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This is to certify that the

thesis entitled

THE USE OF CHLORINE AND OZONE AS A POSTHARVEST WASH?

IN THE REMOVAL OF PESTICIDES ON APPLE FRUIT

presented by

Kheng—Chuan Peter Ong

has been accepted towards fulfillment
of the requirements for

M. S. degree in Food Science

 

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ajor professor

Date January 25, 1995

 

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THE USE OF CHLORINE AND OZONE AS A POSTHARVEST WASH
IN THE REMOVAL OF PESTICIDES ON APPLE FRUIT

By

Kheng-Chuan Peter Ong

A THESIS

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

MASTER OF SCIENCE

Department of Food Science & Human Nutrition

1995

ABSTRACT

USE OF CHLORINE AND OZONE AS POSTHARVEST WASH
IN THE REMOVAL OF PESTICIDES ON APPLE FRUIT

By

Kheng-Chuan Peter Ong

The objective of this study was to determine the effectiveness of
chlorinated and ozonated washes in the dissipation of pesticides in
solution and on and in fresh and processed apples.

Laboratory studies were conducted in a model system to determine
the effects of calcium hypochlorite (50 and 500 ppm) and ozone (0.25
ppm) at pH 4.5. 7.0. 10.7 and at 21°C and 44°C on the degradation of
each pesticide in solution over a 30 minute period. Apple fruits spiked
with the three pesticides were also used to determine the effectiveness of
chlorine and ozone washes on the removal and degradation of the
pesticide residues. All samples were analyzed for residues by gas
chromatography or high performance liquid chromatography.

Chlorination and ozonation were efi'ective in degrading azinphos-
methyl. captan and formetanate-hydrochlorite in solution. Rate of
degradation generally increased at higher pH and temperature. Pesticide
residues on apple fruits and in processed products were reduced by the
chlorine and ozone washes. The 500 ppm chlorine wash was the most

effective wash treatment.

DEDICATED TO

My parents, Robert &.Annie Ong,
for their love and nurture through the years

ACKNOWLEDGMENTS

I wish to express my sincere gratitude to all who have in one way
or another contributed to the successful completion of my Masters
program and this manuscript. I am truly grateful to my Major Professor
Dr. Jerry N. Cash for his trust. support. encouragement and guidance
throughout the entire program. His confidence in my abilities has
helped motivate me. To Dr. Matt Zabik for serving on my committee and
being so gracious in allowing me free access to his lab facilities. His
wealth of knowledge in analytical instruments has been beneficial to
me. To Dr. Gale Strasburg for being on my committee. reviewing this
manuscript and providing many constructive suggestions and
comments. To Dr. John Gill for his assistance in the statistical
analyses.

To Dr. Muhammad Siddiq and Dr. Nirmal Sinha. I would like to
extend my deepest appreciation for their support. many helpful
suggestions. critical evaluation and timely help in the preparation of
this manuscript. To Dr. Gama] Khedr for technical assistance.

I would also like to thank my friends in the lab (Triza. Kim.
Vance. Kevin. Matt. Eboua and Melvin) for their help and friendship.

Acknowledgement is made to the Michigan Agricultural
Experiment Station. Gerber Products Company. Miles. Inc. and the
Michigan Apple Industry for their support of this research.

Finally. I would like to recognize the people who have been an
integral part of my life. My parents and my brother and his family for
their love and support. To my fiancee Chikage. who has always given me
a reason to smile. even when times were tough. I shall always stand in

debt.

TABLE OF CONTENTS

Page

LIST OF TABLES ........................................................................... viii
LIST OF FIGURES ......................................................................... ix
LIST OF APPENDICES ................................................................... xi
INTRODUCTION ............................................................................. 1
LITERATURE REVIEW .................................................................... 4
A. Pesticide Use and Monitoring ............................................ 4

B. Pesticides Invovled ............................................................ 5

C. Pesticide Residues In Fruits And Vegetables ....................... 8

D. Degradation of Pesticides In Solution ................................ 13

I. Hydrolysis .................................................................. 13

II. Chemical Oxidation .................................................... 15

E. Chemistry of Chlorine and Ozone ...................................... 18

I. Chlorine Chemistry ...................................................... 18

II. Ozone Chemistry ......................................................... 22

F. Other Uses of Chlorine and Ozone Treatment ..................... 24

I. Chlorine ...................................................................... 24

II. Ozone ........................................................................ 25
MATERIALS AND METHODS .......................................................... 27
MATERIALS ................................................................................... 27
A. Apple Samples .................................................................. 27

B. Reagents .......................................................................... 27

I. Solvents ...................................................................... 27

11. Chemicals .................................................................. 28

C. Glassware ........................................................................ 28

METHODS .................................................................................... 29

A. Study on Degradation of Pesticides In Solution .................. 29

1. Sample Preparation .................................................... 29

vi

Page

II. Chlorine Determination .............................................. 31
III. Ozone Determination ................................................. 32
IV. pH Determination ...................................................... 33
B. Studies On Fresh and Processed Apples ............................. 33
I. Pesticide Application and Spray Schedule .................... 33
II. Wash Treatments ....................................................... 35
III. Sample Preparation .................................................... 36
C. Pesticide Residue Analyses ................................................ 37
I. Extraction and Cleanup of Azinphos-methyl & Captan.. 37
II. Extraction and Cleanup of Formetanate-HCI ............... 39
D. Recovery Studies .............................................................. 40
E. Chromatographic Analyses ................................................ 41
I. Azinphos-methyl ........................................................ 41
II. Captan ...................................................................... 42
III. Formetanate-HCI ....................................................... 43
F. Calculation of Pesticide Residue Concentration ................. 43
G. Statistical Analyses ......................................................... 44
RESULT AND DISCUSSION ............................................................ 45
A. Model Study ..................................................................... 45
I. Chlorine Monitoring ................................................... 45
II. Ozone Monitoring ...................................................... 45
III. Degradation Of Azinphos-methyl ............................... 47
IV. Degradation Of Captan .............................................. 54
V. Degradation Of Formetanate-HCI ............................... 62
B. Study On Pesticide Dissipation In Fresh And

Processed Apples ............................................................. 68
1. Apple Processing ......................................................... 68

II. Azinphos-methyl Residues On/ In Apple Fruit And
Sauce ....................................................................... 69
III. Captan Residues On/ In Apple Fruit And Sauce ............ 72

III. Formetanate-HCI Residues On/ In Apple Fruit And
Sauce ....................................................................... 77
IV. Pesticide Residues In Wash Water .............................. 80
SUMMARY AND CONCLUSION ..................................................... 84
FUTURE WORK ........................................................................... 88
APPENDICES ............................................................................... 90
BIBLIOGRAPHY ............................................................................ 96

vii

LIST OF TABLES

Page
Table l. Oiddation-Reduction Potentials Of Various Compounds 21
Table 2. 1994 Spray Schedule For Golden Delicious Apples ............ 34
Table 3. Ozone Output In Water From Lifex Ozone System ............ 46

Table 4. Effect Of Various Wash Treatments On Residual
Azinphos-methyl On Apples ............................................ 70

Table 5. Effect Of Various Wash Treatments On Residual
Captan 0n Apples .......................................................... 74

Table 6. Effect Of Various Wash Treatments On Residual
Formetanate-HCI On Apples ........................................... 78

Table 7. Pesticide Resdiues In Wash Water After
Various Washes ............................................................. 81

viii

LIST OF FIGURES

Page
Figure 1. Strcture Of Azinphos-methyl ........................................ 6
figure 2. Strcture Of Captan ...................................................... 7
Figure 3. Strcture Of Formetanate-HCI ....................................... 7
Figure 4. Hydrolysis Of Captan ................................................... 14
Figure 5. Relative Amounts of HOCI and OCI' Formed
at Various pH Levels ..................................................... 20
Figure 6. Simplified Reaction Model of Ozone With Organic
Compounds M in Water ............................................... 23
Figure 7. Schematic Diagram Of Ozone Treatment ....................... 31
Figure 8. GO Chromatogram Of An Azinphos-methyl Standard ..... 48
Figure 9. GO Chromatogram Of An Azinphos-methyl Sample ........ 49
Figure 10. Effect Of Ozone Treatment On The Degradation
OfAzinphos-methyl At 21 °C ......................................... 51
Figure 1 1. Effect Of Ozone Treatment On The Degradation
OfAzinphos-methyl At 44°C ......................................... 51
Figure 12. Efl'ect 0f Chlorine Treatment On The Degradation
OfAzinphos-methyl At 21 °C ......................................... 53
lflgure 13. Efi’ect 0f Chlorine Treatment On The Degradation
OfAzlnphos-methyl At 44°C ......................................... 53
iYg'ure 14. 00 Chromatogram Of A Captan Standard ..................... 55
'gur'e 15. GO Chmmatogram Of A Captan Sample ........................ 56

ix

Figure 16. Effect Of Ozone Treatment On The Degradation

or Captan At 21°C ......................................................

Figure 17. Effect Of Ozone Treatment On The Degradation

or Captan At 44°C ......................................................

Figure 18. Effect Of Chlorine Treatment On The Degradation

Of Captan At 21°C ......................................................

Figure 19. Effect Of Chlorine Treatment On The Degradation

Of Captan At 44°C .......................................................
Figure 20. HPLC Chromatogram Of A Formctanate-HCI Standard
Figure 21. lfl’LC Chromatogram Of A Formetanate-HC] Sample .....

figure 22. Effect Of Ozone Treatment On The Degradation

Of Formetanate-HCI At 21 °C ........................................

Figure 23. Effect Of Ozone Treatment On The Degradation

Of Formetanate-HCI At 44°C ........................................

Figure 24. Efi'ect Of Chlorine Treatment On The Degradation

Of Formetanate-HCI At 21 °C ........................................

Figure 25. Efi'ect Of Chlorine Treatment On The Degradation

Of Formetanate-HCI At 44°C ........................................

Figure 26. Amount Of Azinphos-methyl Residue On / In

Apple Fruit & Sauce .....................................................
Figure 27. Amount Of Captan Residue On/In Apple Fruit & Sauce ..

figure 28. Amount Of Formetanate-HCI Residue On / In

Apple Fruit & Sauce ......................................................
Figure 2.9. Pesticide Residues In Wash Water ..................................

Page

58

58

60

60
63

. 64

66

66

67

67

.71

75

79
82

LIST OF APPENDICES

Page

Appendix 1. pH Readings Of Samples In Model Study ................... 90

Appendix H. Raw Data For Wash Treatment ................................ 92
Appendix M. A Typical Standard Curve For Azinphos-methyl

Standards ............................................................... 93

Appendix IV. A Typical Standard Curve For Captan Standards ........ 94
Appendix IV. A Typical Standard Curve For Formetanate-HCI

Standards ................................................................ 95

xi

 

INTRODUCTION

The demand for produce with good sensory quality by the
consumer has continued to sustain the use of pesticides in the control
of insects and diseases in apple fruits. As a result. there is a need to
develop methods for removing or reducing the levels of pesticide residues
on fresh and processed apples after harvest. Such methods would
alleviate concerns that these chemicals are hazardous to humans and
the environment. Postharvest treatments such as the postharvest water
wash and scrub that have been traditionally employed to remove debris
and dirt. have been shown to reduce residues (El-Hadidi. 1993). The use
of postharvest chlorine dips has also shown potential as an effective
postharvest treatment in the reduction of pesticide residues on apple
fruits (Hendrix. 1991). The use of ozonated water dips shows similar
potential as an alternative postharvest treatment method.

Apple (Malus x domesttca Borkh.) is considered to be a major
agricultural product with substantial economic value. In terms of
annual tonnage produced. apples are the third most important fruit crop
grown in the United States (Downing. 1989). Michigan is one of the
nation's most important apple producing states. with 9% of the total
US. production in 1987-1990 (Ricks and Hull. 1992). As a result of its
high economic value as well as the large number of plant diseases (apple
scab. powdery mildew and sooty blotch). insects (codling moth. apple

maggot. scales and apple aphids). and mites (spider mites) that infest
apples during their growth. significant quantities of pesticides are often
necessary for the protection of this crop. This leads to residues on (or
in) the fruit at harvest. Although these residue levels are generally
below established tolerances. consumer wariness warrants efforts to
further reduce pesticide residues.

Three pesticides. azinphos-methyl. captan and formetanate
hydrochloride. were selected in this study and used in the spray
schedules of apple fruits. These three pesticides are used in the control
of the major diseases. insects and mites that affect apples.
Azinphos-methyl (GuthionQ) is a non-systemic organophosphrous
insecticide that acts both by contact and ingestion. Captan is used
widely as a non-systemic organosulphur fungicide in the prevention of
fungal diseases of pome fruits and grapes. Formetanate-hydrochloride
(CarzolQ) is an insecticide/scaricide that is characterized by its ability
to evoke a variety of behavioral and other effects in several plant insects.
beet fly. mites and thrips. Application of these pesticides before harvest
is often necessary for the protection of fruits during the preharvest
period. Only pesticides with no evidence of carcinogenicity according to
Environmental Protection Agency (EPA) standards were selected for this
study.

The objective of the present study was to determine the
effectiveness of chlorine and ozone as postharvest washes used in the
dissipation of pesticide residues in a solution and on fresh and
processed apple fruits. Such treatments can be used in conjunction
with an Integrated Pest Management (1PM) program to ensure

undetectable or negligible residues of the applied pesticides on fresh and
processed apple fruits.

 

LITERATURE REVIEW

A. Pesticide Use And Monitoring

Between 1964 to 1982. pesticide usage increased from 225 million
to 558 million pounds (Osteen and Szmedra. 1989). Over the years.
organophosphates. carbamates. and pyrethoids have gradually replaced
the more persistent organochlorines. These insecticides. especially the
pyrethoids. are safer and more effective. thereby requiring less active
ingredients (Osteen and Szmedra. 1989). The use of fungicides has also
increased ten fold since 1964 (Osteen and Szmedra. 1989).

The increased use of pesticides has been a direct consequence of
the substantial loss of fruit crops caused primarily by insects and
diseases. In the U.S.. a third of all crops is lost to pests prior to
harvest. and an additional 9% is lost to pests after harvest (Pimental.
1976). A major portion of these losses are due to the demand by the
consumer for cosmetically perfect produce of high quality standards.

With the increased usage of pesticides. consumer concern about
pesticide residues on produce has increased. This concern initiated
increased monitoring of pesticide residues on fresh produce and
processed foods to reassure the public about the safety of the food
supply. The National Food Processors Association Protective Screening

Program was formed in 1960 to evaluate pesticides in processed foods.
The goal of the program was to prevent illegal pesticide residues from
contaminating processed foods (Elkins. 1989). During the same period.
the Food and Drug Administration (FDA) started a large scale
monitoring program for pesticide residues on fresh produce. The
program was divided into two areas of monitoring: (i) regulatory or
commodities monitoring. and (ii) the Total Diet Study. which evaluates
pesticides in prepared food where the original ingredients were
purchased from retail stores. The Total Diet Study evaluates 234 foods
for over 100 pesticides based on the diets of males and females from
various age groups. This study is carried out four times a year in three
cities in each of four geographical regions (Lombardo,1989). The levels
of most pesticides found were orders of magnitude lower than EPA-
established residue tolerances. and less than 1% were in violation.
However. Pimentel (1983) estimated that at least 50% of the food items
contain detectable pesticide residues.

B. Pesticides Involved

Three pesticides. an insecticide. a fungicide and an
acaricide/ insecticide. were selected for use in this study. These
pesticides are classified as non-carcinogenic and are able to control the
major disease. insect and mite pests that damage apples.

 

(i) Azinphos-methyl: It's chemical name is 0.0-dimethyl-S-l(4-oxo-
l.2.3-benzotrizazin-3(4H)-yl)-methyl]-phosphorodithioate and is

commercially known as Guthion®.

0
N
CH O 5
CH O
a N\N

Home 1 : Structure of Azinphoo-methyl

Azinphos-methyl is an insecticide marketed for the control of
many insect pests on a wide range of crops such as fruits. nuts.
vegetables. field crops and omamentals. It is generally applied in ultra-
low volume for control of various insect pests on field. fruit and forage
crops. This pesticide has a broad spectrum of activity. especially against
lepidopterous larvae. bugs. sawfly larvae. fleas. scale insects and aphids
(Worthing and Hance. 1991). Its solubility in water is 28 mg/ L at 20°C.

(ii) Captan: Captan is the common name adopted for N-

trichloromethylthio-4-cyclohexene- 1 .2-dicarboximide.

0

0 \N- SeCCl a
/

C
ll
0

n:

m2:8tructureof0nptnn

Captan is widely used as a surface fungicide in the control of
scabs. blotches. rots. mildew. and other diseases on fruits. vegetables.
nut and ornamental crops at a typical rate of l .2 gram active ingredient
(a.i.) per liter (Worthing and Hance. 1991). It is also used in general
purpose pesticide mixes. The major diseases of apple. pear and grape
which captan is effective against are apple scab. pear scab. downy
mildew, and Botrytis bunch rot. respectively. The solubility of captan in
water is 3.3 mg/ L at 25°C.

(iii) Formetanate-hydrochloride: The chemical name is [m-
[[(dimethylamino)methylene)aminolphenylmethylcarbamate)

hydrochloride.
on.
NICHN < A . HCI
on. NH m© ca.

Figure 8 : Structure of Punchline-hydrochloride

Formetanate-hydrochloride. which is marketed under the
tradename CarzolQ. is used as an acaricide and insecticide for the
control of spider mites. rust mites. certain aphids. thrips. lygus bugs.
leaf hoppers. slugs and snails on a variety of orchard fruit (Jenny and
Kossmann. 1978). It is applied on citrus. pome and stone fruits
(Worthing and Hance. 1991). Formetanate-HCI is especially effective
against organophosphate resistant mites. Formetanate-HCI is
completely soluble in water (> 500 g/ L). while the solubility of

formetanate is < 1 g/ L at room temperature.

C. Pesticide Residues in Fruits and Vegetables

With concerns focused on the potential risk of the pesticides used.
information regarding residue on fruit crops has been sought over the
years on many pesticides. Most data were gathered from controlled field
trial studies. Data on the effect of processing on the residue levels on
various fruits and vegetables have been reported in numerous studies.
Literature on the three pesticides used in this study were readily
available in some instances. and limited in others.

In general. residue levels in crops are dependent on a number of
factors such as rate and frequency of application. nature of the plant
surface. and weather conditions such as rainfall. temperature. humidity.
sunlight. and wind (Anderson et aL. 1974).

The contact and ingestion insecticide. azinphos-methyl was first
field-evaluated against cotton insects in Mexico in 1954 and registered

for use on cotton in the US. in 1956 (The Chemargo Division Research
Staff. 1974). Following the introduction of azinphos-methyl to
American agriculture on cotton. the compound has come into
widespread use on fruits. field crops such as potatoes and apples. forage
crops such as alfaalfa and clover and many vegetables. The maximum
residue limit for azinphos-methyl on apples in the US. is 2 ppm (Code
of Federal Regulations. USA. 1990).

The half-life for azinphos-methyl on vegetables and forage craps
grown under field conditions ranges from three to five days.
Azinphos-methyl persists on tree fruits somewhat longer than on field
crops (Anderson et al.. 1974). The average half-life on apples is six
days. and is considerably longer on citrus fruit due probably to the high
oil and acid content of the rind.

Several supervised residue trials were carried out on apples in
Europe and the US. (FAQ Plant and Protection Paper. 1991). A wet
powder (WP) formulation was applied to the crop. with dosage rates of
0.51-1.68 kg at ha'l (4-6 applications). Residues found in US. trials 7
days after the last application on apples were 0. 14- 1.8 ppm.

Belanger et al. (1991) determined azinphos-methyl residues on
apples in Canada. where the trees were sprayed with the insecticide at
different plant stages. Residue analysis revealed detectable residues on
the foliage until mid season. However. negligible residue levels were
found on the peel and the whole fruit at harvest. In another study.
Winterlin et aL (1974) found azinphos-methyl residues on grape leaves
at approximately 20% of their original levels at harvest 42 days after the

10

initial application. Residue levels on the fruit were 12. 14 and 4.4 ppm
at 28. 31 and 42 days after application. respectively.

The effect of processing has been shown to reduce
azinphos-methyl residues in food products. Gunther et aL (1963)
determined that 71-94% of the azinphos-methyl on orange rind is
removed by normal washing procedures. No azinphos-methyl was
detected in the pulp (edible portion). In another study. Anderson et al.
( 1963) reported that standard washing procedure removed 30% of
azinphos-methyl residues from oranges. Processing of grapes into juice
also resulted in a reduction of azinphos-methyl residues (The Chemargo
Division Research Staff. 1974). When whole grapes were fortified with
azinphos-methyl at 5 ppm. the juice pressed at room temperature
contained 2.6 ppm of azinphos-methyl. Juice pressed from grapes
subjected to heating contained about 1 .7 1 ppm of the pesticide.

The fungicide captan is widely used for the prevention of fungal
diseases of pome fruits and grapes around the world. On a global scale.
official maximum residue limits for captan range from 3 to 50 ppm. The
maximum residue limits for captan on apples in the US. is 25 ppm
(Frank etaL. 1985).

Frank et al. (1985) studied the persistence of captan on apples.
grapes and pears in Canada between 1981-1983 over a 14-day period
following the last application. Residues declined significantly in seven
of nine experiments. with levels on apples below 5 ppm after only 3 days
following the last spray. Correlation between rainfall and captan
residues were also observed. Captan residues on cherry and peach

fruits. where the trees were sprayed with captan at 2.4-4.5 kg ha'l. were

ll

determined by Northover et al. (1986). Residue analysis showed residue
levels of approximately 5 ppm of captan. and greatly decreased with
increased rainfall.

Experiments conducted on the degradation behavior of captan on
greenhouse tomatoes revealed that the maximum concentration (initial
deposit) of captan on the tomatoes were 3.4 ppm after the last
application (El-Zemaity. 1988). The percent dissipation of captan
residues after 7 days from application were 11.5-55.0% and 37 .3-59.5%
when sprayed at 7 and 15 days intervals. respectively.

Several postharvest treatments have been reported to remove
captan residues on some fruits. Following a 20 minute cold water rinse.
14% of residues were removed from strawberries and 95% reduction after
a 5 minutes cook (Ritcey et al.. 1984). Northover et al. (1986)
determined that captan was easily removed by washing. reducing
residues on sweet cherry by 70-74%. The same study also reported that
10 seconds of hand washing removed a maximum of 50% from the
initial deposit of captan in peaches. Vigorous washing with a stiff
bristle brush removed about 70% of the residue from peaches.
Household washing using running tap water reduced captan residues by
97.7-98.9% on tomatoes (El-Zemaity. 1988). Similar levels of reduction
were also obtained by cooking tomatoes for 15 minutes at l 00°C without
washing. Hendrix (1991) showed that captan residues on apples were
reduced to less than detectable levels with a chlorine wash compared to
water washed and brushed fruits.

Frank et al. (1983) determined that captan residues in apples were
reduced by washing. peeling. boiling and cooking or a combination of

12

these procedures. Washing reduced residues of captan by 43-94%.
boiling by 70-98%. and a combination of washing and cooking gave
almost 100% removal.

Formetanate-HCI residues on fruits crops have been studied by
few researchers. In 1985. Hadjidemetriou et al. studied the dissipation
of formetanate-BC] and several other pesticides on citrus foliage.
Formetanate-HCI as carzol" were sprayed at a rate of 1. 1 kg a.i. ha-l .
Formetanate-HCI residue on the citrus did not appear to dissipate at
all. except in the presence of rainfall. The solubility of formetanate-RC1
in water is reported to be 500 ppm (Worthing and Hance. 1991). and as
such is greatly affected by rainfall.

Residues of formetanate-HCI on and in orange fruits were also
studied by Iwata et al. (1985). Test plots of orange trees were treated
with formetanate-HCI at the maximum permitted dose rates (1 .03 kg
at. ha'l) with a low volume airblast sprayer (940 liters ha-1 ). Mature
fruit samples were collected 5. 7. 10. 13. 17 and 31 days after the spray
application. Residues on and in the rind were 0.96. 1.0. 1.2. 1.0. 1.2
and 0.85 ppm. respectively. The residue over the entire sampling period
remained essentially constant at 1 .0 ppm. Similar fruits. sampled on
day 7 and washed under tap water had a residue of only 0.03 ppm.

During 1990-91. a study was conducted at Michigan State
University by El-Hadidi (1993) to determine pesticide residues in fresh
and processed apple fruits under certain developed pest control
programs. A correlation was found between the postharvest intervals
(PI-Ila) and the residue levels of formetanate-HCI and azinphos-methyl.
In general. the longer the PHIs the lower the total residue levels. Of

13

several pesticides applied in the study. azinphos-methyl showed the
highest residue levels on fruits (0.3-0.4 ppm). However. the residues
detected were much lower than the 2.0 ppm tolerance level.
Formetanate-HCI total residues in the whole fruit ranged from 0.07 to
0. 13 ppm. These levels were also lower than the established tolerance of
this pesticide on or in apples.

In the same study by El-Hadidi (1993). washing/ grading of apples
were shown to significantly reduce the residue levels of formetanate-HCl
and azinphos-methyl. Processing of the apples into apple products such
as apple slices. sauce and juice were also significantly effective in
reducing the pesticide residue levels to non-detectable amounts in some

and residues lower than those on fresh fruits in others.

I). Degadatlon of Pesticides In Solution

The fate of pesticides in solution. due to hydrolysis. ozonation
and chlorination must be understood in order to understand its
degradation behavior during a wash treatment. after it is washed off the
fruit and its safe disposal as pesticide waste water.

H) Hydrolysis

Laboratory studies on the effect of pH and temperature on the
breakdown of pesticides in aqueous solution have been conducted to

provide information on their relative persistence.

14

The hydrolysis of azinphos-methyl may proceed under acid.
neutral and alkaline pH. but is generally more persistent under acidic
conditions (Faust & Gomma. 1972). Azinphos-methyl was observed in
this study to have its greatest stability under acidic conditions with
increasing rate of hydrolysis at higher pH. At pH 3.0. 7.0 and 9.0. the
t1 ,2 values for azinphos-methyl were 9. 4.8 and 0.6 hours respectively.
In another study. Liang and Lichtenstein (1972) found that azinphos-
methyl was relatively stable in water below pH 10. At pH 11. 97% of the
pesticide was converted to degradation products such as anthranilic
acid. benzazimide and 3 unidentified compounds.

Faust and Gamma (1972) also studied the effect of temperature on
the degradation of azinphos-methyl. and showed the compound to be
less stable as temperature increased. Liang and Lichtenstein (1972)
showed that rapid degradation of azinphos-methyl occurred above 37°C.

Captan readily undergoes hydrolysis in water with a maximum
half-life of about half a day (Wolfe et al.. 1976). At pH 6. 7 and 8.25. the
half life of captan in water was 250. 175 and 10 minutes. respectively.
No half life data were available for captan at pH 10 and above. In the
same study. the authors determined the products of captan hydrolysis
as 4-cyclohexene- l .2-dlcarboximide. carbon dioxide. hydrochloric acid
and sulfur (Figure 4).

   

Pigme 4 : Hydrolysis of Captan

15

As anticipated. the rate of hydrolysis of captan increased with increasing
temperature in both neutral and alkaline (pH 9) conditions.

Formetanate-HCI is a weak basic compound which hydrolyses
slowly in acidic media but considerably faster in neutral and basic
aqueous solutions. especially at higher temperature (Jenny and
Kossmann. 1978). It was found that formetanate at 1 ppm in aqueous
solution at pH 8 decomposed by 20% after one day at room temperature
(Lawrence et aL . 198 1). Hydrolysis of formetanate-HCI at pH 9 reached
50% in 100 minutes (Su and Zabik. 1972).

(II) Chemical Oxidation

Chlorine. chlorine dioxide. potassium permanganate. and ozone
have been employed historically fOr the oxidation of organic compounds
at water treatment plants, and were consequently investigated for their
capacity to degrade organic pesticides (Gamma and Faust. 1974). The
present study is focused on the use of ozone and chlorine in the
degradation of pesticides. Besides a study on the effect of chlorination
of captan (Suzumoto et al.. 1983). no other literature is available on the
effect of ozonation or chlorination on azinphos-methyl. captan and
formetanate-H01 in solution. However. there are numerous studies that
have investigated the effect of ozone and/ or chlorine on a wide range of
other pesticides.

As a strong oxidant and an electrophile (Kirk and Mitchell. 1980).
chlorine as hypochlorous acid can oxidize various organic compounds

16

(Dychdala. 1977). In their study on the effect of residual chlorine on
the degradation of pesticides in water. Suzumoto et al. (1983) showed
that thirteen kinds of pesticides were easily degraded by chlorine at
concentrations of 1 ppm. It was also shown that pesticides containing
sulfur within their chemical structure seemed to be easier to degrade.
Among the pesticides studied. benthiocarb showed rapid degradation in
solution containing 0.2 ppm residual chlorine where only 6% of the
original concentration remained after 3 hours. Captan at 0.04 ppm in a
solution containing 1 ppm chlorine degraded by only 5% after 24 hours.

Hilden et al. (1979) studied the effectiveness of chlorine bleach in
the removal of some pesticides from clothing fabrics. and determined
that chemical structure and water solubility were two factors that
explained the differences in percent removal of the pesticides. The study
showed that the organophosphate and carbamate insecticides
(parathion. diazinon and carbofuran) were easily degraded by oxidation
due to the weak phosphoric and carbamic acid ester linkages of those
pesticides. However. the pesticide lindane was not susceptible to
oxidation due to its strong saturated cyclic bonding of cyclohexane and
the chlorine-carbon bonding.

An increase in pH from 7 to 8 decreased the half-lives of carbaryl.
l-naphthol. and propoxur from 6- to 162-fold. while chlorinated water
(10 ppm hypochlorite solution) shortened the half-lives of the pesticides
from 3- to 62-fold (Miles at al.. 1988). The authors suggested that the
effect of chlorination on half-life was greater at pH 8 than pH 7. and
was due to the importance of chlorine speciation (HOCI/OCT: pKa=7.5)
in the degradation of the pesticides in chlorinated water.

17

Other fate studies of pesticides in chlorinated water have shown
that paraquat and diquat (Gomma and Faust. 1971). phenylureas.
phenylamides and phenylcarbamates (El-Dib and Aly. 1977).
thiobencarb (Au et al. . 1984) and diazinon (Dennis et al.. 1979) degraded
faster in the presence of chlorine. and that pH was an important factor
in the degradation rate. In general. all the above studies showed that
oxidation was a major efi’ect of chlorination and that other mechanisms
such as hydrolysis and chlorination occurred when organic compounds
react with chlorine in water.

Robeck et al. (1965) ozonated aqueous solutions of lindane.
dieldrin. DDT and parathion and found that dosages of 10 to 38 mg/ L of
ozone were required to destroy these pesticides to acceptable levels.
These dosages were considered to be too high to be practical.

Aqueous solutions containing 10 mg/L of malathion were
ozonized at ozone dosages of 3.5 mg/ L. reducing the concentration of
malathion to 2 mg/ L (Gabovich et al.. 1980). Increasing the ozone
dosage to 9.8 mg/L reduced malathion to 1 mg/L. A dosage of 26 mg/L
of ozone caused 100% destruction of malathion.

Mallevialle et al. (1978) ozonated aqueous solutions of aldrin. and
found this compound to be easily degraded by ozone. Prengle and Mauk
(197 8) showed that ozonation of DDT in water proceeds very slowly. but
the oxidation rate is accelerated by combining UV radiation with
ozonation.

The use of ozone alone as an oxidant for treatment for several

herbicides has been compared to combined UV-03 for 11 major

pesticides and gave comparable rates of oxidation (Kearney et al. . 1987).

18

The pesticides that were used in the study included 9 formulated
herbicides (alachor. atrazine. butylate. cyanazine. 2.4-D. mctolachlor.
metribuzin and trifiuralin) and two formulated insecticides (carbofuran
and malathion). The time required for 90% destruction was dependent
on the concentration and increased as the concentration of pesticide
increased. The average degradation time for all 11 pesticides at
concentrations between 10 and 100 ppm was about 60 minutes.
According to Laplanchc and Martin (1982). organochlorous
pesticides are not easily oxidized and need exhaustive ozonation
conditions. On the other hand. organophosphorous pesticides are very

sensitive to ozonation.

E. Chemistry of Chlorine and Ozone

(I) Chlorine Chemistry

Assessment and prediction of chlorination effects on organic
compounds present in waters and food systems requires a knowledge of
chlorine reaction mechanisms. concentration of reactants and the
concentration of reaction products.

When chlorine as calcium hypochlorite is added to water. a
mixture of hypochlorous acid (HOCI) and hydrochloric (HCl) acids is
formed:

19

C12 + H20 —-—-> HOCI + H+ + Cl' Equation]

This reaction is essentially complete within a few seconds. In
dilute solution and at pH levels above 4. the equilibrium shown in
Equation 1 is displaced to the right and very little C12 exists in solution
(Laubusch. 1962). Hypochlorous acid is a weak acid (Equation 2) with a
dissociation constant at 0°C to 25°C of 1.6 to 3.2 x10-8 and a pKa of 7.8
to 7.5 (Morris. 1966).

HOCl ———> H+ + OCl' Equation 2

As a result. the chlorine species present in the pH range 3.0-8.0
(the range for most foods) would be HOCI and the hypochlorite ion. At
pH 5.0. the species distribution would be 99.7% HOCI vs. 0.03% OCl'
for a 10‘2 M chlorine solution at 20°C. At pH 8.0. species distribution
shifts to 23.2% HOCI vs. 76.8% OCl' for the same 10'2 solution
(Figure 5). Other species besides HOCI including the hypochlorous
hydronium ion. H20C1+. the chloronium ion. C1+ and C13+ may be
present in very low concentrations and/ or have very low specific

reactivities (Laubusch.1962).

 

 

 

s
&

 

 

 

 

 

 

t: .l...
. \ ,0
.. \

 

 

 

 

 

 

 

 

 

 

 

Plane 6 : Relative Amounts of HOCI and 001' Formed
At Var-loin pH Levels (Fair at al.. 1948)

The tendency for chlorine to acquire electrons is so strong that it
may split from the molecule and form the reduced chloride ion by
displacement (Wei et al.. 1985). This is the basis for the oxidation
reactions of HOCI with organic compounds. The antibacterial efiicicncy
and sporicidal effectiveness of chlorine solution has been shown to
decrease with increasing pH (Dychdala. 1977). An increase in
temperature will decrease the percent of HOCI. and consequently its
reactivity with organic compounds (Wei et al.. 1985).

The capability of one substance to oxidize another is measured by
its Oxidation Potential. normally expressed in volts of electrical energy.

21

The oxidation potential is a measure of the relative ease by an atom.
ion. molecule or compound to lose electrons. thereby being converted to
a higher state of oxidation. In general. the higher the oxidation
potential. the stronger it is as an oxidant. As indicated in Table l .
HOCI is a stronger oxidizing agent ( 1.49 V) than is free chlorine (1.36 V).
so that HOCI is actually more desirable when using chlorine as an

oxidant in aqueous solution.

Table 1 : Oxidation-Reduction Potentials 0! Various Compounds

 

 

 

Reactions Potential 1n Volts (E°) 25°C
12 + 2c —> 21:" 2.87
03 + 2H"’ + 2c —> 02 + H20 2.07
H202 + 2H+ + 2c —> 2H20 (acid) 1.76
Mn04' + 41-1+ + 3c —> Mn02 + 2H20 1.68
110102 + 311+ + 4c ——> 01’ + 2H20 1.57
Mn04' + 811+ + 5c ——> Mn2+ + 41120 1.49
HOCI + H+ + 2c —> C1' + H20 1.49
C12 + 2c —> 201' 1.36
HOBr + II" + 2c —> Br' + 1120 1.33
03+H20+2e—>02+20H’ 1.24
C102 (gas) + e —> C102' 1.15
812 + 2c —> 2Br' 1.07
H01 + Ht 4» 2e —> I' + H20 0.99
0102 (sq) + e —> 0102' 0.95
C10' + 21120 + 21: —> C1' + 20H' 090
11202 + 21130+ + 2c —> 41120 (basic) 0.87
C102‘ + 21120 + 4c —> C1’ + 4011' 0.78
OBr' + H20 + 2c -—> Br' 4» 4011’ 0.70
12 + 2c —> 21' 0.54
13 + 3c > 31' 0-53
01' + 1120 + 2c —> 1' + 2011' 0.49
02 + 21120 + 4c —> 40H’ 0-40

 

 

Handbook 01 Chemistry & Physics. 56th Ed. (1975-76)

(II) Ozone Chemistry

Ozone is an unstable gas which is partially soluble in water
(about 10 times the solubility of oxygen) and has a characteristic
penetrating odor. readily detectable at concentrations as low as 0.01 to
0.05 ppm (Katz. 1980). It is a powerful oxidant. having an oxidation
potential (2.07 V) higher than HOCI and free chlorine (Table 1).

Ozone is thought to decompose in water according to Equation 3-
6 as a cyclic chain mechanism as shown in Figure 6.

03 + H20 ———> H03+ + 0H“ Equation 3
H03+ + OH' ———> 2HO2' Equation 4
03 + H02“ ——-> HO‘ + 202 Equation 5
HO‘ + H02‘ —-—> H20 + 02 Equation 6

The overall stoichiometry is shown in Equation 7:

203 ——> 302 Equation 7

Ozone reacts with organic compounds in four pathways as
depicted in Figure 6: (l) ozone with hydroxyl ions (OH’) via intermediate
radicals to H0’ ; (2) ozone with organic molecules (M) via intermediate
radicals to H0' : (3) ozone with M to H202 : (4) ozone with H02“ to H0‘

(Stockingcr et al.. 1994)

 

 

 

 

Mo 'de
"M' 1102'? 320.2
Scavengers
. 03
M
. M+

Figure 6 : Simplified Reaction Model of Ozone With Organic
Compounds M in Water (Stockingcr et al. . 1994)

Decomposition of ozone can be initiated by hydroxide ions.
formate ions. or a variety of other species. and in pure water the chain
ends (Glaze. 1987). A single initiation step can cause the decomposition
of hundreds of molecules of ozone before the chain ends. The
electrophilic direct ozonolyses by molecular ozone of double or triple
bonds and the reactions with HO' radicals are the two most important
steps (Stockingcr et al.. 1994). High formation rates of HO' radicals in
water by ozone and low direct ozonolyses rates occurs at high pH and
vice versa at low pH values.

As such. oxidation mechanisms differ highly with pH. In general.
low pH and high inorganic carbon concentration encourage the direct

molecular attack which is more selective and less hindered by
competitive reactions (i.e. oxidantodemanding substances). On the
other hand. indirect radical attack is favored by high pH. low
concentration of carbonates. and presence of activating substances.
such as hydrogen peroxide.

Under practical conditions. the dose of ozone is never enough to
satisfy the ultimate demand. and the reaction with organic compounds
will generally stop when the supply of ozone is depleted. Typically. this
will be long before the organic substances have become mineralized to
carbon dioxide (Glaze. 1987). However. the use of ozone creates a
distinct advantage over the use of chlorine as the danger of the
formation of harmful degradation products such as chlorinated by-
products can be eliminated.

F. Other Uses of Chlorine and Ozone Treatment

(1) Chlorine

Aqueous chlorine is used extensively in the food industry to
sanitize food processing equipment and food containers (100-200 ppm).
to rinse and convey raw fruits and vegetables (1-5 ppm). and to cool
heat-sterilized canned foods (1-2 ppm) (Foegeding. 1983). Chlorine is
also widely used in the fishing industry. in washing nutmeats. and in
the processing of seafood. poultry. and red meats (Wei et al. . 1985).

Chlorine gas is used in the flour industry as an oxidizing and bleaching
agent to improve the quality of flour (Johnson et al.. 1980).

The use of chlorine as a postharvest chlorine dip has also been
shown to be effective in the control of decay in apples (Baker and Heald.
1932) and d'Anjou pears (Spotts and Peters. 1980) as well as to remove
sooty blotch from oranges (Vanderplank. 1945) and apples
(Hendrix. 1991).

In the United States. chlorine and hypochlorites are acceptable for
use in food processing and for bottled water as prescribed by the 1958
amendment to the Federal Food. Drug and Cosmetic Act of 1938 (FD&C
Act). This amendment allows for the continuing use of generally
recognized as safe (GRAS) substances that were commonly used in the
United States before 1958.

(1!) Ozone

The ability of ozone to disinfect polluted water has been
recognized for many decades. and has become an integral part of many
water treatment facilities around the world. The most common
applications of ozone are for disinfection by-product control and
biological stabilization. or minimization of the microbiological growth
potential of the water (Brink et al.. 1990).

Manifold possibilities for using ozone in the food industry and
agriculture are also possible due to the bactericidal and germicidal
activity of ozone. as well as its spore killing abilities (Horvath et al..

1985). Utilization of these properties has made ozone suitable for
increasing the storage life of perishable foods in refrigerated premises.
This practice first started in Europe in the early 1900s. where ozone is
used in the sterilization of air entering the storage room. During
storage. ozone exerts a three-fold effect by destroying the
microorganisms. oxidizing the odors and affecting the processes of
metabolism. Fruits and foodstuffs exposed to ozone can undergo
changes in its metabolism by inactivating their metabolic products. At
the same time it reacts with other materials present that can be
oxidized and thereby it destroys fragrances and odors (Horvath et al..
1985).

Although few publications or research reports have been made
available. the use of ozone is increasing in several major cold storage
plants in Europe. and even in the us. The storage life of fruits.
vegetables. and meats have been shown to increase when kept in an
atmosphere of ozone gas (Horvath et al.. 1985). Other successful
applications of ozone include uses in the beverage and milk industry.

 

 

Era-7. 1.0“

MATERIALS AND MODS

MATERIALS
A. Apple Suples

Mature Golden Delicious apples were harvested from the Botany
Research Field Laboratory at Michigan State University. East Lansing.
one day alter the last pesticide application. The fruits were hand picked
randomly from various regions of the treated trees. thoroughly mixed.
and representative samples of 8-9 fruits were set aside for each
replication. The samples were stored at -20‘C for approximately 10 days
until they were prepared for residue analysis.

B. Reagents
(I) Solvents
All organic solvents used for preparation of pesticide stock

solutions. in sample extraction. cleanup and high performance liquid
chromatography (HPLC) were distilled-in-glass grade. Acetone and

27

methylene chloride were obtained from Mallinckrodt. Co. (Paris. KY) and
hexane and acetonitrile were obtained from EM Science. Inc.

(Gibbstown. NJ).

(I!) Chemicals

Azinphos-methyl and captan standards were obtained from
AccuStandard. Inc. (New Haven. CT). Formetanate-HCI standard was
obtained from Chem Services. Inc. (West Chester. PA). The stock
solutions of azinphos-methyl and captan were prepared in hexane at a
concentration of 50 ug/ 100 ml. while formetanate-H01 was prepared in
acetonitrile at a concentration of 50 ug/ 100 ml. The standards were
protected from light and stored in a refrigerator.

Chlorine solutions at 50 and 500 [lg/ml were prepared from
calcium hypochlorite (Mallinckrodt. Co.. Paris. KY) as a source of
chlorine. Sodium thiosulfate. sodium sulfate. potassium iodide.
potassium indigo tiisulfonate. sulfuric acid and hydrochloric acid were

all reagent grade.

C. Glassware

All glassware was thoroughly washed with detergent and warm
water then rinsed with distilled water. The glassware was then rinsed

29

twice with acetone and hexane before being placed in an oven overnight

before use.

METHODS

A. Study on Degradation of Pesticides In Solution

(I) Sample Preparation

Laboratory studies were conducted in a model system to determine
the effects of: (1) Calcium hypochlorite at two concentrations (50 and
500 ppm) and Ozone (0.25 ppm): (11) three pH's (4.5-4.8. 7.0. 10.7); and
(iii) 2 temperatures [ambient (21°C) and elevated (44°C)] on each of the
three pesticide over a 30 minute period. There were three replications
per treatment. Aqueous solutions were unbuffered for the control and
ozone treatments and buffered (0.2 M citrate-phosphate) for the chlorine
treatments at pH 4.5. Aqueous solutions buffered at pH 7 .0 (0.2 M
sodium phosphate) and pH 10.7 (0.2 M carbonate-bicarbonate) were
also prepared. The pH values were selected so as to aid in
understanding the degradation behavior of the 3 pesticides in acidic.
neutral and alkaline medium. Degradation of the pesticides was studied
over a 30 minute period because the typical dip time for apples in a
commercial plant is 1 0- 15 minutes and would rarely exceed 30 minutes.
Temperatures of 2111°C and 44: 1°C were maintained in a water bath.

 

 

For the chlorination study. an appropriate amount of calcium
hypochlorite stock solution (5000 ppm) was added to each pH solution
to bring the final chlorine concentration to 50 or 500 ppm. Each pH
solution (pH 4.5. 7.0 and 10.7) was spiked with 4 m1 of the pesticide
stock solution (500 ppm) to give a final concentration of 2 ppm. Total
available chlorine was determined by sodium thiosulfate titration
method (Standard Methods for Examination of Water and Wastewater.
1987) before and after each sampling run. The 1 L sample solution was
placed in a 2 L glass beaker with a magnetic stirrer to ensure thorough
mixing. A 40 m1 aliquot of the sample was transferred at 0. 5. 15 and 30
minutes intervals into 200 ml French square glass bottles. A 0.5% 0.1M
sodium thiosulfate solution (Segall. 1968) and 40ml methylene chloride
were immediately added to the samples to quenched the reaction.
Approximately one minute clasped between transfering the sample to the
bottle and the quenching of the reaction. The samples were stored at
-20°C for subsequent pesticide residue analysis.

For the ozonation study. 1 L of sample solution was pumped from
a 2 L glass beaker through a Lifex EV 200 ozone water system (Lifex
Corporation. Birmingham. MI) using a Variostatic pump (Manostat. NY .
NY) at a flow rate of 1.4-1.5 ml/minutes (Figure 7). The solution was
recirculated during the entire sampling period and 40 ml aliquots were
pipetted from the glass beaker at 0. 5. 15 and 30 minute intervals into
200 m1 French square glass bottles. 40ml methylene chloride was
immediately added to the sample to quenched the reaction.
Approximately one minute then clasped between transfering the sample
to the bottle and the quenching of the reaction. Ozone concentration in

 

 

31

the solution was monitored before and after the sampling period using
the indigo colorimetric method (Standard Methods for the Examination
of Water and Wastewater. 1987). The samples were stored at -20°C for

subsequent pesticide residue analysis.

Lifex
Ozone Water Inlet Hm Variostatic
System Pump
Outlet Hose
Sampling Bucket

Figure 7: Schematic Diagram of Ozone Treatment

 

 

 

 

(I!) Chlorine Determination

Total residual chlorine was measured using the iodometric
method. Ten ml and 100 ml samples from the 500 ppm and 50 ppm
chlorine sample solution. respectively. were pipetted to Erlenmeyer
flasks containing 5 ml acetic acid and 1 gram potassium iodide. The

 

stirred samples were titrated with 0.01 N sodium thiosulfate. Na25203.

until the endpoints were reached.
The total residual C12 was determined using the formula:

mg ClzlL = [(A :I: B) x N x 35450] / ml of sample

where A was the amount Na28203 titrated for the sample (in mi). B was
the amount Na28203 titrated for the blank (in mi) and N was the
normality of Na28203 (0.01 N).

(111) Ozone Determination

Ozone detection and monitoring were performed using the indigo
colorimetric method as described in Standard Methods for the
Examination of Water and Wastewater (1987 ). All reagents were
prepared just prior to use. The ozone concentration was monitored
before and after each sampling run. The ozonated water was collected
directly from the outlet hose leading from the ozonator into a 100 ml
volumetric flask containing 10 ml of the indigo reagent to minimize loss
of ozone. A separate volumetric flask was filled with distilled water
containing 10 ml indigo reagent to serve as a blank. The solutions were
mixed thoroughly and the absorbance of each solution was immediately
measured at 600 nm in a 10 cm cell. A Spectronic- 70 spectrophotometer
(Milton Roy Co.. Rochester. NY) was used to monitor the change in
amorbanee.

 

 

Pu

The concentration of ozone. in mg/ L. was calculated using the

formula:
mgOa/L = (lOOxAA)/(fxbe)

where AA is the difference in absorbance between sample and blank
solution. b is the path length (10 cm). V is the volume of the sample
(90 ml). and f is a constant of 0.42.

(IV) pH Determination

The pH of the sample solutions were determined in duplicate
using a pH meter model 601A (Corning Glass Works. Medfield. MA)
before and after each 30 minutes sampling period to ensure the pH of
the solution did not deviate from the desired pH conditions. Appendix I
shows the pH readings of samples before and afier each sampling period.

B. Studies On Fresh and Processed Apples

(I) Pesticide Application and Spray Schedule

Golden Delicious apples were grown at the Botany Research Field

Laboratory at Michigan State University in East Lansing. Maintenance

sprays of pesticides were applied throughout the growing season. and a
final application of guthion". captan and carzolG at 5X the

 

Table 2 : 1994 Spray Schedule for Golden Delicious Apples

 

 

Dates Chemical Formulation Rate Purpose
April 30 Polyram 80DF 2.4 lbs IA maintenance spray
Rubigan lEC 0.1 lbs IA
Spray Oil 6E 2%I 1.691
May 4 Asana XL 0.66EC 0.04 lbs IA maintenance spray
May 10 Polyram 80DF 2.4 lbsI A maintenance spray
Rubigan lEC 0.07 lbs IA
May 12 Streptomycin 17% 0.34 lbs IA maintenance spray
May 18 Streptomycin 17% 0.34 lbs IA maintenance spray
May 19 Polyram 80DF 2.4 lbs I A maintenance spray
Rubigan IEC 0.1 lbs/A
May 23 Myeoshield 17% 0.68 lbs IA maintenance spray
May 27 Guthion 50W 0.75 lbs IA maintenance spray
Polyram 80DF 2.4 lbs IA
Rubigan lEC 0.07 lbs/A
June 9 Captan 50W 9 lbs/A maintenance spray
Guthion 50W 0.75 lbs/A
June 16 Captan 50W 91bs/A maintenance spray
June 23 Captan 50W 9 lbs IA maintenance spray
Guthion 50W 0.75 lbs IA
July 11 Guthion 50W 0.75 lbs IA maintenance spray
July 28 Guthion 50W 0.75 lbs/A maintenance spray
August 17 Captan 50W 9 lbs/A maintenance spray
Guthion 50W 0. 75 lbs/A
October 3 Captan 50W 2 lbs IA treatment spray
Carzol 9281’ 1.25 lbs IA
Guthion 50W 6 lbs/A

 

mm: chber4. 1994

recommended label rates were applied just before harvest. Table 2
shows the spray schedule for 1994.

Pesticides were applied with an airblast sprayer at 80 gallons/ acre
and 300 psi. For the final application. all three products (Captan 50W.
Carzol 92$P and Guthion 50W) were tank mixed and applied as a single
application. The apples were harvested by hand the following day (1 day
PHI) to ensure the maximum amount of residue on the fruits.

(II) Wash Treatments

While the laboratory model study attempted to show the
degradation patterns of the three pesticides in aqueous solution. apple
fruits spiked with the three pesticides were used to determine the
effectiveness of chlorine and ozone dip washes on the removal and
degradation of the pesticides residues found on the actual fruits. Eight
apples were used per replication (3 replications per treatment) and
placed in a 15 L bucket containing 5 L of water. The five treatments
were: (1) No wash. (2) Water wash. (3) Ozone wash @ 0.25 ppm.
(4) Chlorine wash @ 50 ppm. and (5) Chlorine wash @ 500 ppm. The
apples were agitated every minute to maximize contact between the
water and the surface of the apples. The temperature. pH. chlorine and
ozone concentration were monitored before and after each wash
treatment (Appendix II).

A preliminary study was carried out to determine the appropriate
dip time that would be sufiicient for an effective wash. The preliminary

study utilized 5. 10 and 15 minute dip times for the 5 treatments with
no replications. These three dip times were determined to be the typical
range for apples in a commercial facility. A 15 minute dip time was
subsequently chosen for the actual study. All 5 treatments were used
for the apple washes with three replications per treatment.

(111) Sample Preparation

After the wash treatments. the eight apples in each replication
were divided into two batches. One batch (4 fruits) was chopped in a
Horbart food chopper (Hobart MFG. Co.. Troy. OH) and thoroughly
mixed to ensure homogeneity. The chopped apples were transferred into
plastic Ziplock bags. weighed. and stored at -20°C. These samples were
used for analysis of pesticides on and in the unprocessed apple fruits.

The remaining 4 apples were processed into apple sauce. The
apples were processed at the Fruit and Vegetable Processing Laboratory.
Department of Food Science and Human Nutrition. Michigan State
University. East Lansing. MI. The apples were first sliced with a Sunkist
slicer and subsequently blanched in a steam blancher for 10 minutes at
approximately 1 10°C. Once the apples were cooked. they were passed
through a Langsencamp finisher with a 0.033-0.045 inch screen to
remove coarse fibers. seeds. stems. and peel particles. The applesauce
samples were transferred into plastic Ziplock bags immediately alter
finishing. weighed and stored at -20°C for residue analysis.

37

The water used for the wash treatments was saved and 400 mls
from each wash were pipetted into clean 8 oz. French square glass
bottles. Analysis of the wash water was carried out to determine the
amount of pesticides that were washed off the fruits and did not
undergo degradation either on the fruits or in solution. The samples

were stored at -20°C for residue analysis.

C. Pesticide Residue Analyses

(I) Extraction and Cleanup of Azinphos-methyl And Captan

Both azinphos-methyl and captan were extracted from water and
apple samples with a modification of the method described by Liang and
Lichtenstein (1976). Water samples from the model studies were
transferred quantitatively into 250 ml separatory funnels and extracted
with 3 x 30 ml of methylene chloride. The methylene chloride extracts
were collected through a glass funnel containing a glass wool plug and
anhydrous sodium sulfate into a turbo vap tube. The extract was
evaporated to dryness with a turbo vap evaporator. The dried sample
was flushed with a gentle stream of nitrogen gas to remove any traces of
methylene chloride which may interfere with the GC analysis. The
residue was redissolved in hexane and adjusted to an appropriate
volume for GC analysis.

Azinphos-methyl and captan were similarly extracted from
chopped apple and applesauce samples according to a modified method

of Liang and Lichtenstein (1976). Fifty grams of the apple sample were
blended with 100 m1 of acetone with a homogenizer for 3 minutes. The
sample was filtered under vacuum through a ceramic buchner funnel
with a Whatman #1 filter paper. The filter cake was rinsed twice with
10 m1 acetone and transferred to a separatory funnel. The filtrate was
extracted twice with 140 ml and 35 m1 of methylene chloride. and the
methylene chloride layers (lower layer) were collected through anhydrous
sodium sulfate in a turbo vap tube. The extract was evaporated to
dryness. redissolved in 50 ml of hexane. and transferred through a glass
funnel containing sodium sulfate to a separatory funnel. The turbo vap
tube was rinsed with an additional 50 ml of hexane and transferred to
the separatory funnel. The hexane was partitioned with 3 x 25 ml
portions of acetonitrile. The acetonitrile extracts were combined and
evaporated to complete dryness under vacuum at 40°C. The residue was
redissolved with hexane and brought to an appropriate volume for GO
analysis.

Extraction of the water samples from the wash treatments were
carried out according to the method used for the extraction of the water
samples from the model study. but in proportionally larger amounts.
The 100 m1 samples were extracted with 3 x 70 ml of methylene chloride.
After the methylene chloride extract was dried. the sample was
redissolved in 2 ml of hexane for GC analysis.

39

(II) Extraction and Cleanup of Formetanate-IICI

Extraction and cleanup of both the water and apple samples
containing formetanate-HCI was carried out according to modified
methods of Lawrence et al. (1981). Water samples from the model study
were transferred quantitatively into 250 ml separatory funnels. Ten ml of
saturated sodium chloride and 3 grams of sodium bicarbonate were
added to the samples to adjust the pH of the solution to pH 8-9. The
samples were immediately extracted with 3 x 30 ml of methylene
chloride. The methylene chloride layer was collected through a glass
funnel containing a glass wool plug and approximately 4 grams of
anhydrous sodium sulfate into a turboovap tube. The combined extract
was evaporated to dryness at 30°C in a Zymark Turbo vap evaporator
(Hopkin. MA) using nitrogen gas. The dried extract was then flushed
with a gentle stream of nitrogen gas to remove any traces of methylene
chloride that could interfere with the HPLC analysis. The residue was
redissolved in an appropriate volume of acetonitrile for HPLC analysis.

Formetanate-HCI was extracted from the chopped apples and
applesauce samples with acidified acetonitrile and cleaned up using
acidic and basic aqueous-organic partitioning. Twenty-five grams of the
chopped apple or applesauce were blended with 70 m1 of acetonitrile
containing 0.5% concentrated HCl. using a Pro-200 handheld
homogenizer (Pro Scientific. Inc.) for about 3-5 min. The mixture was
filtered with suction through a ceramic buchner funnel with a Whatman
#1 medium filter paper. The filtrate was transferred into a turbo vap
tube with an additional 20 ml of acidified acetonitrile. and evaporated to

an aqueous residue (approximately 3-4 ml). The aqueous residue was
transferred to a 250 m1 separatory funnel where 20 ml of 0.2 N sulfuric
acid and 40 ml of methylene chloride were added to it. The funnel was
shaken for 1 minute then allowed to separate into layers. The lower
organic layer was discarded. Five grams of sodium bicarbonate and
20 m1 of saturated sodium chloride were added to the aqueous solution
in the funnel and the solution was extracted with 3 x 60 ml of
methylene chloride. The methylene chloride layer was collected through
a glass funnel containing a glass wool plug and anhydrous sodium
sulfate into a turbo vap tube. The combined extract was evaporated to
dryness and flushed with a gentle stream of nitrogen gas to remove any
traces of methylene chloride. The residue was redissolved in an
appropriate volume of acetonitrile for HPLC analysis.

Extraction of the water samples from the wash treatments was
the same as the method used for extraction of water samples from the
model study. but in proportionally larger amounts. The 100 ml samples
were mixed with 25 m1 of NaCl. 5 grams of sodium bicarbonate and
extracted with 3 x 70 ml of methylene chloride. After the methylene
chloride extract was dried. the sample was redissolved in 2 ml of
acetonitrile for HPLC analysis.

D. Recovery Studies

Recovery studies for azinphos-methyl. captan and formetanate-
HCl were carried out by spiking water and apple samples with 0.5 ppm

 

41

and 5.0 ppm of the respective pesticide standards. Both the water and
apple samples were extracted as described above in the extraction and
cleanup methods for the three pesticides.

E. Chromatographic Analyses

The final extracts of captan and azinphos-methyl were dissolved
in hexane. while formetanate-H01 was dissolved in acetonitrile in
known volumes and subsequently analyzed using either the GC or

HPLC.

(I) Azinphos-methyi (GuthionO)

Residues of this pesticide were detected by a Hewlett Packard
Series II 5890 gas chromatograph equipped with a nitrogen phosphorus
detector (NPD). The GC was equipped with a DB—5 fused silica capillary
column (30 m x 0.25 mm id) with a film thickness of 0.25 micron (J .W.
Scientific. Folsom. CA). The oven temperature was programmed
isothermally at 230°C. while the injector and detector temperatures were
set at 250°C and 250°C. respectively. The injection volume was 3 ,ul and
sammes were injected with a HP 76 73 automatic sampler linked to the
GC. Integration was carried out with HP Chemstation software
interfaced to the GC.

 

 

 

 

(II) Captan

Residues of this pesticide were detected by a Hewlett Packard 5890
Series II gas chromatograph equipped with a Ni63 electron capture
detector (ECD). The GC was equipped with a DB-5 fused capillary (60 m
x 0.25 mm i.d.) with a film thickness of 0.25 micron (J.W. Scientific.
Folsom. CA). The oven temperature was programmed isothermally at
180°C. while the injector and detector temperatures were 220°C and
275°C respectively. The injection volume was 2 ul. Integration was
carried out with HP Chemstation software interfaced to the GC.

Gas chromatography-mass spectrometry was used to confirm the
presence of oxidative degradation products from the reaction of calcium
hypochlorite with captan. Degradation products from oxidation
reactions of captan with ozone were not analyzed. The Delsi Di 700 gas
chromatograph was equipped with a capillary column DB- 1 (30m x 0.25
mm i.d.) with a film thickness of 0.25 micron (J .W. Scientific.
Gibbstown. NJ). The GC was programmed in a splitless mode with an
initial oven temperature set at 40°C for 1 minute. and then raised to
180°C for 40 minutes at a rate of 5°C per minute. The injector
temperature was set at 210°C. and the heated interface temperature
between the GC and the mass spectrometer was maintained at 250°C.
The Nermag RIO-10C mass spectrometer was set in an electron
ionization (El). positive ion mode. with the following parameters:
primary pressure = 1.3 x 10'3 Torr: secondary pressure = 1.6 x 10-7
Torr: IE = 0.208 amps: e" = 70.6 eV: focal = -0.01 : ions = -96: external =

 

 

16.3 and multiplier = -3.02. The quadrapoles were scanned from 50 to

500 u at a rate of 2 smns per second.

(III) Formetanate-HCI (CarzolQ)

Formetanate-HCI residues were analyzed by HPLC. A Milton Roy
Spectrophotometer 3 100 variable wavelength UV-visible detector. set at a
wavelength of 254 n.m. (maximum absorbance for formetanate). 0.05
absorbance unit full scale (AUFS). and 0.1 response time was used. The

column used was a Brownlee Spheri-S. RP-18 (5 micron. 4.6 mm i.d. x

220 mm). The mobile phase was 35% acetonitrile in 0.01 N NH4H2PO4
(pH 8) filtered through a 0.45 pm filter and degassed prior to use. An
Anspec 3 l 13 HPLC pump was used for solvent delivery at a flow rate of 2
ml/ minutes. After the system was stabilized (about 30 minutes from
initial warm-up). 50 p1 samples were injected via a Rheodyne syringe-
loop injector (50 pl loop) for analysis. Integration was carried out using
Waters 840 data and chromatography control station software.

F. Calculation of Pesticide Residue Concentration

Pesticide residue concentrations in solution and in fresh or
processed apples were calculated based on the area of the integrated
peaks of the samples compared with known concentrations of analytical
standard of the respective pesticide. Standard curves of the pesticide
standards were plotted and least square linear regression was obtained

 

using a Microsoft Excel (Microsoft Corporation. Redmond. WA) software.
Appendix II - IV show examples of standard curves for each of the three
pesticide standards of known concentration between 0.5-10 ppm.

The concentration of each pesticide residue in solution or in the
apple fruit or sauce was calculated based on the following formula:
(a) Residues in solution in ug/ m1 =-

C0 c. of sam e based on s (1. curve ml x Vol. of final extract m1
Volume of sample analyzed (40 ml) x % Recovery

(b) Residues in apple fruit or sauce in ,ugI g of fruit =

Cone. of sample based on std. curve (ggIml) x Vol. of final extract (ml)
Weight of sample analyzed (g) x % Recovery

G. Statistical Analyses

In the model studies. the experiments were designed as a split plot
(treatments x pH x temperature) randomized model. split across the 30
minutes duration of the treatment (Gill. 1986). The study on effect of
wash treatments on dissipation of pesticides on apple fruits was
designed as a two factor (treatments x replication) and (treatments x
product) randomized model. All determinations for both studies were
made in triplicate. Mean. standard errors. mean square errors. two
factor ANOVA. correlation and interaction of main effects were
calculated using SuperANOVA computer software (Abacus Corporation.
Inc.. Berkeley. CA). Bonferroni's t was used to determine significant
differences between treatment means.

RESULTS AND DISCUSSION

A. Model Study

(I) Chlorine Monitoring

Chlorine. as calcium hypochlorite. was prepared as a stock
solution of 5000 ppm. The stock solution was diluted in proportionate
amounts to obtain a final concentration of 50 or 500 ppm in the model
solutions. The chlorine concentration of the stock solution was
determined to be 5012 :t 8 ppm. The chlorine concentration of each
sample solution was monitored. and determined to be within :2 ppm
(for 50 ppm) and :10 ppm (for 500 ppm) of the intended final

concentrations.

(II) Ozone Monitoring

Water ozonated by circulating water through the Lifex® Ozone
system was monitored for ozone concentration in the water. The
concentration of ozone measured directly from the hose extending from
the machine was 0.25 1 ppm. while the concentration of ozone in the

 

 

 

Table 3 : Ozone Output In Water From Lifex Ozone System

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Sample! Ozonefi'omhosempm) Ozonehomhucketurpm)

1 0.315 0.078

2 0.323 0.157

3 0.246 0.043

4 0.204 0.056

5 0.209 0.1 10

6 0.188 0.094

7 0.220 0.083

8 0.22 1 0.080

9 0.214 0.065

10 0.372 0.068
Mean : 0.251 0.083
Standard Dev. : 0.062 0.032

 

1.Thetemperatureofthewaterwas21 t 1.2°C

 

 

 

47

water sampled from the bucket was determined to be 0.083 ppm
(Table 3). The ozone concentrations were an average of 10 samples. The
difference in the concentration of ozone in the bucket and directly from
the hose indicated that ozone in solution was relatively unstable. Katz
(1980) indicated that ozone in solution was unstable. having a half-life
of about 20-30 minutes in distilled water at 21°C. Also. the half-life of

ozone in water is shortened considerably at higher temperatures.

(III) Degradation of Azinphos-methyl (Guthion®)

In the GC analysis. azinphos-methyl appeared as a single sharp
peak at a retention time of 9.2 minutes. Figure 8 shows a typical
chromatogram of an azinphos-methyl standard at a concentration of
1 ppm. while Figure 9 shows an example of a chromatogram of a sample
in a pH 7 .0 solution ozonated at 44°C and sampled at 5 minutes. The
standard curve shown in Appendix III was representative of the standard
curves used to calculated azinphos-methyl concentration in the sample
solutions. The correlation coefficients (R2) for linear regression of the
standard curves were between 0.903 and 0.998. showing that the
response was linear over the concentration range of 0.5- 10 ppm. The
percent recovery of azinphos-methyl in solution spiked with 0.5 ppm
and 5 ppm pesticide standard was 91.3 i: 7.09%.

Azinphos-methyl was stable in pH 4.5 and 7 .0 solutions at both
21°C and 44°C (Figure 10 and 11) with very little degradation of the
pesticide due to hydrolysis. Between 96-100% (21°C) and 93-96% (44°C)

 

 

 

 

 

 

 

 

 

48
EE
1.41-e4.j g
1 .2e4o:
1 .Oe4—
8000—
6000-4
fl
0 12

Figure 8 : GC Chromatogram Of An Azinphos-methyl Standard

1- 1.0 ppm
2- Rt = 9.2 mins

 

49

9.2

 

 

 

 

O 14-

Figure 9 : GC Chromatogram Of An Azinphos-methyl Sample
1- ozonation in pH 7.0 at 21°C.: time = 5 minutes
2- Rt = 9.2 mins

 

residual pesticide remained after 31 minutes. Azinphos-methyl was
relatively less stable at pH 10.7. with about 87% remaining after 6
minutes and 5 1% remaining after 31 minutes in solution at ambient
temperature. At 44°C. azinphos-methyl was even less stable. with about
76% remaining after 6 minutes and 43% after 31 minutes.

These results are in agreement with various studies that have
been carried out to show the behavior of azinphos-methyl in aqueous
solutions over a wide range of pH and temperature. Faust and Gomaa
(1972) have shown that azinphos-methyl was less stable under basic
than acidic conditions. The half-lives of azinphos-methyl in buffered
solutions at pH 1. 3. 5. 6. 7 and 9 maintained at 21°C were 24. 9. 8.9.
7.5. 4.8 and 0.6 hours. respectively. In another study conducted at
temperatures of 30°C and 50°C. the stability of azinphos-methyl was
shown to be pH and temperature-dependent (Flint et al.. 1970). In
buffers at pH 5. 7 and 9 half-life values were 17. 10 and 0.5 days
respectively at 30°C and 1.8. 1.3 and 0.08 days at 50°C.

Degradation of azinphos-methyl by ozone was greatest at pH 4.5
and decreased with increasing pH (Figure 10 and 1 1). Between 17-39%
of azinphos-methyl remained after 31 minutes at both 21°C and 44°C
for all three pH treatments. As shown in Figure 10. about 60 and 85%
of the initial amount was degraded by ozone treatment at 21°C sampled
at 5 and 30 minutes. respectively. Compared to the control. it appeared
that most of the azinphos-methyl degradation at the low pH was due
mainly to ozonation and little due to hydrolysis. Degradation of
azinphos-methyl at pH 7.0 at both 21°C and 44°C was significantly
different compared to pH 4.5. except at t=16 minutes. The ozone

 

51

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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52

treatment at pH 10.7 was the least effective at both 21°C and 44°C.
Increased temperatures did not significantly (p < 0.05) increase the rate
of degradation of azinphos-methyl.

Kearney et al. (1988) found that an increase in pH decreases the
stability of ozone in water. due to the catalytic effect of hydroxyl ions on
the O3 decomposition process. As such. pH increases reduce the effect
of ozone on the degradation of azinphos-methyl. while the effect of
hydrolysis increases.

In 50 ppm hypochlorite solution. azinphos-methyl was completely
degraded at pH 4.5 at both 21°C and 44°C (Figure 12 and 13). At pH
7.0. almost 85% of the initial amount of azinphos-methyl was degraded
alter only 6 minutes in a 50 ppm hypochlorite solution (Figure 12). The
50 ppm chlorine treatment at pH 10.7 was the least effective. where its
degradation was only about 15% and 56% after 6 and 31 minutes
treatment. respectively. Elevated temperature increased the degradation
of azinphos-methyl at both pH 7.0 and 10.7 (Figure 13). At both pH's.
higher temperature increased the degradation of azinphos-methyl by
about 10% during the entire sampling period.

Chlorination at 500 ppm significantly (p < 0.05) increased the rate
of degradation of azinphos-methyl in all three pH treatments and at
both temperatures. Again. the most effective treatment was
chlorination at 500 ppm in the pH 4.5 solution. while pH 10.7 was the
least effective treatment (Figure 12 and 13). Also. increased
temperatures completely degraded azinphos-methyl sampled at 5
minutes in 500 ppm hypochlorite at both pH 4.5 and 7.0. Only about
4% of the pesticide remained at pH 10.7 after 31 minutes (Figure 13).

417'"

 

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The percent of HOCI is greatest at low pH and decreases as the pH
and temperature of a solution increase (Wei et al.. 1985). Under these
circumstances the oxidation reaction of HOCI with azinphos-methyl
should be greatest at pH 4.5 and least at pH 10.7. as was observed in
the present study.

Also the organophosphate insecticide used in this experiment
contains a phosphoric acid ester linkage that is relatively less stable
and more susceptible to oxidation in a strong oxidizing medium. This
was shown to be the case because of the strong correlation between
the rate of azinphos-methyl degradation and increasing hypochlorite
concentration.

In general. all treatments were significantly difierent (p < 0.05),
with the 500 ppm chlorine treatment being the most effective. Also.
there were significant differences between the pH and temperature
treatments. showing that degradation of azinphos-methyl is dependent
upon various environmental factors such as pH and temperature.

(1V) Degradation of Captan

In the GC analysis. captan appeared as a sharp peak with a
retention of 46 minutes. Figure 1 4 shows a typical chromatogram of a
captan standard at a concentration of 1 ppm. and Figure 15 shows a
typical chromatogram of a sample solution sampled after 5 minutes in a
pH 7 .0 solution treated with 50 ppm calcium hypochlorite at 21°C. The

retention time is considerably long due to the length of

 

 

 

 

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5500-
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5000—
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Figure 14 : GC Chromatogram Of A Captan Standard

1.1pm
2-Rt=46mins

 

 

 

 

5500-
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Figure 15 : GC Chromatogram Of A Captan Sample
1- chlorine 50 ppm in pH 7.0 at 21°C; sampling time = 5 mins
2- Rt = 46 mins

 

57

the column used (60 m) as well as the low oven temperature (180°C).
Setting the oven temperature above 200°C produced a significantly large
second peak at 42 minutes. By lowering the temperature to 180°C. the
second peak was eliminated up to 2.5 ppm. This second peak was
visible at 5 and 10 ppm. but was not large enough to significantly affect
the detection of captan. An example of a standard curve for captan
standards between 0.5- 10 ppm is shown in Appendix IV. The correlation
coefficients (R2) for the linear regression of the curves were between
0.975 and 1.0. showing that the response was linear under the above
conditions over the concentration range of 0.5- 10 ppm. The recovery of
captan spiked with 0.5 and 5 ppm of the standard was 105.9 2 1.71%.

Wolfe et al. (1976) had reported the appearance of a second peak
in the chromatogram along with the captan peak above 200°C. They
assumed that the two peaks were a result of captan decomposing at
such high temperatures. In their work. they used a short column (2 ft)
and a column temperature of 160°C to eliminate the anomalous peak.

The degradation of captan (2 ppm) in solutions due to hydrolysis.
ozonation and chlorination is shown in Figure 16-19. Due to the
insolubility of captan in water. captan was added to the aqueous
solution with a carrier solvent (acetonitrile). Wolfe et al. (1976) reported
that this was necessary because the rate of solution of captan in water
was slow compared to the rate of hydrolysis. and that the addition of
1% organic solvent did not affect the rate constant when compared with
pure water.

At 21°C. captan degradation due solely to hydrolysis was less
significant at pH 4.5 and 7.0. than at pH 10.7 (Figure 16). Captan was

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59

completely unstable at pH 10.7 in both the control and ozonated
samples. even when sampled at 0 minute. After 6 minutes of ozone
treatment at ambient temperature. only 7.3% of captan remained at pH
4.5 and levels were non detectable at pH 7 .0. Elevated temperature
(44°C) accelerated the degradation of captan in solution (figure 17). In
pH 4.5 and 7 .0 solutions. about 47% and 42% of captan remained for
approximately 31 minutes in solution. respectively. With ozonation.
captan was completely degraded at pH 4.5. 7 .0 and 10.7 when sampled
at 5 minutes.

In the ozonation study. the degradation of captan at 21°C and
44°C was significantly different (p < 0.05). The rate of degradation was
significantly greater at the higher temperature (44°C) than at the lower
temperature (2 1 °C).

Various investigators have reported the relative instability of
captan in solution. Melnikov (1971) reported that captan was hydrolyzed
by moisture and the reaction was accelerated by alkali. Von Ri‘rmker and
Horay (1972) have presented data showing that the half-life of captan
decreased with increasing pH at 20°C: at pH 4.0. 4 hours and at pH 10.
<2 minutes. The half-life also decreased when the temperature was
increased to 40°C. Wolfe et al. (1976) reported that the reaction of
captan is independent of pH over the pH range 2-6. and pH dependent
above pH 7.

The effect of chlorine treatment on the degradation of captan at
both ambient and elevated temperatures was significantly greater as
compared to the control (hydrolysis only). Captan was unstable in
chlorinated solution. Figure l 8 shows that captan in a 50 ppm chlorine

 

 

 

 

 

 

 

 

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61

solution was most stable at pH 7 .0 and very unstable at pH 4.5 and
10.7. Almost 80% of the pesticide was degraded in a pH 4.5 solution
when sampled at 0 minute. with only about 3% remaining when
sampled at 5 minutes. Almost all the pesticide was degraded at pH 7 .0
and 10.7. However. the degradation of captan at pH 10.7 was due
almost entirely to hydrolysis and not as a result of chlorine treatment.
On the contrary. almost all the pesticide in the pH 4.5 solutions was
degraded due to chlorination and little due to hydrolysis. This was
evident by comparing the chlorine treatments with the control
treatments. Captan was completely degraded in 50 ppm chlorine
solutions at all three pH‘s (Figure 18 and 19).

Temperature significantly influenced the effect of chlorination on
captan in all treatments. A 20-30% increase was observed in the
degradation of captan at the higher temperature between the 5 to 30
minutes treatment interval at pH 7 .0 (Figure 18 and 19). These results
were consistent with those reported in earlier studies showing similar
increase in the degradation rate of captan when temperature was
increased. Frank et al. (1983) reported the half-life of captan in water
at pH 8.5 was less than 1 hour at 21°C and 13 hours at 5°C. while at
pH 5.5 the halfolives were 13 hours at 21°C and 208 hours at 5°C.

In general. the various treatments (control. ozonation and
chlorination @ 50 and 500 ppm) were significantly different (p < 0.05).
There was also a significant difference (p < 0.05) among the pH
treatments (4.5. 7.0 and 10.7).

Mass spectrometric analysis showed that the major products of
degradation found in the solution treated with calcium hypochlorite

were mainly oxidation products. and that there was no evidence of any
chlorinated by-products. This was based on the isotope molecular ion
patterns for all degradation products.

(V) Degradation of Formetanate-HCI (Carzol!)

In the HPLC analysis of formetanate-HG]. formetanate appeared
as a relatively broad peak with a retention time of 3.4 minutes (Figure
20 and 21). There appeared to be good separation between the peak of
interest and the solvent peak. Dissolving the final extract in water as
described by Lawrence et al. (1981) caused difficulty in obtaining a
consistent peak due to the appearance of a second peak near the solvent
peak on occasion. This inconsistency was probably attributed to the
fact that formetanate-HCI changed between the weakly acidic form and
its basic form. This could be due to the fluctuation of the pH of the
water. Dissolving the final extract in acetonitrile and using a pH 8.0
buffered mobile phase provided consistent separation of the formetanate
form.

Standard curves for formetanate standards between 0.5- 10 ppm
were plotted. and a typical curve is shown in Appendix V. The
correlation coefiicients (R2) for the linear regression of the curves were
between 0.95 and 1.0. This showed that the response was linear at the
specified conditions over the concentration range of 0.5-10 ppm. The
average recovery for formetanate-HCI. spiked at 0.5 and 5 ppm in
solution. was 103.2 :9: 6.19%.

 

15

18

 

 

 

 

 

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an
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Figure 20 : HPLC Chromatogram Of A Formetanate-HCI
Standard

1- 1.0 ppm
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Figure 2 1 : HPLC Chromatogram Of A Formetanate-HCI

 

Sample
1- chlorine 50 ppm in pH 7.0 at 21°C: sampling time = 10 mins
2- Rt = 3.46 mins

Due to the chemical structure of formetanate-HC] and the form it
takes in different pH medium. it appeared that the acidic form was
relatively stable while its basic salt was unstable and subjected to both
hydrolysis and chemical oxidation. Jenny and Kossmann (1978)
reported that formetanate-HCI hydrolyzes slowly in acid medium. and is
extremely susceptible to hydrolysis in neutral or basic medium
especially at higher temperatures.

The rate of degradation of formetanate-HO] due to hydrolysis
generally increased at higher pH and temperature. Formetanate-HCI
was relatively stable at low pH in its hydrochloride salt form.
Formetanate-HCI as formetanate was unstable and degraded rapidly at
alkaline pH (Figure 22 and 23). Almost 100% remained after 30 minutes
in solution at pH 4.5 and 7.0 and at both 21°C and 44°C. At pH 10.7.
only 14.9% remained after 6 minutes in solution at 21°C. and it was
non detectable after 6 minutes at 44°C. Lawrence et al. (1981) reported
that formetanate at 1 ppm in aqueous solution at pH 8.0 decomposed
by 20% after 1 day at room temperature. There are no available data in
the literature on the degradation of formetanate-H01 at pH 10 and
above.

Figure 22 and 23 show ozonation at pH 4.5 was the least effective.
Almost 50% of formetanate-H01 remained after 31 minutes of ozone
treatment at both 21°C and 44°C. At pH 7.0. about 50-60% and 3-23%
remained after 6 and 31 minutes of ozonation at 21°C and 44°C
respectively. Higher temperature did not significantly (p < 0.05)
accelerate degradation of the pesticides by ozonation. Although

formetanate-H01 was degraded to non detectable levels at pH 10.7 at

 

 

 

 

 

 

 

 

 

 

 

 

 

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both temperatures when treated with ozone. most of the degradation
was due to hydrolysis rather than oxidation by ozone.

Formetanate-HCI in chlorinated solution was relatively stable at
low pH. and extremely unstable in its basic form at pH 10.7
(Figure 24 and 25). Formetanate-HCI was degraded by 80-100% in 50
and 500 ppm calcium hypochlorite at pH 10.7. However. this was due
mainly to hydrolysis rather than oxidation by the HOCl
(Figure 24 and 25). Elevated temperature significantly increased the
degradation of the pesticide in chlorinated water at pH 7.0. There was
no significant difference between the two temperature treatments at
pH 4.5. which indicated the relative stability of the pesticide in its acidic
form. Of the three treatments (ozone. 50 and 500 ppm HOCI).
chlorination at 500 ppm was the most effective treatment in the
degradation of formetanate-H01.

B. Study on Pesticide Dissipation In Fresh and Processed Apples

(1) Apple Processing

The apples were either prepared by chopping in a Hobart food
chopper or processed into a commercial type apple sauce. for analysis
on / in the fruit and in the sauce respectively. Appendix II shows raw
data for the various wash treatments such as temperature. pH. ozone or
chlorine concentration and the weight of the fruits before and after
preparation. The average yield of the apple sauce was 31.3 a: 1.66 %.

 

69

The low yield was a direct result of processing. where coarse fibers.
seeds. stems. and peel particles were removed to obtain the finished

apple sauce.

(II) Azinphos-methyl Residues In] On Apple Fruit And Sauce

The data presented in Table 4 and illustrated in Figure 26. show
the effects of the various wash treatments on reduction of
azinphos-methyl residue in/ on apple fruit and sauce. The total amount
of residue on the control unwashed fruit was determined to be 0.67 ppm
or 401 .78 pg. The established tolerance level for azinphos-methyl as
published in the Code of Federal Regulations. USA (1990) is 2.0 ppm.

Almost 53% of azinphos-methyl residue was removed from the
fruit with the water wash. Apples dipped in ozonated water reduced
residue levels by about 75%. Chlorine wash at 50 and 500 ppm removed
about 76% and 83% residue. respectively. The various wash treatments
significantly reduced residue levels as compared to the unwashed
samples. While there appeared to be a decrease in the amount of
azinphos-methyl removed from the water washed fruits to those washed
with either ozone or chlorine. there was no statistical difference between
treatment means (Bonferroni t test).

Processing apples into apple sauce significantly reduced the levels
of azinphos-methyl residue (Figure 26). About 96% of azinphos-methyl
was removed when the unwashed apples were processed into sauce.

Washing the apples followed by processing reduced the amount of

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residue by 98%. The amount of azinphos-methyl remaining in the sauce
from fruit washed with either ozonated or chlorinated water was
between 2-3%.

Studies have shown that the effect of processing can reduce
azinphos-methyl residues in fruits. Gunther et al. (1963) determined
that 7 1-94% of the azinphos-methyl on orange rind was removed by
normal washing procedures. In a study by El-Hadidi (1993) at Michigan
State University. the effects of washing/ grading of apples were shown to
reduce azinphos-methyl by 60%. Processing of apples into apple
products such as apple shoes. sauce and juice were also significantly
effective in reducing the pesticide residue levels to non-detectable
amounts in some and lower than those on fresh fruits in others.
Processing the apples into apple sauce reduced the amount of
azinphos-methyl from 174. l to 6.8 ppb or by 96%. The results from the
present study were all in agreement with those reported by
Gunther et al. (1963) and El-Hadidi (1993).

(III) Captan Residues In/ On Apple Fruit And Sauce

Figure 27 and Table 5 show the amount of captan residue in and
on apple fruits and in apple sauce after various wash treatments. The
amount of captan on the control apples (unwashed) was 0.488 ppm or
291.54 pg. This amount was well below the maximum tolerance level of
25 to 100 ppm established in the United States (CFR-US.1990).

 

 

considering the apples were harvested only one day after the last
pesticide application.

The effect of a simple water wash treatment reduced the amount
of captan by about 50%. Ozone wash removed approximately 72% of
captan. while the 50 and 500 ppm chlorine wash removed 66% and 77%
pesticides. respectively. There was a significant (p < 0.05) difference
between the unwashed and washed fruits. However. there was no
significant difference between the water wash and the ozone or chlorine
at 50 ppm wash treatments. Chlorine wash at 500 ppm was the most
effective treatment for captan removal.

Frank et al. (1983) reported that washing apples with water
removed 43% of the captan residue. The washing in that study involved
rinsing each apple with 500 ml of water at 25°C. The percent removal by
this method was in agreement with the results obtained in this study
for the water wash treatment. Hendrix (1991) reported that 0.42 ppm
captan remained on apples washed with water. while 500 ppm chlorine
dip for 5 minutes reduced residues to less than detectable levels. The
percent reduction of residue from the water wash to the 500 ppm
chlorine wash in this study was about 56% (from 0.255 to 0. 110 ppm).
In the study by Hendrix (1991). the apples were brushed in addition to
washing. while the apples in the present study were simply dipped in
water and agitated every minute during the 15 minute treatment.

Processing the apples into apple sauce significantly (p < 0.05)
reduced the amount of captan. Almost 97% was removed from the
unwashed fruits by processing. while 99% was removed after the fruits

were water washed and processed. No detectable amount of captan was

 

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found in the sauces that were first washed with ozonated or chlorinated
water.

The significant decrease (p < 0.05) in captan residue due to
processing could be due to the high heat and pressure generated during
the blanching of the apples. According to Worthing and Hance (1991).
the melting point of captan is 160-170°C. and it decomposes at or near
its melting point. Therefore. it would be expected that most of the
residual captan would be degraded during the blanching process where
temperature is maintained at 1 10°C for about 10 minutes.

Frank et al. (1983) reported that boiling the whole apple for 5
minutes or cooking the peeled and diced apple removed and/ or destroyed
70% to 98% of the residue. They also showed that the combination of
thorough washing and cooking gave almost 100% removal. Cooking
tomatoes for 15 minutes also reduced captan residues by 97 .7-98.9%
(El-Zemaity. 1988). Ritchey et al. (1984) reported that washing and
cooking strawberries for 5 minutes reduced captan by more than 95%.
All the studies indicated that a combination of washing and high
temperature treatment significantly reduced residues as was the case in
this study.

In general. there were significant differences (p < 0.05) between the
washed fruits compared to the unwashed fruits in terms of captan
reduction. However. there was no statistical difference at the 5% level
between the water wash apples and the ozone and 50 ppm chlorine
washed fruits. although there was a reduction in the residue levels.
Increasing the chlorine concentration to 500 ppm did significantly
increase the effectiveness of the chlorine wash. It is anticipated that

residue levels would be reduced considerably by the ozone treatment if
the concentration of ozone was increased above the 0.25 ppm that was

used in this study.

(IV) Formetanate-HCI Residues In/ On Apple Fruit And Sauce

The amount of formetanate-HCI found on/ in unwashed apples
was 392.23 ug or 0.657 ppm (Table 6). The maximum tolerance level for
formetanate-HCI in the US. is 3.0 ppm (CFR-US. 1990). Reduction in
residual formetanate-H01 was significantly (p < 0.05) influenced by the
effect of various wash treatments. There was significantly less residue
in the water washed apples than apples that were unwashed (Figure 28).
While water wash fruits reduced levels by 23%. the ozone and chlorine
washes reduced formetanate-HCI by 46-58%. The 500 ppm chlorine
wash was the most efiecfive treatment. However. there appeared to be
no statistical difference between the three washes (ozone. 50 and 500
ppm chlorine) at the 5% level.

The reduction of formetanate-HCI by water wash was not as
effective as expected. Studies done by Iwata et al. (1985) and
Hadjidemetriou et al. (1985) showed that simple washing removed a
significant amount of the pesticide on the fruit. One possible
explanation could be that the pesticides were in the apple fruits rather
than on the surface. and would have not been completely washed off by
the water dip. El-Hadidi (1993) reported that residues on golden
delicious apples were found mainly in the fruits rather than on the

78

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surface. Of the total residues detected (90.7-122.1 ppb). 1.5-1.0 ppb
were detected on the fruit and 90.7-122.1 ppb were found in the fruit.

Processing of apples into sauce significantly (p < 0.05) reduced the
amount of formetanate-HG] (Figure 28). Unwashed apples that were
processed into sauce showed an 84.2% reduction in residue level.
Apples that were water washed and subsequently processed into sauce
reduced pesticide residue by 87.3%. Ozone and chlorine washed apples
processed into sauce reduced the pesticide by 91-96%. The 500 ppm
chlorine wash was the most effective treatment. while the ozone
treatment was more effective than the 50 ppm chlorine wash treatment.

In the study by El-Hadidi (1993). processing of apples into apple
products such as apple slices, sauce and juice were significantly effective
in reducing the pesticide residue levels to non-detectable amounts.

(V) Pesticide Residues In Wash Water

Table 7 shows the amount of the three pesticides that were
washed off the apples. The amount of azinphos-methyl. formetanate-
HCl and captan recovered in the water wash treatment was 420. 253
and 137 pg. respectively. There was significant reduction of the three
pesticides in the ozonated water wash treatment as compared to the
simple water wash (Figure 29). The reduction of the three pesticides
ranged between 29-42%. The 50 and 500 ppm chlorine wash treatment
resulted in significantly less pesticide residue in wash water as

compared to the water wash treatment. In the 50 ppm chlorine wash

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Figure 29

treatment. 76%. 93% and 96% of formetanate-HG]. captan and
azinphos-methyl were removed respectively as compared to the water
wash treatment. The 500 ppm chlorine wash removed 93% of
formetanate-H01 and all detectable levels of captan and
azinphos-methyl (i.e. 100%).

The ozone wash was not as effective as would be expected. In the
model studies, each of the three pesticides showed greater rates of
degradation in water at the various pH's and temperatures than in the
ozone wash treatment at similar pH's and temperatures. One possible
explanation could be that the ozone wash at 0.25 ppm was not as
effective due to its low concentration. instability in water. and the high
organic content in the wash water. The presence of organic materials
has been reported by Glaze (1987 ) to accelerate the decomposition of
ozone.

The results indicate that the ozone and chlorine wash treatments
were effective in reducing the amount of pesticide residues in the wash
water after the pesticides have been rinsed off the apples. This would
ensure that the wash water would be 'detoxified' before it is disposed of
as waste. This is an advantage in terms of reducing chemical waste and
ensuring the safe disposal of pesticide waste.

 

SUMMARY AND CONCLUSIONS

The objective of the present study was to determine the
effectiveness of chlorine and ozone as postharvest washes used in the
dissipation of pesticide residues in solution and on fresh and processed
apple fruits. A model study was conducted to determine the effects of
calcium hypochlorite (50 and 500 ppm) and ozone (0.25 ppm) at pH 4.5.
7.0. 10.7 and ambient (21°C) and elevated (44°C) temperatures on the
degradation of azinphos-methyl, captan and formetanate-H01 in
solution over a 30 minute period. Aqueous solutions were unbufiered at
pH 4.5-4.8 and buffered at pH 7.0 (0.2 M sodium phosphate) and pH 0
10.7 (0.2 M carbonate-bicarbonate). Samples from the model study were
analyzed for residues using either GC (captan and azinphos-methyl) or
HPLC ( formetanate-H01).

The rate of degradation of azinphos-methyl, captan and
formetanate-H01 due to hydrolysis generally increased at higher pH and
temperature. Degradation of azinphos -methyl by ozone was greatest at
pH 4.5 and decreased with increasing pH. Between 17-39% of
azinphos-methyl remained at both 21 and 44°C in all three pH
solutions when sampled at 30 minutes. Compared to the control. it
appeared that most of the azinphos-methyl degradation at the low pH
was due mainly to ozonation and little due to hydrolysis. Captan was
extremely unstable when treated with ozone. After 6 minutes in

ozonated water at 21°C. 7.3% and 0% (i.e. nondetectable levels) of
captan remained at pH 4.5 and 7.0. respectively. Captan was unstable
even at time zero at pH 10.7. Formetanate-HCI was relatively stable at
low pH in its hydrochloride salt form. As formetanate at alkaline pH. it
was unstable and degraded rapidly. In general, ozonation at high pH
was less effective due to the instability of ozone in solution as pH
increases. Elevated temperatures did not significantly accelerate
degradation of the pesticides by ozonation, except for captan.

Azinphos-methyl and captan were rapidly degraded in 50 & 500
ppm chlorine solutions at low pH. but degradation decreased at higher
pH. Formetanate-HCI was relatively stable at low pH in its
hydrochloride salt form. while its basic form as formetanate was
unstable. An increase in pH decreases the percent of HOCI. and
consequently its reactivity with the pesticides. Chlorination (50 and
500 ppm) at pH 4.5 and 7.0 decreased azinphos-methyl and captan by
80-100% after only 6 minutes. Formetanate-HCI was degraded by 80-
100% at 50 and 500 ppm chlorination at pH 10.7. However, this was
due mainly to hydrolysis rather than oxidation by HOCI. Elevated
temperature increased the degradation of the three pesticides in
chlorinated water. Chlorination at 500 ppm was the most effective
treatment in the degradation of all three pesticides.

Apples sprayed with the three pesticides were used to determine
the effectiveness of chlorine and ozone dip washes on the removal of the
pesticides on and in fresh and processed fruits. Eight apples were used
per replication (3 replications per treatment) and placed in a 15 L bucket
containing 5 L of water. The five treatments were: (1) No wash.

 

(2) Water wash. (3) Ozone wash @ 0.25 ppm. (4) Chlorine wash @
50 ppm. and (5) Chlorine wash @ 500 ppm. The apples were dipped for
15 minutes at ambient temperatures with constant agitation. The
apples were analyzed for pesticide residues on and in the whole fruit and
in apple sauce using either GO or HPLC.

The amount of pesticide residues found on the unwashed fruits
were well below the EPA tolerance level. The water wash treatment
reduced azinphos-methyl. captan and formetanate-HCI residues on and
in the fruit by 53. 48 and 23%. respectively. Ozone wash removed
46-75% on/in the fruit. while the 50 and 500 ppm chlorine wash
treatments reduced residue levels by 48-76% and 58-83%. respectively.
Processing the apples into sauce significantly reduced all three pesticide
residues in all the treatments. Between 84-100% of the three pesticides
were removed after processing. The 500 ppm chlorine wash was the
most effective wash treatment. Ozone wash at 0.25 ppm was not as
effective due to its low concentration. its instability in water. and the
high organic content of the wash water.

The ozone and chlorine wash treatments resulted in significantly
less pesticide residue in the wash water as compared to the water wash
treatment. This is an advantage in terms of minimizing pesticide wastes
in the wash water and the safe disposal of the waste water.

To conclude. a laboratory-scaled model system was developed and
has proven to be effective in showing rates of degradation and/or
disappearance of azinphos-methyl. captan and formetanate-HG] with

various pH. temperature. ozone and chlorine treatments. Residue

 

 

87

analysis of fresh and processed fruits showed that postharvest and
processing treatments were effective in reducing pesticide residue levels.

 

FUTURE WORK

Possible future research efforts include:

(1) To elucidate possible degradation pathways of azinphos-methyl.
captan and formetanate-H01 during ozonation and chlorination. as well
as to identify degradation products as a result of chemical oxidation.
Assessment of toxicity should also be carried out on the degradation
products. especially as applied to chlorinated products.

(2) The author found no indication that ozonated water has been
used as a postharvest wash treatment of fruits before this study. The
present research indicates that the use of ozone as a postharvest wash
treatment is a promising alternative to chlorine washes that are
currently used in commercial facilities. More research should be carried
out to study concentrations of ozone that can be used to maximize
reduction of pesticide residue levels. while ensuring that the amount
used do not exceed current safe levels. Studies should also be carried
out to determine the possible use of ozonated water washes in replacing
chlorine wash as a method of reducing/eliminating various diseases on
fruit crops after harvest.

 

89

(3) This study determined that the various wash treatments and
processing methods were effective in the degradation/ removal of
pesticide residues on apples at the pilot plant level. Future work should
focus on the possibility of scaling up to a commercial size operation.
especially as it applies to the ozone treatment. This would help
determine the feasibility of using such methods (e.g. ozone washes) on a
commercial scale.

 

APPENDICES

 

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"IWilli!Iliiiiili“