INTERNATIONAL PROGRAMME ON CHEMICAL SAFETY
ENVIRONMENTAL HEALTH CRITERIA 145
METHYL PARATHION
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.
Published under the joint sponsorship of
the United Nations Environment Programme,
the International Labour Organisation,
and the World Health Organization
First draft prepared by Dr R.F. Hertel and co-workers,
Fraunhofer Institute of Toxicology and Aerosol
Research, Hanover, Germany
World Health Orgnization
Geneva, 1993
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WHO Library Cataloguing in Publication Data
Methyl parathion.
(Environmental health criteria ; 145)
1.Environmental exposure 2.Methyl parathion - adverse effects
3.Methyl parathion - poisoning 4.Methyl parathion - toxicity
I.Series
ISBN 92 4 157145 4 (NLM Classification: WA 240)
ISSN 0250-863X
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CONTENTS
ENVIRONMENTAL HEALTH CRITERIA FOR METHYL
PARATHION
1. SUMMARY AND EVALUATION, CONCLUSIONS, 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
2.1.1. Primary constituent
2.1.2. Technical product
2.1.2.1. Purity
2.2. Physical and chemical properties
2.3. Conversion factors
2.4. Analytical methods
2.4.1. Sampling, extraction, clean-up
2.4.1.1 Plant material (tobacco,
fruits, vegetables, crops
with low oil (fat) content)
2.4.1.2 Dairy products, products with a
high fat content (edible fats)
2.4.1.3 Blood, body fluids
2.4.1.4 Soil, sediments
2.4.1.5 Water
2.4.1.6 Air
2.4.1.7 Formulations
2.4.2. Instrumental analytical methods
2.4.2.1 Gas chromatography
2.4.2.2 High performance liquid chroma-
tography (HPLC)
2.4.2.3 Thin layer chroma-
tography (TLC)
2.4.2.4 Spectrophotometry
2.4.2.5 Polarography
2.4.2.6 Mass spectrometry
2.4.3. Detection limits
2.4.4. Confirmatory method
3. SOURCES OF HUMAN AND ENVIRONMENTAL EXPOSURE
3.1. Natural occurrence
3.2. Man-made sources
3.2.1. Production process
3.2.2. Loss into the environment
3.2.3. Production
3.2.4. World consumption
3.2.5. Formulations
3.3. Uses
4. ENVIRONMENTAL TRANSPORTATION, DISTRIBUTION, AND TRANSFORMATION
4.1. Transportation and distribution between media
4.1.1. Air
4.1.2. Water
4.1.3. Soil
4.1.4. Vegetation and wildlife
4.1.5. Entry into the food-chain
4.2. Biotransformation
4.2.1. Degradation involving biota
4.2.2. Abiotic degradation
4.2.2.1 Photodegradation
4.2.2.2 Hydrolytic degradation
4.2.3. Bioaccumulation
4.3. Interaction with other physical,
chemical, and biological factors
4.4. Ultimate fate following use
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
5.1.5. Terrestrial and aquatic organisms
5.2. General population exposure
5.3. Occupational exposure during
manufacture, formulation, or use
6. KINETICS AND METABOLISM
6.1. Absorption
6.2. Distribution
6.3. Metabolic transformation
6.4. Elimination and excretion in expired air,
faeces, or urine
6.5. Retention and turnover
7. EFFECTS ON ORGANISMS IN THE ENVIRONMENT
7.1. Microorganisms
7.1.1. Bacteria and fungi
7.1.2. Algae
7.2. Aquatic animals
7.2.1. Short-term toxicity in
aquatic invertebrates
7.2.1.1 Laboratory studies on
single species
7.2.1.2 Mesocosmic studies
7.2.2. Fish
7.2.2.1 Laboratory studies on
single species
7.2.2.2 Mesocosmic studies
7.2.3. Amphibians
7.3. Terrestrial organisms
7.3.1. Plants
7.3.2. Invertebrates
7.3.3. Birds
7.3.4. Non-laboratory mammmals
8. EFFECTS ON EXPERIMENTAL ANIMALS AND IN VITRO TEST SYSTEMS
8.1. Single exposure
8.2. Skin and eye irritation, sensitization
8.3. Short-term exposures
8.4. Long-term exposures
8.5. Reproduction, embryotoxicity,
and teratogenicity
8.6. Mutagenicity related end-points
8.7. Carcinogenicity
8.8. Special studies
8.9. Factors toxicity
8.10. Mode of action
8.10.1. Inhibition of esterases
8.10.2. Possible alkylation of
biological macromolecules
8.10.3. General
9. EFFECTS ON MAN
9.1. General population exposure
9.1.1. Acute toxicity
9.1.2. Effects of short- and
long-term exposure,
controlled human studies
9.2. Occupational exposure
9.2.1. Epidemiological studies
10. PREVIOUS EVALUATIONS BY INTERNATIONAL BODIES
REFERENCES
ANNEX I
RESUME
RESUMEN
WHO TASK GROUP ON ENVIRONMENTAL HEALTH
CRITERIA FOR METHYL PARATHION
Members
Dr L.A. Albert, Consultores Ambientales Asociados, S.C.,
Xalapa, Veracruz, Mexico (Vice-Chairman)
Dr S. Dobson, Ecotoxicology and Pollution Section, Institute of
Terrestrial Ecology, Monks Wood Experimental Station, Abbots
Ripton, Huntingdon, Cambridgeshire, United Kingdom
Dr D.J. Ecobichon, Pharmacology and Therapeutics, McGill
University, Montreal, Canada (Chairman)
Dr R.F. Hertel, Fraunhofer Institute of Toxicology & Aerosol
Research, Hanover, Germany (Co-rapporteur)
Dr S.K. Kashyap, National Institute of Occupational Health,
Meghaninagar, Ahmedabad, India
Dr I. Nordgren, Department of Toxicology, Karolinska Institute,
Stockholm, Sweden
Dr K.C. Swentzel, Toxicology Branch II, Health Effects Division,
US Environmental Protection Agency, Washington, DC, USA
(Co-rapporteur)
Dr M. Tasheva, Department of Toxicology, Institute of Hygiene and
Occupational Health, Medical Academy, Sofia, Bulgaria
Dr L. Varnagy, Department of Agrochemical Hygiene, University of
Agricultural Sciences, Institute for Plant Protection,
Keszthely, Hungary
Observers
Dr W. Flucke, Bayer AG, Fachbereich Toxikologie, Institut für
Toxikologie Landwirtschaft, Wuppertal, Germany
Secretariat
Dr K.W. Jager, International Programme on Chemical Safety, World
Health Organization, Geneva, Switzerland (Secretary)
Dr E. Matos, Unit of Carcinogen Identification and Evaluation,
International Agency for Research on Cancer (IARC), Lyon,
France
NOTE TO READERS OF THE CRITERIA
MONOGRAPHS
Every effort has been made to present information in the
criteria monographs as accurately as possible without unduly
delaying their publication. In the interest of all users of the
environmental health criteria monographs, 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 -
7985850).
NOTE: The proprietary information contained in this monograph
cannot replace documentation for registration purposes, because the
latter has to be closely linked to the source, the manufacturing
route, and the purity/impurities of the substance to be registered.
The data should be used in accordance with paragraphs 82-84 and
recommendations paragraph 90 of the Second FAO Government
Consultation (1982).
ENVIRONMENTAL HEALTH CRITERIA FOR METHYL
PARATHION
A WHO Task Group on Environmental Health Criteria for Methyl
Parathion met at the World Health Organization, Geneva from 19 to
23 August 1991. Dr K.W. Jager, IPCS, welcomed the participants on
behalf of Dr M. Mercier, Director 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 methyl parathion.
The first draft of the EHC on methyl parathion was prepared by
Dr R.F. Hertel and his co-workers of the Fraunhofer Institute of
Toxicology and Aerosol Research in Hanover, Germany. The same group
assisted in the preparation of the second draft, incorporating
comments received following circulation of the first drafts to the
IPCS contact points for Environmental Health Criteria monographs.
Dr K.W. Jager of the IPCS Central Unit was responsible for the
scientific content of the monograph, and Mrs M.O. Head of Oxford
for the editing.
The efforts of all who helped in the preparation and
finalization of the monograph are gratefully acknowledged.
1. SUMMARY AND EVALUATION, CONCLUSIONS, RECOMMENDATIONS
1.1 Summary and evaluation
1.1.1 Exposure
Methyl parathion is an organophosphorus insecticide that was
first synthesized in the 1940s. It is relatively insoluble in water,
poorly soluble in petroleum ether and mineral oils, and readily
soluble in most organic solvents. Pure methyl parathion consists of
white crystals; technical methyl parathion is a light tan colour with
a garlic-like odour. It is thermally unstable and undergoes fast
decomposition above pH 8.
Gas chromatography, with either alkali flame ionization (AFID) or
flame photometric (FPD) detectors, is the most common method for the
determination of methyl parathion. Detection limits range from 0.01 to
0.1 µg/litre in water, and from 0.1 to 1 ng/m3 in air. HPLC and TLC
are also useful methods of detection.
The distribution of methyl parathion in air, water, soil, and
organisms in the environment is influenced by several physical,
chemical, and biological factors.
Studies using model ecosystems and mathematical modelling
indicate that methyl parathion partitions mainly into the air and soil
in the environment with lesser amounts going to plants and animals.
There is virtually no movement through soil and neither the parent
compound nor its breakdown products will normally reach ground water.
Methyl parathion in air mainly arises from the spraying of the
compound, though some volatilization occurs with the evaporation of
water from leaves and the soil surface. Background atmospheric levels
of methyl parathion in agricultural areas range from not detectable to
about 70 ng/m3. Air concentrations after spraying have been shown to
decline rapidly over 3 days reaching background levels after about 9
days. Levels in river water (in laboratory studies) declined to 80% of
the initial concentration after 1 h and 10% after 1 week. Methyl
parathion is retained longer in soil than in air or water, though
retention is greatly influenced by soil type; sandy soil can lose
residues of the compound more rapidly than loams. Residues on plant
surfaces and within leaves decline rapidly with half lives of the
order of a few hours; complete loss of methyl parathion occurs within
about 6-7 days.
Animals can degrade methyl parathion and eliminate the
degradation products within a very short time. This is slower in lower
vertebrates and invertebrates than in mammals and birds.
Bioconcentration factors are low and the accumulated methyl parathion
levels transitory.
By far the most important route for the environmental degradation
of methyl parathion is microbial degradation. Loss of the compound in
the field and in model ecosystems is more rapid than that predicted
from laboratory studies. This is because of the variety of
microorganisms capable of degrading the compound in different habitats
and circumstances. The presence of sediment or plant surfaces, which
increases the microbial populations, increases the rate of breakdown
of methyl parathion.
Methyl parathion can undergo oxidative degradation, to the less
stable methyl paraoxon, by ultraviolet radiation (UVR) or sunlight;
sprayed films degrade under UVR with a half-life of about 40 h.
However, the contribution of photolysis to total loss in an aquatic
system has been estimated to be only 4%. Hydrolysis of methyl
parathion also occurs and is more rapid under alkaline conditions.
High salinity also favours hydrolysis of the compound. Half-lives of
a few minutes were recorded in strongly reducing sediments, though
methyl parathion is more stable when sorbed on other sediments.
In towns in the centre of agricultural areas of the USA, methyl
parathion concentrations in air varied with season and peaked in
August or September; maximum levels in surveys were mainly in the
range of 100-800 ng/m3 during the growing season. Concentrations in
natural waters of agricultural areas in the USA ranged up to 0.46
µg/litre, with highest levels in summer. There are only small numbers
of published reports on residues of methyl parathion in food
throughout the world. In the USA, residues of methyl parathion in food
have generally been reported at very low levels with few individual
samples exceeding maximum residue limits (MRLs). Only trace residue
levels of methyl parathion were detected in the total dietary studies
reported. Methyl parathion residues were highest in leafy (up to 2
mg/kg) and root (up to 1 mg/kg) vegetables in market basket surveys in
the USA between 1966 and 1969. Food preparation, cooking, and storage
all cause decomposition of methyl parathion residues further reducing
exposure of humans. Raw vegetables and fruits may contain higher
residues after misuse.
The production, formulation, handling, and use of methyl
parathion as an insecticide are the principal potential sources of
exposure of humans. Skin contact and, to a lesser degree, inhalation
are the main routes of exposure of workers.
In a study on farm spray-men (with unprotected workers using
ultra-low-volume (ULV) handsprays) an intake of 0.4-13 mg of methyl
parathion per 24 h was calculated from the excreted p-nitrophenol in
the urine. Early re-entry into treated crops is a further source of
exposure.
The general population may be exposed to air-, water-, and
food-borne residues of methyl parathion as a consequence of
agricultural or forestry practices, the misuse of the agent resulting
in the contamination of fields, crops, water, and air through
off-target spraying.
1.1.2 Uptake, metabolism, and excretion
Methyl parathion is readily absorbed via all routes of exposure
(oral, dermal, inhalation) and is rapidly distributed to the tissues
of the body. Maximum concentrations in various organs were detected
1-2 h after treatment. Conversion of methyl parathion to methyl
paraoxon occurs within minutes of administration. A mean terminal
half-life of 7.2 h was determined in dogs following intravenous (i.v.)
administration of methyl parathion. The liver is the primary organ of
metabolism and detoxification. Methyl parathion or methyl paraoxon are
mainly detoxified in the liver through oxidation, hydrolysis, and
demethylation or dearylation with reduced glutathione (GSH). The
reaction products are O-methyl O-p-nitrophenyl phosphorothioate or
dimethyl phosphorothioic or dimethylphosphoric acids and
p-nitrophenol. Therefore, it is possible to estimate exposure by
measuring the urinary excretion of p-nitrophenol; urinary excretion
of p-nitrophenol by human volunteers was 60% within 4 h and
approximately 100% within 24 h. The metabolism of methyl parathion is
important for species selective toxicity, and the development of
resistance. The elimination of methyl parathion and metabolic products
occurs primarily via the urine. Studies conducted on mice with
radiolabelled (32P-methyl parathion) revealed 75% of radioactivity in
the urine and up to 10% radioactivity in the faeces after 72 h.
1.1.3 Effects on organisms in the environment
Microorganisms can use methyl parathion as a carbon source and
studies on a natural community showed that concentrations of up to 5
mg/litre increased biomass and reproductive activity. Bacteria and
actinomycetes showed a positive effect of methyl parathion while fungi
and yeasts were less able to utilize the compound. A 50% inhibition of
growth of a diatom occurred at about 5 mg/litre. Cell growth of
unicellular green algae was reduced by between 25 and 80 µg methyl
parathion/litre. Populations of algae became tolerant after exposure
for several weeks.
Methyl parathion is highly toxic for aquatic invertebrates with
most LC50s ranging from < 1 µg to about 40 µg/litre. A few
arthropod species are less susceptible. The no-effect level for the
water flea (Daphnia magna) is 1.2 µg/litre. Molluscs are much less
susceptible with LC50s ranging between 12 and 25 mg/litre.
Most fish species in both fresh and sea water have LC50s of
between 6 and 25 mg/litre with a few species substantially more or
less sensitive to methyl parathion. The acute toxicity for amphibians
is similar to that for fish.
Population effects have been seen on communities of aquatic
invertebrates in experimental ponds treated with methyl parathion. The
concentrations needed to cause these effects would occur only with
overspraying of water bodies and, even then, would last for only a
short time. Population effects are, therefore, unlikely to be seen in
the field. Kills of aquatic invertebrates would be unlikely to lead to
lasting effects.
Care should be taken to avoid overspraying of ponds, rivers, and
lakes, when using methyl parathion. The compound should never be
sprayed under windy conditions.
Methyl parathion is a non-selective insecticide that kills
beneficial species as readily as pests. Kills of bees have been
reported following spraying of methyl parathion. Incidents concerning
bees were more severe with methyl parathion than with other
insecticides. Africanized honey bees are more tolerant of methyl
parathion than European strains.
Methyl parathion was moderately toxic for birds in laboratory
studies, with acute oral LD50s ranging between 3 and 8 mg/kg body
weight. Dietary LC50s ranged from 70 to 680 mg/kg diet. There is no
indication that birds would be adversely affected from recommended
usage in the field.
Extreme care must be taken to time methyl parathion spraying to
avoid adverse effects on honey bees.
1.1.4 Effects on experimental animals and in vitro test systems
Oral LD50 values of methyl parathion in rodents range from 3 to
35 mg/kg body weight, and dermal LD50 values, from 44 to 67 mg/kg
body weight.
Methyl parathion poisoning causes the usual organophosphate
cholinergic signs attributed to accumulation of acetylcholine at nerve
endings. Methyl parathion becomes toxic when it is metabolized to
methyl paraoxon. This conversion is very rapid. No indications of
organophosphorous-induced, delayed neuropathy (OPIDN) have been
observed.
Technical methyl parathion was found not to have any primary eye
or skin irritating potential.
In short-term toxicity studies, using various routes of
administration on the rat, dog, and rabbit, inhibition of plasma, red
blood cell, and brain ChE, and related cholinergic signs were
observed. In a 12-week feeding study on dogs, the no-observed-
adverse-effect level (NOAEL) was 5 mg/kg diet (equivalent to 0.1 mg/kg
body weight per day). In a 3-week dermal toxicity study on rabbits,
the no-observed-effect-level (NOEL) was 10 mg/kg body weight daily.
Inhalation exposure for 3 weeks indicated a NOEL of 0.9 mg/m3 air.
At 2.6 mg/m3, only slight inhibition of plasma ChE was observed.
Long-term toxicity/carcinogenicity studies were carried out on
mice and rats. The NOEL for rats was 0.1 mg/kg body weight per day,
based on ChE inhibition. There is no evidence of carcino genicity in
mice and rats, following long-term exposure. In another 2-year study
on rats, however, there was evidence of a peripheral neurotoxic effect
at a dose of 50 mg/kg diet.
Methyl parathion has been reported to have DNA-alkylating
properties in vitro. The results of most of the in vitro
genotoxicity studies on both bacterial and mammalian cells were
positive, while 6 in vivo studies using 3 different test systems
produced equivocal results.
In reproduction studies, at toxic dose levels (ChE inhibition),
there were no consistent effects on litter size, number of litters,
pup survival rates, and lactation performance. No primary teratogenic
or embryotoxic effects were noted.
1.1.5 Effects on human beings
Several cases of acute methyl parathion poisoning have been
reported. Signs and symptoms are those characteristic of systemic
poisoning by cholinesterase-inhibiting organophosphorous compounds.
They include peripheral and central cholinergic nervous system
manifestations appearing as rapidly as a few minutes after exposure.
In case of dermal exposure, symptoms may increase in severity for more
than one day and may last several days.
Studies on volunteers, following repeated, long-term exposures,
suggest that there is a decrease in blood cholinesterase activities
without clinical manifestations.
No cases of organophosphorous-induced, delayed peripheral
neuropathy (OPIDN) have been reported. Neuro-psychiatric sequelae have
been reported in cases of multiple exposure to pesticides including
methyl parathion.
An increase in chromosomal aberrations has been reported in cases
of acute intoxications.
No human data were available to evaluate the teratogenic and
reproductive effects of methyl parathion.
The available epidemiological studies deal with multiple exposure
to pesticides and it is not possible to evaluate the effects of
long-term exposure to methyl parathion.
1.2 Conclusions
Methyl parathion is a highly toxic organophosphorus ester
insecticide. Overexposure from handling during manufacture, use,
and/or accidental or intentional ingestion may cause severe or fatal
poisoning. Methyl parathion formulations may, or may not, be
irritating to the eyes or to the skin, but are readily absorbed. As a
consequence, hazardous exposures may occur without warning.
Methyl parathion is not persistent in the environment. It is not
bioconcentrated and is not transferred through food-chains. It is
degraded rapidly by many microorganisms and other forms of wild life.
This insecticide is likely to cause damage to ecosystems only in
instances of heavy over-exposure resulting from misuse or accidental
spills; however, pollinators and other beneficial insects are at risk
from spraying with methyl parathion.
Exposure of the general population to methyl parathion residues
occurs predominantly via food. If good agricultural practices are
followed, the Acceptable Daily Intake (0-0.02 mg/kg body weight),
established by FAO/WHO, will not be exceeded. Dermal exposure may
also occur through accidental contact with foliar residues in sprayed
fields or in areas adjacent to spraying operations as a consequence of
off-target loss of the chemical.
With good work practices, hygienic measures, and safety
precautions, methyl parathion is unlikely to present a hazard for
those occupationally exposed.
1.3 Recommendations
* For the health and welfare of workers and the general population,
the handling and application of methyl parathion should be
entrusted only to competently supervised and well-trained
applicators, who must follow adequate safety measures and use the
chemical according to good application practices.
* The manufacture, formulation, agricultural use, and disposal of
methyl parathion should be carefully managed to minimize
contamination of the environment.
* Regularly exposed workers should receive appropriate monitoring
and health evaluation.
* To minimize risks for all individuals, a 48-h interval between
the spraying and re-entry into any sprayed area is recommended.
* Pre-harvest intervals should be established and enforced by
national authorities.
* In view of the high toxicity of methyl parathion, this agent
should not be considered for use in hand-applied, ULV spraying
practices.
* Do not overspray water bodies. Choose spraying times to avoid
killing pollinating insects.
* Information on the health status of workers exposed only to
methyl parathion (i.e., in manufacture, formulation) should be
published, in order to better evaluate the risks of this chemical
for human health.
* More definitive studies should be conducted on residues of methyl
parathion in fresh foods.
* A more definitive genotoxic assessment of methyl parathion should
be conducted.
2. IDENTITY, PHYSICAL AND CHEMICAL PROPERTIES, ANALYTICAL METHODS
2.1 Identity
2.1.1 Primary constituent
Molecular formula: C8H10NO5PS
Relative molecular mass: 263.23
Common names: methyl parathion
accepted by
ESA (Entomological Society of
America)
JMAF (Japanese Ministry of
Agriculture, Fisheries and Food)
WHO (World Health Organization)
parathion-methyl
accepted by
BSI (British Standards Institution)
ISO (International Organization for
Standardization)
metaphos
accepted by the USSR
CAS chemical name: O,O-dimethyl O-(4-nitro-phenyl)
phosphorothioate
IUPAC systematic name: O,O-Dimethyl O-4-nitrophenylphos-
phorothioate
CAS registry number: 298-00-0
RTECS number: TG 0175000
EINECS number: 206-050-1
EEC number: 015-035-00-7
Common synonyms:
Demethylfenitrothion; dimethyl para-nitrophenyl
monothiophosphate; O,O-dimethyl O-( para-nitrophenyl)
phosphorothioate; dimethyl para-nitrophenyl phosphorothionate;
dimethyl 4-nitrophenyl phosphorothionate; O,O-dimethyl
O-(para-nitrophenyl) thionophosphate; dimethyl
para-nitrophenyl thiophosphate;
O,O-dimethyl- O-(para-nitrophenyl) thiophosphate; dimethyl
parathion; ENT 17292; metaphos; methyl-parathion; methylthiophos;
MPT; NCI CO2971; parathion methyl homolog; phosphorothioic acid
O,O-dimethyl O-(4-nitro-phenyl) ester; phosphorothioic acid
O,O-dimethyl O-(para-nitrophenyl) ester BAY 11405; 8056 HC;
E601
2.1.2 Technical product
Major trade names:
A-Gro; Azofos; Azophos; Bladan M; Cekumethion; Dalf; Divithion;
Drexel Methyl Parathion 4E & 601; Dygun; Dypar; Ekatox; Folidol
M, M40 & 80; Fosferno M50; Gearphos; Mepaton; Meptox; Metacid 50;
Metacide; Metafos; Metaphos; Methyl-E 605; Methyl Fosferno;
Methylthiophos; Metron; M-Parathion; Niletar; Niran M-4; Nitran;
Nitrox; Nitrox 80; Oleovofotox; Parapest M-50; Parataf; Paratox;
Paridol; Parton M; Penncap M & MLS; Sinafid M-48; Sixty-Three
Special E.C. Insecticide; Tekwaisa; Thiophenit; Thylpar M-50;
Toll; Unidol; Vertac Methyl Parathion; technical product 80%,
Wofatox; Wolfatox.
2.1.2.1. Purity
Technical methyl parathion is available as a solution containing
80% active ingredient (a.i.), 16.7% xylene, and 3.3% inert
ingredients.
The following impurities were identified in one sample of
technical-grade methyl parathion: O,O-dimethyl- S-methyl
dithiophosphate, nitroanisol, nitro-phenol, isomers of methyl
parathion, and the dithio-analogue of methyl parathion (Warner, 1975).
2.2 Physical and chemical properties
Physical state: pure: white crystalline solid or powder
(National Fire Protection Association, 1986)
technical (80%) pure: light to dark tan
liquid (Worthing & Walker, 1987)
Melting point: 37-38 °C (The Merck Index, 1983)
35-36 °C (Worthing, 1983)
Freezing point: about 29 °C (technical product)
(Worthing & Walker, 1987)
Density/specific gravity:
1.358 at 20 °C/40 °C (d204 1.358)
(The Merck Index, 1983)
Vapour pressure: 1.3 mPa at 20 °C
(Worthing & Walker, 1987)
Octanol/water partition coefficient:
log Kow = 2.68 (measured)
log Kow = 1.81-3.43 (reported range)
(Hansch & Leo, 1987)
Water solubility: 55-60 mg/litre at 25 °C (pure)
(Midwest Research Institute, 1975;
National Research Council, 1977)
37.7 mg/litre at 19 °C (pure)
(Bowman & Sans, 1979)
57 mg/litre at 22 °C (anal. grade)
(Sanders & Seiber, 1983)
Nonaqueous solubility: soluble in ethanol, chloroform,
aliphatic solvents, and slightly
soluble in light petroleum
Volatility (pure): 0.14 mg/m3 at 20 °C (Spencer, 1982)
Odour: like rotten eggs or garlic (technical grade)
(Midwest Research Institute, 1975; Anon.,
1984)
Odour threshold: 0.0125 mg/m3 (Akhmedov, 1968)
Other properties: hydrolyses and isomerizes easily
(White-Stevens, 1971)
Half-life in aqueous solution at 20 °C, pH 1-5:
175 days (Melnikov, 1971)
2.3 Conversion factors
1 ppm methyl parathion= 10.76 mg/m3 at 25 °C, 1066 mbar
1 mg methyl parathion/m3 = 0.0929 ppm
2.4 Analytical methods
2.4.1 Sampling, extraction, clean-up
Standardized methods for the determination of various residues
are reported in the Manual of pesticide residue analysis (Thier &
Zeumer, 1987).
2.4.1.1 Plant material (tobacco, fruits, vegetables, crops with low
oil (fat) content)
(a) Extraction
Three extraction methods have mainly been used, all of which are
suitable for multiresidue analysis.
(1) Soxhlet extraction with chloroform - 10% methanol has been
proposed for field-weathered crops by Bowman (1981).
(2) Acetonitrile combined with various amounts of water has been used
by Mills et al. (1963), Wessel (1967), Osadchuk et al. (1971),
Luke et al. (1975), and Stahr et al. (1979). The plant material
is homogenized in a blender with acetonitrile, in some instances
after the addition of Celite (Nelson, 1967; Funch, 1981;).
High-moisture products (fruits and vegetables) are extracted with
pure acetonitrile while samples of dry products (hays, grains,
feedstuff) are blended with acetonitrile-water (65:35).
Extraction is followed by solvent partitioning into petroleum
ether with the addition of sodium chloride (Mills et al., 1963;
Wessel, 1967; Nelson, 1967) into dichloromethane (Funch, 1981),
and dichloromethane/hexane (10:200) (Osadchuk et al., 1971).
(3) Acetone was preferred as the solvent in particular in
multiresidue analysis by Becker (1971), Pflugmacher & Ebing
(1974), Sagredos & Eckert (1976), Becker (1979), Specht & Tillkes
(1980), Miellet (1982), Sonobe et al. (1982), Luke & Doose
(1983), Luke & Doose (1984), Ebing (1985), Andersson & Ohlin
(1986), Vogelsang & Thier (1986), Gyorfi et al. (1987), Thier &
Zeumer (1987), and Becker & Schug, (1990). In some instances,
celite was added. Depending on the water content of the sample,
water was added. In a second step, the acetone extracts were
further extracted with either dichloromethane, dichloro
methane/petroleum ether, or dichloromethane/ n-hexane. The
extract was dried over anhydrous sodium sulfate, reduced in
volume in a Kuderna-Danish concentrator, and subjected to
further clean-up.
Extraction with acetone- o-xylene (19:1) (Ross & Harvey, 1981),
toluene/hexane (75:25) (Johansson, 1978), chloroform (Ault et
al., 1979), or supercritical fluid extraction using methanol
(Capriel et al., 1986), has also been reported.
(b) Column clean-up
The published clean-up procedures are usually suitable for
multiresidue analysis. For plant material with a low fat content, 3
column clean-up procedures have been developed.
(1) The oldest method involves the use of chromatography on Florisil
(often topped with anhydrous sodium sulfate) (Mills et al., 1963;
Nelson, 1967; Schnorbus & Phillips, 1967; Wessel, 1967; Beckman
& Garber, 1969; Osadchuk et al., 1971; Luke et al., 1975;
Johansson, 1978; Gretch & Rosen, 1984, 1987). Although it has
been claimed that organo phosphorous pesticides are partially
lost during Florisil clean-up (Luke et al., 1975), high
recoveries (usually > 80 %) have been reported for methyl
parathion. Various solvents and solvent mixtures are used for
chromatography on Florisil including: diethylether/petroleum
ether, ethyl ether/hexane, and acetone/toluene,
diethylether/petroleum ether being the most frequently used.
Fractionation is achieved by increasing successively the
diethylether content. Florisil clean-up is usually used for a
combined clean-up of organochlorine and organophosphorous
pesticides. Luke et al. (1975) reported that gas chromatography
(GC) with a thermionic detector was sufficiently selective to
detect organophosphorous pesticides without Florisil clean-up.
(2) Alternatively, clean-up of pesticides in multiresidue analysis
has been achieved by chromatography on charcoal (Becker, 1971,
1979; Miellet, 1982; Sonobe et al., 1982; Luke & Doose, 1984;
Ebing, 1985; Gyorfi et al., 1987). To this end, charcoal is mixed
with silica gel (1:15) (and sometimes also celite or magnesia).
In most instances, elution is achieved with mixtures of
dichloromethane/acetone/toluene (e.g., 5:1:1) (Ebing, 1985; Thier
& Zeumer, 1987). Recoveries are high (often > 90 %). Charcoal
clean-up is particularly suited for dry products (< 10 % water).
The simultaneous clean-up of organochlorine and organo-
phosphorous pesticides is also possible with chromatography on
charcoal.
(3) In recent years, a clean-up of pesticides in multiresidue
analysis by gel permeation chromatography (GPC) has become
popular (Pflugmacher & Ebing, 1974; Ault et al., 1979; Specht &
Tillkes, 1980; Andersson & Ohlin, 1986; Vogelgesang & Thier,
1986; Steinwandter, 1988). The stationary phase consists, in most
instances, of Bio Beads SX3 (a polystyrene gel). Ethyl
acetate/cyclohexane (1:1), dichloromethane/cyclohexane (1:1) and,
more recently, acetone/cyclohexane (3:1) have been used as
elution mixtures. Gel permeation chromatography is mainly used to
protect the GC column and the GC detector against contam-
ination. GPC removes material of higher relative molecular mass.
Recoveries > 85% have been reported. Frequently, GPC is combined
with the additional purification step of silica gel
chromatography (Specht & Tillkes, 1980; Andersson & Ohlin, 1986;
Vogelsaifng & Thier, 1986) where elution is achieved with
toluene/hexane (35:65), followed by toluene and acetone/toluene,
with increasing acetone content. However, while the additional
clean-up by silica gel column chromatography is important when
organo chlorine pesticides are present, it is not necessary for
organophosphorous pesticides if analysis is performed by gas
chromatography with flame photometric detection.
2.4.1.2 Dairy products, products with a high fat content (edible
fats)
Clean-up techniques for products with a high fat content have
been reviewed by Waters (1990). Florisil column chromatography and gel
permeation chromatography are also suited for a clean-up of samples
with a high fat content. In addition, clean-up using normal phase HPLC
has been reported (Gillespie & Waters, 1986). Fat is dissolved in
n-hexane and fractionated on silica gel HPLC using
dichloromethane/hexane as solvent. However, complete separation
ofmethyl parathion from the fat is not achieved. As an alternative,
fat is adsorbed on aluminum oxide (Luke & Doose, 1984) or on Calflo E
(calcium silicate) (Specht, 1978; Thier & Zeumer, 1987). Finally, a
sweep codistillation clean-up of edible oils has been reported by
Storherr et al. (1967) and Watts & Storherr (1967). This method has
been standardized also for plant material (Thier & Zeumer, 1987).
After extraction of the sample with ethyl acetate, the concentrated
extract is injected into a heated glass column packed with glass wool
or glass beads followed by the injection of ethyl acetate or petroleum
ether in a nitrogen stream. The nitrogen carrier gas sweeps the
volatile component through the tube to a condensing bath and through
an Arnakrom scrubber tube to a collection tube. Sweep codistillation
may be followed by a further Florisil clean-up.
The extraction and clean-up of vegetable oil can be speeded up by
performing extraction and clean-up in one step using a system of three
ready-to-use cartridges in series (Extralut-3, Sep-Pack silicade1 and
Sep-Pack C18) where the assembled columns are eluted with
acetonitril (saturated with n-hexane) (Di Muccio et al., 1990).
2.4.1.3 Blood, body fluids
Methyl parathion is extracted from blood with hexane or benzene
and analysed without further clean-up (Gabica et al., 1971; De Potter
et al., 1978). No extraction is necessary if methyl parathion is
determined by polarography (Zietek, 1976).
Measurement of the urinary metabolites and the cholinesterase
activity were used to supervise the exposure of workers coming into
contact with methyl parathion or parathion and to observe their
elimination in cases of poisoning (see section 5.3) (Elliot et al.,
1960; Arterberry et al., 1961; Shafic & Enos, 1969; Wolfe et al.,
1970; Ware et al., 1974b; NIOSH, 1976).
2.4.1.4 Soil, sediments
Methyl parathion is extracted from soil with acetone,
acetone/ n-hexane or hexane/isopropanol (Schutzmann et al., 1971;
Agishev et al., 1977; Garrido & Monteoliva, 1981; Wegman et al., 1984;
Kjoelholt, 1985). It is partitioned in a second step into
dichloromethane. While several authors determine the pesticides
without further clean-up, additional silica gel adsorption
chromatography has been used by Wegman et al., (1984) and Kjoelholt
(1985). The recovery of methyl parathion is 70-85%.
When sediments are analysed, elemental sulfur represents a
particular problem. Kjoelholt et al. separated the sulfur by tetra
butylammonium hydrogensulfate (Kjoelholt, 1985), while Schutzmann et
al. (1971) refluxed the sediment extract with Raney copper.
For the extraction, the sediment mixed with sand and sodium
sulfate can be placed into a column and eluted using acetone :
dichloromethane (1:1) (Belisle & Swineford, 1988).
2.4.1.5 Water
Extraction and concentration of methyl parathion from water is
achieved either by liquid/liquid extraction (Kawahara et al., 1967;
Pionke et al., 1968; Mestres et al., 1969; Konrad et al., 1969; Zweig
& Devine, 1969; Schutzmann et al., 1971; Coburn & Chau, 1974; Chmil et
al., 1978; Chernyak & Oradovskii, 1980; Miller et al., 1981; Spingarn
et al., 1982; Bruchet et al., 1984; Albanis et al., 1986; Li & Wang,
1987; Brodesser & Schoeler, 1987), or by adsorption on polymeric
material (Paschal et al., 1977; Le Bel et al., 1979; Agostiano et al.,
1983; Xue, 1984; Clark et al., 1985). Various solvents have been used
for solvent extractions including: diethyl ether/hexane (1:1),
benzene, petroleum ether, hexane/isopropanol; chloroform,
dichloromethane, and ethyl acetate. Recoveries have been high (in
most instances > 90 %). If the liquid/liquid extraction is scaled up
using a "Goulden large sample extractor" and 120 litre of water,
detection limits may be lower by a factor of about 150 compared with
1-litre samples (i.e., a detection limit of 2.5 ng/litre (ppt) has
been achieved for methyl parathion) (Foster & Rogerson, 1990). The
extraction efficiency can be further improved by continuous
liquid-liquid extraction, which allows the use of non-polar solvents
as n-pentane (Bruchet et al., 1984; Brodesser & Schoeler, 1987).
Water samples are frequently analysed for pesticides without further
clean-up, while Florisil clean-up has been used in some instances
(Mestres et al., 1969; Miller et al., 1981).
High concentration factors are achieved, if methyl parathion (and
other pesticides) are adsorbed on polymeric material, such as XAD-2
(Paschal et al., 1977; Le Bel et al., 1979), XAD-4 (Xue et al., 1984),
Tenax (Agostiano et al., 1983) or Porapack Q (Clark et al., 1985).
Elution from XAD is achieved with diethyl ether, acetone/hexane
(15:85), diethyl ether-hexane (85:15). Recoveries are >90 %. If Tenax
is used, both solvent elution (diethyl ether) or thermoelution can be
used to desorb the pesticides. Solid-phase extraction (using C-18
cartridges) will become the method of choice for the rapid extraction
of organophosphorous insecticides from water (Swineford & Belisle,
1989; Sherma & Bretschneider, 1990).
2.4.1.6 Air
Most methods for the determination of pesticides in air have been
developed as multiresidue methods. Pesticides in air are either
absorbed in liquids or adsorbed on polymeric material. Thus,
pesticides may be trapped in ethylene glycol, which is subsequently
extracted with dichloromethane (Tessari & Spencer, 1971; Sherma &
Shafik, 1975) or they may be trapped on glass beads coated with
cottonseed oil (Compton, 1973). Further clean-up is achieved by silica
gel or Florisil column chromatography.
Among the solid polymeric material used to trap pesticides,
polyurethane foam (PUF) is by far the most popular (Lewis et al.,
1977; Rice et al., 1977; Lewis & McLeod, 1982; Lewis & Jackson, 1982;
Belashova et al., 1983; Beine, 1987). Air can be collected both with
low-volume (approx. 4 litre/min) or high-volume samplers (up to 250
litre/min). PUF can be reused after careful cleaning (e.g., with 5%
diethyl ether in n-hexane). In some instances, Tenax, Chromosorb
102, or Porapack R is sandwiched between PUF plugs to enhance the
collection efficiency. Collection efficiencies in excess of 80% have
been reported for methyl parathion. A filter may be added to remove
particulate matter (Lewis et al., 1977). Methyl parathion is usually
determined without further clean-up. Finally, XAD-4 (Wehner et al.,
1984) and silica gel (Klisenko & Girenko, 1980; Liang & Zhang, 1986)
have been used as solid trapping materials.
2.4.1.7 Formulations
When analysing formulations, the determination of by-products and
impurities is an important objective. A variety of instrumental
techniques have been used for the analysis of formulations including:
gas chromatography (Jackson, 1976; Jackson, 1977a), high performance
liquid chromatography (Jackson, 1977b), infrared analysis (Goza,
1972), P-31-nuclear magnetic resonance spectroscopy (Greenhalgh et
al., 1983), and spectrophotometry after alkaline hydrolysis to
p-nitrophenol (Blanco & Sanchez, 1989). An inter laboratory study
has been carried out using both GC (Jackson, 1977a) and HPLC (Jackson,
1977b). With both methods, coefficients of variation of 1.7% have been
determined. The instrumental techniques are described below.
2.4.2 Instrumental analytical methods
2.4.2.1 Gas chromatography
Gas chromatrophic (GC) methods for the determination of
pesticides (including methyl parathion) have been reviewed by Ebing
(1987).
Organophosphorous pesticides, including methyl parathion, are
sufficiently volatile and thermally stable to be amenable to gas
chromatography and it is by far the most important method for the
determination of methyl parathion. This technique provides the good
resolution necessary for multiresidue analysis. Moreover, very
sensitive and specific detectors are available, in particular for the
analysis of organophosphorous pesticides.
(a) Detectors
The two most widely used detectors for organophosphorous
pesticides are the alkali flame ionization detector (AFID) and
variations of this detector (thermionic detector (Patterson, 1982),
nitrogen-phosphorous detector) and the flame photometric detector
(FPD) (Bowman, 1981). The AFID makes use of the phenomenon that the
flame ionization detector yields enhanced response to nitrogen- and
phosphorus-containing compounds, in the presence of alkali metal
salts. The detection limit is in the low picogram range. The detector
discriminates against other compounds 30-50 fold. The flame
photometric detector (FPD) operates with a cool, hydrogen rich flame
for the detection of phosphorus- and sulfur-containing compounds,
which form POH and S2 species. These species emit light at 526 nm
(POH) and 394 nm (S2), which is monitored by using interference
filters and a photomultiplier. The detector is easy to operate and
results are reproducible. The detector is highly specific. The
response of 100 ng of parathion is 130 000 times greater than that of
an equal amount of aldrin. Furthermore, It is of advantage that any
solvent can be used with the detector. For the determination of methyl
parathion the P mode is the method of choice, though the S mode can
also be used (sensitivity 10 times lower) as methyl parathion contains
both P and S atoms.
Finally, the electron capture detector (ECD) is sometimes used
for the analysis of methyl parathion as it responds not only to the
P=S moiety, but in particular to the NO2 group.
(b) Columns
A definite identification of a pesticide by its retention time on
one column is not possible. Analysis on at least one further column
with a stationary phase of different polarity is necessary to confirm
the identity of a compound.
Packed columns are frequently used for pesticide residue
analysis, though resolution is substantially poorer compared with
capillary columns and identification of the pesticides is less
specific. Solid supports are usually of the Chromosorb W type. In some
instances, Gaschrom Q has also been used. A large variety of
stationary phases, used either alone or in admixture, have been
employed. The most frequently used phases are DC 200, QF-1, OV 17,
OV-101, OV-210, and SE-30. Relative retention times for many
stationary phases have been reported by several authors for a large
variety of pesticides (up to 600 compounds including other industrial
chemicals) (Bowman & Beroza, 1967; Ambrus et al., 1981b; Daldrup et
al., 1981; Prinsloo & de Beer, 1987; Saxton, 1987; Suprock & Vinopal,
1987; Omura et al., 1990).
Packed column GC allows the separation of only a limited number
of pesticides. Capillary columns exhibit a considerably better
separation efficiency than packed columns. Such capillary columns have
been used by several authors for methyl parathion analysis (Krijgsman
& van den Kamp, 1976; Ripley & Braun, 1983; Stan & Goebel, 1983;
Ebing, 1985; Andersson & Ohlin, 1986; Vogelsang & Thier, 1986).
Retention time data on a SE-30 capillary column have been reported
(Ripley & Braun, 1983). Several injection techniques for capillary
columns have been compared (Stan & Goebel, 1984; Stan & Mueller,
1988). Cold splitless (PTV) injection appears to be best suited for
organophosphorous pesticide analysis. The resolution can be further
improved by applying two-dimensional capillary gas chromatography
using two columns of different polarity (Stan & Mrowetz, 1983).
2.4.2.2 High performance liquid chromatography (HPLC)
The main advantage of HPLC is its ability to analyse compounds
that are heat labile, such as phenylurea and carbamates. As stated
above, organophosphorous pesticides including methyl parathion are
sufficiently heat stable for analysis using gas chromatography and
there is no direct need to use HPLC. Thus, relatively few studies
dealing with the HPLC analysis of methyl parathion have been reported.
HPLC analysis has been achieved using reversed phase
chromatography, with acetonitrile/water (60:40) (Funch, 1981), or
methanol/acetic acid/water (32:0.6: 47.4) as solvents, and UV-
detection (Zhao & Wang, 1984). HPLC conditions for 166 pesticides
including methyl parathion were reported by Lawrence & Turton (1978).
Retention data of 560 pesticides and other industrial chemicals have
been published by Daldrup et al. (1981, 1982) using two gradient
systems.
Sharma et al. (1990) developed a method for the rapid
quantitative analysis of organophosphorus (including methyl parathion)
and carbamate pesticides using HPLC and refractive index detection.
HPLC appears to be particularly suited for the analysis of polar
metabolites of methyl parathion (Abe et al., 1979).
Fluorogenic labelling of organophosphorous pesticides leads to an
improvement in sensitivity. Such labelling can be achieved by
hydrolysis of the compounds to the corresponding phenols and
derivatization with dansyl chloride (5-dimethylamino-naphthalene-1-
sulfonyl chloride) (Lawrence et al., 1976). Besides the UV and
fluorescence detector, electrochemical detectors have been used for
the detection of methyl parathion using amperometric detection in the
reductive mode (Bratin et al., 1981; Clark et al., 1985) or polaro-
graphic detection (Koen & Huber, 1970). Acetonitrile/water with
additional acetate buffer is used as solvent. The response is similar
to the UV detector, but there is less interference from the plant
material (Clark et al., 1985).
2.4.2.3 Thin layer chromatography (TLC)
Thin layer chromatography is well suited for the analysis
organophosphorous pesticides, even if it is not as specific as GC
(Kawahara et al., 1967; Schütz & Schindler, 1974; Thielemann, 1974;
Katkar & Barve, 1976; Lawrence et al., 1976; Curini et al., 1980;
Daldrup et al., 1981; Pfeiffer & Stahr, 1982; Korsos & Lantos, 1984).
Usually, silica gel G plates are used with a variety of solvent or
solvent mixtures. These include benzene, chloroform/cyclohexane,
n-hexane/acetone, chloroform/benzene, dichloro-methane/acetone.
Silver nitrate is frequently used as spray reagent, which, in the
presence of organophosphorous pesticides, leads to white spots against
a black background (Pfeiffer & Stahr, 1982).
As an alternative, an enzymatic reaction has been frequently
applied to detect organophosphorous compounds on TLC plates (Mueller,
1973; Leshev & Talanov, 1977; Ambrus et al., 1981a; Bhaskar & Kumar,
1981; Devi et al., 1982). This method makes use of the fact that
cholinesterase (from horse serum or cow liver) hydrolises 1-naphthyl
acetate to 1-naphthol, which reacts either with Fast Blue Salt B or
p-nitrobenzenediazoniumfluoroborate to form a coloured complex. If
methyl parathion is inhibiting the enzyme reaction, white spots on a
red or orange background appear. The sensitivity may be enhanced if
methyl parathion is oxidized to methylparaoxon by reaction with
bromine or hydrogen peroxide.
2.4.2.4 Spectrophotometry
Colorimetric methods, which were of importance during the early
years of organophosphorous pesticide analysis, have largely been
replaced by chromatographic methods.
The inhibition of cholinesterase by organophosphorous pesticides,
described above, is also the basis of a photometric method (Archer &
Zweig, 1959; Kumar & Ramasundari, 1980; Bhaskar & Kumar, 1982, 1984;
Kumar, 1985). Sadar et al. (1970) made use of the fact that
cholinesterase hydrolyses the non fluorescent N-methyl-
indoxylacetate to the highly fluorescent indoxyl. This reaction is
again inhibited by methyl parathion.
In another spectrophotometric method, methyl parathion is treated
with hydroxylamine hydrochloride and sodium nitroprusside, under
alkaline conditions, to form a water-soluble, coloured complex (Sastry
& Vijaya, 1986). The method is rapid and accurate and can be used for
formulations and for residues in fruits and vegetables.
2.4.2.5 Polarography
Polarography and various modifications of this method, i.e., the
"differential pulse polarography" (DPP), have been used repeatedly to
determine methyl parathion and other organophosphorous compounds with
a nitro group (Nangniot, 1966; Gajan, 1969; Kheifets et al., 1976;
Zietek, 1976; Smyth & Osteryoung, 1978; Kheifets et al., 1980; Khan,
1988; Reddy & Reddy, 1989). The method allows the simultanous
determination of parathion, methyl parathion, paraoxon, EPN, and the
metabolite 4-nitrophenol (Zietek, 1976) in blood, without prior
extraction. Polarography has been proposed as confirmatory method for
the determination of methyl parathion (and three further pesticides).
A collaborative study of 10 laboratories showed a coeffient of
variation of 15-16% (Gajan, 1969). In addition the method was applied
to water analysis (Kheifets et al., 1976, 1980; Bourquet et al.,
1989). Bourquet et al. (1989) showed a 20-50 increase in sensitivity
when "adsorptive stripping voltametry" was used instead of DPP.
2.4.2.6 Mass spectrometry
Coupled gas chromatography/electron impact mass spectrometry
(GC/MS) is a particularly valuable method for confirming pesticide
residues in various environmental samples. Methyl parathion shows an
abundant m/z=109, 125, and 263 (M+.) under electron impact
conditions (Mestres et al., 1977; Wilkins, 1990). Under positive ion
chemical ionization mass spectrometry (methane), the protonatic
molecule is the most abundant ion (m/z 264) while the structure
specific fragment at m/z 125 is due to (CH3O)2 P=S+ (8.8%)
(Holmstead & Casida, 1974). The negative ion chemical ionization
spectrum shows the typical thiophenolate fragment at m/z=154
(-S-C6H4-NO2) (Nielsen, 1985).
In addition, field ionization (FI) and field desorption (FD) mass
spectrometry have been applied repeatedly in the determination of of
methyl parathion (Damico et al., 1969; Klisenko et al., 1981; Schulten
& Sun, 1981; Golovatyi et al., 1982). The FD spectra show little
fragmentation and, thus, are not well suited for environmental
analysis. Among the newer mass spectrometric techniques, tandem mass
spectrometry (MS/MS) shows more promise for organophosphorous
pesticide analysis, as this technique enhances the selectivity of the
method and thus may reduce the necessary clean-up. Under MS/MS
conditions (chemical ionization), the protonated molecule forms an
abundant fragment at m/z 125 ((CH3O)2 P=S+) (Hummel & Yost, 1986;
Roach & Andrzejewski, 1987).
HPLC/MS of methyl parathion has been demonstrated (De Wit et al.,
1987; Betowski & Jones, 1988; Farran et al., 1990). As this method is
more difficult to handle and less sensitive and reproducible than
GC/MS, there is no need to use it in routine analysis, except when
other thermally labile pesticides are to be determined together with
organophosphorous compounds.
2.4.3 Detection limits
Detection limits are rarely reported. When plant material was
analysed, the detection limit for the overall method (extraction,
clean-up, analysis) was 10-100 µg/kg when gas chromatography with AFID
or FPD was used. In water analysis, substantially better detection
limits were achieved (usually 0.01-0.1 µg/litre), which may be further
reduced if a large-scale extractor is used (Foster & Rogerson, 1990).
In air analysis, detection limits have been reported to be 0.1-1
ng/m3.
2.4.4 Confirmatory method
A confirmatory derivatization method was proposed by Lee et al.
(1984). Following hydrolysis with KOH, 4-nitrophenol was derivatized
with pentafluoro benzyl bromide to the corresponding ether. Analysis
is carried out by GC with ECD. Levels as low as 0.01 ppb can be
confirmed.
Table 1. Sampling, extraction, clean-up, and determination of methyl parathiona
Matrix Sampling, extraction, clean-up Analytical Recovery (%) Detection limitb References
method (µg/kg or litre)
fruits, extr.: acetonitrile, GC (ECD, TID) 86-92 n.r. Wessel (1967)
vegetables part.: petroleum ether, TLC
clean-up: Florisil
plant material, extr.: propylene carbonate, GC (ECD, TID) 82-95 n.r. Schnorbus &
dairy products clean-up: Florisil Phillips (1967)
fruits, extr.: acetonitrile, GC (ECD) 90-98 n.r. Osadchuck et al.
vegetables, part.: dichloromethane + hexane, (1971)
fat, oil clean-up: Florisil
vegetables extr.: acetone, GC (ECD, TID) 93 (celery) n.r. Luke et al. (1975)
part.: dichloromethane/petroleum
ether,
clean-up: Florisil
apples extr.: toluene + n-hexane, GC (ECD) 93 1-20 Johansson (1978)
clean-up: Florisil
vegetables autom. extraction + n.r. 91-104 n.r. Gretch & Rosen
clean-up: Florisil (pepper) (1984)
food extr.: acetone, GC n.r. n.r. Specht & Tillkes
part.: dichloromethane, (1980)
clean-up: GPC + silica gel
Table 1 (continued)
Matrix Sampling, extraction, clean-up Analytical Recovery (%) Detection limitb References
method (µg/kg or litre)
fruits, extr.: acetone, GC (ECD,FPD, > 80 10-100 Andersson &
vegetables part.: dichloromethane hexane, TID) Ohlin (1986)
clean-up: GPC and silica gel
vegetables, extr.: trichloromethane, GC (FPD) 93-105 n.r. Ault et al. (1979)
fruits, clean-up: GPC
crops
vegetables extr.: acetone, GC (TID) 85-95 n.r. Pflugmacher &
part.: dichloromethane, Ebing (1974)
clean-up: GPC
- clean-up: GPC n.r. n.r. n.r. Steinwandter
(1988)
- clean-up: cellulose column n.r. 82 n.r. Stahr et al. (1979)
fruits, extr.: acetonitrile, HPLC (UV 280) 77-87 10 Funch (1981)
vegetables part.: dichloromethane
honey bees, extr.: acetone o-xylene GC (FPD) 92-101 1 Ross & Harvey
beewax, pollen (1981)
plants, soil extr.: supercritical methanol GC (ECD, AFID) 38 n.r. Capriel et al.
(1986)
tobacco extr.: hexane/acetone, GC (FPD) 99-104 20 Sagredos & Eckert
clean-up: alumina (1976)
Table 1 (continued)
Matrix Sampling, extraction, clean-up Analytical Recovery (%) Detection limitb References
method (µg/kg or litre)
vegetables extr.: acetone, GC (ECD,TID, n.r. n.r. Gyorfi et al.
part.: dichloromethane, FPD) (1987)
clean-up: charcoal
plant material extr.: acetone, GC (AFID, ECD) 92-103 n.r. Becker (1971)
part.: dichloromethane
plant material extr.: acetone, GC (ECD, AFID) 92-103 n.r. Becker (1979)
part.: dichloromethane,
clean-up: charcoal
plant material extr.: acetone, HPLC n.r. n.r. Miellet (1982)
clean-up: charcoal/Florisil
barley, malt, extr.: acetone or acetonitrile, GC (FPD) 82 30 Sonobe et al.
hops part.: hexane, (1982)
clean-up: charcoal
low moisture extr.: acetone, GC (FPD) 93 n.r. Luke & Doose
products part.: dichloromethane/petrol, (1983)
(pepper) ether,
clean-up: charcoal
ready-to-eat extr.: acetone GC (ECD, TID) n.r. 0.7-1.8 Vogelsang & Thier
foods part.: dichloromethane, (1986)
clean-up: + GPC silica gel
honey bees extr.: acetone GC (ECD) 91 15 Ebing (1985)
clean-up: charcoal
Table 1 (continued)
Matrix Sampling, extraction, clean-up Analytical Recovery (%) Detection limitb References
method (µg/kg or litre)
milk, oilseeds fat adsorbed on alumina GC (ECD, FPD) n.r. 80 Luke & Doose
extr.: acetonitrile, (1984)
part.: petroleum ether
fat ad.: of fat on Calflo E n.r. n.r. Specht (1978)
edible oils sweep co-distillation GC (TID) 95 10 (mg/kg) Storherr et al.
(1967)
edible oils extr.: petroleum ether, GC(FPD) 83-107 n.r. Gillespie &
clean-up: HPLC Walters (1989)
milk sweep co-distillation GC (TID) > 87 n.r. Watts & Storherr
(1967)
blood extr.: n-hexane GC (FPD) n.r. 3 Gabica et al.
(1971)
serum extr.: benzene GC (AFID) 69 2 De Potter et al.
(1978)
blood no extr. polarography 7x10-8 mol Zietek (1976)
soil extr.: acetone/hexane GC (TID) n.r. n.r. Agishev et al.
(1977)
soil extr.: acetone/hexane TLC (silica n.r. n.r. Garrido &
gel) Monteoliva (1981)
Table 1 (continued)
Matrix Sampling, extraction, clean-up Analytical Recovery (%) Detection limitb References
method (µg/kg or litre)
soil, sediment extr.: acetone/hexane, GC (AFID) 71 0.17 Kjoelholt (1985)
clean-up: ad. chrom.
soil extr.: acetone, GC (TID) 78-85 5 Wegman et al.
part.: dichloromethane, (1984)
clean-up: silica gel
soil, water, extr.: hexane/isopropanol, GC (ECD) 45 n.r. Schutzmann et al.
sediment desulfurization with Raney copper (1971)
water diethylether/hexane or benzene/ GC (ECD) n.r. n.r. Kawahara et al.
n-C6, (1967)
clean-up: TLC
water extr.: benzene GC (TID) 95 n.r. Pionke et al.
(1968)
water extr.: benzene GC 92-101 0.001 (?) Konrad et al.
(1969)
water extr.: petroleum ether GC 98 0.04 Zweig & Devine
(1969)
water extr.: trichloromethane TLC 60-95 1 Chmil et al.
(1978)
water extr.: trichloromethane GC(TID) n.r. 0.01 Chernyak &
Oradovskii (1980)
Table 1 (continued)
Matrix Sampling, extraction, clean-up Analytical Recovery (%) Detection limitb References
method (µg/kg or litre)
water/ extr.: at pH 11: dichloromethane; GC/MS 60-85 5 Spingarn et al.
wastewater at pH 2: dichloromethane (1982)
water extr.: dichloromethane/hexane, GC (ECD) n.r. n.r. Albanis et al.
clean-up: Florisil (1986)
water extr.: ethylacetate GC (FPD) 85-91 0.08 ng(abs.) Li & Wang (1987)
wastewater extr.: dichloromethane, GC (FPD) 90 0.75 Miller et al.
clean-up: Florisil (1981)
water extr.: petroleum ether, GC (ECD) n.r. 0.5 Mestres et al.
clean-up: Florisil (1969)
water extr.: dichloromethane GC/MS 75 n.r. Bruchet et al.
(continuous) liquid-liquid) (1984)
water extr.: n-pentane (continous GC (TID) 90 0.01 Brodesser &
liquid-liquid) Schoeler (1987)
water hydrolysis KOH, derivat. penta GC (ECD) 95 0.1 Coburn & Chau
fluoro-benzylbromide, (1974)
clean-up: silica gel
water ad.: on Tenax, thermoelution GC (FID/ECD) 62 0.01 Agostiano et al.
(1983)
water, run-off ad.: XAD-2, HPLC (rev. 99 2 Paschal et al.
water elut.: diethylether phase, UV) (1977)
Table 1 (continued)
Matrix Sampling, extraction, clean-up Analytical Recovery (%) Detection limitb References
method (µg/kg or litre)
water, ad.: XAD-2, GC (TID, FID) 93-100 15 pg(abs.) Le Bel et al.
drinking-water elut.: acetone/hexane (1979)
water ad.: XAD-4, GC n.r. n.r. Xue (1984)
elut.: diethylether/hexane
water ad.: Porapack Q, HPLC (rev. 96-105 < 1 Clark et al. (1985)
elut.: acetonitrile phase
electro-chem.)
water ad.: C-18, TLC n.r. 0.2 ng(abs.) Sherma &
elut.: ethyl acetate Bretschneider
(1990)
water ad.: C-18, acetone GC (FPD) > 79 n.r. Swineford &
Belisle (1989)
water extr.: dichloromethane GC/MS 48 0.0025 Foster & Rogerson
(large-scale extractor) (1990)
air ab.: ethylene-glycol, GC (FPD) 87-97 n.r. Sherma & Shafik
extr.: dichloromethane, (1975)
clean-up: silica gel
air ab.: cotton seed oil coated glass GC (FPD) 91 0.04 ng/m3 Compton (1973)
beads,
clean-up: Florisil
air clothscreen with ethylene glycol, GC (ECD/FPD) 93 n.r. Tessari & Spencer
extr.: acetone/hexane, (1971)
clean-up: alumina + Florisil
Table 1 (continued)
Matrix Sampling, extraction, clean-up Analytical Recovery (%) Detection limitb References
method (µg/kg or litre)
air ad.: silica gel, activated GC (ECD/FPD) n.r. 1 ng (abs.) Klisenko &
charcoal Girenko (1980)
air ad.: silica gel GC (FPD) 101-104 30 pg (abs.) Liang & Zhang
(1986)
air ad.: XAD-4, GC (ECD, TID) 74 1-3 ng/m3 Wehner et al.
elut: ethylacetate, (1984)
clean-up: HPLC
air ad.: PUF, GC (ECD) 100 n.r. Rice et al. (1977)
elut: petroleum ether
air ad.: PUF (high volume sampler) GC (ECD, FPD) 86 0.1 ng/m3 Lewis et al.
(1977)
air ad.: PUF (low volume sampler), GC (ECD, FPD) 80 20 ng/m3 Lewis & MacLeod
elut: diethylether/hexane (1982)
air ad.: PUF/other polymers (high GC 72-91 n.r. Lewis & Jackson
volume sampler) (1982)
air ad.: PUF, n.r. n.r. n.r. Belashova et al.
elut.: trichloromethane or (1983)
acetaldehyde
air ad.: Tenax, GC (FID) n.r. 2.5 µg/m3 Beine (1987)
elut.: toluene
formulations - GC or HPLC - - Jackson (1976)
Table 1 (continued)
Matrix Sampling, extraction, clean-up Analytical Recovery (%) Detection limitb References
method (µg/kg or litre)
formulations - GC - - Jackson (1977a)
formulations - HPLC - - Jackson (1977b)
formulations - IR - - Goza (1972)
formulations - P-31 NMR - - Greenhalgh et al.
(1983)
formulations hydrolysis to p-nitrophenol Spectr. - - Blanco & Sanchez
(1989)
a Abbreviations: GC = gas chromatography, TLC = thin-layer chromatography, GPC = gel
permeation chromatography, MS = mass spectrometry, HPLC = high performance liquid
chromatography, NMR = nuclear magnetic resonance, IR = infrared spectroscopy,
ECD = electron capture detector, FID = flame ionization detector, AFID = alkali flame
ionization detector, FPD = flame photometric detector, TID = thermionic detector,
UV = ultraviolet detector, spectr. = spectrophotometry, extr. = extraction, part. = partitioning,
ad. = adsorption, ab. = absorption, elut. = elution, n.r. = not reported, (abs.) = absolute.
b µg/kg or litre unless stated otherwise.
Table 2. Methods used in the determination of methyl parathion
Method Detection limit Remarks References
HPLC (UV) n.r. analysis Abe et al. (1979)
of metabolism
HPLC (UV) n.r. in mixtures Zhao & Wang
(rev. phase, methanol/ (1984)
acetic acid)
HPLC n.r. review on HPLC Lawrence & Turton (1978)
methods
HPLC (fluorescence) 10-20 µg (abs.)- deriv. with dansyl Lawrence et al. (1976)
chloride
HPLC 1. acetonitrile n.r. retention times of Daldrup et al. (1982)
2 acetonitrile/phosphoric 560 compounds
acid KH2PO4/H2O
HPLC 1. acetonitrile n.r. retention times of Daldrup et al. (1981)
2 acetonitrile/phosphoric 570 compounds
acid KH2PO4/H2O
HPLC (rev. phase, 10 µg/kg fruits and vegetables Funch (1981)
acetonitrile/H2O)
Table 2 (continued)
Method Detection limit Remarks References
HPLC (rev. phase, 1 µg/kg reduction amperometric Clark et al. (1985)
acetonitrile/0.01 KC1 detection
0.03 M potassium (vegetables, water)
acetate/H20)
HPLC (rev. phase, n.r. electrochemical Bratin et al. (1981)
acetonitrile/sodium detection
acetate/H2O)
HPLC rev. phase (H2O 30 µg/kg polarographic Koen & Huber (1970)
ethyl alcohol/acetic detection
acid/NaOH)
GC < 2 ng TID Patterson (1982)
GC n.r. retention times of Daldrup et al. (1981)
570 compounds
GC (TID) 20 µg/kg retention times Ambrus et al. (1981a,b)
GC n.r. retention times of Saxton (1987)
600 compounds
GC n.r. retention times of Prinsloo & de Beer (1987)
42 pesticides
n.r. retention times of Suprock & Vinopal (1987)
78 pesticides
Table 2 (continued)
Method Detection limit Remarks References
GC n.r. retentions times of Bowman & Beroza (1967)
20 OP-pesticides
(milk, corn silage)
GC n.r. two dimensional Stan & Mrowetz (1983)
GC
GC (FPD) 100 pg capillary columns, Krijgsman & Van de Kamp (1976)
relative retention
times
GC (ECD, TID) n.r. capillary columns, Stan & Goebel (1983)
simultaneous
detection of ECD, TID
GC n.r. retention times Ripley & Braun (1983)
of 194 pesticides
GC < 0.1 ng relative retention Omura et al. (1990)
times of 40 pesticides
on 11 phases
Table 2 (continued)
Method Detection limit Remarks References
GC (ECD) n.r. hydrolysis of Lee et al. (1984)
methyl parathion
to 4-nitrophenol,
derivat.
penta-fluorobenzylbromide
Clean-up: silica gel
TLC (silica gel G) n.r. detection with GC Kawahara et al. (1967)
TLC (silica gel) 0.1 µg 4 solvent mixtures, Schütz & Schindler (1974)
reduct. to amines
TLC (silica gel) 0.06-0.6 µg saponification and Thielemann (1974)
reduct. to
p-amino-phenol
TLC (silica gel G) n.r. elut.: n-hexane/acetone Katkar & Barve (1976)
TLC (silica gel) n.r. 17 solvent systems, Curini et al. (1980)
spray reagent: AgNO3
TLC (silica gel) n.r. elut.: 1.methanol/NH3H2O Daldrup et al. (1981)
2. dichloromethane/
acetone
TLC (silica gel) n.r. elut.: n-heptane/acetone Pfeiffer & Stahr (1982)
Table 2 (continued)
Method Detection limit Remarks References
TLC (silica gel) elut.: petroleum ether/ Korsos & Lantos (1984)
diethylether, two
dimensional TLC
TLC n.r. elut.: benzene/acetone, Mueller (1973)
detect. enzymatic
reaction
TLC (silica gel/ elut.: 4 solvent Leshchev & Talanov (1977)
starch) mixtures, milk,
feed, animal tissue,
extr: acetone, detect.
enzymatic reaction
TLC (silica gel G) n.r. detect. enzymatic Bhaskar & Kumar (1981)
reaction
TLC (silica gel G) 5 µg (abs.) elut.: dichloromethane Ambrus et al. (1981a,b)
or ethyl acetate,
detect. enzymatic
reaction
TLC n.r. detect. enzymatic Devi et al. (1982)
reaction
Table 2 (continued)
Method Detection limit Remarks References
polarography 140 µg/kg oscillographic Nangniot (1966)
polarography,
pesticide
residues
polarography 10 µg/kg single sweep Gajan (1969)
oscillographic
polarography,
non-fatty foods
polarography n.r. differential Kheifets et al. (1976)
oscillographic
polarography
(water)
polarography 7x10-6 mol/litre methyl parathion and Zietek (1976)
metabolites in blood
polarography 10-8 mol/litre - Smyth & Osteryoung (1978)
polarography n.r. adsorptive stripping Bourquet et al. (1988)
polarography n.r. - Kahn (1988)
polarography 3.9.10-9 mol/litre polargaraphy, diff. Reddy & Reddy (1989)
pulse polargraphy
cyclic voltametry
Table 2 (continued)
Method Detection limit Remarks References
differ. n.r. water Kheifets et al. (1980)
chronoamperometry
spectrophotometry n.r. enzymatic reaction Kumar (1985)
(cholinesterase,
Fast Blue B)
spectrophotometry n.r. reduction to amine, Sastry & Vijaya (1986)
formation of a
coloured complex
spectrophotometry n.r. reaction with 3-methyl- Sastry & Vijaya (1987)
2-benzothiazolinone
spectrophotometry n.r. hydrolysis to Ramakrishna & Ramachandran
4-nitro-phenol (1978)
a Abbreviations: GC = gas chromatography, HPLC = high performance liquid chromatography, TLC= thin layer chromatography,
ECD = electron capture detector, TID = thermionic detector, FPD = flame photometric detector, UV = ultraviolet
detector, elut. = elution, n.r. = not reported, (abs.) = absolute.
3. SOURCES OF HUMAN AND ENVIRONMENTAL EXPOSURE
3.1 Natural occurrence
Natural occurrence of methyl parathion is unlikely.
3.2 Man-made sources
3.2.1 Production process
Methyl parathion is a representative of the highly active
insecticides, the thiophosphorus esters, developed in the 1940s by
Schrader, a German chemist. Methyl parathion was introduced as a
commercial chemical in 1949. It is synthesized by the reaction of
O,O-dimethyl phosphoro-chloridothioate with the sodium salt of 4-
nitrophenol (Schrader, 1963).
3.2.2 Loss into the environment
Emissions of methyl parathion during the production process can
be disregarded when compared with those from its use as an
insecticide. The air emission from a factory in the USA was reported
to be around 0.1% of the production level (Archer et al., 1978). The
major losses of this insecticide are directly caused by spraying, and
evaporation from water surfaces, leaves, and from the soil (Woodrow et
al., 1977).
3.2.3 Production
According to the European Directory of Agrochemical Products
(1986) and the Directory of World Chemical Producers (1990), methyl
parathion is produced throughout the world by many companies. World
production in 1966 was 31 700 tonnes, including 14 800 tonnes produced
in the USA.
In Table 3, selected countries producing methyl parathion are
listed together with their production capacities (Bayer, 1988).
Table 3. Methyl parathion production capacities in different
countriesa
Country Production capacity in
tonnes/year
Brazil 3000
Denmark 15 000
German Democratic Republic 3500
Mexico 8000
India 3000
China 40 000
USSR 5000-10 000
a From: Bayer (1988).
3.2.4 World consumption
Recent data from Bayer concerning the consumption of the active
ingredient only are reported in Table 4 (Bayer, 1988).
Table 4. Methyl parathion consumption in tonnes in some areas of the
worlda
Region 1984 1985 1986
Africa 191 308 152
North America 2 045 2 776 2 932
South America 9 135 6 555 5 587
Asia, New Zealand, 2 757 3 028 2 620
Australia
Western Europe 894 1 087 1 019
Total 15 022 13 754 12 310
aFrom: Bayer (1988).
In 1984, the USA exported 3010 tonnes of methyl parathion (HSDB,
1990).
3.2.5 Formulations
Methyl parathion is used in following formulations:
(1) emulsifiable concentrates (EC) with 19.5%, 40%, 50%, 60% active
ingredient (a.i.)
(2) wettable powders containing 40% a.i.
(3) dusts 1.5%, 2%, and 3% methyl parathion,
(4) microencapsulated methyl parathion, and
(5) ready-to-use liquid (less than 1% a.i.).
The usual carriers are: petroleum solvents and clay carriers
(such as propargite).
Combinations are available containing parathion, omethoate,
tetradifon, prothoate, and petroleum oil.
3.3 Uses
Methyl parathion is a broad-spectrum insecticide with
non-systemic contact and stomach action. The normal method of
application is foliar spraying by aircraft or ground equipment. Data
from 1971 show that most methyl parathion was used for protecting
cotton fields (Table 5).
Table 5. Methyl parathion consumption pattern (1971)a
Protection of consumption (%)
cotton 83
soybeans 8
grain including corn 5
wheat 2
tobacco, peanuts, vegetables, and citrus fruits 2
aFrom: HSDB (1990).
Only foliar application of methyl parathion is known. It is used
as a contact insecticide and acaricide. There are different routes of
application depending on the type of plant to be protected and the
organisms killed. The recommended application rate is 0.5-1 kg a.i./ha
for vegetables, 1-2 kg/ha for cereals, 1.5-6 kg/ha for fruit trees,
2-5 kg/ha for citrus fruits, and 0.12-1.0 kg/ha for cotton.
4. ENVIRONMENTAL TRANSPORTATION, DISTRIBUTION, AND TRANSFORMATION
4.1 Transportation and distribution between media
The transportation and distribution of methyl parathion in air,
water, soil, fauna, and flora are influenced by several physical,
chemical, and biological parameters. The transportation and fate of
methyl parathion were studied by Gile & Gillett (1981). They used the
simulated ecosystem developed at the Corvallis Environmental Research
Laboratory of the US EPA (Gillett & Gile, 1976). A 16-h daily light
cycle with an average of 27 000 lx at the soil surface was used. The
temperatures varied from 18 °C at night to 30 °C during the day. The
ecological compartment was ventilated with 10 litre air/min. The
simulated ecosystem included alfalfa (Medicago sativa) and
perennial ryegrass (Lolium perenne). Twenty days after planting,
different representative kinds of invertebrates (earthworms,
nematodes, garden snails) were added to the microcosms. Ten days
later, radioactive labelled 14C-methyl parathion (50 µCi) was
applied at rates of 0.3, 0.6, and 2.4 kg/ha. One week following the
methyl parathion application, a gravid gray-tailed vole (Microtus
canicaudus) was placed in the model ecosystem. The relative 14C
mass balance of the study is shown in the Table 6.
Most radioactivity was found in the upper 5 cm of soil. A
comparable experiment with p-nitrophenol showed a lower soil content
and no residues in the groundwater as well.
Crossland & Elgar (1983) used a mathematical model to predict the
dispersion and degradation of methyl parathion in freshwater ponds.
Basic assumptions of the model were that loss processes could be
adequately described in terms of simple partition phenomena and
first-order rate kinetics. Predictions of the model were compared with
experimentally-obtained data for concentrations of methyl parathion in
water and sediment. They started with a concentration of 100 µg methyl
parathion/litre pond water. At the limit of the analytical method
(0.005 µg/g), they could not find any residues of methyl parathion, 16
days after treatment. The authors described the degradation by a
pseudo first order rate constant that was temperature-dependent.
Since the degradation of methyl parathion in distilled water (pH not
given) was faster than expected and the bacteria concentration was
only 106/litre, a sediment-catalysed hydrolysis was supposed.
Crossland & Bennett (1984) compared degradation of methyl parathion in
experimental ponds and laboratory aquaria. Degradation was faster in
the natural ponds and faster than predicted from simple mathematical
models. Addition of plants, sediment, or sediment with plants, to the
laboratory aquaria increased the rate of breakdown of methyl
parathion; sediment had the greatest effect reducing half-life from
300 h in water alone to 90-140 h. These findings support the
investigation of Goedicke & Winkler (1976), who considered, from their
testing of the persistence of different formulations of methyl
parathion in soils, that the compound would not contaminate
groundwater, if applied at suggested rates and intervals.
Table 6. 14C mass balance of methyl parathion in a model ecosystema
Samples Application rate of methyl parathion
0.3 kg/ha 0.6 kg/ha 2.4 kg/ha
air 57b 46 33
soil 30 30 28
groundwater 0.0 0.1 0.0
plants 12 23 38
animals 1.0 0.6 1.1
a From: Gillett & Gile (1976).
b %.
4.1.1 Air
Most of this insecticide is directly liberated by spraying.
However, a perceptible amount is released simultaneously with
evaporation from water surfaces, leaves, or soil (Woodrow et al.,
1977).
Air samples were analysed after the application of methyl
parathion at a concentration of 1.12 kg/ha (Jackson & Lewis, 1978).
The conventional emulsifiable concentrate was compared with an
encapsulated formulation. The filter collection efficiency was
determined to be 105% and the extraction efficiency was 92%. During
the experimental period, the temperature varied from 18 to 34 °C at an
average relative humidity of 72%. The results of the analysis of the
air samples collected in tobacco-growing areas of North Carolina are
shown in Table 7.
Table 7. Concentration of methyl parathion in the air after applicationa
Time (days) Methyl parathion (mg/m3)
emulsifiable concentrate encapsulated formulation
0 7.408 3.783
1 3.338 0.330
3 0.584 0.107
6 0.036 0.025
6 0.054 0.019
9 0.013 0.016
a From: Jackson & Lewis (1978).
Since the usual atmospheric levels of methyl parathion in the
surroundings of agricultural areas range from not detectable to 71
ng/m3, Jackson & Lewis (1978) discussed the possibility that the
concentrations measured on day 9 may have been the result of the
background level in the air of the heavily treated areas
The atmospheric concentration of methyl parathion after spraying
in the Kalinin District, Tashkent Province of the Uzbek USSR, during
July and August, was determined by Akhmedov (1968). He found that the
concentrations measured were dependent on the size of the area of
methyl parathion application, the time of application, the
temperature, and the wind velocity. In addition, the odour threshold
was estimated, and effects on the brain electrical activity,
resorption action, dark adaptation, and the light sensitivity of the
eyes were studied.
After the aerial treatment of forests, Vrochinsky & Makovsky
(1977) measured the following concentrations of methyl parathion in
the air (Table 8).
The concentrations of methyl parathion increased in foggy
conditions because of the adsorption of the compound on the surface of
water aerosols (Goncharuk et al., (1988).
Table 8. Methyl parathion in air after spraying forestsa
Time (days) Methyl parathion (mg/m3)
0 0.12
1 0.05
5 0.024
10 0.0015
a From: Vrochinsky & Makovsky (1977).
14C-Methyl parathion was subjected to simulated rainfall (total
amount: 2.5, 25, and 38 mm/h) after application of 177 µg ai/cm2 to
an octadecylsilane/trimethylsilane-treated glass slide. The amounts of
14C remaining after washoff were 56%, 6%, and 2% respectively; thus,
methyl parathion shows a high rate of washoff (Cohen & Steinmetz,
1986).
4.1.2 Water
Various mechanisms exist for the transportation of methyl
parathion following its application to aquatic environments,
including: application-associated losses, volatilization, wind
erosion, rinsing by rain into groundwater, and transportation as a
soil-methyl parathion complex.
Eichelberger & Lichtenberg (1971) estimated the water pollution
factor by investigating the persistence of methyl parathion in river
water. They used a sealed glass jar containing river water and methyl
parathion and applied sunlight and artificial fluorescent light. The
initial concentration of methyl parathion was 10 µg/litre (Table 9):
Badawy & El-Dib (1984) found that methyl parathion was more
stable in water of high salinity, such as sea water, than in fresh
water.
Table 9. Persistence of methyl parathion in river watera
Time % of the initial concentration (10 µg/litre)
1 hour 80b
1 week 25
2 weeks 10
4 weeks 0
a Adapted from: Eichelberger & Lichtenberg (1971).
b Recoveries were rounded off to the nearest 5%.
Because of a collision between two ships in the Mediterranean Sea
near Port-Said, Egypt, the sea became contaminated with more than
10 000 kg methyl parathion. Maximum methyl parathion concentrations
(96 µlitre/litre) were found 50 m in the drifting direction (surface
current, wind). In general, the concentration decreased with distance
and time and reached the detection limit up to 80 days after the
accident. The residues in sediment gradually increased during the
first 20 days (concentration factor 49.5) (Badawy et al., 1984).
Crossland et al. (1986) gave mathematical tools for calculating
the fate of chemicals in aquatic systems (because of the importance of
the degradation of methyl parathion in water, see also section 4.2).
4.1.3 Soil
Lichtenstein (1975) incorporated an emulsifiable concentration of
methyl parathion into the upper 5 inches of a silt loam at a rate of
3.1 mg/kg). One month after treatment, 3.5% of the methyl parathion
could be detected in the soil. The author showed that percolating
water transported metabolites vertically as well as horizontally.
Methyl parathion moved less than 20 cm in a loamy soil following an
annual precipitation of 1500 mm (Haque & Freed, 1974).
Bound residues of [ring-14C] methyl parathion in a silt loam
were monitored during an incubation period of 49 days (Gerstl &
Helling, 1985). After this period, 54% of the initial 14C remained
in the soil; of this, 13% was soxhlet-extractable with methanol and
87% was bound residue. Several treatments indicated that bound
residues of methyl parathion are not easily released (i.e., converted
to an extractable form), but that they are slowly mineralized to
CO2.
A simulated spillage of emulsifiable or microencapsulated
formulations of methyl parathion on soil (sandy loam; pH ranging from
6.6 to 7.8, with a mean of 7.2) was studied for 45 months by Butler
and coworkers (1981). The uptake of the insecticide was studied in
five different experiments. The soil was contaminated with: a) 51%
emulsifiable concentrate formulation