Fenitrothion (EHC 133, 1992)

INTERNATIONAL PROGRAMME ON CHEMICAL SAFETY

ENVIRONMENTAL HEALTH CRITERIA 133

FENITROTHION

This report contains the collective views of an international group of
experts and does not necessarily represent the decisions or the stated
policy of the United Nations Environment Programme, the International
Labour Organisation, or the World Health Organization.

First draft prepared by Dr. J. Sekizawa
(National Institute of Hygienic Sciences, Japan)
and Dr. M. Eto (Kyushu University, Japan) with
the assistance of Dr. J. Miyamoto and
Dr. M. Matsuo (Sumitomo Chemical Company)

Published under the joint sponsorship of
the United Nations Environment Programme,
the International Labour Organisation,
and the World Health Organization

World Health Orgnization
Geneva, 1992

The International Programme on Chemical Safety (IPCS) is a
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chemicals.

WHO Library Cataloguing in Publication Data

Fenitrothion.

(Environmental health criteria ; 133)

1.Fenitrothion - adverse effects 2.Fenitrothion - toxicity
3.Environmental exposure I.Series

ISBN 92 4 157133 0 (NLM Classification: WA 240)
ISSN 0250-863X

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CONTENTS

ENVIRONMENTAL HEALTH CRITERIA FOR FENITROTHION

1. SUMMARY AND EVALUATION, CONCLUSIONS AND RECOMMENDATIONS

1.1. Summary and evaluation
1.1.1. Exposure
1.1.2. Uptake, metabolism, and excretion
1.1.3. Effects on organisms in the environment
1.1.4. Effects on experimental animals and
in vitro test systems
1.1.5. Effects on human beings
1.2. Conclusions
1.3. Recommendations

2. IDENTITY, PHYSICAL AND CHEMICAL PROPERTIES, ANALYTICAL METHODS

2.1. Identity
2.2. Physical and chemical properties
2.3. Conversion factors
2.4. Analytical methods

3. SOURCES OF HUMAN AND ENVIRONMENTAL EXPOSURE

3.1. Natural occurrence
3.2. Man-made sources
3.2.1. Production
3.2.2. Uses

4. ENVIRONMENTAL TRANSPORT, DISTRIBUTION, AND TRANSFORMATION

4.1. Transport and distribution between media
4.2. Abiotic and biotic transformation
4.2.1. Abiotic transformation
4.2.1.1 Thermal degradation
4.2.1.2 Photolysis in air
4.2.1.3 Hydrolysis and photolysis
in water
4.2.1.4 Photolysis on soil
4.2.2. Biotransformation
4.2.2.1 Biodegradation in soil
4.2.2.2 Biodegradation and bioaccumulation
in organisms
4.2.2.3 Abiotic and biological
degradation in/on plants

5. ENVIRONMENTAL LEVELS AND HUMAN EXPOSURE

5.1. Environmental levels
5.1.1. Air
5.1.2. Water
5.1.3. Soil
5.1.4. Food
5.2. Human exposure
5.2.1. Food

6. KINETICS AND METABOLISM

6.1. Absorption, distribution, metabolic
transformation, elimination, and excretion
6.2. Retention and turnover

7. EFFECTS ON EXPERIMENTAL ANIMALS AND IN VITRO TEST SYSTEMS

7.1. Single exposure
7.2. Skin and eye irritation; skin sensitization
7.2.1. Skin and eye irritation
7.2.2. Skin sensitization
7.3. Short-term studies
7.3.1. Rat
7.3.2. Dog
7.3.3. Rabbit
7.3.4. Guinea-pig
7.4. Long-term and carinogenicity studies
7.5. Reproductive effects, embryotoxicity, and
teratogenicity
7.5.1. Reproductive effects
7.5.2. Embryotoxicity and teratogenicity
7.6. Mutagenicity
7.7. Neurotoxicity
7.8. Effects on hepatic enzymes
7.9. Effects on hormonal balance
7.10. Toxicity of metabolites and the S-isomer
7.11. Factors modifying toxicity
7.12. Mechanism of toxicity - mode of action
7.12.1. Mode of action
7.12.2. Selective toxicity
7.12.3. Potentiation of toxicity of
other chemicals

8. EFFECTS ON MAN

8.1. General population exposure
8.1.1. Acute toxicity
8.1.2. Poisoning incidents

8.1.3. Contact dermatitis
8.1.4. Possible links with Reye's syndrome
8.2. Occupational exposure

9. EFFECTS ON ORGANISMS IN THE ENVIRONMENT

9.1. Microorganisms and algae
9.2. Aquatic organisms
9.2.1. Fish
9.2.2. Invertebrates
9.2.3. Amphibians and arthropods
9.3. Terrestrial organisms
9.3.1. Terrestrial invertebrates
9.3.2. Birds
9.3.3. Mammals

10. PREVIOUS EVALUATIONS BY INTERNATIONAL BODIES

REFERENCES

ANNEX I. TREATMENT OF ORGANOPHOSPHATE INSECTICIDE POISONING IN MAN

ANNEX II. NO-OBSERVED-EFFECT LEVELS IN PLASMA, RED BLOOD CELLS, AND
BRAIN ChE, IN ANIMALS TREATED WITH FENITROTHION

RESUME ET EVALUATION, CONCLUSIONS ET RECOMMANDATIONS

RESUMEN Y EVALUACION, CONCLUSIONES ET RECOMENDACIONES

WHO TASK GROUP ON ENVIRONMENTAL HEALTH CRITERIA FOR TRICHLORFON
AND FENITROTHION

Members

Dr V. Benes, Department of Toxicology and Reference Laboratory,
Institute of Hygiene and Epidemiology, Prague, Czech and Slovak
Federal Republic

Dr C. Carrington, Division of Toxicological Review and Evaluation,
Food and Drug Administration, Washington, DC, USA (Joint
Rapporteur)

Dr W. Dedek, Department of Chemical Toxicology, Academy of
Sciences, Leipzig, Germany

Dr S. Dobson, Institute of Terrestrial Ecology, Monks Wood
Experimental Station, Huntingdon, United Kingdom

Dr D.J. Ecobichon, Department of Pharmacology and Therapeutics,
McGill University, Montreal, Canada

Dr M. Eto, Department of Agricultural Chemistry, Kyushu
University, Fukuoka-shi, Japan (Vice-Chairman)

Dr Bo Holmstedt, Department of Toxicology, Karolinska Institute,
Stockholm, Sweden

Dr S.K. Kashyap, National Institute of Occupational Health,
Ahmedabad, India

Dr J. Miyamoto, Takarazuka Research Centre, Hyogo, Japan

Dr H. Spencer, United States Environmental Protection Agency,
Washington, DC, USA (Chairman)

Dr M. Takeda, National Institute of Hygienic Sciences, Tokyo,
Japan

Observers

Dr M. Matsuo, Biochemistry and Toxicology Laboratory, Sumitomo
Chemical Co. Ltd, Osaka-shi, Japan (representing GIFAP)

Secretariat

Dr K.W. Jager, IPCS, World Health Organization, Geneva,
Switzerland (Secretary)

Dr J. Sekizawa, National Institute of Hygienic Sciences, Tokyo,
Japan (Joint Rapporteur)

NOTE TO READERS OF THE CRITERIA DOCUMENTS

Every effort has been made to present information in the
criteria documents as accurately as possible without unduly delaying
their publication. In the interest of all users of the Environmental
Health Criteria documents, readers are kindly requested to
communicate any errors that may have occurred to the Director of the
International Programme on Chemical Safety, World Health
Organization, Geneva, Switzerland, in order that they may be
included in corrigenda.

* * *

A detailed data profile and a legal file can be obtained from
the International Register of Potentially Toxic Chemicals, Palais
des Nations, 1211 Geneva 10, Switzerland (Telephone No. 7988400 or
7985850).

ENVIRONMENTAL HEALTH CRITERIA FOR FENITROTHION

A WHO Task Group on Environmental Health Criteria for
Trichlorfon and Fenitrothion met at the World Health Organization,
Geneva, from 10 to 14 December 1990. Dr K.W. Jager, IPCS, welcomed
the participants on behalf of Dr M. Mercier, Manager of the IPCS,
and the three IPCS cooperating organizations (UNEP/ILO/WHO). The
Group reviewed and revised the draft and made an evaluation of the
risks for human health and the environment from exposure to
fenitrothion.

The first draft was prepared by Dr J. Sekizawa of the National
Institute of Hygienic Sciences of Japan in collaboration with Dr J.
Miyamoto and Dr M. Matsuo of Sumitomo Chemical Company, and Dr M.
Eto of Kyushu University. Dr J. Sekizawa also prepared the second
draft, incorporating comments received following circulation of the
first drafts to the IPCS contact points for Environmental Health
Criteria.

Dr K.W. Jager of the IPCS Central Unit was responsible for the
scientific content and Mrs M.O. Head of Oxford for the editing.

The fact that Sumitomo Chemical Company Limited, Japan
(trichlorfon and fenitrothion) and Bayer AG, Germany (trichlorfon)
made available to the IPCS and the Task Group their proprietary
toxicological information on the products under discussion is
gratefully acknowledged. This allowed the Task Group to make its
evaluation on the basis of more complete data.

The efforts of all who helped in the preparation and
finalization of the document are gratefully acknowledged.

1. SUMMARY AND EVALUATION, CONCLUSIONS AND RECOMMENDATIONS

1.1 Summary and evaluation

1.1.1 Exposure

Fenitrothion is an organophosphorus insecticide that has been
in use since 1959. It is used in agriculture to control insects on
rice, cereals, fruits, vegetables, stored grains, and cotton. It is
also used to control insects in forests and for fly, mosquito, and
cockroach control in public health programmes. It is formulated as
emulsifiable concentrates, ultra-low-volume concentrates, powders,
granules, dusts, oil-based sprays, and in combination with other
pesticides. Between 15 000 and 20 000 tons of fenitrothion are
produced per year.

Fenitrothion enters the air by volatilization from contaminated
surfaces and may drift beyond the intended target area during
spraying. It leaches very slowly from most soils, but some run-off
can be expected.

Fenitrothion is degraded by photolysis and hydrolysis. In the
presence of ultraviolet radiation (UVR) or sunlight, the half-life
of fenitrothion in water is less than 24 h. The presence of
micro-flora may also accelerate degradation. In the absence of
sunlight or microbial contamination, fenitrothion is stable in
water. In soil, biodegradation is the primary route of degradation,
though photolysis may also play a role.

Airborne concentrations of fenitrothion may be as high as 5
µg/m³ directly after spraying, but may decrease markedly with time
and distance from the application site. Levels in water may be as
high as 20 µg/litre, but decrease rapidly.

Bioconcentration factors for fenitrothion with continuing
exposure have been estimated to range from 20 to 450 for a number of
different aquatic species.

Levels of fenitrothion residues in fruits, vegetables, and
cereal grains may range from 0.001 to 9.5 mg/kg immediately after
treatment, but decline rapidly, with a half-life of 1-2 days.

1.1.2 Uptake, metabolism, and excretion

Fenitrothion is rapidly absorbed from the intestinal tract of
experimental animals and distributed to various body tissues. The
half-life for the dermal absorption of fenitrothion in the monkey
was 15-17 h. Fenitrothion has been shown to be metabolized through
the major pathways of O-demethylation and by cleavage of the
P-O-aryl bond. The nitro group of fenitrothion is reduced by
intestinal microorganisms, in ruminants only. The major route of

elimination is via the urine, most of the metabolites being
eliminated within 2-4 days in the rat, guinea-pig, mouse, and dog.
The major metabolites reported are demethyl fenitrothion, demethyl
fenitrooxon, dimethylphosphorothioic acid and dimethyl phosphoric
acid, and 3-methyl-4-nitrophenol and its conjugates. Differences in
the composition of metabolites found among most laboratory test
animals and between sexes of the same species appear to be mainly
quantitative in nature. Only rabbits appear to excrete fenitrooxon
and aminofenitrooxon in small, though quantifiable, amounts in the
urine.

Evidence from studies on rabbits and dogs showed preferential
deposition of fenitrothion in the adipose tissue.

Residues found in the milk of cows following exposure to
fenitrothion were not detected two days later.

Though fenitrothion is readily absorbed via the oral route, it
is rapidly metabolized and excreted and is unlikely to remain in the
body for any prolonged period.

1.1.3 Effects on organisms in the environment

The concentrations of fenitrothion that are likely to be found
in the environment do not have any effects on microorganisms in soil
or water.

Fenitrothion is highly toxic for aquatic invertebrates in both
freshwater and seawater with LC₅₀ values of a few µg/litre for
most species tested. The no-observed-effect level (NOEL) for
Daphnia, in 48-h tests, was < 2 µg/litre; in life-cycle tests, a
maximum acceptable toxicant concentration (MATC) of 0.14 µg per
litre was established. Field observations and studies on
experimental ponds have shown effects on populations of
invertebrates. However, most of the changes observed were temporary,
even at concentrations considerably higher than those likely to
occur after recommended usage.

Fish are less sensitive to fenitrothion than invertebrates and
show 96-h LC₅₀ values in the range of 1.7-10 mg/litre. The most
sensitive life stage is the early larva. Long-term studies have
established a MATC at, or above, 0.1 mg/litre for 2 species of
freshwater fish. Field studies after application of fenitrothion to
forests showed no effects on wild populations of fish or on the
survival of caged test fish with measured water concentrations of
fenitrothion of up to 0.019 mg/litre. Repeated application of
fenitrothion to forests had no effect on fish populations.

In laboratory tests, freshwater molluscs showed LC₅₀ values
in the range 1.2 to 15 mg/litre. No field effects were seen after
forest spraying at 140 g/ha.

Fenitrothion is highly toxic for bees (topical LD₅₀,
0.03-0.04 µg/bee). Field effects have been reported with high
numbers of honey bees and other species killed locally. However, the
total numbers killed represented only a small percentage of the hive
population.

Acute oral LD₅₀ values for birds range between 25 and 1190
mg/kg body weight and most 8-day dietary LC50s exceeded 5000 mg/kg
diet. NOEL values for reproduction were 10 mg/kg body weight for the
quail and 100 mg/kg body weight for the mallard. Song-bird deaths
occurred soon after application of fenitrothion at a rate of 280
g/ha and were markedly increased at 560 g/ha for species living in
the forest canopy. After spraying at 420 g/ha followed by 210 g/ha a
few days later, the reproductive success of White-throated Sparrows
was reduced. In many studies, song-birds showed inhibition of ChE
soon after the fenitrothion spraying of forests.

Field observations have not revealed any effects of
fenitrothion on populations of wild small mammals.

1.1.4 Effects on experimental animals and in vitro test systems

Fenitrothion is an organophosphate and causes cholinesterase
activity depression in plasma, red blood cells, and brain and liver
tissues. It is metabolized to fenitrooxon, which is more acutely
toxic. Its toxicity may be potentiated by some other organophosphate
compounds.

Fenitrothion is an insecticide of moderate toxicity with oral
LD₅₀ values in rats and mice ranging from 330 to 1416 mg/kg body
weight. Acute dermal toxicity in rodents ranged from 890 mg/kg body
weight to more than 2500 mg/kg body weight.

Fenitrothion is only minimally irritating to the eyes and is
nonirritating to the skin. The chemical showed dermal sensitizing
potential in one of two studies on guinea-pigs.

Fenitrothion has been tested in short-term studies on rats,
dogs, guinea-pigs, and rabbits and in long-term carcinogenicity
studies on rats and mice. In short-term studies on rats and dogs,
the no-observed-adverse-effect levels (NOAELs), based on brain-ChE
activity, were, respectively, 10 mg/kg diet and 50 mg/kg diet.

Long-term studies on rats and mice indicated a NOAEL (based on
brain ChE activity) of 10 mg/kg diet.

No carcinogenic effects were found in any of the long-term
studies reported.

Fenitrothion was not mutagenic in in vitro and in vivo
studies.

Fenitrothion has not been found to be teratogenic at doses of
up to 30 mg/kg body weight in rabbits and up to 25 mg/kg body weight
in rats. Dose levels exceeding 8 mg/kg body weight were maternally
toxic.

Developing young rats exhibited behavioural deficits
post-natally following in utero exposure. A NOEL for this effect
was established at 5 mg/kg body weight per day.

Multigeneration reproduction studies on rats did not indicate
any morphological effects. A NOAEL of 120 mg/kg diet, based on
reproductive parameters, was demonstrated in these studies.

Delayed neurotoxicity has not been reported as a result of
exposure to fenitrothion.

1.1.5 Effects on human beings

Administration of fenitrothion as a single oral dose of 0.042-
0.33 mg/kg body weight and in repeated doses of 0.04-0.08 mg/kg body
weight to human volunteers did not cause inhibition in plasma and
erythrocyte ChE. The urinary excretion of a metabolite,
3-methyl-4-nitrophenol, was complete within 24 h.

Several cases of poisoning have occurred. The signs and
symptoms of poisoning were those of parasympathic stimulation. In a
few cases, the toxic manifestations were delayed in onset and
recurred for up to a few months. It has been suggested that the slow
release of the insecticide from adipose tissue can give rise to a
protracted clinical course or late symptoms of intoxication. In some
cases, contact dermatitis has been attributed to exposure to this
insecticide. There is no evidence of delayed neurotoxicity or of an
association with Reye's syndrome following exposure to fenitrothion.

Within WHO programmes, fenitrothion has been used in a few
countries for indoor residual spraying for malaria control
(application dose: 2.0 g of active ingredient/m²). No evidence of
toxicity was noted in thousands of inhabitants observed, with the
exception of one study in which less than 2% inhabitants reported
mild complaints. However, approximately 25% of spray operators
showed up to 50% inhibition of whole blood ChE activity. Following

aerial application of a 50% EC formulation, some workers developed
symptoms of poisoning and decreased whole blood ChE activity within
48 h. Occupational exposure for a period of over 5 years of male
workers in a production plant and female workers in the packaging
unit produced clinical signs and symptoms of poisoning in 15% of
male and 33% of female workers. The measured air concentration of
fenitrothion in the workplace ranged between 0.028 and 0.118
mg/m³.

1.2 Conclusions

* Fenitrothion is a moderately toxic organophosphorus ester
insecticide. However, over-exposure from handling during
manufacture or use and accidental or intentional ingestion may
cause serious poisoning.

* Exposure of the general population, resulting mainly from
agricultural and forestry practices and public health
programmes, should not constitute a health hazard.

* With good work practices, hygienic measures, and safety
precautions, fenitrothion is unlikely to present a hazard for
those occupationally exposed.

* Despite its high toxicity for non-target arthropods,
fenitrothion has been extensively used for pest control with
few, or no, adverse effects on populations in the environment.

1.3 Recommendations

* For the health and welfare of workers and the general
population, the handling and application of fenitrothion should
only be entrusted to competently supervised and well-trained
operators who will follow adequate safety measures and use
fenitrothion according to good application practices.

* The manufacture, formulation, use, and disposal of fenitrothion
should be carefully managed to minimize contamination of the
environment, particularly surface waters.

* Regularly exposed workers should receive periodic health
evaluations.

* Application rates of fenitrothion should be limited, to avoid
effects on non-target arthropods. The insecticide should never
be sprayed over water bodies or streams.

2. IDENTITY, PHYSICAL AND CHEMICAL PROPERTIES, ANALYTICAL METHODS

Fenitrothion was first prepared in Czechoslovakia in 1956
(Drabek, Truchlik, 1957). Later, it was prepared independently by
Sumitomo Chemical Co. and by Bayer A.G. in 1959 and later by
American Cyanamid Co.

Its basic insecticidal activity was described by Nishizawa et
al. (1961).

2.1 Identity

Primary constituent

Chemical formula: C₉H₁₂NO₅PS

Chemical structure:

Relative molecular mass: 277.25

Common name: fenitrothion

CAS chemical name: O,O-dimethyl O-(3-methyl
-4-nitro-phenyl) phosphorothioate

IUPAC name: O,O-dimethyl O-(4-nitro-m-tolyl)
phosphorothioate

RTECS Registry number: TG0350000

CAS Registry number: 122-14-5

Synonyms: Accothion, Agrothion, Bayer 41831, Bayer S
5660, Cytel, Dybar, Fenitox, MEP,
Novathion, Nuvanol, Cyfen, Sumitomo 1102A

Technical product (FAO/WHO, 1988b)

Major trade names: Metathion, Novathion, Sumithion, Folithion

Purity: > 93% (Sumithion)

Impurities: O,O-dimethyl O-3-nitro- m-tolyl-
phosphorothioate < 1.5%
O-methyl O,O-bis(4-nitro- m-tolyl)
phosphorothioate < 2.5%
O-methyl S-methyl
O-(4-nitro- m-tolyl)
phosphorothioate(S-isomer) < 0.8%
O,O-dimethyl O-2-nitro- m-tolyl
phosphorothioate < 3.0%
O,O-dimethyl O-6-nitro- m-tolyl
phosphorothioate < 2.5%
O,O-dimethyl O-2,4-dinitro- m-tolyl
phosphorothioate < 2.0%
O,O-dimethyl O-4,6-dinitro- m-tolyl
phosphorothioate < 1.5%
3-methyl-4-nitrophenol < 0.5%

Isomeric composition: S-isomer, < 0.8%

2.2 Physical and chemical properties

Some physical and chemical properties of Fenitrothion are given
in Table 1.

2.3 Conversion factors

1 ppm = 11.5 mg/m³ (at 20 °C)
1 mg/m³ = 0.087 ppm.

2.4 Analytical methods

Methods for the determination of fenitrothion in foods,
environmental samples, technical products, and formulations are
summarized in Tables 2 and 3. The common procedure for determining
residues in foods and environmental media consists of (1)
extraction, (2) partition, (3) chromatographic separation
(clean-up), and (4) qualitative and quantitative analysis using
analytical instruments.

Fenitrothion levels in technical products and formulations are
usually determined by the diazo method, the colorimetric method, or
gas-liquid chromatography. The common procedure consists of: (1)
dissolution or extraction, (2) separation of impurities and (3)
determination. Granules should be pulverized before analysis.

The joint FAO/WHO Codex Alimentarius Commission has given
recommendations for the methods of analysis to be used for the
determination of fenitrothion residues (FAO/WHO, 1989d).

Table 1. Some physical and chemical properties of fenitrothion^a

Physical state liquid

Colour yellow-brown

Odour chemical odour

Melting point 0.3 °C

Boiling point 140-145 °C (decomp.)/0.1 mmHg

Flash point 157 °C

Vapour pressure 18 mPa at 20 °C; 6 x 10^-6 mmHg at 20 °C

25 25
Density d 1.32-1.34; d 1.3227
25 4

n-Octanol/water partition
coefficient (log P) 3.16

Solubility in water 14 mg/litre at 30 °C

Solubility in organic freely soluble in alcohols, esters,
solvents ketones, and aromatic hydrocarbons;
> 1000 g/kg dichloromethane, methanol,
xylene; 193 g/kg propan-2-ol; 42 g/kg
hexane at 20-25 °C

Stability hydrolysed by alkali: half-life
4.5 h in 0.01 N NaOH at 30 °C
decomposed by heat: 145 °C

^a From: Martin & Worthing (1981); Worthing & Walker (1983);
Meister et al. (1985); Moody et al. (1987a).

Table 2. Analytical methods for the determination of fenitrothion in food and environmental samples

Sample Sample preparation Determination GLC MDC^c Recovery (%), Reference
Extraction Partition Clean-up Elution or HPLC conditions; (mg/kg) (fortification
solvent column detector^a, column, level, mg/kg)
temperature, RT^b

Residue analysis

apple, orange acetone ES^d florisil acetone/ GC: FTD, NPD, FPD, 2% 0.1 95-96 (0.1) Ferreira &
peach, grape /2%Na₂SO₄ hexane DC-200 + 3% OF-1, 1.5% 86-97 (0.2) Fernandes
tomato, /n-hexane (4/96) OV-17 + 1.95% OF-1, 10% 88-102 (0.5) (1980)
cabbage DC-200 86-98 (1.0)
94-95 (2.0)

chinese methanol/ benzene GC: FPD, 3% OV-1, 89 (0.5) Talekar
cabbage acetone/ 10% DC-200 et al.
benzene (1977)
(Soxhlet)

onion acetonitrile Amberlite methanol GC: FPD, 4% OV-1, 200 °C 99 (0.5) Iwata
CH₂Cl₂/ XAD-8 benzene et al.
benzene (1:4) charcoal (1981)

apple,lettuce acetone ES^d florisil benzene GC: ECD 0.1 70-102 Möllhoff
carrot,onion /CH₃Cl₃ 5% SE-30, 190 °C, 6.3 min 64-89 (0.5) (1967)
tomato,potato 5% OF-1, 190 °C, 5.6 min 88-114 (1.0)
5% DC-200, 190 °C, 3.4 min
5% E-301, 190 °C, 2.9 min

Table 2 (contd).

orange,potato ethyl acetonitrile/ florisil petroleum sp/ GC:NPD, 0.001 Mestres
acetate petroleum ethyl et al.
CH₂Cl₂ spirit ether or (1974)
(4:1) ethyl
acetate

peach acetone water/ charcoal+ CH2Cl2 GC:NPD Ambrus et al.
potato CH₂Cl₂ MgO 3% OV-22; 3% OV-101; (1981)
1.95% SP-2401/1.5%

acetone alumina N hexane SP-2250; 3% NPGS;
3% SE-30 on 100-120
mesh Gas-Chrom Q
acetone silica gel benzene
5% water

apple acetonitrile ES^d HPLC: UV (280 nm) 0.03 81-87 (0.5) Funch (1981)
salad 2% Nacl Radpak A with ODS
/CH₂Cl₂

unpolished n-hexane I. n-hexane charcoal/ acetone/ GC: FPD Aoki et al.
rice (Soxhlet) /CH₃CN avicel n-hexane 10% DC-200 + 15% 76 (0.4) (1975)
(1/10) (50/50)
wheat OF-1, 180 °C, 7.9 min
buck wheat II. CH₃CN 2% DEGS + 0.5% H₃PO₄, 0.0007 92 (0.4)
string bean /5% NaCl/ 180 °C, 10.2 min
soybean benzene 10% DC-200 + 15% 0.0008 79-101 (0.4)
pear OV-17, 190 °C, 9.4 min

Table 2 (contd).

water melon acetone ES^d GC-MS 0.1 91-102 (0.5) Kobayashi
tomato NaCl/ 5% OV-1, 150 °C et al.
n-hexane (1979)

wheat grain methanol GC: AFI, FPD, 5% 0.1 86 (0.5) Smart
OV-17 + Epikote 1001 94 (1.0) (1980)

apple methanol/ GC: FTD 0.005 80-97 (0.1) Takimoto &
strawberry CH₃CN/CHCl₃ 10% DC-200 + 20% OF-1, 97 (0.2) Miyamoto
pear, tomato 210 °C (1976b)
cucumber

potato methanol/ florisil benzene/ GC: FTD, 10% DC-200 0.005 96 (0.01) Takimoto &
CH₃CN/CHCl₃ ethyl + 20% OF-1, 210 °C Miyamoto
acetate (1976b)
(10/1)

soybean methanol/ CH₃CN/ silica benzene 0.005 98 (0.2, 0.02) Takimoto &
(fresh) CH₃CN/ n-hexane gel OF-1, 210 °C Miyamoto
CH₃Cl₃ (1976b)

green tea CH₃CN/ CH₃CN/ florisil benzene/ 0.005 90-93 (0.02) Takimoto &
rice grain benzene n-hexane ethyl 92-98 (0.5) Miyamoto
acetate/ (1976b)
(10/1)

Table 2 (contd).

milk methanol/ CH₃CN/ 0.005 89 (0.1) Takimoto &
CH₃CN/ n-hexane Miyamoto
CHCl₃ (1976b)

butter hexane I. hexane/ GC: ECD, 5% DC-200, 0.02 95 Gajduskova
CH₃CN 180 °C (1974)
II. aq.
Na₂SO₄
CH₃CN/
CH₂Cl₂

milk acetone I. acetone silica benzene GC: FPD, 10% DC-200, 0.001 96 (0.5), Bowman &
CH₂Cl₂ gel Bcraza
II. hexane/ (20% H2O) 180 °C 2.9 min 94 (0.05) (1969)
CH₃CN

meat ethanol/ CH₃CN/ TLC benzene/ GC: FTD, 10% DC-200 0.005 95 (0.1), Takimoto &
benzene n-hexane ethyl + 20% OF-1 86 (0.2) Miyamoto
acetate (1976b)
(4/1)

lettuce, petroleum- petroleum- TLC methanol Spectrophotometry 0.05- 89-115 Kovac &
apple ether ether (A12O3) 400 nm, after hydrolysis 0.1 (0.25-1) Sohler
cherries +CH₃CN(1:1) (NaOH+ (1965)
plums H₂O₂) Cerna &
kohlrabi Benes
cauliflower (1972)

Table 2 (contd).

cabbage
citrus, acetone ES^d silica hexane/ TLC 3% OV-225 ng Gardner
potato CH₃CCl₃ gel acetone 170-240 °C 0.05 94 (0.5) (1971)
(9/1) Martindale
(1988)

Environmental analysis

water amberlite ethyl HPLC: UV (245 nm) RP-8 0.001 94 (0.05- Volpe &
XAD-4 acetate CH3CN/H2O (50/50) Mallet
(1981)
water amberlite CH₂Cl₂ or GC: FPD, 3.6% OV-101 90 (0.05- Volpe &
XAD-4 or 7 ethyl + 5% OV-210 0.005) Mallet
acetate (1980)

drinking- amberlite acetone/ GC: NPD, -MS, 3% 0.001 104 (0.1), LeBel
water XAD-2 hexane OV-17 96 (0.01) et al.
(15/85) (1979)

water amberlite ethyl GC: FPD, 4% OV-101 + 0.001 91.5 (0.01) Mallet
acetate et al.
XAD-2 6% OV-210, 195 °C (1978)

water uBondapak HPLC: UV (280 0.005 95.6 (0.737) Takaku
Phenyl uBondapak Phenyl H₂O/ et al.
CH₃CN (100/0-0/100) (1979a)

Table 2 (contd).

water petroleum GC: FPD, 5% SE-30, 180 °C 98-102 Grift &
ether 5% DC-200, 180 °C (0.005-0.0005) Lockhart
(1974)

pasture CH₃CN/ CH₃CN/ florisil benzene/ GC: FTD, 10% DC-200 + 0.005 95 (0.1) Takimoto &
ethyl
grass benzene n-hexane acetate 20% OF-1, 210 °C Miyamoto
(1976b)

corn methanol/ silica benzene GC: FPD, 10% DC-200, 0.002 99-100 (5) Bowman &
gel Bcraza
grass CHCl₃ (20% H₂O) 180 °C, 2.9 min 98-99 (0.5) (1969)
97-98 (0.05)

jack pine ethyl I.carbon/ benzene GC: NPD, 6% SE-30 + 96-100 (0.2) McNeil
foliage acetate celite 4% OF-1, 225 °C et al.
(1979)
(1/6) II. 60%
florisil benzene
Si600 in hexane

water n-hexane GC: FPD, 11% OV-17 + 0.00001 100-108 Ripley
OF-1 3.6% OV-101, 225 °C (0.01-0.0001) et al.
(1974)

Table 2 (contd).

fish ethyl ES^d florisil benzene/ GC: FPD 0.05 93-110 Grift &
ethyl Lockhart
acetate CH₃CN acetate 5% DC-200, 180 °C (1974)
sediment /hexane 5% SE-30, 180 °C 0.05 88-102 (5-0.1)

bivalve ethyl bio- CH₂Cl₂/ GC: FPD, -MS, 3% OV- 0.0009 94.4 (10-0.01) Sergeant
acetate beads, cyclohexane 101, 180 °C, 11% OV-17/ et al.
(Soxhlet) SX-3 OF-1, 200 °C (1979)
(50/50)

soil acetonitrile Amberlite ethyl GC: FPD, 3.6% OV-17 +0.05 98-112 (0.5) Hache
XAD-2 acetate et al.
chicken liver 5% OV-210, 210 °C (1981)
wine, clam
pine needle

soil acetone acetone florisil benzene GC: ECD 0.1 58-100 (0.1) Möllhoff
/CHCl3 5% SE-30, 190 °C, 6.3 min 76-98 (0.5) (1967)
5% QF-1, 190 °C, 5.6 min 98-122 (1.0)
5% DC-200, 190 °C, 3.4 min
5% E-301, 190 °C, 2.9 min

Table 2 (contd).

Ambient air

vapour trapped on 10% OV-101 on chromosorb GC: FPD, 3% OV-1, 5 x Krzymien
aerosol W packed in a glass tube and 205 °C 10-12 (1979)
thermally released and carried to GC column

aerosol consecutive plates of cascade 5 x 100 (30) Krzymien
impactor, plates washed 10-12 (1979)
with n-hexane, n-hexane solution
injected into GC

^a Detectors for GC (FPD = flame photometric detector; FTD = flame thermionic detector; ECD = electron capture detector;
NPD = NP specific detector; AFI = alkali flame ionization detector), MS = mass spectrometry.
^b RT = Retention time.
^c MDC = minimum detectable concentration.
^d ES = extraction solvent.

Table 3. Analytical methods for fenitrothion in technical products and formulations^a

Sample Sample preparation Determination

Diazo method

TG and EC dissolution (ether) reduction (Zn-acetic acid)
partition (ether/1% Na₂CO₃) titration (NaNO₂)
end-point (potentiometer or
iodide-starch paper)

Colorimetric method

TG and EC dissolution (methanol) addition (1% Na₂CO₃)
determination (free NMC);

WP and dust extraction (methanol) 400 nm hydrolysis (5N KOH)
determination (total NMC);
Granule pulverization extraction (methanol) 400 nm

TLC-UV method

TG and EC dissolution (CHCl₃) determination; 271 nm
TLC (benzene/diethyl ether=19/1)

WP extraction (methanol)
TLC (benzene/diethyl ether=19/1)

Dust extraction (CHCl₃)
TLC (benzene/diethyl ether=19/1)

Granule pulverization extraction (CHCl₃)
TLC (benzene/diethyl ether=19/1)

TLC-phosphorus method

TG and EC dissolution (CHCl₃) TLC digestion (H₂SO₄ and HNO₃)
colouring (ammonium metavanadate

WP extraction (methanol) TLC and ammonium molybdate)
determination;

Dust extraction (CHCl₃) TLC 420 nm

Table 3. (cont'd).

Sample Sample preparation Determination

Granule pulverization extraction (CHCl₃) TLC

GC method

TG and EC dissolution (IS solution) GC: FID
2% DC-QF-1, 170 °C

WP and dust extraction (IS solution) centrifuge

Granule pulverization extraction (IS solution)
centrifuge

^a From: Takimoto et al. (1975).
TG = technical grade; EC = emulsifiable concentrate; WP = water-dispersible
powder; NMC = 3-methyl-4-nitrophenol; IS = internal standard (dibutyl
sebacate);
GC = gas-liquid chromatography.

3. SOURCES OF HUMAN AND ENVIRONMENTAL EXPOSURE

3.1 Natural occurrence

Fenitrothion is not a natural product.

3.2 Man-made sources

3.2.1 Production

The global production volume is not available. However, the
global manufacturing capacity has been estimated to be between 15
000 and 20 000 tonnes. Production figures in Japan (a major
manufacturing country) are 5346 tonnes in 1982 increasing up to
about 10 000 tonnes in 1988 (Japan Plant Protection Association,
1984, 1986, 1988, 1989). Production in India was reported to be 400
tonnes in 1978, 350 tonnes in 1979, and 100 tonnes in 1980
(Battelle, 1982). Production in Czechoslovakia in 1989 was 964
tonnes (Benes, personal communication).

Fenitrothion is formulated as an emulsifiable concentrate
(50%), an ultra-low-volume concentrate, flowable (20%), a wettable
powder (40%), granules (3%), dust (3%), an oil-based liquid spray
alone or in combination with other pesticides, e.g., trichlorfon,
malathion; BPMC; fenvalerate (insecticide), tetramethrin (house-hold
insecticide); IBP, phthalide, thiophanate-methyl (fungicide).

3.2.2 Uses

Fenitrothion is mainly used in agriculture for controlling
chewing and sucking insects on rice, cereals, fruits, vegetables,
stored grains, cotton, and in forest areas. It is also used for the
control of flies, mosquitos, and cockroaches in public health
programmes and/or indoor use.

4. ENVIRONMENTAL TRANSPORT, DISTRIBUTION, AND TRANSFORMATION

4.1 Transport and distribution between media

Several studies were performed to elucidate the mechanism of
the apparent rapid disappearance of fenitrothion from the water
phase after the field spraying of fenitrothion formulation. The
processes most likely to explain the phenomena include sorption by
the sediments, photolysis, microbial degradation, hydrolysis, and
volatilization.

Marshall & Roberts (1977) discounted volatilization as a major
pathway for the disappearance on the basis of the calculated
half-life of 93 days obtained in a 1-m water column, designed as a
simple model for small, well-mixed lentic systems with compartments
representing the major pools, i.e., the water, the hydrosol, and the
suspended solids, which include both biotic and abiotic material.

Maguire & Hale (1980) studied the kinetics of fenitrothion
distribution and transformation in water and sediment, both
experimentally and after field spraying (see section 5.1.2 for
results after field spraying). Laboratory experiments demonstrated
that volatilization of fenitrothion from true solutions (5 mg/litre)
in distilled water followed first-order kinetics and that the
half-life of disappearance at 20 °C was estimated to be 64 ± 5 days.
The fact that the half-life was considerably longer (> 180 days) in
the presence of 5 mg fulvic acid/litre indicated that the rate would
be considerably reduced in natural waters too. In contrast with
this, the volatilization of fenitrothion that had been sprayed on
the surface of water appeared to be a very fast process in the
laboratory (half-life = 18 min for volatilization from the surface
of water). Surface volatilization was suggested to play a
significant role in the dissipation of fenitrothion from a small
pond after spraying the formulation.

Metcalf et al. (1980) also reported the significance of
volatilization in the disappearance of fenitrothion in a lake by
taking account of the effects of winds and water currents on natural
water bodies in experiments using various rates of aeration.
Observed half-lives of fenitrothion in Palfrey Lake and Brook in
Southwestern New Brunswick (water temperature: 11 °C, average pH
value in the lake: 6.7) were 6.3 days (bottom) - 7.2 days (surface)
and 0.9 days, respectively.

In a laboratory leaching study, ¹⁴C fenitrothion and its
degradation products hardly moved with water in 3 loam soils,
whereas, in Muko sand containing 0.2% clay and less than 0.1%
organic matter, about 15% of the applied ¹⁴C was eluted from the
soil column. Preincubation of the fenitrothion in sandy soil for 60

days before leaching decreased the degree of mobility. In the
effluent from sandy soil, a trace amount of fenitrothion (0-0.1%)
together with water-soluble products, such as
3-methyl-4-nitro-phenol [9]¹ (0.6%) and amino-fenitrothion [13]
(11.3%), were detected (Takimoto et al., 1976, see Fig. 3).

Baarschers et al. (1983) examined the adsorption of
fenitrothion and 3-methyl-4-nitrophenol [9] in water-soil suspension
systems, using 4 different soils and 1 sediment as adsorbents. The
Freundlich k values were 15.5-354.8 for fenitrothion and 2.1-147.8
for 3-methyl-4-nitrophenol [9]. Both of the k values increased when
the organic matter content increased from 0.9 to 33.1%. The
adsorption characteristics of fenitrothion may be correlated with
the lower degree of mobility in the leaching study.

4.2 Abiotic and biotic transformation

4.2.1 Abiotic transformation

4.2.1.1 Thermal degradation

Tsuji et al. (1980) examined the mechanisms of thermal
degradation of fenitrothion in air and found that 3 major exothermic
steps were involved (Fig. 1). The first step was formation of
fenitrooxon [1], and ^S-methyl fenitrothion [8] with evolution of
sulfur dioxide at 150-160 °C.

The second step was formation of fenitrooxon [1], ^S-methyl
^O,O-bis(3-methyl-4-nitrophenyl) phosphorothioate [11] and
polymetaphosphate [12] with evolution of dimethyl sulfide from
^S-methyl fenitrothion [8] at 210-235 °C. The third step was
carbonization of the phenolic ring of [12] and gas evolution from
[11] at 270-285 °C. In a nitrogen atmosphere, the first step did not
take place and only the other two steps were involved. ^S-methyl
fenitrothion was produced by heating fenitrothion up to 193 °C.

The thermal degradation of fenitrothion in a closed system was
more rapid than that in an open system. Maeda et al. (1982) proposed
that dimethyl sulfide, which was evolved during thermal degradation
of ^S-methyl fenitrothion [8], catalysed isomerization of
fenitrothion to [8]. In fact, addition of 0.4-1.6% of dimethyl
sulfide in a closed system enhanced the degradation of fenitrothion.
Although metal salts, such as zinc, aluminum, ferric chloride, and
stannic chloride, also accelerated isomerization of fenitrothion,
calcium dodecylbenzene sulfonate (surfactant) showed no effect.

¹ Chemical structures in Fig. 1-7 are referred to giving the
numbers in brackets.

4.2.1.2 Photolysis in air

Addison (1981) examined the photolysis of fenitrothion by UV
radiation (200-400 nm) from a xenon lamp in the vapour phase
(10-15 mg/50-1 reaction chamber) at about 85-90 °C, and computed the
half-life of disappearance to be 61 ± 11 min and 24 ± 3 min in the
absence or presence of ozone (0.7-0.9 ± 1 mg/m³), respectively.

Brewer et al. (1974) also studied the vapour phase photolysis
of fenitrothion at 313 nm UV radiation, and detected
3-methyl-4-nitrophenol [9] and an unidentified product as primary
photo-products (Fig. 2).

4.2.1.3 Hydrolysis and photolysis in water

Fenitrothion underwent hydrolysis in the absence of light
through a pH-independent process below pH 7 and a base-catalysed
process above pH 10, while both processes occurred between pH 7 and
pH 10. The half-lives of fenitrothion within the pH range of 5-9
(normally found in natural water) were about 200-630 days at 15 °C,
17-61 days at 30 °C, and 4-8 days at 45 °C. The predominant
hydrolysis products were 3-methyl-4-nitrophe-nol [9] above pH 10 and
demethylated fenitrothion [7] below pH 8 (Fig. 2; Mikami et al.,
1985a).

[Phenyl-¹⁴C]-fenitrothion was dissolved at 1.0 mg/litre in
aqueous buffer solutions at pH values of 5, 7, and 9 and kept at 25
± 1 °C in the dark for 30 days, free from microbial contamination.
Fenitrothion was less stable at pH 9 with a half-life of 100-101
days, compared with those of 180-186 days and 191-200 days at pH 7
and pH 5, respectively. Cleavage of the P-O-methyl linkage to form
demethylated fenitrothion [7] was predominant at pH 5 and pH 7,
while at pH 9 cleavage of the P-O-aryl linkage to form
3-methyl-4-nitrophenol [9] was the major hydrolytic path-way (Ito
et al., 1988).

Greenhalgh et al. (1980) and Aly & Badawy (1982) demonstrated
that hydrolysis of fenitrothion follows pseudo-first-order kinetics,
yielding mainly the phenol [9] at alkaline pH and the demethylated
form [7] under acidic conditions.

The rate of hydrolysis of fenitrothion may be accelerated
through the addition of peroxide ion (1.7 x 10^-4 mol/litre),
particularly under alkaline conditions, since energies of activation
were reduced to 7.8 kcal/mol for peroxide hydrolysis from
16.3 kcal/mol for alkaline hydrolysis (Desmarchelier, 1987).

The photostability of fenitrothion in water is dependent on
both pH and energy of UVR or sunlight (Miyamoto, 1977a).
Fenitrothion rapidly decomposed in distilled water under sunlight
and in pH 7 and pH 9 solutions at ambient temperatures, but was
considerably more stable at pH 3. The half-life of fenitrothion was
10, 50, 20, and 6 h, respectively, in distilled water and in
solutions at pH 3, pH 7, and pH 9. Fenitrothion decomposed nearly 8
times faster at pH 9 than at pH 3.

Mikami et al. (1985a) determined the quantum yield of the
photodecomposition reaction of fenitrothion in distilled water (8.0
x 10^-4) and calculated that the half-life of photolysis by
sunlight at the 40° north latitude was 7.6, 6.8, 11.3, and 17.0 h in
spring, summer, autumn and winter, respectively. The actual
half-life in autumn in Takarazuka, Japan, at a latitude of 35°
north, was 12 h, agreeing with the above calculation.
Photode-composition of fenitrothion in sterile lake water and sea
water was also rapid and the half-life in both these solutions was
less than 1.1 days.

Fenitrothion degraded fairly rapidly under sunlight to form
CO₂; ¹⁴C ring-labelled fenitrothion released 39.4, 40.4, and
45.0% CO₂ in 32 days in distilled water, in a buffer solution (pH
7), and in sterilized sea water (pH 7.8), respectively (Mikami et
al., 1985a).

[Phenyl-¹⁴C]-fenitrothion was dissolved at 1.0 mg/litre in
aqueous acetate buffer (pH 5.0), free from microbial contamination
and irradiated with artificial sunlight (wave length > 290 nm,
xenon arc lamp), for 30 days (10 h/day irradiation) at 25 ± 1 °C.
Fenitrothion was degraded rather rapidly with a half-life of
3.33-3.65 days (70.8-140.9 days under dark conditions).
Photo-degradation reactions were oxidation of the aryl methyl group
to a carboxyl group to form compound [3] (a main product, 8.0-12.4%
in 14 days), oxidation of the P=S group to P=O group, cleavage of
the P-O-CH₃ or P-O-aryl linkage, and further decomposition to
¹⁴CO₂ (41.2-42.0%) during 30 days (Katagi et al., 1988).

Kanazawa (1977) demonstrated that fenitrothion (20 µg/litre)
degraded to 8% of the original concentration under greenhouse
conditions and only to 55% in the absence of light, in sea water,
over 2 weeks.

Fenitrothion (about 0.1 mg/litre) degraded in sea waters
collected from various coasts of Japan to 44-62% and 63-94%, with
and without sediments, respectively, after 2 weeks in the absence of
sunlight and aeration (Environment Agency of Japan, 1978).

The effects of several factors on the persistence of
fenitrothion in sea water were examined using the experimental
design with an L₁₆ orthogonal layout (Kodama & Kuwatsuka, 1980).
The persistence of fenitrothion was affected mainly by water quality
(river water or sea water) and sunlight (exposed or unexposed), but
also partially by temperature; it was not affected by the presence
of suspended solid or vaporization. After 72 h, the persistence of
fenitrothion in sea water was 56-97% of the original concentration
under varying conditions, while that in river water was 1-28%. When
river water was boiled, the rate of disappearance of fenitrothion
was the same as that in sea water, indicating that microbial
degradation was one of the most important contributing factors.

The photodegradation of fenitrothion (1 mg/litre) in sea water
collected along 3 different coastlines of Japan was very rapid with
a half-life of about 3 h, twice as fast as that in distilled water
(Takimoto et al., 1980).

A microcosm study using distilled, estuarine, and lake water
revealed that the ionic complement and/or microflora content of
estuarine water contributed more to the degradation of fenitrothion
than the pH. Sunlight irradiation in the static lake/bay models
decomposed 80% of fenitrothion to polar products within 6 h
(Weinberger et al., 1982a).

Twenty-one out of at least 50 radioactive photoproducts of
¹⁴C ring-labelled fenitrothion in water at various pHs were
identified. The major photoproducts were ^O,O-dimethyl
^O-(3-carboxy-4-nitrophenyl) phosphorothioate [3] in distilled
water and in buffer solutions at pH 3 and 7. A dimeric compound [5]
composed of [3] and the corresponding amino analogue [4] was more
predominantly formed in buffer solutions at pH 7 and 9, in natural
river (pH 7.4) and sea (pH 7.8) water. On prolonged irradiation with
sunlight, these photoproducts decreased to less than 4% of the
initial concentration with concomitant increases in carbon dioxide
(21.5-45%) and the unextractable residues (29.3-51.4%) consisting of
polymeric humic acids. Demethylated products [6,7] and hydrolysis
products at the P-O-aryl linkage, such as 3-methyl-4-nitrophenol
[9], were of minor importance, independent of pH values. S-Methyl
fenitrothion [8] was occasionally detected in trace amounts (Mikami
et al., 1985a).

The UV irradiation of fenitrothion in oxygenated hexane
solution produced fenitrooxon [1] and O,O-dimethyl
O-(3-formyl-4-nitrophenyl)phosphorothioate [2] (Greenhalgh &
Marshall, 1976). However, these photochemical reactions might not
play a major role in the environmental photochemistry of
fenitrothion in water.

4.2.1.4 Photolysis on soil

When fenitrothion was applied to thin-layer plates with a 2 mm
thickness of 7 different types of soil and exposed to sunlight, it
took 50-150 days for the 90% disappearance of fenitrothion from the
soils (Miyamoto, 1977a). No clear correlation existed between the
rate of disappearance of fenitrothion and the physical and chemical
parameters of the soils. S-Methyl fenitrothion and
aminofenitrothion similarly applied to the soil decreased much more
rapidly than fenitrothion. The order of stability was fenitrothion
> S-methyl fenitrothion > aminofenitrothion. Under dark
conditions, decomposition of these 3 compounds proceeded more
slowly, the range of stability among them being the same as that
observed under irradiated conditions. At most, 10% of the applied
chemical was lost, probably by evaporation, from the soil after 14
days. Fenitrothion was degraded on the soil surface mainly by
oxidation of the P = S to the P = O group and cleavage of the P-O-
aryl linkage.

The rapid photodecomposition of fenitrothion on soil surfaces
was also demonstrated by Mikami et al. (1985a). Unlike photolysis in
water, the principal products were fenitrooxon [1] and
3-methyl-4-nitrophenol [9], amounting to 3.6-9.4% and 20.4-23.1% of
the applied 14C, respectively, after 12 days.

A photolysis study was conducted with
[phenyl- 14C]-fenitrothion applied on the surface of soil at a rate
of 23.4 µg/cm². The samples were continuously irradiated (290 nm)
using an artificial light source (xenon arc lamp) over 30 days, the
soil temperature being maintained at 25 ± 1 °C throughout the
experiment. The rate constant and the half-life of photolysis were
determined to be 0.00814/day and 85 days, respectively, while under
dark conditions these were 0.0038/day and 182 days. Degradation
products identified included fenitrooxon [1] (2.0% at day 30),
demethyl fenitrothion [7] (2.1%) and 3-methyl-4-nitrophenol [9]
(3.0%) (Dykes & Carpenter, 1988).

Sunlight irradiation of fenitrooxon [1], 3-methyl-4-nitrophenol
[9], or carboxy-fenitrothion [3] on silica gel TLC plates resulted
in degradation and polymerization to humic acids, with half-lives of
3.9, 4.3, and 1.8 days, respectively (Ohkawa et al., 1974).

4.2.2 Biotransformation

4.2.2.1 Biodegradation in soil

The degradation pathways of fenitrothion in soils are shown in
Fig. 3.

When fenitrothion was incorporated at 10 mg/kg (on a dry-weight
basis) in soils with various physical and chemical properties, and
kept at 25 °C in the dark, under upland or submerged conditions, the
adsorption and decomposition of fenitrothion were quite variable,
depending on the properties of the soils and on the incubation
conditions (Takimoto et al., 1976; Miyamoto, 1977a). The half-life
of fenitrothion was 12-28 days under upland conditions, and 4-20
days under submerged conditions. However, no direct relationship was
observed between the decomposition of fenitrothion in soil and any
of the physical or chemical properties measured, namely clay
content, organic matter content, ion exchange capacity, and pH.
Under upland conditions, 3-methyl-4-nitrophenol [9] was formed at an
early stage of incubation, amounting to 10-20% of the applied
radioactivity ( m-methyl position). Levels of
3-methyl-4-nitrophenol decreased with longer incubation. Another
major decomposition product was radioactive carbon dioxide, which
amounted to approximately 40% of the initial fenitrothion after 60
days. No aminofenitrothion [13] was detected.

On the other hand, under submerged conditions,
3-methyl-4-nitrophenol [9] and carbon dioxide were minor products.
The major decomposition product was aminofenitrothion [13], its
formation being parallel to the decrease in fenitrothion. The
maximum amounts of aminofenitrothion were 18-66% of the initial
fenitrothion. Aminofenitrothion tended to disappear slowly on longer
incubation.

In soils, ¹⁴C-ring-labelled fenitrothion (10 mg/kg) degraded
at 25 °C in the dark with a half-life of 2-5 days under upland and
submerged conditions; after 8-26 weeks, levels declined to less than
0.1 mg/kg. After one year, the carbon dioxide evolved amounted to
60-70% of the initial radiocarbon under upland conditions and to
23-40% under submerged conditions, while the remaining radiocarbon
was mostly incorporated into the organic matter fractions of the
soil. When the soils containing the bound residues of the
radiocarbon were mixed with fresh soil, the release of radioactive
carbon dioxide was accelerated. Under upland conditions, degradation
of 3-methyl-4-nitrophenol [9] was more rapid than that of
fenitrothion (Mikami et al., 1985b).

Adhya et al. (1981a) also found that fenitrothion was degraded
primarily by reduction of the nitro group to aminofenitrothion in
flooded soil with lower redox potentials. Sterilization of the
prereduced flooded soil samples by autoclaving prevented the rapid
decomposition of fenitrothion in soil.

Aminofenitrothion was further degraded to demethyl
amino-fenitrothion [14] in typical flooded acid sulfate soils from
Kerala, India. Dealkylation also occurred in low sulfate soils under
submerged conditions, when supplemented with extraneous sulfate
(e.g., ammonium sulfate or ferrous sulfate). Hydrogen sulfide,
evolved as an end product of the anaerobic metabolism of sulfate,
catalysed the dealkylation of aminofenitrothion (Adhya et al.,
1981b).

Fenitrothion was stable when incubated in soil suspensions
containing streptomycin, cycloheximide, and mineral salts. However,
it decomposed rapidly when the soil suspension was added to a
culture medium suitable for fungal or bacterial growth (Takimoto et
al., 1976). The major decomposition product in the culture was
aminofenitrothion [13], the content of which reached 40-65%, and a
maximum 60-80% when formylamino-[15] and acetylamino- fenitrothion
[16] were combined. Demethyl fenitrothion [7] and
3-methyl-4-nitrophenol [9] were detected among other products. The
dominant species of microorganisms (Fusarium and Bacillus species),
isolated from the above soils, metabolized fenitrothion well.

When ring-labelled fenitrothion (7.4 mg/kg) was incubated with
two kinds of forest soils collected from the State of Maine, USA,
the half-life of fenitrothion at 30 °C was about 3 days. In 50 days,
94-97% of the fenitrothion had been decomposed yielding 35%
radioactive carbon dioxide, 5-7% 3-methyl-4-nitrophenol [9], 4%
3-methyl-4-nitroanisole [17], and approximately 50% of soil- bound
radioactivity (Spillner et al., 1979a).

It has been reported (National Research Council of Canada,
1975) that several species of soil and water bacteria, including
Bacillus subtilis, Escherichia coli, E. freundii, Pseudomonas
reptilovora, and P. aeruginosa, can metabolize or inactivate
fenitrothion.

The fungus Trichoderma viride can also hydrolyse fenitrothion
and fenitrooxon, and the hydrolysed product,
3-methyl-4-nitro-phenol, is co-metabolized by this fungus
(Baarschers & Heitland, 1986).

Flavobacterium sp. ATCC 27551, isolated from paddy field,
hydrolysed fenitrothion to yield 3-methyl-4-nitrophenol [9] in
culture solutions containing mineral salts (Adhya et al., 1981c).

A crude cell extract from a mixed bacterial culture growing on
parathion also hydrolysed fenitrothion to yield
3-methyl-4-nitro-phenol [9]. The chemical hydrolysis of fenitrothion
was 3-5 times slower than that of parathion. However, the rate of
enzymatic hydrolysis was 24-205 times faster than that of chemical
hydroly-sis by 0.1 N sodium hydroxide at 40 °C (Munnecke, 1976).

Liu et al. (1981) studied the biodegradability of fenitrothion
using a mixed-culture of microorganisms from activated sludge, soil,
and sediments, under aerobic and anaerobic conditions. Fenitrothion
was more readily degraded under anaerobic co-metabolic conditions
(half-time = 1.0 day) than under aerobic conditions (half-time = 5.5
days). When fenitrothion was applied to the medium as the sole
source of carbon, its stability was greater under aerobic
conditions, 77% of the initial dose being recovered after 164 h
incubation.

4.2.2.2 Biodegradation and bioaccumulation in organisms

a) Aquatic organisms

The accumulation and partitioning of fenitrothion residues
among different tissues and organs in wild trout were investigated
following 2 applications of the compound to a lake (280 g a.i./ha
with a 9-day interval). Fenitrothion residues accumulated fairly
rapidly in the tissues of both brook trout and lake trout. Peak
levels of fenitrothion were reached 2-4 days after the first
application (in lake trout, fat: 280 µg/kg, muscle: 96.8 µg/kg,
intestine: 96.3 µg/kg, liver: 16.1 µg/kg, ovary: 48.2 µg/kg) and 8
days after the second application (in lake trout, fat: 665 µg/kg,
muscle: 133 µg/kg, intestine: 114 µg/kg, liver: 39.6 µg/kg). These
levels were many times higher than those in the surrounding waters
of Lac Ste-Anne. Fenitrothion residues continued to persist in lake
trout tissues (but not in the tissues of brook trout) up to at least
8 days after the second application, even though the residues in the
water had declined to non-detectable levels 4 days earlier (Holmes
et al., 1984).

When exposed to running water containing 0.1 or 0.02 mg
fenitrothion/litre, both underyearling rainbow trout ( Salmo
gairdneri) and southern top-mouthed minnow ( Pseudorasbora parva)
rapidly absorbed the chemical (Takimoto & Miyamoto, 1976a). The
fenitrothion concentration in the fish reached a maximum after 1-3
days of exposure, and then remained virtually constant. The
bioaccumulation ratio did not increase on longer exposure and was
more or less independent of the fenitrothion concentration in water.
The ratio was similar in the 2 fish species, being approximately
250, 230, and 200 (at its maximum) in underyearling trout, yearling
trout, and minnow, respectively. Once the fish were transferred
from fenitrothion-containing water to fresh water, the levels of
fenitrothion in the fish decreased rapidly to about 0.01 mg/kg in 5
days. None of the fish species exhibited noticeable signs of
intoxication during the exposure period. In another study, the
bioaccumulation ratio for the fresh-water species, top-mouthed
minnow, was 246 (Kanazawa, 1981).

Killifish (Oryzias latipes) took up fenitrothion in a flow
system with bioaccumulation ratios at different developmental stages
of: 115 in embryos, 173 in yolk sac fry, 88 in postlarval stages,
441 in juveniles, 520 in adult males, 540 in adult females, and 224
in eggs produced from fenitrothion-exposed adults (Takimoto et al.,
1984a). However, the half-lives of disappearance of the compound in
clean water were less than 2 days, independent of fat content.

Similar results were reported with southern top-mouthed minnows
in a static aquarium test; the fenitrothion concentration in water
at 23 °C decreased from 0.81 mg/litre to 0.002 mg/litre in 28 days,
while the observed maximum concentration of fenitrothion in the fish
(162 mg/kg on the 4th day) decreased to 4.9 mg/kg after 28 days
(Kanazawa, 1975).

With respect to the distribution and metabolism of
fenitrothion, autoradiograms of rainbow trout exposed to labelled
fenitrothion under static water conditions for 6 h revealed that the
concentration of radiocarbon was highest in the gall bladder and
intestines; after 24 h, the radiocarbon was present in every tissue,
except the brain and heart. Twenty-four hours after the transfer of
the fish to fresh water, most of the radioactivity in the tissues
had disappeared. Only the gall bladder, intestines, and pyloric
caeca still contained an appreciable amount of the radiocarbon.
Intact fenitrothion accounted for 90% of the absorbed radioactivity
in fish. The remaining 10% comprised fenitrooxon [1], demethyl
fenitrothion [7], 3-methyl-4-nitrophenol [9], and its glucuronide
[27]. In water, the percentage of these degradation products
increased with time and amounted to 25% of the radioactivity.
Because fenitrothion is stable in water under the experimental
conditions, the degradation products are presumably derived from
fish metabolism (Takimoto & Miyamoto, 1976a) (see Fig. 4).

All developmental stages of killifish metabolized fenitrothion
mainly to 3-methyl-4-nitrophenyl-ß-glucuronide [27] (comprising
20-40% of ¹⁴C), except the embryo, which had the lowest metabolic
activity. Yolk sac fry contained the highest concentration (28%) of
demethyl fenitrothion [7]. Fenitrooxon [1] and demethyl fenitrooxon
[20] were present in small amounts, at the most, 0.5%. These
metabolites and the intact fenitrothion were eliminated into the
surrounding water, when the fish were transferred to fresh water
(Takimoto et al., 1984a).

Absorption of [methyl-¹⁴C]-fenitrothion at 0.1 mg/litre in
running water to a similar plateau level in the killifish (Oryzias
latipes) was more rapid at 25 °C than at 15 °C; the bioaccumulation
ratios of fenitrothion were 235 and 339, respectively. Water of
higher salinity (2.3%) resulted in slightly higher accumulation

ratios of fenitrothion in both killifish (303) and mullet, Mugil
cephalus (179), than fresh water (235 and 30, respectively), but the
half-lives were independent of temperature and salinity, with values
of 0.24-0.36 day. Fenitrothion was metabolized, primarily through
hydrolysis, to [9] by the killifish, demethylation to demethyl
fenitrothion [7] by the mullet, and conjugation of the liberated
phenol with glucuronic acid [27] by both species. Although the
metabolism of the compound in both fish was not affected by the
different salinities and temperatures, the glucuronide conjugate was
more directly excreted into water under conditions of lower
temperature and higher salinity. ¹⁴C-labelled compounds were
distributed primarily to the gall bladder, as shown by whole-body
radioautography (Takimoto et al., 1987a).

Bluegill sunfish (Lepomis macrochirus) was exposed to
[phenyl-¹⁴C] - fenitrothion or non-radiolabelled fenitrothion in a
flow-through system at concentrations of 0.049 mg/litre and 0.043
mg/litre, respectively, for a 28-day exposure period. The
concentrations of labelled and non-labelled fenitrothion in whole
fish reached an equilibrium on days 1-3 of exposure at levels of 5.4
and 1.3 mg/litre, respectively. Mean bioconcentration factors for
labelled and non-labelled fenitrothion during the uptake period were
respectively 111 and 29 for whole fish, 26 and 10 for the edible
portion, and 279 and 36 for the non-edible portion. When the exposed
fish were transferred to running fresh water, the concentrations of
labelled and non-labelled fenitrothion in the fish decreased
rapidly, with biological half-lives of less than 1 day in both the
edible and non-edible portions of the fish. A non-linear
2-compartment, kinetic modelling computer programme estimated 81.9
and 111 as the uptake rate constants (K1), 0.69 and 3.72 as the
depuration rate constants (K2), and 118 and 30 as the
bioconcentration factors (BCF) for labelled and non-labelled
fenitrothion, respectively. Fenitrothion was metabolized through the
oxidation of P=S to P=O, demethylation of the P-O-alkyl linkage,
cleavage of the P-O-aryl linkage, and conjugation of the phenol with
glucuronic acid. The major metabolites were demethylfenitrothion [7]
and 3-methyl-4-nitrophenyl-ß-glucuronide [27], amounting to 29-40%
and 11-15% of the recovered ¹⁴C from the whole fish, respectively
(Ohshima et al., 1988).

Freshwater teleosts ( Tilapia mossambica; body weight, 5-9 g;
length, 5-7 cm) were exposed to 200 mg fenitrothion/kg body weight
for 24 h. Fenitrothion and its metabolites, extracted from the
liver, kidney, and brain, were separated and identified using HPLC
and preparative silica gel TLC. The metabolites extracted from the
liver were identiied as fenitrooxon, N-acetylaminofenitrothion
[16], and fenitrothion. The metabolites from the kidney were
identified as demethyl- N-acetylaminofenitrooxon [37]. The
metabolites from the brain were identified as 3-methyl-4-nitrophenol
[9] and demethyl- N-acetylamino-fenitrooxon [37] (Anjum & Qadri,
1986).

McLeese et al. (1979) reported that accumulation ratios of
fenitrothion were independent of the exposure levels, and were
19-35, 78-130, and 9, in marine clam (Mya arenaria), mussel (Mytilus
edulis), and freshwater clam (Anodonta cataractae), respectively.

When freshwater snails ( Cipangopaludina japonica and Physa
acuta) were exposed to 0.1 mg [methyl-¹⁴C]-fenitrothion/litre in
a dynamic flow system, the concentrations of fenitrothion and
¹⁴C-label in the body reached equilibrium on day one of exposure.
The maximum bioaccumulation ratios of fenitrothion were 18 and 53 in
C. japonica and P. acuta, respectively. These snails metabolized
the compound primarily by demethylation to [7], hydrolysis to [9],
and reduction to [13], and [14]. The liberated phenol moiety was
conjugated with sulfate [26] in C. japonica and mainly with
glucose [18] in P. acuta. When the snails were transferred to a
freshwater stream, fenitrothion and its metabolites were rapidly
eliminated, and the half-life of the parent compound was less than
0.5 days in both snails. In P. acute, fenitrothion and its
decomposition products were mainly distributed in the liver as shown
by whole-body radioautography (Takimoto et al., 1987b).

When the waterflea Daphnia pulex and the shrimp Palaemon
paucidens were exposed to 1.0 µg [methyl-¹⁴C]-fenitrothion/litre
in a flow-through system, the concentrations of fenitrothion and
¹⁴C-label in the body reached equilibrium (on day one of exposure)
and the maximum bioaccumulation ratios of fenitrothion were 71 and 6
in the daphnia and shrimp, respectively. These crustaceans primarily
metabolized the compound through oxidation of P = S to P = O to form
compound [1], hydrolysis of P-O-aryl linkage to form compound [9],
and demethylation to give compounds [7] and [20]. The liberated
phenol was conjugated with sulfate to form compound [26] in D.
pulex and with glucose to form compound [18] in the shrimp. When
the organisms were transferred to a freshwater stream, fenitrothion
and its metabolites were rapidly eliminated from their bodies, and
the half-life of the parent compound was less than 0.2 day in both
species (Takimoto et al., 1987c) (see Fig. 4).

The uptake rate of radiolabelled fenitrothion by the blue crab
(Callinectes sapides) increased with temperature and salinity. The
highest concentrations of radioactivity were found in the
hepato-pancreas and stomach. The blue crab can metabolize
fenitrothion to produce fenitrooxon, aminofenitrothion,
3-methyl-4-nitrophe-nol, 3-methyl-4-aminophenol, demethyl
fenitrothion, demethyl fenitrooxon, and glycoside and sulfate
conjugates of the phenols (Johnston & Corbett, 1986).

Aquatic plants were collected and analysed after the aerial
application of fenitrothion (280 g/ha) in Manitoba, Canada, (Moody
et al., 1978); the fenitrothion residues present in surface-
dwelling duckweed, obtained from stagnant water, disappeared rapidly
from 1.44 mg/kg after 1 h to 0.03 mg/kg after 192 h, while the
submerged hornwort, also from stagnant water, contained rather
persistent, but low, residues of fenitrothion ranging from 0.12 to
0.15 mg/kg after 192 h. No fenitrothion was detected in the
submerged flowering rush in running water.

Chlorella pyrenoidosa exposed to 10 mg radioactive
fenitrothion per litre rapidly took up the compound and the ¹⁴C
level reached equilibrium after 4 h with a bioaccumulation ratio of
417. On transfer to fresh water, the fenitrothion in the chlorella
was rapidly desorbed (Weinberger et al., 1982b). Other algae
( Chlamydomonas reinhardii and Euglena gracilis) showed less
bioaccumulation of fenitrothion. The aquatic macrophyte, Elodea
densa, showed a bioaccumulation ratio of 24-76 (Weinberger et al.,
1982b).

Three types of algae, Chlorella vulgaris, Nitzschia
closterium, and Anabaena flos-aquae, also rapidly absorbed
fenitrothion with maximum bioaccumulation ratios of 44, 105, and 53,
respectively (Kikuchi et al., 1984). Only A. flos-aquae (blue-green
algae) actively degraded fenitrothion. When transferred to a
fenitrothion-free medium, these algae released fenitrothion, as well
as its metabolites, with half-lives of the compounds of less than 1
day, except in the case of A. flos-aquae when the half-life was 2.6
days (see Fig. 4).

Bioaccumulation ratios for fenitrothion in 2 species of
blue-green algae (Anabaena sp. and Aulosira fertilissima) were
reported to be 42-347 and 136-784, respectively, when exposed to 1,
5, or 10 mg/litre (Lal et al., 1987).

In a field test in which fenitrothion was sprayed twice at 210
g/ha, to give a maximum concentration of 0.9 µg/litre in surface
water and 0.42 µg/litre in subsurface water (3 m depth),
phyto-planktons and zooplanktons contained maximum levels of 0.05
and 0.014 µg fenitrothion/litre, respectively, the concentrations
decreasing with time (Lakshminarayama & Bouque, 1980).

b) Birds

When male Hubbert chickens were intubated with fenitrothion at a
dose of 10 mg/kg, twice every other week, for 2-8 weeks, the residue
levels in the brain, blood, liver, and adipose tissue were less than
0.071 mg fenitrothion equivalent/kg wet tissue. None of the tissues
retained any significant amounts of fenitrothion or its metabolites,
and no tendency towards bioaccumulation was observed (Trottier &
Jankowska, 1980).

White Leghorn hens, dosed with 2 mg fenitrothion/kg body weight
for 7 consecutive days, discharged 95% of the radioactivity in the
excreta within 6 h following the last administration. The
radioactivity in the hen egg-white decreased sharply after the last
dosage, with the highest concentration (0.02 mg/kg) recorded on the
third day of administration. The egg yolk showed a maximum
radiocarbon level of 0.10 mg/kg (fenitrothion, 0.006 mg/kg), 1 day
after the last dose, followed by a decline to 0.02 mg/kg after 1
week (Mihara et al., 1979).

After oral administration of ring-labelled ¹⁴C fenitrothion
at 5 mg/kg body weight to female Japanese quails, 99% of the
radio-carbon was eliminated during the first 24 h (Miyamoto, 1977a).

When [phenyl-¹⁴C]-fenitrothion was administered orally to
Japanese quails in a single dose of 5 mg/kg body weight or to White
Leghorn hens at a daily dose of 2 mg/kg body weight for 7 days,
97-99% of the radiocarbon was eliminated in the mixture of urine and
faeces within one day. The radioactivity in the eggs was, at most,
0.2% of the parent compound (0.055 mg/kg). More than 18 metabolites
were found in the excreta. The major metabolites were
3-methyl-4-nitrophenol [9] and its sulfate conjugate [26], which
accounted for 70.5% of the dose in quails and 50.8% in hens.
Demethylfenitrothion [7] and demethylfenitrooxon [20] were found as
minor metabolites; several m-methyl oxidation products were also
detected. In vitro studies revealed that the oxidation activity of
hen, quail, pheasant, and duck liver enzymes at the m-methyl group
of fenitrooxon was higher than that of mammalian liver enzymes,
though the avian enzymes had extremely low O-demethylase activity
(Mihara et al., 1979) (see Fig. 5).

c) Terrestrial organisms

Lactating Japanese Sannen goats were treated orally with
[phenyl-¹⁴C]-fenitrothion at 0.5 mg/kg body weight per day for 7
days. One day after treatment, no residues of intact fenitrothion
were found in the organs and tissues, but a small amount of
aminofenitrothion [13] was detected in the digestive tracts (rumen,
omasum, and large intestine). The administered radiocarbon was
essentially quantitatively eliminated during the week following
treatment; 50% of the dose was recovered in the urine, 44%, in
faeces, and 0.1%, in the milk with a maximum concentration of 0.011
mg/litre. The major metabolites in the urine, faeces, and milk were
aminofenitrothion [13] and O-methyl O-hydrogen
O-(3-methyl-4-acetyl-aminophenyl) phosphate [37], and
O,O-dimethyl O-(3-methyl-4-sulfo-aminophenyl) phosphorothioate
(N-sulfo-aminofenitrothion) [38], respectively. No intact
fenitrothion or fenitrooxon was found in the milk, urine, or faeces
(Mihara et al., 1978) (see Fig. 6).

When 30 calves (1-1.5 years old, average weight, 243 kg) were
confined on a pasture sprayed with 378 g fenitrothion/ha (initial
residue on grass, 11.8 mg/kg), the meat and fat contained about 0.01
mg fenitrothion residues/kg on the first day. No fenitrothion
residues were found in the meat from the third day on, and only
0.004-0.007 mg fenitrothion/kg was found in the fat on the third
day; these amounts decreased to almost control levels by the seventh
day (Miyamoto & Sato, 1969).

Silage prepared from corn treated with 1.1, 2.2, or 3.4 kg
fenitrothion/ha was fed to lactating Jersey cattle for 8 weeks.
Although traces (0.001-0.005 mg/kg) of aminofenitrothion [13] were
found in the milk of cows fed 3.4 kg fenitrothion/ha silage, no
residues (< 0.001 mg/kg) were found in the milk of cows that had
consumed the silage treated at lower levels (Leuck et al., 1971).

Jersey cows, administered 3 mg fenitrothion/kg body weight for
7 consecutive days, produced milk containing fenitrothion and
aminofenitrothion [13] levels of up to 0.002 and 0.003 mg/kg,
respectively. However, levels were undetectable within 2 days of the
last dose (Miyamoto et al., 1967).

Johnson & Bowman (1972) reported that neither fenitrothion nor
its metabolites were detected in the milk of lactating Jersey cows,
7 days after being fed (for 28 days) a diet containing the pesticide
at a concentration of 1.84 mg/kg.

Topical application of a lethal dose of fenitrothion to spruce
budworm ( Choristoneura fumiferana) resulted in the formation of
3-methyl-4-nitrophenol (2-17%) and desmethyl fenitrothion (2-4%).
Trace levels (1-2% of the applied dose) of fenitrooxon were also
detected (Sundaram, 1988).

4.2.2.3 Abiotic and biological degradation in/on plants

The photolysis and metabolic pathways of fenitrothion in plants
are illustrated in Fig. 7.

One half the amount of fenitrothion applied at 12 mg/kg to rice
plants at the preheading stage was lost by evaporation and only 10%
was left on the plant surface after 24 h, 50% penetrating into
tissues (Miyamoto & Sato, 1969). Although fenitrooxon [1] was
detected at 0.01-0.86 mg/kg in leaf sheaths and blades (not in
harvested grains), it disappeared faster than fenitrothion.

The half-lives of fenitrothion were 1-3 days on, and in,
fenitrothion-treated apples (approx. 4.5 mg/kg) growing on the tree
under natural conditions, with fenitrooxon [1] (0.005 mg/kg) and
S-methyl fenitrothion [8] (approx. 0.005 mg/kg), on the fruit and
demethyl fenitrothion [7] (0.012 mg/kg), 3-methyl-4-nitro-phenol

[9] (0.024 mg/kg), and its glucose conjugate [18] in the fruit after
21 days (Hosokawa & Miyamoto, 1974). It was concluded that the fruit
metabolized the penetrating fenitrothion gradually to
3-methyl-4-nitrophenol [9], and further to the glucose conjugate
(e.g., [18]) in the tissues; this was combined with the
disappearance of fenitrothion on the fruit surface through
photodecomposition and volatilization.

A number of residue data are available on various feed plants
(Sumitomo, 1969; Takimoto & Miyamoto, 1976b). Coastal Bermuda grass
and corn treated with fenitrothion at 1, 2, and 3 kg/ha were
analysed for residues of the parent compound and some metabolites
(Leuck & Bowman, 1969); the residues of fenitrothion diminished
rapidly to approximately one hundredth of the initial levels after
14 days. The fenitrooxon [1] contents were low, declining more
rapidly, and none was detected after 21 days. While the amounts of
3-methyl-4-nitrophenol [9] were highest in the 1- and 7-day samples,
the total residues on both crops diminished to less than 1 mg/kg in
28 days.

Under operational spraying (280 g/ha) for the control of
budworm, fenitrothion deposits (2-4 mg/kg, wet weight) on the
foliage of red and white spruce and balsam fir decreased by about
50% within 4 days, and 70-85% within two weeks. In some cases, about
10% of the initial deposit (0.05-0.5 mg/kg) persisted for most of
the year following spraying (Yule & Duffy, 1972).

To monitor the persistence of fenitrothion in the Canadian
forest, LaPierre (1985) measured residues in leaves. Immediately
following application (15 min) of fenitrothion to poplar ( Populus
tremuloidus) and gray birch trees ( Betula populifolia),
fenitrothion levels of 22 and 18 mg/kg, respectively, were detected.
Residue levels decreased to less than 1 mg/kg and 0.1 mg/kg,
respectively, within 30 and 120 days. No fenitrooxon was detected in
any of the samples. The observation, made by McNeil & McLeod (1977),
indicating that sawfly populations were depressed by persistent
fenitrothion residues in jack pine foliage apparently supported the
persistence of fenitrothion within leaf tissues. However, it may be
that, in this case, the fenitrothion was rather persistent because
of the special circumstances (in micro sink).

A complete disappearance of fenitrothion from spruce foliage
was observed, within 45 days, following operational spraying with
280 g/ha. The hardwood species within mixed forests, such as red
maple, appeared to collect 3-4 times higher deposits on their
foliage when exposed to the same operational spraying (National
Research Council of Canada, 1975), but the residues decreased
rapidly.

During environmental surveillance of aerial spraying of
fenitrothion, carried out from 1979 to 1982 in Quebec, the
insecticide concentrations were measured in foliage samples taken
from 1 to 4 h after spraying, when residue levels were likely to
have peaked. Over the 4 years studied, the median residue level of
fenitrothion found in balsam fir foliage was 3.81 mg/kg (dry
weight), with a maximum concentration of 111 mg/kg. On conifer
foliage, feni-trothion had a half-life of 2-4 days; 70-95% of the
residue dissipated in less than 2 weeks (Morin et al., 1986).

Takimoto et al. (1978) examined the stability of fenitrothion
(6 and 15 mg/kg) in stored rice grains. The insecticide decomposed
after 12 months to 22.0-26.3% and 64.7-65% of the initial dose at 30
and 15 °C, respectively. The major metabolites in rice grains were
demethyl fenitrothion [7] and 3-methyl-4-nitrophenol [9], which
amounted to 10.0-19.2% and 16.0-38.0% of the dose, respectively. In
addition, trace amounts of S-methyl fenitrothion [8], S-methyl
demethyl fenitrothion [21], fenitrooxon [1], demethyl fenitrooxon
[20], 3-hydroxymethyl-4-nitrophenol [22], 3-methyl-4-nitroanisole
[17], 1,2-dihydroxy-4-methyl-5-nitro-benzene [23], and
1,2-dimethoxy-4-methyl-5-nitrobenzene [24] were detected (see Fig.
7). Fenitrothion and its degradation products were distributed in
the outer portions of the endosperm and at 100 µm in depth from the
surface of rice grains stored for 12 months, as determined by
whole-body autoradiography. On cooking, the unpolished rice grains
treated with fenitrothion yielded 3-methyl-4-nitrophenol [9] and
demethyl fenitrothion [7] as primary degradation products.

Abdel-Kader & Webster (1980) and Abdel-Kader et al. (1982)
studied the stability of fenitrothion (8 mg/kg) in stored wheat.
Very little (< 3%) breakdown of the insecticide residue occurred on
wheat stored at -35 or -20 °C for 72 weeks. However, fenitrothion
residues decreased as the temperature increased. After 72 weeks, 18,
35, 56, 90, 96% of the initial deposit had degraded in wheat stored
at -5, 5, 10, 20, at 20 °C respectively. The major metabolites in
wheat stored at 20 °C for 12 months were demethyl fenitrothion [7],
3-methyl-4-nitrophenol [9], and dimethyl phosphorothioic acid [19]
(Fig. 7), as determined by GLC. Concentrations of demethyl
fenitrothion [7] and dimethyl phosphorothioic acid [19], which were
highest (2.01 and 0.55 mg/kg, respectively) after 6 months storage,
decreased to 0.98 and 0.21 mg/kg, respectively, at the end of
storage. The residue level of 3-methyl-4-nitrophenol [9] gradually
increased to 0.96 mg/kg after 12 months. No fenitrooxon [1] or
S-methyl fenitrothion [8] was detected throughout the experimental
period (Abdel-Kader & Webster, 1982).

When labelled fenitrothion was applied to bean leaves at a rate
of 84.5 µg/12.5 cm², 26 and 64% of the radioactivity was lost by
volatilization after 1 and 3 days, respectively. The decrease of the
parent compound was rapid, both on and in the leaf.

After 12 days, the major products remaining on the bean leaves were
fenitrooxon [1] (0.1%), carboxy-fenitrothion [3] (0.1%), and
3-carboxy-4-nitrophenol [10] (0.1%) (Ohkawa et al., 1974).

The residues of fenitrothion in coastal Bermudagrass and corn
diminished to less than 0.13 mg/kg in 28 days, with half-lives of
less than 1 day, following a spray of the emulsifiable concentrate
at 1, 2, or 3 kg a.i./ha. The major metabolite was
3-methyl-4-nitrophenol [9], with smaller amounts of fenitrooxon [1].
After 28 days, the residues had declined to less than 1 mg/kg for
all 3 rates of application (Leuck & Bowman, 1969).

In leaves of shrubbery ( Maesa japonica) sprayed twice with
fenitrothion at 735 g/ha, fenitrothion was detected at 78.3 mg/kg on
the day of application, but 99% had disappeared within a week.
Although fenitrooxon [1] was detected at levels of 0.1-0.3% of
fenitrothion in the leaves, it disappeared after strong rainfall,
35-37 days after application. Fenitrothion was detected in grasses,
and the upper and lower layers of the soil, at levels of 0.1, 0.01,
and 0.001 mg/kg, respectively, 144 days after application (Ohmae et
al., 1981).

Hallett et al. (1973) observed the transport of fenitrothion to
the embryo, and its metabolism in seed tissues, when pine seeds were
germinated for up to 54 days in an aqueous solution or suspension of
fenitrothion (10 or 1000 mg/litre). Laboratory studies of
fenitrothion on seeds of eastern white pine demonstrated penetration
and accumulation of the parent compound, its oxon, and the
S-methyl metabolites in the embryo and perisperm. This appeared to
alter the amino acid metabolism in the seed but did not affect the
later growth of seedlings (Hallett et al., 1974). No significant
differences in germination and growth were reported between the
seeds of white pine from areas sprayed at 140-280 g/ha and from
unsprayed (control) areas (Pomber et al., 1974).

Similarly, the seeds of white pine, white spruce, and yellow
birch readily absorbed fenitrothion when germinated for up to 21
days in an aqueous solution or suspension of fenitrothion (10 or
1000 mg/litre). Fenitrooxon [1], demethyl fenitrothion [7], and
S-methyl fenitrothion [8] were detected as primary metabolites in
all 3 species. The highest concentrations of [1], [7], and [8] were
1.4-75 mg/kg, 10-37 mg/kg, and 1-8 mg/kg, respectively. Hallett et
al. (1977) proposed that the formation of S-methyl fenitrothion [8]
resulted from the alkylation of demethyl fenitrothion by excess
fenitrothion in the conifer seeds. It is probable that [8] will be
formed in plants via the non-enzymatic alkylation reaction, if the
concentrations of fenitrothion and [7] are extremely high. However,
formation of [7] will be extremely low or negligible, when
fenitrothion is used at the recommended dosage.

Sundaram & Prasad (1975) established the uptake and
transportation of fenitrothion in young spruce trees by growing the
plants in a nutrient solution containing the insecticide. However,
when fenitrothion was applied to the needles of spruce and fir
trees, which are the part of the tree most exposed to the
insecticide during spraying, the foliar penetration of fenitrothion
was found to be extremely small. Furthermore, less than 0.1% of the
fenitrothion that had penetrated was translocated laterally and
upward to the untreated parts of the foliage. The amounts found in
the stems and roots were also negligible (Sundaram et al., 1975).

On the other hand, Moody et al. (1977) using an
autoradiographic technique, suggested the systemic potential of
fenitrothion applied to 4-year-old seedlings of balsam fir and, to a
lesser extent, white spruce, and jackpine.

Prasad & Moody (1976) also found that, mainly because of
volatilization, 70% of the applied fenitrothion was lost one day
after treatment, though low levels of the insecticide (0.48 mg/kg
after 21 days) persisted in conifer tissues.

When labelled fenitrothion was applied to the leaves of
Japanese cypress at about 300 µg per leaf, approximately 70-80% of
the applied dose disappeared, mainly through evaporation, within 24
h. The major metabolites in the treated leaves were demethyl
fenitrothion [7], 3-methyl-4-nitrophenol [9] (approx. 2-10 µg), and
its glucoside conjugate [18] (Tabata & Okubo, 1980).

Immediately following the application of fenitrothion to poplar
( Populus tremuloidus) and birch trees ( Betula populifolia),
levels of 22 and 18 mg/kg, respectively, were detected. Residue
levels dropped to under 1 mg/kg within 30 days of treatment, and
under 0.1 mg/kg by 120 days. The oxygen analogue, fenitrooxon, was
not detected in any of the samples (La Pierre, 1985).

5. ENVIRONMENTAL LEVELS AND HUMAN EXPOSURE

5.1 Environmental levels

5.1.1 Air

In the 1980 spray programme in Canada, fenitrothion was
detected occasionally in air, the maximum concentration being 12
ng/m³ (Mallet, 1980), when the compound was sprayed at 140-280
g/ha.

Collaborative field studies were initiated in 1978 in Canada to
obtain relevant information concerning long-range pesticide drift
during the aerial spraying of fenitrothion in forest pest control,
using a surrogate (tris(2-ethylhexyl)phosphate) (Crabbe et al.,
1980a). At approximately 7.5 km downwind of the spray, the peak
treetop concentration of the drifting cloud varied from 1.4 ng/litre
in relatively neutral conditions to 5.0 ng/litre in the most stable
conditions. The fraction of the tracer material still airborne, 7.5
km from the spray line, was 6 and 16% for the neutral and most
stable environmental tests, respectively.

In 1980, a study was conducted to measure the atmospheric
fenitrothion exposure levels at breathing height near aerial
forestry spray operations (Crabbe et al., 1980b). The results
revealed an aerial concentration (or dosage) of 40 ng/min per litre¹
at the spray line (flight path of aircraft) falling to an average of
8 ng/min per litre, 700 m from the spray line, in the first hour
after delivery. During the first hour after spraying, 30% of the
material collected in the samplers was vapour and the rest, aerosol.
Droplets of approx. 4.0 µm diameter contributed most to the mass of
drifting spray cloud at 500 m, about 15% of the airborne aerosol
mass consisting of droplets larger than 25 µm in diameter. The peak
aerosol concentration at chest height underneath the sprayed swath
of forest was approximately 15 ng/litre. One result of considerable
interest was the degree of volatilization of fenitrothion from an
early morning spray, which resulted in a sustained vapour plume
during the afternoon with a concentration

¹ The value nanograms/min per litre represents the time
integrated aerial concentration of fenitrothion consisting of
the mean aerosol cloud concentration of agent (nanograms per
litre) divided by the residence time (minutes) of the cloud.

of 25 ng/litre at the spray line, falling to approximately 1.0
ng/litre 100 m downwind of the swath at an ambient temperature of
20-25 °C. The vapour plume persisted throughout the day and, in a
10-h period following spraying, was estimated to contribute up to
0.4 µg/person of respirable fenitrothion.

A pesticide residue survey was conducted in relation to the
1980 spruce budworm spray programme (210 g a.i./ha applied twice
with a 3-day interval) in New Brunswick, Canada. Fenitrothion was
detected occasionally in the air, the maximum level being 1.2
µg/m³. Amino-fenitrothion was sometimes present in the air at a
maximum level of 12.0 µg/m³ (Mallet & Volpe, 1982).

A chemical residue survey was undertaken to determine the
extent of the deposition and persistence of fenitrothion in the
environment in relation to the 1981 spruce budworm spray programme
(210 g a.i./ha applied twice with a 7-day interval) in New
Brunswick, Canada. Fenitrothion was only detected twice in the air
at levels of 0.08 and 0.04 µg/m³ (Mallet & Cassista, 1984).

When a 1.0% emulsion of fenitrothion was applied to a 61.2 m³
room (3.7 ± 0.3 g a.i./room) at 23.5-25.4 °C, using a compressed air
sprayer, the airborne concentrations of fenitrothion on days 0 and 3
after application were 3.3 µg/m³ and 0.5 µg/m³, respectively
(Wright et al., 1981).

5.1.2 Water

In actual field spraying in Canada, concentrations of
fenitrothion in stream waters varied greatly, depending on the spray
history and the weather. Spraying at 210 g/ha resulted in measurable
concentrations (> 0.03 µg/litre) in streams as far as 4 km from the
sprayed area. However, at 140-210 g/ha, most peak concentrations
were lower than 15 µg/litre and diminished very rapidly in
fast-flowing streams. Disappearance was still faster when a rain
storm followed spray application (Eidt & Sundaram, 1975).

High peak concentrations of fenitrothion were recorded in a few
cases, e.g., 64 µg/litre in flowing stream water approximately 1 h
after completion of spraying, and 75.5 µg/litre in stagnant water
some 17 h after spraying at 140-280 g/ha (Lockhart et al., 1977).
Fenitrothion concentrations usually dropped to less than 1 µg/litre
within a few days in forest streams and beaver ponds after
experimental and operational applications of 140-280 g/ha by
aircraft (Flannagan, 1973; Peterson & Zitko, 1974; Sundaram, 1974;
Eidt & Sundaram, 1975), and no measurable traces of fenitrothion
have been found in water longer than 40 days after spraying.
According to Symons (1977), the fenitrothion concentration in water
immediately after aerial spray at 140-280 g/ha in Canada seldom
exceeded 15 µg/litre.

One hour after the first application of fenitrothion (280 g
a.i./ha, applied twice with a 9-day interval) to a lake,
fenitrothion residues in the water were concentrated near the
surface (0.80-0.90 µg/litre), with small amounts (0.06 µg/litre) at
the bottom. Six hours later, residues were fairly evenly distributed
throughout the water column (0.91-1.49 µg/litre). Residue levels, 97
h after treatment, were similar at all depths at 0.41-0.46 µg per
litre, but declined rapidly in the next 48 h to < 0.01-0.06
µg/litre. Similar results were obtained after the second application
(Holmes et al., 1984).

Sundaram (1973) also reported that concentrations of
fenitrothion in aqueous systems diminished rapidly by dilution and
by physicochemical and microbial degradation to low levels (0.03
µg/litre) within a period of 40 days. The half-lives were found to
be short, ranging from 0.25 to 3.5 days.

In the 1980 spruce budworm spray programme in Canada,
fenitrothion was usually detected in water in the im