849.

(42) Edwards, M., Patel,S., McNeill,L., Chen,H., Frey,M., Eaton,A., Antweller,R.,
Taylor,H. J.A. W. WA. 1998, 90, 104-113.

(43) Miller, G., Norman,D., Frisch,P. Water Research 2000, 34, 1397-1400.

(44) Le, X., Yalcin,S., Ma,M. Environ. Sci. Technol. 2000, 34, 2342-
2347.

(45) Kim, M. Bull. Environ. Contam. Toxicol. 2001, 67, 46-51.

(46) Grabinski. A. Anal. Chem. 1981, 53, 966-968.

(47) Ding, H., Wang,J., Dorsey,J.,Caruso,J. J. Chromat. A 1995, 694, 425-432.

(48) Yalcin, S., Le,X. Talanta 1998, 47, 787-796.

(49) Le, X., Ma,M. Anal. Chem. 1998, 70, 1926-1933.

(50) Mattusch, J., Wennrich,R. Anal. Chem. 1998, 70, 3649-3655.

(51) Spuznar, J., McSheehy,S.,Polee,K., Vacchina,V., Mounicou,S., Rodriguez,l.,
Lobinski,R. Spectrochim. Acta B 2000, 55 , 779-793.

(52) Brinckman, F., Jewett,K., Iverson,W., Irgolic,K., Ehrhardt,K., Stockton,R. J. Chrom.
1980, 191, 31—46.

(53) Tye, C., Haswell.S., O'neill,P. Bancroft,K. Anal. Chim. Acta 1985, 169, 195-
200.

(54) Ebdon, L., Hill,S., Walton,A. Ward,R. Analyst 1988. 113, 1159-1165.

(55) Bohari, Y., Astruc,A.M., Astruc,M., Cloud,J. J. Anal. Atomic Spec. 2001, 16, 774-
778.

(56) Martin, I., Lopez-Gonzalves,M., Gomez,M., Camara,C., Palacios,M. J. ChromB:
Biom. Appl. 1995, 66, 101-109.

78

(57) Le, X., Ma,M., Wong,N. Anal. Chem. 1996, 68, 4501-4506.
(58) Larsen, E. Spect. Acta Part B 1998, 53, 253-265.

(59) Londesborough, S., Mattusch,J., Wennrich,R. F res.J. Anal. Chem. 1999, 363, 577-
581.

(60) Borho, M., Wilderer,P. J. Water Supply Research and Technology-Aqua
1997, 46, 138-143.

(61) Volke, P., merkel,B. Acta Hydrochimica 1999, 27, 230-238.
(62) Russeva, E., Havezov, I., Detcheva,A., F res. J. Anal. Chem. 1993, 347, 320-323
(63) Davies, A. Organotin Chemistry; VCH: New York, 1997.

(64) Shkinev, V., Spivakov, S., Shkinev,V., Vorob'eva,G., Zolotov,Y. Analytica Chimica
Acta 1985, 167, 145-160.

(65) Spivakov, S., Shkinev,V., Vorob'eva,G., Zolotov,Y. 1983, 716-720.

(66) Ochsenkuhn-Petropolu, M., Ochsenkuhn,K., Millonas,I., Parassakis,G. Canadian
Journal of Applied Spectroscopy 1995, 40, 61-65.

(67) IUPAC Pure and Applied Chemistry 1995, 67, 1699-1723.

(68) Jaganathan, J. Atomic Spectrometry 2001, 22, 280-283.

79

Chapter 3

Stability of Arsenic Species in Groundwater

3.1 Introduction

The stability of arsenic species in aquatic systems is limited due to chemical and
biochemical reactions. The conversion of arsenic species in aqueous samples can be
affected by redox reactions, precipitation, adsorption or changes by microbial activities.
Changes in redox potential or pH often take place in environmental systems by mixing
waters from different sources, due to contact with the atmosphere or the reduction of the
oxygen concentration through various processes. The time between on-site sampling and
analysis in the laboratory is normally at least one day. However, within this period
significant changes in the chemical composition of the sample may occur. Preservation
conditions to maintain integrity and stability of environmental samples are a prerequisite
to the successful implementation of the analytical method. Changes in species
composition need be to avoided in order to provide reproducible results between the time
of sampling and the time of the analysis. If this is not possible, suitable procedures should

be accomplished for the preservation of the Species.

The preservation of AS (111) and As (V) in natural waters has been investigated by a
number of scientists (1-17) in an effort to stabilize the original distribution of arsenic
species during Shipment to the laboratory. Among the variables studied have been
temperature, presence of light, darkness, and different chemicals (HCl, I'INO3, H2804,

ascorbic acid, EDTA, etc.). A summary of these studies is shown in Table 3.1.

80

Table 3.1 Literature Review for the stability of arsenic species

 

 

 

 

 

 

 

 

 

Sample As Container Tempe- Chemical Results Refe-
concentra- light/dark rature PH rence
tion

Spiked 1; 10; Glass Room Ascorbic As(HD-) As (V) 10 ug/L 1
100; 1,000 temperatu acid in 4 d; 100 rig/L in 7 d;
rig/L re 1mg/mL 1,000 rig/L in 18d.

As(III), No changes occur using
As(V) ascorbic acid

Spiked 20 mg/L Borosilica Total As constant for 56 2
As (III). te days. Container does not
As (V) Soda glass absorb As. 50 % As (HI)

Polyethyle -) As (V) in 33 days. No
ne difference in light and
dark

Spiked 1-10 rig/L Pyrex Room 2%v/v No losses in polyethylene 3

Hamilton AS (111), Polyethyle tempera- Sulfuric acid bottles

Harbor As(V) ne ture 1.5 Substantial losses in

water pyrex bottles at pH) 5.4

No As losses over 125 d
at pH 1.5. Algal growth
after 6 weeks

Spiked 0.02 — 2 -15 ° C HC10.05N AS (111) 9 As (V) after 1 4

Natural rig/L Room week . At -15 ° C initial

Water AS (111), tempera- 0.02 rig/L loss of AS (111)

AS (V) ture but remains constant after
MMA,D prolonged storage
MA

Spiked 50 rig/L Room 2-10.5 No oxidation As (III) in 5

Groundwa AS (111) tempera- three weeks 6

ter and As(V) ture 5-7% As(HI) -) As(V) in

2.5 months

Spiked As(III), 20 °C Solution of four As 7
As(V). 40 °C species at pH adjusted in
MMA, 4 °C the dark are stable for 1
DMA, AC year. After 4 m As (HI)-)

As(V) at 20 °C (light).
But only slight ox.

At 40 °C (dark). Mixtures
DMA, AC, As (V) after 2
m and 4 m MMA and As
(III) present at 20 °C. At
40° C MMA and As (III)
present after 2 m but
disappear after 4 m. At 4°
C no changes of As. In
presence of ions As
(IH)-)As(V) at three
temperatures

Spiked 0.001-10 Room MMA,DDMA stable at 8
mg/L tempera- room temp. for 5-6 m but
As(III), Ture As(III) and As(V). At 4
As(V),M 4 °C °C all species stable for
MA,DMA 21 d. after 29 days As

 

 

 

 

 

 

 

81

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

(HI)-)As(V) (0.5-1mg/L)
at room temperature
Ground As(III)/As EDTA As(III)/As(V) stable for 9
water Fe- (V) 500 mg/L 10 (1. Change of 2 rig/L
(ppt) 19-38 As (IH)-9A8 (V) over 30
rig/L d. With no EDTA As (HI)
As(total) oxidation in less 1 d
Spiked 60 rig/L Room Fe (11) As (III) stable up to 7 d 10
AS (111) tempera- HCl with 500 mg/l Fe(II) and
ture pH<2 HCl
Ground 41.5-278 Poly- Room As(t) stable up to 1 y at
Water rig/L As ethylene tempera- pH<2 and up to 6 m at 4 11
(total) 90 darkness ture °C in darkness (no acid.).
rig/L As 4 °C As (HI) oxidation in 3 m
(111) up to 70%
Spiked 0.5-20 5 °C 0.1-0.4% As(V) -)As(III) (1-5 12
and river rig/L 22 °C HCl jig/L) in 2 d at 22 °C and
water As(III), HNO; no reverse reaction after
As(V 10 d in spiked water, in
river water reverse
reaction after 2 d .No
changes at 5 °C in both
waters. In river water
samples As(III) oxidation
with HNO; and HCI
Spiked 6-24 rig/L Teflon 20 °C HCl Teflon and Borisilicate 13
Natural AS (111). Borosilica 4 °C bottles-9 complete As
water As (V) te (III) conversion in 7 d. No
Polyethyle AS (111) oxidation in 30 at
ne pH=2. After 30 d 72 and
4% AS (111) is left at 4 °C
and 20 °C
Distilled 50 jig/L Polyethyle Room HCI No changes in distilled 14
water As(III) , ne tempera H2804 and de-ionized water at 4
Deionizid As(V) Light Ture Ascorbic °C and H2804 after 40 d.
water Darkness 4 °C acid Reduction of As (V) in
Tap water de-ionized water in
presence of light after 40
(1. At room temperature.
light and chemicals As
reduction and oxidation
were found after 40 d.
Sterile 100 rig/L Glass Room No AS (111) oxidation in 15
water AS (111), temperatu 14 d at 4 C.
Groundwa As(V) re AS (111) oxidation in 3 d at
ter 30-ug/L 4 °C room temp., no AS (111)
id. left after 14 d in
groundwater
Natural 1.3-10 Polyethyle As(V) -)AS(III) after 7 d 16
water rig/L ne
7-83 ug/L Opaque Room EDTA As species stable up to 3 17
As(IlI) Polyethyle tempera- HCl months with EDTA
13-220 ne ture (0.06M) At 10 rig/L As species

 

82

 

 

 

 

 

rig/L H2804 stable for 120 h using

As(V) (0.09M) EDTA, 100 h using

10 rig/L HNO; H2804. HNO3 preserved

As(IH),As 0.08M) As species in darkness.

(V) HCl changes the As
species in 2 d (light,
darkness)

 

 

 

 

 

 

The literature is not in complete agreement with respect on how to preserve As (HI) and
AS (V), although some type of acidification and low temperature is usually recommend.

However, no paper has been published with on site arsenic speciation.

The aim of this study was to evaluate the stability of arsenic species As (IH) and As (V)
in groundwater samples under, a) different temperatures (4 °C. room temperature and 40
°C), b) pH (< 2 using hydrochloric acid and water natural pH), c) oxygen concentrations
(0, 2-3 mg/l, 5-6 mg/l and saturation), and (1) length of storage (24 hours, 48 hours, 7
days and 14 days). Losses and species transformations were also investigated. The initial
arsenic species distribution was determined on site using arsenic Speciation methodology

developed in our laboratory, so comparisons could be done.

3.2 Experimental Procedure

Standards and reagents

A stock solution containing 1 mg/mL of arsenic was prepared utilizing Arsenic trioxide
AS203 (As (IH)), arsenic pentoxide Asz05 (As(V)). As (V) was dissolved in distilled
water. As (IH) was dissolved in a minimal volume 1M NaOH and neutralized with 1M

HCl using the appropriate indicator and diluted with distilled water up to 1L. Stock

83

solutions were stored at 4 °C in darkness. A second As (HI) Stock solution was prepared
containing 10 mg/L and stored at 4 °C. It remained stable at least for four months when
checked against freshly prepared stock solution and oxidation redox potential
measurements weekly. Standard solutions, which were used for the calibration and spiked
samples, were prepared daily by dilution of the stock solutions. Palladium chloride
(PdClz), bidistilled hydrochloric acid 6M, citric acid, ammonium paratungstate
(N114)10HZW12024.H20, were used to prepare the matrix modifier. All reagents were
analytical grade of high purity.

Sampling Procedure

The groundwater sampling procedure was designed to assure that the samples reflected
the in-situ conditions of the arsenic species distribution. The pumping rate was kept very
low to prevent detachment of colloidal materials. All samples were filtered using 0.2-um
membrane syringe filter to minimize any contamination. Since 20-30 mL of the filtrate is
required for the arsenic speciation, filtration should not represent further problem.
Groundwater samples were taken from East Lansing. Samples were collected in 160 mL
glass containers (previously cleaned with 5% nitric acid and rinsed with ultrapure water)
and then placed into a temperature controlled environment. Oxygen was removed from
glass containers by bubbling with inert nitrogen gas until oxygen could no longer be
detected. Field measurements included temperature, pH, Eh, Fe (H), dissolved oxygen,
specific conductance and alkalinity. Samples were also collected for anions (Cl', NO3’,
NO;‘, 3042') and metals (As, Fe, Ca2+,Mg2+, Nat, K+, Mn) for later analysis in the

laboratory.

84

Experiments in the laboratory

The following set of experiments was carried out to study arsenic species stability.
Samples were storage for 24, 48, 168, and 336 hours under four oxygen concentrations
(0, 2-3 mg/L, 5-6 mg/L and saturation), three temperatures (4 °C, 20 °C and 40 °C) and
two pHS (<2 and natural pH of the sample). Arsenic Speciation, pH, Fe (H), total Fe and
total As analysis were carried out at 24, 48, 168 and 336 hours.

Analytical Methods

Specific conductance, pH, temperature, dissolved oxygen (DO) and Eh were measured
with a flow cell (Yellow Springs Instruments). Fe (II) was determined by the
phenanthroline colorimetric method (18,19) and alkalinity by titration with sulfuric acid
(19). Anions and cations concentrations were quantified by ion chromatography and

atomic absorption spectroscopy respectively.

Arsenic speciation was done using the method developed in our laboratory (20). The
basic strategy involves three columns and a selective elution procedure. The first
cartridge used a cation exchange resin to remove interfering cations. The pH of the
sample was then reduced to less than 1.5, which resulted in formation of the protonated
cation of DMA. This was then extracted in a second cartridge containing a cation
exchange resin, and later eluted with acid. The pH of the effluent was increased to a
range of 2.5 to 3.5. This effuent was then passed through a third cartridge utilizing a
silanized diatomaceous earth modified with dioctyltin dichloride to retain the As (V) and
MMA. These were then eluted with different strength acids. As (HI) was not retained in

any of the cartridges so remains as the effluent from the third cartridge. The whole

85

procedure was carried out at the field site. It was found that DMA and MMA
concentrations were negligible, so for this study arsenic speciation was done using the

first and the third cartridges.

3.3 Results and Discussion

Initial values for the East Lansing groundwater were: pH, 6.98; specific conductance,
0.816 um S; temperature, 11.26 °C; dissolved oxygen, 1.02mg/L; Eh, -24.5 mV; As (HI),

12.1 p. g/L; total A8, 14.3 rig/L; Fe (II), 980 rig/L and total Fe,1150 rig/L.

In order to understand the natural processes of arsenic in water and its toxicological
effects, it is important to be able to speciate arsenic on-site as the species may change
under storage conditions. This set of experiments provides information relative to the
effects of pH, oxygen concentration and temperature effects on As (IH) stability over
time. Figures 3.1, 3.2, 3.3 and 3.4 indicate, that As (HI) was stable over the period of the
study at pH<2, independently of oxygen concentration with only slight variation found

due to a change in temperature. Similar observations have been reported in (12,21).

However, at a natural pH of the sample, a loss of AS (111) was observed at all three
temperatures tested, ranging from 22 to 58%, after 48 hours. Additionally, in this set of
experiments, a pale yellow color change was observed in the water samples in the form of
a precipitate after 48 hours. It may be assumed that the color changes were probably due
to coprecipitation with or adsorption on the iron oxyhydroxide present (see section 1.2.2).

Figures 3.5, 3.6, 3.7 and 3.8 Show AS (111) and total As variations at the natural pH. From

86

these results it can be concluded that As (HI) losses were due to an oxidation reaction to
AS (V), but, decrease of the total As concentration was probably related to As (V)
adsorption on the iron oxyhydroxide. These results are in agreement with previous papers
(22,23,24). Dissolved oxygen was not able to oxidize As (IH) significantly under these

conditions.

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The variation of Fe (II) and total Fe at pH<2 was similar to As (III) and total As since no
variation in Fe (H) and total Fe concentrations were found. This is in agreement with the
results at pH<3.5 where the oxidation rate of Fe is independent of pH and the presence of
oxygen does not affect significantly (25,26). Figures 3.9, 3.10, 3.11 and 3.12 show the
variation of Fe (II) and total Fe concentrations at different temperatures, oxygen
concentrations and the natural pH of the sample. Fe (H) oxidation was fast within 48
hours since more than 70 % of Fe (II) was oxidized. These results indicated that once Fe
precipitated it readily adsorbs arsenic, which results in a decrease of As (HI) and total As

after 48 hours under the same conditions.

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3.4 References

l.

10.

ll.

12.

Feldman, C., Improvements in the Arsine Accumulation-Helium Glow Detector
Procedure for Determining Traces of Arsenic. Analytical Chemistry, 1979. 51(6): p.
664-669.

Al-Sibaai, A.A., Fogg,A.G., Stability of Dilute Standard Solutions of Antimony,
Arsenic, Iron and Renium Used in Calorimetry. Analyst, 1973. 98: p. 732-738.

Cheam, V., Agemian,H., Preservation of Inorganic Arsenic Species at Microgram
Levels in Water Samples. Analyst, 1980. 105(1253): p. 737-743.

Andreae, M.O., Determination of Arsenic Species in Natural Waters. Analytical
Chemistry, 1977. 49(6): p. 820-823.

Cherry, J.A., Shaikin,A.U., Talman,D.E., Nicholson,R.V., Arsenic Species as an
Indicator of Redox Conditions in Groundwater. Journal of Hydrology, 1979. 43: p.
373—392.

Tallman, D.E., Shaikh,A.U., Redox Stability of Inorganic Arsenic (III) and Arsenic
(V) in Aqueous Solutions. Analytical Chemistry, 1980. 52: p. 196-199.

Quevauviller, P., de la Calle-Guntifias,M.B., Maier,E.A., Cémara,C., A Survey on
Stability of Chemical Species in Solution During Storage: the BCR Experience.
Mikrochimica Acta, 1995. 118: p. 131-141.

Jokai, Z., Hegoezki,J., Fodor,P., Stability and Optimization of Extraction of Four
Arsenic Species. Microchemical Journal, 1998. 59: p. 117-124.

Gallagher, P.A.. Schwegel,C.A., Wei,X., Creed,J.T., Speciation and Preservation of
Inorganic Arsenic in Drinking Water Sources Using EDTA with IC Separation and
ICP-MS Detection. Journal of Environmental Monitoring, 2001. 3: p. 371-376.

Borho, M., Wilderer,P., A reliable method for preservation and determination of
arsenate ( III) concentration in groundwater and water works. Journal of Water
Supply Research and Technology-Aqua, 1997. 46: p. 138-143.

Rassler, M., Michalke,B.;, Speciation of Inorganic Arsenic and Selenium in
Contaminated Ground-Water Samples-Distribution and Long-Term Stability of
Species. International Journal of Environmental Analytical Chemistry, 1998. 72(3): p.
195-203.

Hall, G.E., Pelchat,J.C., Gauthier,G., Stability of Inorganic Arsenic (III) and Arsenic
(V) in Water Samples. Journal of Analytical Atomic Spectrometry, 1998(November):
p. 205-213.

101

13.

14.

15.

16.

17.

18.

19.

20.

21.

22.

23.

24.

25.

van Elteren, J .T., Hoegee,J., van der Hoek,E.E., Das,N.A., de Ligny,C.L.,
Agterdenbos,J., Preservation of As (III) and As (V) in Some Water Samples. Journal
of Radioanalytical Chemistry, 1991. 154(5): p. 343-355.

Volke, P., Merkel,B., Using of a New Field Analysis Method to Investigate the
Stability of Arsenic and it Inorganic Species. Acta Hydrochimica et Hydrobiologica,
1999. 4: p. 230-238.

Hambsch, B., Raue,B., Brauch,H.J., Determination of Arsenic (III) for the
Investigation of the Microbial Oxidation of Arsenic (III) to Arsenic (V). Acta
Hydrochimica et Hydrobiologica, 1995. 23(4): p. 166-172.

Stummeyer, J ., Harazim,B., Wippermann,T., Speciation of Arsenic in Water Samples
by High-Perfomance Liquid Chromatography-Hydride Generation Atomic
Spectrometry at Trace Levels Using a Post-Column Reaction System. Fresenius
Journal of Analytical Chemistry, 1996. 354: p. 344-351.

Bednar, A.J., Garbarino,J.R., Ranville,J.F., Wilderman,T.R., Preserving the
Distribution of Inorganic Arsenic Species in Groundwater and Acid Mine Drainage
Samples. Environmental Science & Technology, 2002. 36(10): p. 2213-2218.

Standard Methods for the Examination of Water and Wastewater, 1992, 18th.

Susuki, Y., Kuma,I., Kudo,K., Hasebe,K., Matsunaga,K., Existence of Stable Fe (II)
Complex in Oxic River Water and its Determination. Water Research, 1992. 26(11):
p. 1421-1424.

Havezov, I., Flores-del-Pino, L., Voice, T.C., Long,D., On-site Arsenic Speciation in
Drinking Water. Submitted to be published, 2003.

Aggett, J ., Kriegman,M.R., Preservation of Arsenic (III) and Arsenic (V) in Samples
of Sedimentn Interstitial Water. Analyst, 1987. 112: p. 153-1570.

Pierce.M.L., M., C.B, Adsorption of Arsenite and Arsenate on Amorphous Iron
Hydroxide. Water Research, 1982. 16: p. 1247-1253.

Edwards, M., Chemistry of Arsenic Removal During Coagulation and Iron-
Manganese Oxidation. Journal American Water Works Association, 1994. 86(9): p.
64-78.

Meng, X.G., Korfiatis,G.P., Christodoulatos,C., Bang,S., Treatment of arsenic in
Bangladesh well water using a household co-precipitation and filtration system.

Water Research, 2001. 35: p. 2805-2810.

Stumm, W., Morgan,J.J., Aquatic Chemistry: Chemical Equilibria and Rates in
Natural Waters. Third ed. 1996, London: John Wiley & Sons.

102

26. Emett, M.T., Khoe,G.H., Photochemical oxidation of arsenic by oxygen and iron in
acidic solutions. Water Research, 2001. 35: p. 649-656.

103

Chapter 4

Human Exposure and Risk Assessment to Inorganic Arsenic fi'om Food

and Drinking Water

4.1 Introduction

Toxicological, biological and pharmaceutical properties of elements often depend on the
species within these elements. There is an increasing demand for analytical techniques to
provide for the qualitative and quantitative determination of elemental species.
Commonly, methods for speciation analysis consist of hyphenated systems such as high
performance liquid chromatography (HPLC), gas chromatography (GC) or capillary
electrophoresis (CE) combine with an element specific detector such as inductively
coupled plasma mass spectrometry (ICP-MS), atomic absorption spectrometry (AAS), or
atomic fluorescence spectrometry (AFS). One disadvantage of such systems is the loss of
structural information during the element specific detection process. Therefore, the
identification of species, depends on a comparison of retention times, and is only possible
when the elemental species are available as standards. However, samples often contain
species, for which thera are no commercially available standards or the species present
have yet to be identified. In the case of arsenic there are limited numbers of standards of
organoarsenic species commercially available. To enable the identification of these
species, which are not available comercially, a different approach is necessary, which

includes the use of a detector that provides structural information of the species.

104

For arsenic, the two major exposure routes are food and drinking water. Estimation of
arsenic dietary exposure is needed to evaluate the public cancer risk. Drinking water
contains primarily inorganic forms of arsenic. Arsenic in food unlike drinking water can
contain numerous forms of arsenic, which vary significantly in their toxicity. Many foods
are comprised of less toxic forms of arsenic than inorganic As (III) or As (V). For
example, seafood accounts for the majority of dietary arsenic ingested, and, it is tought
that most of it is in relatively non-toxic organic forms. However, there are little data on
the chemical species of arsenic in foods and water in which to base a reliable human
health risk assessments. Accurate risk assessments require the knowledge of the

contribution of inorganic arsenic from both drinking water and dietary sources.

Inorganic arsenic As (HI) and As (V) have been recognized as the most potent toxic
species of arsenic compounds. The LD50 for As (HI), and As (V) are 14 and 20 mg/kg
respectively (1). Inorganic arsenic is also recognized as a human carcinogen and is
associated mainly with internal (lung, bladder, kidney) and skin cancers (2-5).
Monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), arsenobetaine (AsB),
arsenocholine (ASC) and arsenosugars are the most commonly organic forms of arsenic.
The LD50 values for MMA and DMA are significantly higher than those for inorganic
species, 700—1800 mg/kg for MMA and 700—2600 mg/kg for DMA (1). AsB, AsC and
arsenosugars are the primary, organic arsenicals found in marine organisms and are
generally considered to be non-toxic (1). Because of the variable toxicity levels of arsenic
species found in foods, total arsenic determinations alone do not provide adequate

information for accurate human health assessment, as the determination of individual

105

arsenic species is necessary. To evaluate precisely the risk due to arsenic exposure, it is

necessary to quantify all the major arsenic species in sensitive food products. This will

improve the reliability of risk assessment associated with exposure to arsenic compounds.

The main objectives of this study were:

- To evaluate the available information of arsenic speciation in food

- To determine the exposure to inorganic and total arsenic in the population of Unites
States. To show the relative importance of the arsenic exposure through consumption
of food and drinking water

- To evaluate the risk of inorganic arsenic associated to the consumption of food and

drinking water using EPA old and new risk analysis procedures.

4.2 Review of Analytical Methods

Speciation is generally carried out in the following steps: sampling, sample preparation
(extraction), species separation and detection.

Sampling

The first step in any analytical process is the sampling of the food to be analyzed. Often,
factors such as geographic location, ecology and seasonal time periods need to be taken
into consideration when evaluating the sample representativeness. The sampling needs to
be time specific, designed for each type of material to be sampled, documented and
controlled efficiently to assure quality. The sampling procedures reported in the literature
are based on sample foods collected from the local market, and retail outlets. For example
studies carried out in USA are based on the US Department of Agriculture Continuing

Survey of Food Intakes by Individuals (USDA) of consumption of foods in large

106

quantities in the USA population. This criterion is very helpful in deciding the types of
food to analyze for a specific study. For risk assessment evaluation, it is crucial to know
where the samples come from and when they were collected, since each growing region
may have different agricultural practices that can lead to different arsenic concentrations.
Generally, the commodities that have been sampled include: cereals, vegetable, fruits
(including juices), meat, poultry, fish, milk, etc. Further, the preservation method needs
to be specified for the commodities sampled, since the analysis usually is carried out after
48 hours or more. Commonly, low temperatures prevent biological activity that can
modify the nature of the sample. Freeze—drying can assist in concentrating the sample and
improving its handling. Once, the sample is freeze-dried, it can be homogenized,
minimizing variation in quantification process. Careful weighing of the sample before
and after freeze-drying allows calculation of the percentage of moisture in the sample so
a mass balance of the arsenic species can be done.

Sample preparation

Sample preparation consists of the isolation of different species from the matrix,
sometimes with a preconcentration step. This is a very critical stage necessary to
efficiently dissolve the species without degradation. The method should quantitatively
extract all arsenic species without altering their original species distribution. Also, the
solvent used to extract samples should not interfere with the species to be analyzed.
Arsenic speciation in food samples is always preceded by total arsenic determination.
The sample is dry-ashed (6,7), or submitted to wet ashing (8-11). Both methods
decompose the organic matter present in the food, however no comparison can be done

since the studies do not report percentages of recovery.

107

Sample digestion, Arsenic speciation and detection techniques

Arsenic speciation in food samples constitutes a challenge since the arsenic species must
be first extracted from the matrix. Moderate but efficient extraction conditions are
required to guarantee total removal of arsenic compounds from the matrix without
modifying the identity and concentration of individual arsenic species. A variety of
methods have been applied for the extraction of arsenic from solid foods, including
solvent extraction (12-20), acid digestion with HCl (21-24), trifluoroacetic acid digestion
(25), basic digestion with NaOH (23,26), microwave assisted extraction (27,28),
microwave assisted distillation (29,30), enzymatic extraction (12,15,18,31) and
accelerated solvent extraction (20,32). Sonication (13,15,18,20,28,33,34) or mechanical
shakers (13,16,19) are generally employed to aid in the solvent extraction processes.
Methanol, water and chloroform or combinations of these solvents in different ratios have
been commonly used for the extraction of arsenic. Selection of the appropriate extraction
method is based on the matrix and the subsequent speciation plan. To minimize possible
interferences among the extraction solvent, chromatographic mobile phase and method of
detection compatibility is required. The anionic, cationic and neutral nature of arsenic
compounds allows the application of both ion exchange and reversed phase
chromatography for their separation. (12,35). However, the adaptability of anion
exchange chromatography for arsenic speciation (12,17—21,27,30,31,35-38) makes it
more accepted than reversed phase chromatography (1). Using this technique only the
quaternary arsonium compounds (AsB, AsC, TMAs) or arsenic uncharged compounds
can be separated. The most common detection methods for arsenic speciation are hydride

generation atomic absorption spectrometry (HGAAS) (13,14,19,23,24,26, 29,30,39,40)

108

and inductively coupled plasma mass spectrometry (ICP-MS) (l7,18,20-22,27,31,33,35-
37,41). Other methods used are: HG-ICP-MS (22,28,38), hydride generation atomic
fluorescence spectrometry (HG-AFS) (12,42), purge and trap chromatography with
atomic fluorescence detection (16) and electrospray ionization mass spectrometry ESI-

MS (31,33,34).

4.3 Evaluation of Analytical Data and Analytical Methods

Table 4.1 shows a summary of the analytical methods for determining arsenic in food and
Table 4.2 shows arsenic speciation in food.

It is important that the analytical method does not in any way change the naturally
occurring species distribution in the matrix. This requires implementation of a controlled
procedure that maintains the species in its original form. The steps involved in the
analytical methods (extraction, separation and detection) are potentially sources of error,
which may alter the result from that of the real value. Sources of error should be kept
under control with quality control (QC) procedures. The need to assure quality in modern
analysis justifies interlaboratory studies, which also serve to develop and promote new
analytical techniques. Only Schoof and et a1. (21) indicate interlaboratory analysis with

relatively reproducibility in multiple analyses of the samples.

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The toxicity of inorganic As (III) is assumed to be due to of its binding to thiol groups (-
SH) of cytosolic proteins and macromolecular constituents (43,44). Therefore, in order to
carry out a quantitative extraction of inorganic AS (111) in samples, a hydrolysis of the
proteins to break the S-As bond must be accomplished. The most common procedure
mentioned uses acid digestion. However, a legitimate concern may be raised for using
acid digestion in arsenic speciation due to the potential breakdown of organic compounds
in digestions used. This problem may be present in any analytical method used to
speciate arsenic. Quantitative recovery of inorganic As (III) has been reported using acid
digestion, base digestion, microwave assisted distillation for arsenic speciation in food.
Most of the reported studies show a 70-120 % of recovery of total arsenic (see Table 4.1).
In addition, arsenic speciation in oyster tissues using hydrochloric acid digestion reported

101 % recovery of AsB showing that there is no breakdown of organic compounds (17).

Liquid chromatography is the most popular technique for the separation of arsenic
species, since in general they are readily soluble in an aqueous solution. The most
commonly used technique is HPLC because of the ease of coupling it with element-
specific detectors such as ICP-MS or HGAAS. However, the volume of sample that can
be injected is sometimes insufficient to detect minor species. Off-line preparative work
should be done for the injection and separation in large quantities of samples. The eluent
can be monitored by analysis of the eluting fractions. Liquid chromatography of the

collected fractions may be used to isolate and purify the specie of interest.

113

A comparison of techniques indicates that HPLC-HG-ICP-MS can be used for
multielement studies while HPLC-HG-FAAS can be used for more routine studies (45).
The advantage of AAS is that is simple to use and well understood. On the other hand,
HPLC-ICP-MS is more commonly used as a speciation technique, for identification and
determination because of the separation achievable by HPLC and the sensitivity and
selectivity of ICP-MS. However, if structural information on the species extracted is
needed Electrospray Mass Spectrometry (ESMS) is the instrument of choice as it

provides both quantitative and qualitative information (45).

The disadvantages of using HPLC-ICP—MS are: a) organic solvents present in the eluent
form HPLC may produce carbon built-up in the plasma region. To prevent carbon
deposits it is imporant to use a mimimal amount of organic solvent or use oxygen, b) the
most obvious interference is caused by the formation of 40Ar35Cl+ in the plasma and it is
related to the chloride presence in the samples. Since arsenic is monoisotopic it is not
possible to avoid this isobaric interference with a conventional quadrupole instrument.
However, this problem can be reduced by adding nitrogen into the plasma or using an
anion exchange column that will retain the chloride, thereby preventing its entering into

the plasma.

The disadvantages of using HG-ICP-MS are: a) interference due to the chloride presence
that can be eliminated because arsenic compounds are converted to their volatile arsines
which can subsequently be separated from the liquid eluent and introduced in the IPC-

MS without interference, b) AsB and arsenosugars do not form volatile hydrides so HG

114

can not be used to separate them. However, HG can be useful as a screening method to

separate inorganic arsenic, which is the greatest risk to the environment.

4.4 Human Exposure Estimates and Risk Assessment Estimation

Consumption of drinking water is a route of exposure to inorganic arsenic and the level
of exposure depends on the arsenic concentration in the water. However, dietary intake of
inorganic arsenic is more difficult to assess. A study carried out in Canada recently
provided an estimate for the daily intake of total arsenic. The mean value reported for
males and females age 12 and above was 40 ug/d (8). This value is very close to 38 jig/d
reported for Dutch 18 years old males (46). Also 34 ug/d has been reported in a study in
the USA for males and females age 14 and above (23). The Canadian evaluation of the
health risks from exposure to inorganic arsenic estimated that the daily intake through
food was approximately equal to intake through drinking water consumption for the
general population (47). In the same study arsenic exposure from air was also evaluated

and was considered to be negligible.

The relative contribution of food and water consumption to inorganic arsenic exposure
can be calculated as a function of the concentration of arsenic in drinking water, if a
reasonable value for dietary intake of inorganic arsenic can be estimated. In terms of risk
assessment, arsenic speciation in rice is particularly interesting because rice forms a
major dietary staple for many populations and may contain a relatively high
concentration of total and inorganic arsenic when compared with other foods (21-24,48).

To calculate the risk associated with food and water consumption, data on dietary

115

inorganic arsenic in Taiwan reported by Schoof et al (21) was used. Minimum, average
and maximun values found in the rice and yams analysis reported in Taiwan were
considered to obtain dietary intake of inorganic arsenic (21). Table 4.3 shows the

concentration of arsenic in drinking water and dietary intake of inorganic arsenic.

Table 4.3 Dietary intake and water consumption of inorganic arsenic

 

 

 

 

Dietary intake Inorganic As in water, pg/L Total dietary intake of
of inorganic As, inorganic As (food and
_Eg/d water), jig/d

Minimum
15 1 17

2.8 20.6

7.6 28.2

50 l 15

75 165
Average
50 l 52

2.8 55.6

7.6 65.2

50 150

75 200
Maximum
21 l l 213

2.8 216.6

7.6 226.2

50 261

75 361

 

 

 

 

 

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daily intake of inorganic arsenic as a function of the arsenic concentration in drinking
water. In the Figures 4.1 and 4.2 the contribution to the daily intaike of inorganic arsenic
from food and water are the same at 7.5 and 25 jig/L of inorganic As concentration.
Below these values food becomes more important than the contribution from drinking
water consumption. Figure 4.3 shows that a very low arsenic concentration in drinking

water is insignificant when compared with food consumption.

116

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Figures 4.4, 4.5 and 4.6 shows the calculated excess risk using the following formulas:
1. Excess risk calculation based on skin cancer (49).
R = (C)(W)(CI)/BW
where:
R = excess risk

C = arsenic concentration in rig/L (for food was calculated based in W)

q = cancer potency factor (5.3 x10'3 (p.g/kg-d)'l
W: daily water consumption (2 L/d)
BW = body weight (70 kg)
2. Estimation Risk based in the EPA new regulation, which considers bladder and lung
risk cancers (50,51):
R = (C)(LERF)(Rumt>
R: Risk
C: arsenic concentration in ug/L

LREF =Lifetime relative Exposure Factor (eo'73

, considering average male total water
consumption)

Rumm = unit risk factor for the specific end point of concern (bladder cancer or lung

cancer), in this case an average for both cases was considered (2.64x10'S cases/person per

Pig/L)

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123

From Figures 4.4, 4.5 and 4.6 it my be concluded that the new risk assessment based on
bladder-lung cancers compared with the old skin cancer risk assessment in all cases the
risks below 10 ug/L concentration of inorganic As gives almost the same risk. However,
at higher arsenic levels the risk based on bladder-lung cancers is 2 times lower than the
risk based on skin cancer. Food consumption is a very important component of risk

assesment and should include the dietary intake for various scenarios.

124

 

4.5 References

10.

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Hopenhayn-Rich, C., Biggs,M.L., Fuchs,A., Bergolio,R., Tello,E.E., Nicolli,H.,
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Thomas, P., Sniatecki, Inductively-Coupled Plasma-Mass Spectrometry, Applications
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Dabeka, R.W., McKenzie, A.D.,Lacroix,G.M.,Cleroux,C., Bowe,S., Graham,R.A.,
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of AOAC International, 1993. 76(1): p. 14-25.

Bae, M., Watanabe,C., Tsukasa,I., Sekiyama,M., Sudo,N., Bokul,M.H., Ohtsuka,R.,
Arsenic in cooked rice in Bangladesh. The Lancet, 2002. 360: p. 1839-1840.

Tsuda, T., Inque,T.,Kojima,M., Aoki,S., Market Basket and Duplicate Portion
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125

 

11.

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dietary intake of arsenic in the region Lagunera, Mexico. Food and Chemical
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of Monomotheylarsonic and Dimethylarsinic Acids in Seafood Products by Coupling
Liquid Chromatography with Hydride Generation Atomic Absorption Spectrometry.
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Zbinden, P., Andrey,D., Blake,C., A Routine Ion Chromatography ICP-MS Method
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Carusso, J ., Heitkemper,D.T., B'Hymer,C.B., An evaluation of extraction techniques
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Slejkovec, 2., van Elteren,].T., Byrne,A.R., A dual asrenic speciation system
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Beauchemin, D., Bednas,M.E., Berrnan,S.S., McLaren,J.W., Siu,K.W.,
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Branch, 8., Ebdon,L., O'Neil,P., Determination of arsenic species in fish by directly
coupled High _perfomance Liquid Chromatography-Inductively Coupled Plasma-Mas
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Velez, D., Ibanez,N., Montoro,R., Determination of arsenobetaine in manufactured
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McKierman, J .W., Creed,J.T., Brockhoff,C.A., Carusso,].A., Lorenzana,R.M., A
comparison of automated and traditional methods for the extraction arsenicals from
fish. Journal of Analytical Atomic Spectrometry, 1999. 14: p. 607-613.

Schoof, R.A., Yost,L.J., Crecelius,E.A., Irgolic,K., Goessler,W., Guo,H.R.,

Greene,H., Dietary Arsenic Intake in Taiwanese Districts with Elevated Arsenic in
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126

22.

23.

24.

25.

26.

27.

28.

29.

30.

31.

32.

Schoof, R.A., Yost,L.J., Eickhoff,J., Crecelius,E.A., Cragin,D.W., Meacher,D.M.,
Menzel,D.B., A Market Basket Survey of Inorganic Arsenic. Food and Chemical
Toxicology, 1999. 37: p. 839-846.

Schoof, R.A., Yost,L.J., Eickhoff,J., Crecelius,E.A., Cragin,D.W., Meacher,D.M.,
Menzel,D.B., Dietary Exposure to Inorganic Arsenic, in Arsenic Exposure and health
Effects, W.R. Chappell, Abemathy,C.O., Calderon, R.L., Editor. 1999, Elsevier
Science: New York. p. 81-88.

Yost, L.J., Schoof,R.A., Aucoin,R., Intake of Inorganic Arsenic in the North
American Diet. Human and Ecological Risk Assessment, 1998. 4(1): p. 137-152.

Heitkemper, D.T., Vela,N.P., Stewart,K.R., Westphal,C.S., Determination of total
and speciated arsenic in rice by ion chromatography and inductively coupled plasma
mass spectrometry. Journal of Analytical Atomic Spectrometry, 2001. 16: p. 299-306.

Mohri, T., Hisanaga,A., Ishinishi,N., Arsenic Intake and excretion by Japanese
Adults: A 7-Day Duplicate Diet Study. Food and Chemical Toxicology, 1990. 28: p.
521-529.

Helgensen, H., Larsen,E.H., Bioavailability and speciation of arsenic in acrrots
grown in contaminated soil. Analyst, 1998. 123: p. 791-796.

Roychowdhury, T., Uchino,T., Tokunaga,H., Ando,M., Survey of arsenic in food
composites from an arsenic-afiected area of West Bengal, India. Food and Chemical
Toxicology, 2002. 40: p. 1611-1621.

Munoz, 0., Velez,D., Cervera,M.L., Montoro,R., Rapid and quantitative release,
separation and determination of inorganic arsenic [As(III)+AS(V)] in seafood
products by microwave-assisted distillation and hydride generation atomic
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1607-1613.

Lopez, J.C., Reija,C., Montoro,R., Determination of Inorganic Arsenic in Seafood
Products by Microwave-assisted Distillation and Atomic Absorption Spectrometry.
Journal of Analytical Atomic Spectrometry, 1993.

Pardo-Martinez, M., Vinas,P., Fisher,A., Hill,S.J., Comparison of enzimatic
extraction procedures for use with directly couple high perfomance liquid

chromatography-inductively coupled plasma mass spectrometry for the speciation of
arsenic in baby foods. Analytica Chimica Acta, 2001. 441: p. 29-36.

Gallagher, P.A., Shoemake,J.A., Wei,X., Brockhoof-Schwegel,C, Creed,J.T.,
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with ion chromatographic separtion and ICP-MS detection. Fresnius Journal of
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127

 

33.

34.

35.

36.

37.

38.

39.

40.

41.

42.

43.

McSheehy, S., Pohl,P.L., Lobinski,R., Szpunar,J., Investigation of arsenic speciation
in oyster test reference material by multidimensional HPLC-ICP-MS and
eleoctrospray tandem mass spectrometry (ES-MS). Analyst, 2001. 126: p. 1055-1062.

McSheehy, S., Marcinek,M., Chasssaigne,H., Szpunar,J., Identification of
dimethylarsinol-riboside derivatives in seaweed by pneumatically assisted
electrospray tandem mass spectrometry. 2000: p. 71-84.

Mattusch, J ., Wennrich,R., Determination of Anionic, Neutral,, and Cationic Species
of Arsenic by [on Chromatography with ICPMS Detection in Environmental Samples.
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Van den Broeck, K., VAndecasteele,C., Geuns,J.M., Speciation by liquid
chromatography-inductively coupled plasma-mass spectrometry of arsenic in mung

bean seedlings used as bio-indicator for the arsenic contamination. Analytica
Chimica Acta, 1998.361: p. 101-111.

Demesmay, C., Olle,M., Porthault,M., Arsenic speciation by coupling high-
perfomance liquid-chromatography with inductively-coupled plasma-mass
spectrometry. Fresenius Journal of Analytical Chemistry, 1994. 348: p. 205-210.

Magnuson, M.L., Creed,J.T., Brockhoof,C.A., Speciation of arsenic compounds by
ion chromatography with inductively coupled plasma mas spectrometry dtection
utilizing hydride genenration with membrane separator. Journal of Analytical Atomic
Spectrometry, 1996. 11: p. 893-898.

Styblo, M., Yamauchi,H., Thomas,D.J., Comparative in vitro methylation of trivalent
and pentavalent arsenicals. Toxicology adn Applied Pharmacology, 1995. 135: p.
172-178.

Styblo, M., Del Razo,L.M., LeCluyse,E.L., Hamilton,G.A., Wang,C.Q., Cullen,W.R.,
Thomas,D.J., Metabolism of arsenic in primary cultures of human and rat
hepatocytes. Chemical Research in Toxicology, 1999. 12: p. 560-565.

Le, X.C., Cullen,W.R., Reimer,K.J., Speciation of arsenic compounds in some marine
organisms. Environmental Science and Technology, 1994. 28: p. 1598-1604.

van Elteren, J .T., Slejkovec,Z., Ion-exchange separation of eight arsenic compounds
by high-perfomance liquid chromatography UV decomposition hydride generation
atomic fluoresence spectrometry and stability tests for food treatment procedures.
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Liebl, B., Muckter,H., Nguyen,P.T., Doklea,E., Islambouli,S., Fichtl,B., Forth,W.,
Dijferential-efiects of various trivalent and pentavalent organic and inorganic

128

arsenic-species on glucose-metabolism in isolated kidney cells. Applied
Organometallic Chemistry, 1995. 9: p. 531-540.

44. Styblo, M., Hughes,M.F., Thomas,D.J., Liberation and analysis of protein-bound
arsenicals. Journal of Chromatography B, 1996. 677: p. 161-166.

45. Stewart, I.I., Electrospray mass spectrometry: a tool for elemental speciation.
Spectrochimica Acta Part B, 1999. 54: p. 1649-1695.

46. Vaessen, H., van Ooik,A., Speciation of arsenic in Ducth total diets: methodology
and results. Z.Lebensm Unters Forcsh, 1989. 189: p. 232-235.

47. Hughes, K., Mek, M.E., Burnett,R., Inorganic Arsenic: Evaluation of Risks to health
from Environmental Exposure in Canada. Environmental, Carcinogenesis and
Ecotoxicology Rewievs, 1994. C12: p. 145-159.

48. Tao, S.H., Bolger,P.M., Dietary arsenic intakes in the United States: FDA total diet
study, September I991-december 1996. Food Additives and Contaminants, 1999. 16:
p. 465-472.

50. EPA 815-R-00-026, Arsenic in Drinking Water Rule Economic Analysis, 2000.

51. Morales,K.H., Ryan,L., Kuo,T.L.,Wu,M.M., Chen,C.J., Risk of Internal cancers from
Arsenic in Drinking Water. Environmental Health Perspectives, 2000. 108:

129

Chapter 5

General Conclusions and Engineering Significance

The results from this study conclude that the method developed to speciate arsenic
in water can be easily used on-site and it is applicable at arsenic levels of concern for
drinking water.

The arsenic species stability study suggest that to maintain the original integrity of
a water sample it should be stored at pH<2 since As (IH) and As (V) are stable a different
temperatures and is not affected by the dissolved oxygen present.

Placing arsenic speciation information into the health risk assessment procedure is
crucial to reduce uncertainty because biochemical and toxicological behavior of arsenic
are strongly dependent upon the chemical species. In addition, processes for the removal
of arsenic from drinking water can be optimized according to the actual arsenic species
present in the water (arsenite or arsenate). Simple determination of total arsenic
concentrations in environmental samples does not reflect the level of hazard of this
element, and it is becoming increasingly important that the concentrations of various
species of arsenic be determined to provide a much clearer view of the risk associated

with exposure to arsenic in the environment

130

 

   

 

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