INTERNATIONAL PROGRAMME ON CHEMICAL SAFETY
ENVIRONMENTAL HEALTH CRITERIA 94
PERMETHRIN
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
World Health Orgnization
Geneva, 1990
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development of know-how for coping with chemical accidents,
coordination of laboratory testing and epidemiological studies, and
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chemicals.
WHO Library Cataloguing in Publication Data
Permethrin.
(Environmental health criteria ; 94)
1.Pyrethrins. I.Series
ISBN 92 4 154294 2 (NLM Classification: WA 240)
ISSN 0250-863X
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CONTENTS
ENVIRONMENTAL HEALTH CRITERIA FOR PERMETHRIN
INTRODUCTION
1. SUMMARY, EVALUATION, CONCLUSIONS, AND RECOMMENDATION
1.1. Summary and evaluation
1.1.1. Identity, physical and chemical properties, analytical
methods
1.1.2. Production and use
1.1.3. Human exposure
1.1.4. Environmental fate
1.1.5. Kinetics and metabolism
1.1.6. Effects on organisms in the environment
1.1.7. Effects on experimental animals and in vitro test systems
1.1.8. Effects on human beings
1.2. Conclusions
1.2.1. General population
1.2.2. Occupational exposure
1.2.3. Environment
1.3. Recommendations
2. IDENTITY, PHYSICAL AND CHEMICAL PROPERTIES, ANALYTICAL METHODS
2.1. Chemical identity
2.2. Physical and chemical properties
2.3. Analytical methods
3. SOURCES OF HUMAN AND ENVIRONMENTAL EXPOSURE; ENVIRONMENTAL LEVELS
3.1. Industrial production
3.2. Use pattern
3.3. Residues in food and other products
3.4. Residues in the environment
4. ENVIRONMENTAL TRANSPORT, DISTRIBUTION, AND TRANSFORMATION
4.1. Transport and distribution between media
4.2. Photodecomposition
4.3. Degradation in plants
4.4. Degradation in soils
5. KINETICS AND METABOLISM
5.1. Metabolism in mammals
5.1.1. Mouse
5.1.2. Rat
5.1.3. Goat
5.1.4. Cow
5.1.5. Man
5.2. Metabolism in hens
5.3. Enzymatic systems for biotransformation
6. EFFECTS ON THE ENVIRONMENT
6.1. Toxicity to aquatic organisms
6.1.1. Aquatic microorganisms
6.1.2. Aquatic invertebrates
6.1.3. Fish
6.1.4. Field studies and community effects
6.2. Toxicity to terrestrial organisms
6.2.1. Soil microorganisms
6.2.2. Terrestrial invertebrates
6.2.3. Birds
6.2.4. Mammals
6.3. Uptake, loss, bioaccumulation, and biomagnification
7. EFFECTS ON EXPERIMENTAL ANIMALS AND IN VITRO TEST SYSTEMS
7.1. Acute toxicity
7.2. Subacute and subchronic toxicity
7.2.1. Oral exposure
7.2.1.1 Mouse
7.2.1.2 Rat
7.2.1.3 Dog
7.2.1.4 Rabbit
7.2.1.5 Cow
7.2.2. Dermal exposure
7.2.3. Inhalation exposure
7.3. Primary irritation
7.3.1. Skin irritation
7.3.2. Eye irritation
7.4. Sensitization
7.5. Long-term toxicity
7.5.1. Mouse
7.5.2. Rat
7.6. Carcinogenesis
7.6.1. Mouse
7.6.1.1 ICI study
7.6.1.2 FMC II study
7.6.1.3 BW study
7.6.1.4 Appraisal of mouse studies on carcinogenicity
7.6.2. Rat
7.6.2.1 ICI study
7.6.2.2 BW study
7.6.2.3 Appraisal of rat studies on carcinogenicity
7.7. Mutagenicity
7.7.1. Microorganism and insects
7.7.2. Mammals
7.8. Teratogenicity and reproduction studies
7.8.1. Teratogenicity studies
7.8.1.1 Mouse
7.8.1.2 Rat
7.8.1.3 Rabbit
7.8.2. Reproduction studies
7.8.2.1 Rat
7.9. Neurotoxicity
7.9.1. Rat
7.9.2. Hen
7.10. Behavioural effects
7.11. Miscellaneous studies
7.12. Mechanism of toxicity (mode of action)
8. EFFECTS ON HUMANS
8.1. Occupational exposure
8.2. Clinical studies
9. PREVIOUS EVALUATIONS BY INTERNATIONAL BODIES
REFERENCES
APPENDIX I
FRENCH TRANSLATION OF SUMMARY, EVALUATION, CONCLUSIONS, AND RECOMMENDATIONS
WHO TASK GROUP ON ENVIRONMENTAL HEALTH CRITERIA FOR PERMETHRIN
Members
Dr V. Benes, Department of Toxicology and Reference Laboratory, Insti-
tute of Hygiene and Epidemiology, Prague, Czechoslovakia
Dr S. Dobson, Institute of Terrestrial Ecology, Monks Wood Experimental
Station, Huntingdon, United Kingdom
Dr Y. Hayashi, Division of Pathology, National Institute of Hygienic
Sciences, Tokyo, Japan
Dr S. Johnson, Hazard Evaluation Division, Office of Pesticide Pro-
gramme, US Environmental Protection Agency, Washington DC, USA
(Chairman)
Dr S.K. Kashyap, National Institute of Occupational Health (ICMR)
Ahmedabad, India (Vice-Chairman)
Dr Yu. I. Kundiev, Research Institute of Labour, Hygiene, and Occu-
pational Diseases, Kiev, USSR
Dr J.P. Leahey, ICI Agrochemicals, Jealotts Hill Research Station,
Bracknell, United Kingdom (Rapporteur)
Dr J. Miyamoto, Takarazuka Research Centre, Sumitomo Chemical Company,
Takarazuka, Hyogo, Japan
Dr Y. Takenaka, Division of Information on Chemical Safety, National
Institute of Hygienic Sciences, Tokyo, Japan
Representatives of Other Organizations
Dr M. Ikeda, International Commission on Occupational Health. Depart-
ment of Environmental Health, Tohoku University, School of Medicine,
Sendai, Japan
Dr H. Naito, World Federation of Poison Control Centres and Clinical
Toxicology. Institute of Clinical Medicine, University of Tsukuba,
Tsukuba-Shi, Ibaraki, Japan
Observers
Dr M. Matsuo, Sumitomo Chemical Company, Biochemistry & Toxicology
Laboratory, Osaka, Japan
Dr Y. Okuno, Sumitomo Chemical Company, Biochemistry & Toxicology
Laboratory, Osaka, Japan
Dr N. Punja, International Group of National Association of Manufac-
turers of Agrochemical Products (GIFAP), ICI Plant Protection
Division, Fenhurst, Haslemere, United Kingdom
Secretariat
Dr K.W. Jager, International Programme on Chemical Safety, World Health
Organization, Geneva, Switzerland (Secretary)
Dr R. Plestina, Division of Vector Control, Delivery and Management of
Vector Control, World Health Organization, Geneva, Switzerland
Dr J. Sekizawa, Section of Information and Investigation, Division of
Information on Chemical Safety, National Institute of Hygienic
Sciences, Tokyo, Japan (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 pub-
lication. 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 Manager of the International Pro-
gramme on Chemical Safety, World Health Organization, Geneva, Switzer-
land, in order that they may be included in corrigenda, which will
appear in subsequent volumes.
* * *
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).
* * *
The proprietary information contained in this document 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 (FAO, 1982).
ENVIRONMENTAL HEALTH CRITERIA FOR PERMETHRIN
A WHO Task Group on Environmental Health Criteria for Fenvalerate,
Permethrin, and d-Phenothrin met in Tokyo from 4 to 8 July 1988. This
meeting was convened with the financial assistance of the Ministry of
Health and Welfare, Tokyo, Japan, and was hosted by the National Insti-
tute of Hygienic Sciences (NIHS) in Tokyo.
Dr T. Furukawa and Dr K. Shirota opened the meeting on behalf of
the Ministry of Health and Welfare, and Dr A. Tanimura, Director-Gen-
eral of the NIHS welcomed the participants to the Institute. Dr M.
Mercier, Manager of the International Programme on Chemical Safety wel-
comed the participants on behalf of the three IPCS cooperating organ-
izations (UNEP/ILO/WHO). The group reviewed and revised the draft mono-
graph and made an evaluation of the risks for human health and the
environment from exposure to permethrin.
The first draft of this document was prepared by DR J. MIYAMOTO and
DR M. MATSUO of Sumitomo Chemical Company with the assistance of the
staff of the National Institute of Hygienic Sciences, Tokyo, Japan.
Dr I. Yamamoto of the Tokyo University of Agriculture and Dr M. Eto of
Kyushu University, Japan, assisted with the finalization of the draft.
The second draft was prepared by DR J. SEKIZAWA, NIHS, Tokyo, incor-
porating comments received following circulation of the first draft to
the IPCS contact points for Environmental Health Criteria documents.
Dr K.W. Jager and Dr P.G. Jenkins, both members of the IPCS Central
Unit, were responsible for the technical development and editing,
respectively, of this monograph.
The assistance of the Sumitomo Chemical Company, Japan, and ICI
Agrochemicals, United Kingdom, in making available to the IPCS and the
Task Group their toxicological proprietary information on permethrin is
gratefully acknowledged. This allowed the Task Group to make its
evaluation on the basis of more complete data.
* * *
The United Kingdom Department of Health and Social Security
generously supported the cost of printing.
ABBREVIATIONS
ai active ingredient
Cl2CA 3-(2,2-dichlorovinyl)-2,2-dimethylcyclopro-
panecarboxyclic acid
ECG electrocardiogram
EEG electroencephalogram
FID flame ionization detector
GC gas chromatography
GC-ECD gas chromatography with electron capture
detector
GC-SIM gas chromatography with selected ion
monitoring
GLC gas-liquid chromatography
HPLC high-performance liquid chromatography
JMPR Joint FAO/WHO Meeting on Pesticide Residues
NOEL no-observed-effect level
PBacid 3-phenoxybenzoic acid
PBalc 3-phenoxybenzyl alcohol
PBald 3-phenoxybenzaldehyde
TLC thin-layer chromatography
INTRODUCTION
SYNTHETIC PYRETHROIDS - A PROFILE
1. During investigations to modify the chemical structures of natural
pyrethrins, a certain number of synthetic pyrethroids were produced
with improved physical and chemical properties and greater biologi-
cal activity. Several of the earlier synthetic pyrethroids were
successfully commercialized, mainly for the control of household
insects. Other more recent pyrethroids have been introduced as
agricultural insecticides because of their excellent activity
against a wide range of insect pests and their non-persistence in
the environment.
2. The pyrethroids constitute another group of insecticides in ad-
dition to organochlorine, organophosphorus, carbamate, and other
compounds. Pyrethroids commercially available to date include
allethrin, resmethrin, d-phenothrin, and tetramethrin (for insects
of public health importance), and cypermethrin, deltamethrin,
fenvalerate, and permethrin (mainly for agricultural insects).
Other pyrethroids are also available including furamethrin, kadeth-
rin, and tellallethrin (usually for household insects), fenpropath-
rin, tralomethrin, cyhalothrin, lambda-cyhalothrin, tefluthrin,
cyfluthrin, flucythrinate, fluvalinate, and biphenate (for agricul-
tural insects).
3. Toxicological evaluations of several synthetic pyrethroids have
been performed by the FAO/WHO Joint Meeting on Pesticide Residues
(JMPR). The acceptable daily intake (ADI) has been estimated by
the JMPR for cypermethrin, deltamethrin, fenvalerate, permethrin,
d-phenothrin, cyfluthrin, cyhalothrin, and flucythrinate.
4. Chemically, synthetic pyrethroids are esters of specific acids
(e.g., chrysanthemic acid, halo-substituted chrysanthemic acid, 2-
(4-chlorophenyl)-3-methylbutyric acid) and alcohols (e.g.,
allethrolone, 3-phenoxybenzyl alcohol). For certain pyrethroids,
asymmetric centre(s) exist in the acid and/or alcohol moiety, and
the commercial products sometimes consist of a mixture of both
optical (1R/1S or d/1) and geometric (cis/trans) isomers. However,
most of the insecticidal activity of such products may reside in
only one or two isomers. Some of the products (e.g., d-phenothrin,
deltamethrin) consist only of such active isomer(s).
5. Synthetic pyrethroids are neuropoisons acting on the axons in the
peripheral and central nervous systems by interacting with sodium
channels in mammals and/or insects. A single dose produces toxic
signs in mammals, such as tremors, hyperexcitability, salivation,
choreoathetosis, and paralysis. The signs disappear fairly rap-
idly, and the animals recover, generally within a week. At near-
lethal dose levels, synthetic pyrethroids cause transient changes
in the nervous system, such as axonal swelling and/or breaks and
myelin degeneration in sciatic nerves. They are not considered to
cause delayed neurotoxicity of the kind induced by some organo-
phosphorus compounds. The mechanism of toxicity of synthetic
pyrethroids and their classification into two types are discussed
in the Appendix.
6. Some pyrethroids (e.g., deltamethrin, fenvalerate, cyhalothrin,
lambda-cyhalothrin, flucythrinate, and cypermethrin) may cause a
transient itching and/or burning sensation in exposed human skin.
7. Synthetic pyrethroids are generally metabolized in mammals through
ester hydrolysis, oxidation, and conjugation, and there is no tend-
ency to accumulate in tissues. In the environment, synthetic py-
rethroids are fairly rapidly degraded in soil and in plants. Ester
hydrolysis and oxidation at various sites on the molecule are the
major degradation processes. The pyrethroids are strongly adsorbed
on soil and sediments, and hardly eluted with water. There is
little tendency for bioaccumulation in organisms.
8. Because of low application rates and rapid degradation in the
environment, residues in food are generally low.
9. Synthetic pyrethroids have been shown to be toxic for fish, aquatic
arthropods, and honey bees in laboratory tests. But, in practical
usage, no serious adverse effects have been noticed because of the
low rates of application and lack of persistence in the environ-
ment. The toxicity of synthetic pyrethroids in birds and domestic
animals is low.
10. In addition to the evaluation documents of FAO/WHO, there are sev-
eral good reviews and books on the chemistry, metabolism, mammalian
toxicity, environmental effects, etc. of synthetic pyrethroids,
including those by Elliott (1977), Miyamoto (1981), Miyamoto &
Kearney (1983), and Leahey (1985).
1. SUMMARY AND EVALUATION, CONCLUSIONS, RECOMMENDATION
1.1 Summary and Evaluation
1.1.1 Identity, physical and chemical properties, analytical methods
Permethrin was first synthesized in 1973 and marketed in 1977 as a
photostable pyrethroid. It is an ester of the dichloro analogue of
chrysanthemic acid, 3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane-carb-
oxylic acid (Cl2CA), and 3-phenoxybenzyl alcohol. Technical products
are a mixture of four stereoisomers with the configurations [1R,trans],
[1R,cis], [1S,trans], and [1S,cis] in the approximate ratio of 3:2:3:2.
The ratio of cis:trans is around 2:3 and 1R:1S is 1:1 (racemic). The
[1R,cis] isomer is the most insecticidally active of the isomers,
followed by the [1R,trans] isomer.
Technical grade permethrin is a brown or yellowish brown liquid
which may crystallize partly at room temperature. The melting point is
approximately 35°C and the boiling point is 220°C at 0.05 mmHg. The
specific gravity is 1.214 at 25°C and the vapour pressure is 1.3 µPa
at 20°C. Permethrin is almost insoluble in water (0.2 mg/litre at
30°C), but is soluble in organic solvents such as acetone, hexane, and
xylene. It is stable to light and heat, but unstable in alkaline
media.
Residue and environmental analyses are performed using a gas
chromatograph equipped with an electron capture detector (minimum
detectable concentration of 0.005 mg/kg). Technical products are ana-
lysed using a gas chromatograph with a flame ionization detector.
1.1.2 Production and use
Approximately 600 tonnes per year of permethrin is at present used
world-wide, mostly for agricultural purposes. It has a potential appli-
cation in the protection of stored grain and it has been used in aerial
application for forest protection and vector control, for the control
of noxious insects in the household and on cattle, for the control of
body lice, and in mosquito nets.
Permethrin is formulated as emulsifiable concentrate, ultra-low-
volume concentrate, wettable powder, and dustable powder.
1.1.3 Human exposure
The rate of decline of residue levels in various crops is fairly
slow, half-lives ranging from about 1 to 3 weeks depending on the crop.
However, when permethrin is used as recommended, there is no signifi-
cant increase in residues following repeated application.
Exposure of the general population to permethrin is mainly via
dietary residues. Residue levels in crops grown according to good agri-
cultural practice are generally low. The resulting exposure of the
general population is expected to be low, but precise data in the form
of total-diet studies is lacking.
Information on occupational exposure to permethrin is very lim-
ited.
1.1.4 Environmental fate
In laboratory studies, permethrin has been shown to degrade in soil
with a half-life of 28 days or less. The trans isomer degraded more
rapidly than the cis isomer, ester cleavage being the major initial
degradative reaction. The compounds generated by ester cleavage were
then further oxidised, eventually yielding carbon dioxide as the major
terminal product. Studies to investigate the leaching potential of
permethrin and its degradates showed that very little downward movement
occurs in soil.
Permethrin deposited on plants degrades with a half-life of
approximately 10 days. Ester cleavage and conjugation of the acid and
alcohol released is the major degradation pathway. Hydroxylation at
various positions of the molecule and photo-induced cis-trans inter-
conversion also occur.
In water and on soil surfaces permethrin is photodegraded by sun-
light. Ester cleavage and cis-trans interconversion are, as with
plants, the major reactions.
In general, the degradative processes which occur in the environ-
ment lead to less toxic products.
Permethrin disappears rapidly from the environment, in 6-24 h from
ponds and streams, 7 days from pond sediment, and 58 days from foliage
and soil in a forest. From cotton leaves in a field, 30% of the com-
pound was lost within 1 week.
Under aerobic conditions in soil, permethrin degrades with a half-
life of 28 days.
There is very little movement of permethrin in the environment, and
it is unlikely that it will attain significant levels in the environ-
ment.
1.1.5 Kinetics and metabolism
Permethrin administered to mammals was rapidly metabolized and
almost completely excreted in urine and faeces within 12 days. The
trans isomer, being much more susceptible to esterase attack than the
cis isomer, was eliminated faster than the cis isomer. The major meta-
bolic reactions were ester cleavage and oxidation, particularly at the
terminal aromatic ring of the phenoxybenzyl moiety and the geminal
dimethyl group of the cyclopropane ring, followed by conjugation. Less
than 0.7% of the dose was detected in the milk of goats or cows admin-
istered permethrin orally.
1.1.6 Effects on organisms in the environment
In laboratory tests, permethrin has been shown to be highly toxic
for aquatic arthropods, LC50 values ranging from 0.018 µg/litre for
larval stone crabs to 1.26 µg/litre for a cladoceran. It is also
highly toxic for fish, with 96-h LC50 values ranging from 0.62 µg/litre
for larval rainbow trout to 314 µg/litre for adult rainbow trout.
The no-observed-effect level for early life stages of the sheepshead
minnow over 28 days is 10 µg/litre and the chronic no-effect level
for fathead minnow is 0.66-1.4 µg/litre. Permethrin is less toxic to
aquatic molluscs and amphibia, 96-h LC50 values being >1000 µg/litre and
7000 µg/litre, respectively.
In field tests and in the use of the compound under practical con-
ditions, this high potential toxicity is not manifested. An extensive
literature exists on the effects of using permethrin in agriculture,
forestry, and in vector control in many parts of the world. Some
aquatic arthropods are killed, particularly when water is over-sprayed
but the effects on populations of organisms is temporary. There have
been no reports of fish killed in the field. This reduced toxicity in
the field is related to the strong adsorption of the compound to sedi-
ments and its rapid degradation. Sediment-bound permethrin is toxic to
burrowing organisms but this effect also is temporary.
Permethrin is highly toxic for honey bees. The topical LD50 is
0.11 µg/bee, but there is a strong repellent effect of permethrin to
bees which reduced the toxic effect in practice. There is no evidence
for significant kills of honey bees under normal use. Permethrin is
more toxic to predator mites than to the target pest species.
Permethrin has very low toxicity to birds when given orally or fed
in the diet. The LD50 is >3000 mg/kg body weight for acute single
oral dosage and for dietary exposure it is >5000 mg/kg diet. It has no
effect on reproduction in the hen at a dose of 40 mg/kg diet.
Permethrin is readily taken up by aquatic organisms, bioconcen-
tration factors ranging from 43 to 750 for various organisms. In all
the aquatic organisms studied, absorbed permethrin is rapidly lost on
transfer to clean water. There is no bioaccumulation in birds. The
compound can, therefore, be regarded as having no tendency to bio-
accumulate in practice.
1.1.7 Effects on experimental animals and in vitro test systems
Permethrin has a low acute toxicity to rats, mice, rabbits, and
guinea-pigs, though the LD50 value varies considerably according to
the vehicle used and the cis:trans isomeric ratio. Signs of acute
poisoning become apparent within 2 h of dosing and persist for up to
3 days. [1R, cis ]- and [1R, trans ]-permethrin belong to the type I
group of pyrethroids, which typically cause tremor (T-syndrome), inco-
ordination, hyperactivity, prostration, and paralysis. Core temperature
is markedly increased during poisoning.
None of the metabolites of permethrin shows a higher acute (oral or
intraperitoneal) toxicity than permethrin itself.
Permethrin caused a mild primary irritation of the intact and
abraded skin of rabbits but did not cause a photochemical irritation
reaction after exposure of treated areas of rabbit skin to ultra-violet
light. Permethrin did not cause a sensitization reaction in guinea-
pigs.
Oral subacute and subchronic toxicity studies of permethrin have
been performed in rats and mice at dose levels up to 10 000 mg/kg diet
and for 14 days to 26 weeks in duration. Changes detected at the
higher level were an increase in liver/body weight ratio, hypertrophy
in the liver, and clinical signs of poisoning such as tremor. The no-
observed-effects levels (NOEL) in rats ranged from 20 mg/kg diet (in
studies lasting 90 days or 6 months) to 1500 mg/kg diet (in a 6-month
study).
NOEL values in dogs ranged from 5 mg/kg body weight in 3-month
studies to 250 mg/kg body weight in 6-month studies.
In long-term studies in mice and rats, an increase in liver weight
was found which was considered to be associated with an induction of
the liver microsomal enzyme system.
The NOEL in a 2-year rat study was 100 mg/kg diet, corresponding to
5.0 mg/kg body weight.
There were indications, from three long-term mouse studies, of
oncogenicity in the lungs of one strain of mouse (females only) at the
highest dose level (5 g/kg diet). Studies in rats revealed no oncogenic
potential in either sex.
Permethrin was not mutagenic in in vivo or in vitro studies.
Toxicological evidence from mutagenicity studies and from long-term
mouse and rat studies suggests that permethrin's oncogenic potential is
very low, is limited to female mice, and is probably epigenetic.
Permethrin is not teratogenic to rats, mice, or rabbits at dose
levels up to 225, 150, and 1800 mg/kg body weight, respectively.
In a 3-generation reproduction study, permethrin did not induce
adverse effects at levels up to 2500 mg/kg diet.
Permethrin fed to rats at high dose levels (6600-7000 mg/kg diet)
for 14 days induced sciatic nerve damage in one study but did not
produce any ultrastructural changes in the sciatic nerve in another
study. Permethrin did not cause delayed neurotoxicity in hens.
1.1.8 Effects on human beings
Permethrin can induce skin sensations and paraesthesia in exposed
workers, which develop after a latent period of approximately 30 min,
peak by 8 h and disappear within 24 h. Numbness, itching, tingling, and
burning are symptoms frequently reported.
No poisoning cases have been reported.
The likelihood of oncogenic effects in human beings is extremely
low or non-existent.
There are no indications that permethrin has an adverse effect on
human beings when used as recommended.
1.2 Conclusions
1.2.1 General population
The exposure of the general population to permethrin is expected to
be low. It is not likely to present a hazard provided it is used as
recommended.
1.2.2 Occupational exposure
With reasonable work practices, hygiene measures, and safety pre-
cautions, permethrin is unlikely to present a hazard to those exposed
occupationally.
1.2.3 Environment
It is unlikely that permethrin or its degradation products will
attain levels of environmental significance provided that recommended
application rates are used. Under laboratory conditions permethrin is
highly toxic to fish, aquatic anthropods, and honey bees. However,
lasting adverse effects are not likely to occur under field conditions
provided it is used as recommended.
1.3 Recommendations
Although dietary levels arising from recommended usage are con-
sidered to be low, confirmation of this through inclusion of permethrin
in monitoring studies should be considered.
No adverse effects have been reported following human exposure to
permethrin during the many years of its use. Nevertheless, it would be
wise to maintain observations of human exposure.
2. IDENTITY, PHYSICAL AND CHEMICAL PROPERTIES, ANALYTICAL METHODS
2.1 Chemical Identity
Permethrin was synthesized as one of the new photostable
pyrethroids by Elliott et al. (1973). It is prepared by the esterifi-
cation of the dichloro analogue of chrysanthemic acid, i.e. (1R, cis;
1R, trans; 1S, cis; 1S, trans )-3-(2,2-dichlorovinyl)-2,2-dimethyl-cyclo-
propanecarboxyclic acid (Cl2CA), with 3-phenoxybenzyl alcohol (PBalc).
It contains four stereoisomers due to the chirality of the cyclopropane
ring (Fig. 1). The cis:trans isomer ratio is reported to be 2:3 and the
optical ratio of 1R:1S is 1:1 (racemic) (FAO/WHO, 1980b). Thus,
permethrin contains the [1R,trans], [1R,cis], [1S,trans], and [1S,cis]
isomers in the approximate ratio of 3:2:3:2. Table 1 gives further
details of the chemical identity of permethrin.
The [1R,cis] isomer is the most insecticidally active among the
isomers, followed by the [1R,trans] isomer.
Molecular formula: C21H20Cl2O3
Table 1. Chemical identity of permethrin and its various stereoisomeric compositions
------------------------------------------------------------------------------------------------------
Common name/ CAS Index name (9Cl) Stereoisomeric Synonyms and
CAS Registry No./ compositionc trade names
NIOSH Accession No.a Stereospecific nameb
------------------------------------------------------------------------------------------------------
Permethrin Cyclopropanecarboxylic acid, (1):(2):(3):(4) Permethrina, Ambush,
52645-53-1 3-(2,2-dichloroethenyl)-2,2-dimethyl-, =3:2:3:2 Pounce, Outflank,
GZ1255000 (3-phenoxyphenyl)methyl ester Extin, Ectiban,
Stockade, NRDC143,
3-Phenoxybenzyl (1RS, cis,trans )-3- FMC33297, S-3151,
(2,2-dichlorovinyl)-2,2-dimethyl- SBP-1513, PP557,
cyclopropanecarboxylate A13-29158, BW-21-Z
(+)- cis -Permethrin same as permethrin - -
54774-45-7
GZ1257000 3-Phenoxybenzyl (1R, cis )-
3-(2,2-dichlorovinyl)-2,2-dimethyl-
cyclopropanecarboxylate
Permethrin same as permethrin cis:trans =2:3 -
(racemic mixture)
- 3-Phenoxybenzyl (1R, cis,trans)-3-
GZ1261000 (2,2-dichlorovinyl)-2,2-dimethyl-
cyclopropanecarboxylate
(+)- trans -Permethrin same as permethrin - -
51877-74-8
GZ1260000 3-Phenoxybenzyl (1R, trans )-3-
(2,2-dichlorovinyl)-2,2-dimethyl-
cyclopropanecarboxylate
cis-Permethrin same as permethrin
61949-76-6
GZ1251540 3-Phenoxybenzyl (1RS, cis )-3- - -
(2,2-dichlorovinyl)-2,2-dimethyl-
cyclopropanecarboxylate
------------------------------------------------------------------------------------------------------
a Registry of Toxic Effects of Chemical Substances (RTECS) (1981-1982 edition).
b (1R), (+) or (1S), (-) in the acid part of permethrin signifies the same stereospecific
conformation, respectively.
c Numbers in parentheses identify the structures shown in Fig. 1.
2.2 Physical and Chemical Properties
The physical and chemical properties of technical permethrin
(cis/trans isomeric ratio = 40:60, purity not less than 89%) are
summarized in Table 2. Permethrin is stable to heat and light. It is
more resistant in acidic media than alkaline, with an optimum stability
at pH 4.
Table 2. Physicochemical properties of technical permethrina
----------------------------------------------------------------------
Physical state crystal or viscous liquid
Colour yellow brown to brown
Relative molecular mass 391.31
Melting point 34 - 39 °C
63 - 65 °C (cis); 44 - 47 °C (trans)
Boiling point 220 °C (6.67 Pa), 200 °C (1.33 Pa)
Water solubility (30 °C) 0.2 mg/litre
Solubility in organic soluble or miscible with most organic
solvents (25 °C) solvents: acetone (450 g/litre), hexane
(> 1 kg/kg), methanol (258 g/kg), xylene
(> 1 kg/kg)
Density (25 °C) 1.214
Vapor pressure (20 °C) Technical grade : 1.3 µPa
Pure : 2.5 µPa (cis), 1.5 µPa (trans)
Octanol-water partition 6.5b
coefficient (log Pow)
----------------------------------------------------------------------
a From: Meister et al. (1983); Worthing & Walker (1987); FAO/WHO
(1980b); Wells et al. (1986)
b From: Schimmel et al. (1983)
2.3 Analytical Methods
Methods for the analysis of permethrin are summarized in Table 3.
The common procedure of residue and environmental analysis consists of
(a) extraction, (b) partition, (c) chromatographic separation (clean
up), and (d) quantitative and qualitative analysis of the insecticide
by analytical instruments. Table 3 also indicates minimum detectable
concentration (MDC) and percentage recovery.
To analyse technical grade permethrin, the product is dissolved in
chloroform, together with dioctyl phthalate (as an internal standard),
and the solution is injected into a GLC system equipped with flame
ionization detector (FID) (Horiba et al., 1977).
The Joint FAO/WHO Codex Alimentarius Committee has published rec-
ommendations for methods of analysis of permethrin residues (FAO/WHO,
1985c).
In the internationally accepted CIPAC (Collaborative International
Pesticide Analytical Council) method for permethrin analysis, the prod-
uct is dissolved in 4-methylpentan-2-one containing n-octacosane as
internal standard. Separation is carried out by GLC on a column of
chromosorb W-HP coated with silicone OV 210 (Henriet et al., 1985).
A gas chromatographic method for determining permethrin in techni-
cal and formulated products has been developed and subjected to a col-
laborative study involving 19 laboratories (Tyler, 1987). The column
used was a 1.0 m x 4 mm glass column packed with 3% OV-210 on chromo-
sorb W-HP. When five samples of technical material (90-95%), eight of
emulsifiable concentrates (10-50%), two of wettable powders (20-30%),
one of dustable powder (1-2%), and one of water-dispersible granules
(1-2%) were analysed, the coefficient of variation of the results
obtained ranged from 0.79 to 4.24%. The method was adopted as an
official first-action method by the Association of Official Analytical
Chemists.
Table 3. Analytical methods for permethrin
-------------------------------------------------------------------------------------------------------------------------------------
Sample Sample preparation Determination MDCc % Recovery Reference
GLC or HPLC; detector,b (fortification
Extraction Partition Clean up carrier, flow, column, level)
solvent Column Elution temperature, retention (mg/litre)d
time
-------------------------------------------------------------------------------------------------------------------------------------
Residue analysis
apple n-hexane/ ext.sol.a Silica gel CH2Cl2 ECD-GC,N2, 50 ml/min, 0.01 91 - 106 Baker &
acetone : /H2O 1 m, 3% OV-7, 235 °C (0.1 - 1.0) Bottomley
(1/1) (1982)
pear n-hexane/ ext.sol.a Silica gel CH2Cl2 HPLC UV-206 nm, 25 cm 0.05 81 - 95 Baker &
acetone : /H2O ODS, propan-2-ol, (0.1 - 1.0) Bottomley
(1/1) 1 ml/min (1982)
blueberry acetone n-hexane/ Florisil benzene/ ECD-GC, N2, 60 ml/min, 0.01 cis:79.6 - 87.1 MacPhee
sat.NaCl n-hexane 0.9 m, 3% OV-210, 200 °C, (0.05 - 0.25) et al.
(4/1) 7.0(cis), 8.3 (trans) min trans:73.3 - 84.2 (1982)
(0.05 - 0.25)
celery CH3CN n-hexane/ Florisil CH3CN/ ECD-GC, N2, 100 ml/min 0.005 94.2 - 97.0 Braun &
2% NaCl CH2Cl2/ 1.8 m, Ultra-Bond 20M, (0.01 - 1.0) Stanek
n-hexane 220 °C, 3.5, 4.1 min (1982)
(0.35/50/50)
corn pentane CH3CN/ Alumina pentane/ FID-GC, N2, 28 ml/min 0.2 87.5 - 105 Simonaitis
pentane ethyl acetate 1.22 m, 5% OV-225, 250 °C, (0.2 - 22) & Cail
(97/3) 9.5(cis), 10.0 (trans) min (1977)
beef CH3CN/ n-hexane Florisil CH3CN/ ECD-GC, N2, 100 ml/min 0.005 82.9 - 89.9 Braun &
muscle H2O 2% NaCl CH2Cl2/ 1.8 m, Ultra-Bond 20M, (0.01 - 1.0) Stanek
(85/15) n-hexane 220 °C, 3.5(cis), (1982)
(0.35/50/50) 4.1 (trans) min
-------------------------------------------------------------------------------------------------------------------------------------
Table 3 (contd.)
-------------------------------------------------------------------------------------------------------------------------------------
Sample Sample preparation Determination MDCc % Recovery Reference
GLC or HPLC; detector,b (fortification
Extraction Partition Clean up carrier, flow, column, level)
solvent Column Elution temperature, retention (mg/litre)d
time
-------------------------------------------------------------------------------------------------------------------------------------
Environmental analysis
waste XAD-2 Florisil n-hexane GC-SIM/MS, He, 25 ml/min, 50 95 (0.11) Siegel
water resin, /ether 1.8 m, SP-2250, 230 °C, ng/litre 95 (0.26) et al.
ether (9/1) 3.5(cis), 3.7 (trans) min (1980)
runoff n-hexane ECD-GC, N2, 150 ml/min, 100 97 Carroll
(sediment 0.91 m, 5% SP-2330, 215 °C, ng/litre et al.
+ water) 3(cis), 4 (trans) min (1981)
Product analysis
technical CHCl3 FID-GC, N2, 40 ml/min, Horiba
grade 2% LAC-2R-446, 200 °C et al.
(1977)
-------------------------------------------------------------------------------------------------------------------------------------
a ext. sol = extraction solvent.
b detector (ECD-GC = Coulson electrolytic conductivity detector-GC; GC-SIM/MS = GC-selected ion monitoring with mass spectroscopy).
c MDC = minimum detectable concentration (mg/kg, unless stated otherwise).
d fortification level indicates the concentration of permethrin added to control samples for the measurement of recovery.
3. SOURCES OF HUMAN AND ENVIRONMENTAL EXPOSURE; ENVIRONMENTAL LEVELS
3.1 Industrial Production
Permethrin was first marketed in 1977. Worldwide production fig-
ures (1979-1982) are shown in Table 4.
Table 4. World-wide production of permethrin
---------------------------------------------------------
Year Production Reference
(tonnes)
---------------------------------------------------------
1979 800 Wood Mackenzie (1980)
1980 860 Wood Mackenzie (1981)
1981 660 - 700 Wood Mackenzie (1982, 1983)
1982 650 Wood Mackenzie (1983)
1983 600 Wood Mackenzie (1984)
1984 335 Battelle (1986)
---------------------------------------------------------
3.2. Use Pattern
Permethrin is a photostable synthetic pyrethroid. It possesses a
high level of activity against Leptidoptera and is also effective
against Hemiptera, Diptera, and Coleoptera. It is a stomach and contact
insectide, but it has very little fumigant activity. Permethrin is not
plant systemic. It is fast acting and effective against all growth
stages, particularly larvae. Permethrin also has significant repellent
action. It is effective against insects at low rates of application
and is sufficiently photostable to be of wide-ranging practical use in
agriculture.
Permethrin is mostly used on cotton plants (61% of consumption).
The major consumer countries in 1980 were the USA (263 tonnes), Brazil
(38 tonnes), Mexico (36 tonnes), and Central America (27 tonnes)
(Battelle, 1982).
Other crops to which permethrin is applied are corn, soybean, cof-
fee, tobacco, oil seed rape, wheat, barley, alfalfa, vegetables, and
fruits. In addition to its pre-harvest usage, permethrin has a poten-
tial application in the protection of stored grain. For example, per-
methrin has been applied to sorghum or wheat in large scale trials in
Australia (FAO/WHO, 1981b, 1982b).
Permethrin is also used for the control of insects in household and
animal facilities (Battelle, 1982) or in forest pest control, as a fog
in mushroom houses, and as a wood preservative. Other applications are
in public health, particularly for insect control in aircraft, treat-
ment of mosquito nets, and human lice control.
It is formulated in emulsifiable concentrates (1.25-50%), ultra-low-
volume formulations (5%), wettable powders (25%), and fogging formu-
lations (2-5%) (FAO/WHO, 1980b). Permethrin is normally effective at
50 g ai/ha on leaf brassicae, whereas 100 g ai/ha is often needed under
more severe conditions in the Americas, Africa, and South-East Asia.
The concentration in most working dilutions is 0.04-0.08% (w/v).
3.3 Residues in Food and Other Products
As might be expected for a compound which is non-systemic and also
fairly stable on leaf surfaces, the amount of residue found on differ-
ent parts of crops depends largely on the direct exposure at the time
of application. This is particularly marked with leafy vegetables such
as lettuce and cabbage where residue levels on wrapper leaves are
usually many times (e.g., 10-100) higher than those on central heads
(as trimmed for commercial distribution). Similarly, residues on fruit
such as lemons, citrus, and kiwi fruits are almost entirely confined to
the peel or similar outer protective surfaces. This is illustrated by
the 1979 Joint FAO/WHO Meeting on Pesticide Residue (JMPR) evaluation,
which contains findings from the examinations of samples of cabbage,
lettuce, oranges, melons, and kiwi fruit (FAO/WHO, 1980b).
Residue levels in cotton seeds are influenced by the degree of boll
ripening/opening at the time of last spraying. Levels in root and tuber
vegetables are usually less than 0.05 mg/kg (FAO/WHO, 1980b).
Ground and aerial applications have been found to yield similar
residue levels in a wide range of vegetable and field crops. Simi-
larly, there were no major differences in residue levels in greenhouse
curcurbitae and solanaceae following spray and fogging applications at
effective rates under similar conditions (FAO/WHO, 1980b).
Supervised trials and residue analyses have been performed on a
variety of crops such as field crops, foliar and root vegetables,
trees, soft fruits, and fruiting vegetables. Comprehensive summaries of
reports (more than 5000 individual residue results on approximately 60
crops from 17 countries) were described in the evaluation reports of
the JMPR, (FAO/WHO 1980b, 1981b, 1982b, 1983b, 1984b, 1985b, 1986b). A
comprehensive list of maximum residue limits for a large number of
commodities resulted from these evaluations (FAO/WHO 1986c).
The rate of decline of residue levels in various crops is fairly
slow, half-life periods ranging from about 1 to 3 weeks depending on
the crop. However, there is no obvious build-up of residues following
repeated application within the rates and frequencies that are needed
to obtain good insect control (FAO/WHO, 1980b).
Residues were measured in cotton seeds in supervised trials during
1975-1977 in the USA. When emulsifiable concentrate formulations (25-
40%) of permethrin were applied to fields at rates of 110 or 450 g
ai/ha (3 to 16 times, until 0 to 76 days before harvest), the average
residue level in cotton seeds was 0.03-0.08 mg/kg, the highest values
ranging from 0.03 to 0.27 mg/kg in 27 samples (FAO/WHO, 1980b).
Similar results were obtained when sweet corn was treated 6-13
times with 25% emulsifiable concentrate at a rate of 280-450 g ai/ha.
The residue levels at 0-4 days after the last application were <0.01-
0.12 mg/kg (Ussary, 1978, 1979).
Wheat grains treated with permethrin at a rate of 0.5-5.0 mg/kg
revealed a residue level of 0.36-4.5 mg/kg after 9 months of storage
(Halls, 1981). When wheat containing a residue level of 1.09 mg/kg was
subjected to milling and baking processes, the level of the permethrin
residue declined to 0.12 mg/kg in white bread (Halls & Periam, 1980).
Groups of three cows were fed cis/trans (40/60)-permethrin at rates
of 0.2, 1.0, 10, 50, or 150 mg/kg diet for 28-31 days. Mean plateau
levels in whole milk were <0.01 µg/g and 0.3 µg/g at dietary levels
of 0.2 mg/kg and 150 mg/kg, respectively. These levels, however, de-
clined rapidly to <0.01 µg/g within 5 days after permethrin adminis-
tration ceased. Residue levels of <0.01-0.04 µg/g fat and 2.8-6.2 µg/g
fat were found in the perirenal fat of cows that were given permethrin
at dietary levels of 0.2 mg/kg and 150 mg/kg, respectively (Edwards &
Iswaran, 1977; Swaine & Sapiets, 1981a, 1981b).
In studies by Ussary & Braithwaite (1980), cows were given six
whole-body sprays of permethrin at a rate of 1.0 g ai/cow with an
interval of 14 days between each spray. They were allowed free access
to a self-oiler containing a solution of 0.03 g ai/litre (ensuring at
least two applications per day for a period of 10 weeks). The cows were
housed in premises that were sprayed at a rate of 0.06 g ai/m2, six
sprays taking place with a 14-day interval between sprays (the cows had
free access to the premises during spraying). This degree of exposure
is at the highest end of the range that is likely to occur in normal
husbandry practice. When cows were slaughtered five days after the
sixth application, the permethrin levels in muscle, liver, and kidney
were low (<0.01 mg/kg tissue). The highest residue levels detected were
0.10 mg/kg and 0.04 mg/kg in the intestinal and subcutaneous fat,
respectively.
Lactating cows (three/group) fed permethrin at dose levels of 0,
0.2, 1.0, 10, or 50 mg/kg diet for 28 days showed no mortality, and
growth and milk production were normal. Permethrin residues were ob-
served in the milk within 3 days at the two highest dietary levels;
levels appeared to reach a plateau rapidly and not to increase with
time. Analysis of individual cis and trans isomers showed that the
ratio of permethrin isomers in milk appeared to change during the
course of the study with the cis isomer predominating. Permethrin resi-
dues were not found in the tissues of animals that received doses of
1 mg/kg or less. At dose levels of 10 or 50 mg/kg, residues were de-
tected in the tissues, predominantly in the fat. Low levels were also
present in the muscle and kidney at the highest dose level. Permethrin
did not appear to accumulate in the fat but to reach a plateau rapidly
(Edwards & Iswaran, 1977).
3.4 Residues in the Environment
Data on precise levels of permethrin residues in the air, water, or
soil are not available. However, an assessment of the environmental
residues resulting from permethrin application has been made in some
studies.
Permethrin deposits and airborne concentrations have been measured
downwind from a single swath application using a back-pack mist blower.
Samples from Kromekote cards (to assess droplet density and size dis-
tribution), glass plates, water surface, bronze rods, and air samplers
were collected, cleaned up, and analysed by HPLC (Sundaram et al.,
1987). Permethrin deposits on all static collectors were greatest
within 30 m of the spray swath. Beyond 30 m downwind, the amounts of
the insecticide trapped by various collectors were extremely low and
were barely detectable.
Lindquist et al. (1987) measured permethrin concentrations in
greenhouse air and deposition on glass plates following application by
several different methods. Highest airborne residues were found after
thermal pulse-jet applications and lowest after hydraulic sprayings.
Most airborne residues were detected within 4 h of application. Surface
residues were highest after hydraulic and mechanical aerosol appli-
cations. Thermal pulse-jet applications resulted in low surface resi-
dues.
Agnihotri et al. (1986) evaluated the persistence of permethrin in
water and sediment contained in open trenches (3 m x 1 m x 30 cm) lined
with alkathene sheet. Insecticide emulsion was sprayed on the surface
of water at the normal recommended dosage and at twice this value. The
dissipation of the insecticide from the water was rapid, about 87-90%
of the pesticide being lost within 24 h at both rates of application.
However, residues were found to be absorbed by the sediment and these
persisted even beyond 30 days. In soil, persistence was moderate,
lasting for around 30 days.
4. ENVIRONMENTAL TRANSPORT, DISTRIBUTION, AND TRANSFORMATION
The degradation pathways of permethrin by ultraviolet light, in
soils, and in plants are summarized in Fig. 2.
4.1 Transport and Distribution between Media
In laboratory studies, permethrin in water was rapidly adsorbed
onto lake sediments or soil columns and was not desorbed or eluted
easily from them. However in forest spray trials, permethrin residues
were not only dissipated from water streams very rapidly but also did
not accumulate much in the bottom sediment. This was explained by the
fact that the low density of permethrin and its insolubility in water
prevented it from reaching bottom sediments. Residues in forest litter
and exposed soils were more stable. Low levels of degradation products
can be translocated from soils to plants.
When a 640-ha forest block in northern Ontario, Canada, was sprayed
once with permethrin at 17.5 g ai/ha, residues in water persisted for
less than 96 h and attained peak concentrations of 147.0 µg/litre in
ponds and 2.5 µg/litre in streams after one hour. Accumulation and
persistence of the pesticide in bottom sediment were negligible. Resi-
due levels in the treated streams ranged from 0.05 to 0.89 µg/litre and
persisted for a maximum of 96 h, but in another case, residues fell to
a non-detectable level (less than 0.05 µg/l) after 6-24 h. Permethrin
residues appeared 2.1 km downstream from the treatment block 6 h after
spraying. The level reached a peak of 0.18 µg/litre at 12 h and did
not persist beyond 96 h. Accumulation of the insecticide in pond sedi-
ment was minimal (5-8 µg/kg) and persisted for less than 7 days. No
permethrin residue was found in stream sediments. The sprayed per-
methrin formulation had a density (0.88 g/ml) less than that of water
and was practically insoluble in water. It therefore formed a surface
film when brought into contact with stagnant or slowly moving water.
This significantly reduced the likelihood of the insecticide reaching
the bottom sediment or exposing fish in the treated ponds and streams.
Insecticide residues in foliage, soil, and litter were more stable than
in water and remained at detectable concentrations to the end of the
58-day sampling period. Deciduous and coniferous foliage contained
permethrin residues ranging from 0.02 to 0.78 mg/kg and retained con-
centrations of 0.02-0.05 mg/kg for at least 57 days. Forest litter
within the treatment block showed a residue level of 0.07 mg/kg 58 days
after the pesticide application. The permethrin residue levels in ex-
posed soil in the treatment block were fairly constant (0.04-0.07mg/kg)
for up to 58 days (Kingsbury & Kreutzweiser, 1980a).
In another field test where permethrin was sprayed (17.5 g ai/ha)
twice at intervals of 9 or 10 days in two forest blocks in Quebec,
Canada, the stagnant water in the sprayed region contained permethrin
levels of no more than 0.62 µg/litre and 0.84 µg/litre after the
initial and second applications, respectively. Samples from the streams
showed residue levels ranging from 0.05 to 1.84 µg/litre. Permethrin
concentrations in the water persisted at mean levels of 0.15 µg/litre
for 96 h and 0.03 µg/litre for 48 h after the first and second appli-
cations, respectively (detection limit: 0.01 µg/litre). Sediments
collected from a pond and streams, contained 30-95 µg permethrin/kg.
Accumulation of residual permethrin in stream sediment 4.5 km down-
stream from the treatment block was minimal. Permethrin residue levels
in forest litter increased substantially following the second appli-
cation. Mean concentrations ranged from 0.01 mg/kg to 0.053 mg/kg but
fell to non-detectable levels within 59 days (Kreutzweiser, 1982).
In a laboratory adsorption-desorption study, more than 95% of per-
methrin in aqueous solutions (6-42 µg/litre) was rapidly adsorbed
onto lake sediment, and the adsorbed insecticide was not easily de-
sorbed from the sediment by several water rinses. A high distribution
coefficient (i.e., g adsorbed per g sediment divided by g per ml of
solution) of 389 ml/g was obtained from the adsorption isotherm. Per-
methrin in aqueous solution applied to the surface of a sediment column
did not penetrate through more than 2 cm of the sediment (Sharom &
Solomon, 1981).
In a laboratory soil-leaching experiment, 14C-labelled (+)- cis or
(+)- trans- permethrin was incubated with two types of soils (light
clay soil of Kodaira and sandy clay loam soil of Azuchi) for 0 day or
21 days, then these permethrin-soil mixtures were applied to the top of
a soil column and eluted with water. When a mixture with no pre-
incubation was applied to the column, only 1.0 to 3.4% of the radio-
carbon was found in lower layer and no radiocarbon was eluted. However,
the degradation products from the pre-incubated samples were eluted
with water to a slight extent (see section 4.4) (Kaneko et al., 1978).
Similar results were obtained by Kaufman et al. (1981) in soil
mobility studies using soil TLC methods.
The uptake of permethrin and its degradation products by plants
from soil was studied by Leahey & Carpenter (1980). Sandy loam soil was
treated separately with [14C-cyclopropyl]- and [14C-phenyl]-permethrin
at a spray application rate of 2 kg/ha. The top 8 cm of the treated
soil was thoroughly mixed, and sugar beet, wheat, lettuce, and cotton
seeds were sown at intervals of 30, 60, and 120 days after treatment.
Low radioactive residues (up to 0.86 mg/kg) were detected in mature
plants, but the residues were higher in crops grown in soil treated
with [14C-cyclopropyl]-permethrin. It appeared that certain carboxylic
acid metabolites formed in the soil were subsequently taken up by the
plants. However, under field conditions, no residues of permethrin or
its metabolites were detected in crops sown 60 days or more after soil
treatment (Swaine et al., 1978).
4.2 Photodecomposition
Appraisal
Photochemical studies of permethrin in thin films and in solution
have shown it to be much more stable to light (10-100 times) than
synthetic pyrethroids developed earlier. In solution, photoisomeriz-
ation at the 1,3-bond of the cyclopropane ring and ester cleavage were
shown to be the major reactions.
In a thin film on plywood, permethrin remained insecticidally
active after 26 days, compared with 4-8 days and <2 days for phenothrin
and resmethrin, respectively. When exposed to daylight as a thin film
(0.2 mg/cm2) indoors near a window, phenothrin photodecomposed with a
half-life of about 6 days, whereas 60% of applied permethrin remained
undecomposed after 20 days. Thus, replacement of the isobutenyl group
with the dichlorovinyl substituent significantly enhanced the photo-
stability of permethrin. Permethrin was reported to be 10-100 times
more photostable than other pyrethroids synthesized earlier (Elliott et
al., 1973).
The photolysis of [1RS, trans ]- or [1RS, cis ]-permethrin (5)a has
been examined using materials labelled with 14C at the carboxy (acid)
or benzyl (alcohol) group (Fig. 2). On irradiation with ultraviolet
light (peak wavelength: 290-320 nm), both permethrin isomers decomposed
slightly faster in hexane than in methanol. In both solvents, the cis
isomer photodecomposed about 1.6 times faster (T´ = 43-58 min) than the
trans isomer. The photodecomposition reaction involved extensive
isomerization of the cyclopropane ring, i.e. interconversion of the
trans and cis isomers. This probably occurred via a triplet energy
state forming the diradical intermediate through Cl-C3 bond fission,
since the reaction was efficiently quenched by 1,3-cyclohexadiene. The
isomerization reaction reached a state of equilibrium after 1-4 h of
irradiation and the more thermodynamically stable trans isomer
constituted 65-70% of the isomer mixture. Apart from the isomerization
reaction, ester cleavage was the major photolytic reaction. As the
result of ester cleavage and other photolytic reactions, products
formed from permethrin also included smaller or trace amounts of
monochloro-permethrin (22) (from reductive dechlorination), 3-phenoxy-
benzaldehyde (PBald) (11), 3-phenoxybenzoic acid (PBacid) (12),
3-phenoxybenzyl-3,3-dimethylacrylate (23) (from diradical intermedi-
ate), and benzyl alcohols (9,10), as well as their corresponding acids
(15,16). In addition, large amounts of unidentified polar products were
-----------------------------------------------------------------------
a Numbers in parentheses refer to the corresponding numbers in Fig.2
detected, especially in water. Permethrin and monochloro-permethrin
(0.1-0.5 g) did not undergo photo-oxidation or other reactions within 7
days in oxygenated methanol solution using Rose Bengal as a sensitizer.
Thus the chlorine atoms at the vinyl position had a pronounced effect
in protecting this substituent from oxidation or epoxidation, as com-
pared with the isobutenyl in chrysanthemate (Holmstead et. al., 1978).
Holmstead et al. (1978) also investigated the photodegradation of
permethrin on a soil surface. The degradation on soil was similar to
the degradation pathways established in solution, but the rate of de-
gradation was slower and photo-isomerisation less important. Exposure
of the permethrin isomers on Dunkirk silt loam soil for 48 h resulted
in about a 55% loss of permethrin under sunlight and about a 35% loss
in the dark. The amount of unextractable material was about 6% in the
dark and about 18% in the light. On soil, permethrin did not undergo
extensive isomerization of the cyclopropane ring as it did in solution.
There was little difference in the amount of free acid detected in the
dark or in light, and 3-phenoxybenzyl alcohol (PBalc) (6) (approxi-
mately 5%) was the major cleavage product of the alcohol moiety. Other
products detected in trace amounts were essentially similar to those
present in solutions that had undergone photolysis.
4.3 Degradation in Plants
Appraisal
Thorough investigations of the fate of permethrin in plants have
been performed using bean plants and cotton plants. No significant
differences in the types of metabolic pathways were detected for the
two plant species. Very little translocation of permethrin or its
metabolites was observed following either topical application or stem
injection of permethrin to plants. Photochemical reactions played an
important role in the fate of permethrin applied to the surface of
plants. A major degradation pathway in plants was ester cleavage,
followed by rapid conjugation with sugars of the Cl2 CA and PBalc thus
formed.
The metabolism of the [1R,trans] and [1R,cis] isomers of 14C-per-
methrin, labelled separately in the dichlorovinyl and benzyl carbon
atoms, in snap bean seedlings has been studied in the greenhouse.
Whole-body autoradiography of the plants showed that little trans-
location of radiolabelled permethrin or its metabolites had occurred.
The amounts of radiocarbon remaining after 14 days were 13-17% of the
dose in the surface wash, 46-58% in the methanol extract, and 8-14% un-
extracted in the plant residues. Some interconversion of the trans and
cis isomers occurred and the cis isomer was slightly more persistent
than the trans isomer. The initial half-lives of the cis and trans
isomers of permethrin in the seedlings were 9 and 7 days, respectively.
A large number of metabolites were detected in the plant extracts, the
major ones from the alcohol moiety being PBalc (6) and its correspond-
ing 2'- (8) or 4'-hydroxy (7) derivatives, which occurred mainly as
glucoside conjugates (Fig. 1). There were seven or eight additional
minor unidentified products. The cis and trans isomers of 3-(2,2-
dichlorovinyl)-2,2-dimethylcyclopropanecarboxyclic acid (Cl2CA) (17)
were the major metabolites from the acid moiety and occurred mainly as
conjugated forms. In addition, trace amounts of the 2'- (24) or 4'-
hydroxy (26) derivatives of permethrin were also detected. From the
hydrolysis experiments using beta-glucosidase, it was inferred that the
sugar concerned was glucose, but no detailed evidence of the identity
was obtained (Ohkawa et al., 1977).
In a separate study, Gaughan & Casida (1978) examined the metab-
olism of the [1RS,trans] and [1RS,cis] isomers of permethrin in snap
beans in the glasshouse and in cotton both in the glasshouse and out-
doors. Individual leaves of snap beans and cotton plants were treated
with 1 µg of cis- or trans-14C-permethrin labelled either at the
carboxy or methylene carbon. Under field conditions, about 30% of the
radiolabel was lost from cotton plants within one week after appli-
cation and some trans/cis isomerization at the cyclopropane ring took
place by photodecomposition. trans-Permethrin was metabolized more
rapidly than the cis isomer. The major degradation pathway was again
hydrolysis, followed by rapid conjugation of Cl2CA (17) and PBalc (6)
with sugars. There were at least two types of conjugates; the minor one
was a glycoside readily cleaved by beta-glucosidase and the major one
was a conjugate which was resistant to beta-glucosidase but was readily
cleaved by cellulase. Other products identified included the hydroxy-
lated compounds reported by Ohkawa et al. (1977) in their study of
beans treated with permethrin. In addition, hydroxylation at either of
the two methyl groups in the acid moiety (27) with subsequent conju-
gation occurred to a greater extent with the more stable cis isomer.
Similar metabolites to those formed under field conditions were
detected in bean and cotton plants under glasshouse conditions.
Roberts & Wright (1981) studied the conjugation of 14C-PBalc in
cotton plants using abscised leaves to obtain more information on the
nature of the conjugates produced. The alcohol was rapidly converted
to glucosyl 3-phenoxybenzyl ether and subsequently to more polar sub-
stances such as disaccharide conjugates with glucose and pentose (prob-
ably xylose or arabinose) sugars. The alcohol and its monosaccharide
and disaccharide conjugates underwent interconversion in the cotton
leaves. The evidence was obtained from experiments with 14C-glucose,
which showed the ready exchange of the glucose units of the conjugates
with free glucose in the leaves. No larger sugar conjugates of PBalc
were detected in plants.
From the above studies, it can be concluded that the types of prod-
ucts formed from permethrin in plants are similar to those formed in
mammals, except for the nature of the conjugates (see section 5.1).
4.4 Degradation in Soils
Appraisal
Several studies on the degradation of permethrin in a wide variety of
soil types have been carried out. These studies used permethrin labelled
with 14 C at different positions, so that the fate of virtually all of the
significant sub-units of the molecule has been traced. In all soil types
degradation is fairly rapid under aerobic conditions, conversion to 14CO2
being the major ultimate fate of the 14 C. With all soils and all positions
of radiolabelling, the formation of unextractable residues is a major occur-
rence. Under anaerobic conditions, similar degradation processes seem to
occur, but the rate of ultimate conversion to 14 CO2 is slower than under
aerobic conditions.
Kaufman et al. (1977) studied the degradation of cis and trans iso-
mers of permethrin in five soils under aerobic, anaerobic, and steril-
ized conditions. Soils were treated with 14C-permethrin labelled sep-
arately in the carboxy and methylene groups at a dose rate of 224 g/ha
and stored under aerobic conditions at 25°C. Degradation of permethrin
was rapid in four of five soils, with the trans isomer decomposing more
rapidly than the cis isomer. The initial half-lives were less than 28
days in all but one soil. Rapid evolution of 14CO2 was observed. In
Hagerstown silty clay loam soil, 62% of methylene- and 52% of carboxy-
labelled permethrin were converted to 14CO2 in 27 days. Only 15%
(methylene-labelled) to 19% (carboxy-labelled) of the applied radio-
label was extractable with methanol, 25-27% remaining unextracted and
associated with soil organic matter. Microbial metabolism was involved
in permethrin degradation and the major route was hydrolysis of the
ester linkage to form PBalc and Cl2CA, the former product being
subsequently oxidized to PBacid. In contrast, less than 0.3% of
14CO2 was evolved from soils treated with sodium azide (an inhibitor
of microbial growth) or when the soil was incubated under waterlogged
anaerobic conditions.
Kaneko et al. (1978) reported the degradation in two Japanese soils
of 14C-permethrin labelled separately in the dichlorovinyl and methy-
lene groups. The initial half-lives of the trans and cis isomers were
6-9 days and 12 days, respectively, in soils treated at a rate of 1 mg/
kg and stored at 25°C under aerobic upland conditions. 14CO2 was
evolved at rates similar to those observed by Kaufman et al. (1981). As
one of the 14C-preparations was different in labelled position from
those used in the earlier work, the evolution of 14CO2 was the evi-
dence for extensive degradation of the cyclopropyl moiety after hy-
drolysis in the soils. In addition to the hydrolysis products, several
oxidation products were identified, including 3-(2,2-dichlorovinyl)-
2-methyl-2-hydroxymethyl-cyclopropanecarboxylic acid (19) and 3-(4-
hydroxyphenoxy)benzyl- 3-(2, 2-dichlorovinyl)-2,2-dimethylcyclopropane-
carboxylate (26).
The degradation of permethrin was studied in a flooded Memphis silt
loam soil incubated at 25°C, [14C-carbonyl]- cis-, [14C-carbonyl]- trans-,
and [methylene-14C]- cis-permethrin being added to the soil at rates
of 0.1 and 1.0 mg/kg. The soils were analyzed after 0, 4, 8, 16, 32,
and 64 days to determine the distribution of 14C in CO2, solvent-
extractable compounds, water-soluble polar compounds, and soil-bounds
residues. Thin-layer chromatographic analysis of the organic solvent
extracts showed that trans-permethrin was more rapidly degraded than
the cis isomer. After 64 days, the amounts of 14C-trans-permethrin remain-
ing were 34.2% (at 0.1 mg/kg) and 30.3% (at 1.0 mg/kg) of the applied
14C, and those of 14C- cis-permethrin were 73.4% (at 0.1 mg/kg) and
69.8% (at 1.0 mg/kg). Two metabolites, 3-(2,2-dichloro-vinyl)-2,2-
dimethylcyclopropanecarboxylic acid (17) and PBalc (6), resulting from
permethrin hydrolysis were identified. Other metabolites were PBacid
(12) and PBald (11). Fragmentation of (17) and (12) to CO2 was not
extensive, and cumulative 14CO2 recoveries were less than 3.5% for
all treatments during the 64-day incubation period. The metabolism
of trans-permethrin resulted in the accumulation of polar compounds in
the water. Soil-bound residues gradually increased with time and
accounted for 3.3-11.4% of the 14C activity after 64 days. The
largest percentage of soil-bound 14C residue was in the fulvic acid
fraction (Jordan & Kaufman, 1986).
When 14C-permethrin preincubated with soil for 21 days was applied
on top of a soil column and eluted with water, 7.9-17.2% of the applied
radiocarbon was recovered in the lower layers of the column and 0.3-
2.6% was found in effluents (Kaneko et al., 1978). Only degradation
products of permethrin, such as PBacid (12) and 3-(4-hydroxyphenoxy)-
benzyl-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropanecarboxylate (26)
were identified in the effluent. Permethrin was not present in the
effluent (see section 4.1).
The persistence of permethrin in soil was studied in aqueous sus-
pensions of soil spiked with permethrin at a rate of 17.8 mg/kg under a
range of redox potential (-150, +50, +250, and +450 mV) and at pH 5.5,
7.0, and 8.0. The results of this study indicated that both the pH and
redox potential significantly influence the degradation of permethrin.
After 25 days, permethrin disappeared almost completely under well
oxidized (+450 mV) conditions at all three pH levels. Under reduced
conditions (-150 mV), only about 40% of the applied permethrin was
degraded. The rate of degradation of permethrin was moderate at weakly
oxidized (+250 mV) and moderately reduced (+50 mV) conditions at pH 8.
Thus, permethrin was lost more rapidly under oxidizing conditions, and
increasing the pH enhanced this loss under moderately reduced and
weakly oxidized conditions (Gambrell et al., 1981).
Jordan et al. (1982) investigated the effect of temperature on the
degradation of permethrin in soil. Dubbs fine sandy loam soil was
treated with [14C-carbonyl]- cis, trans-permethrin at a rate of 1
mg/kg and incubated at 10, 25, and 40°C for up to 64 days. The half-
lives of disappearance for trans and cis isomers were 14 and 55 days at
10°C, 5 and 12 days at 25°C, and 4 and 27 days at 40°C, respectively.
The most rapid rate of degradation of permethrin occurred at 25°C, per-
methrin being converted to Cl2CA (17) and ultimately to 14CO2. At
40°C rapid degradation of permethrin to Cl2CA also occurred, but
further degradation of Cl2CA to 14CO2 was reduced. The amount of
14CO2 evolved after 64 days was 56% at 25°C, compared with 29% at
10°C and 24% at 40°C.
Lord et al. (1982) investigated the factors affecting the persist-
ence of permethrin in three loam soils under laboratory conditions.
The degradation of trans-permethrin (4 mg/kg) at 30°C was similar at
three moisture contents ranging from 40 to 80% of water-holding
capacity, but more rapid degradation occurred in an aqueous soil sus-
pension system probably due to better distribution of the insecticide.
Four repeated applications of permethrin (4 mg/kg) at 20-day intervals,
or addition of nutrients including sucrose (1 mg/kg), powdered cellu-
lose (100 mg/kg), and NH4Cl (80 mg/kg) plus K2HPO4 (260 mg/kg) to
soils caused no drastic changes in the rate of degradation of per-
methrin.
The influence of organic materials on the degradation of permethrin
in soil was also studied by Doyle et al. (1981). [14C-carbonyl]- cis-per-
methrin was added to silty loam soil which had been pretreated with
sewage sludge or dairy manure at rates of 0, 50, or 100 tonnes/ha, and
total CO2 and 14CO2 evolution were monitored regularly throughout a
60-day incubation period at 25°C. The incorporation of sewage or dairy
manure at the rate of 50 and 100 tonnes/ha increased permethrin break-
down by 87% and 149% (sewage), or 64% and 134% (dairy manure) based on
the values measured in unamended soil, respectively. In the waste-
amended soils, a lag period of 28-38 days during which time virtually
no 14CO2 was evolved, was followed by a rapid evolution of 14CO2 before
the rate became stabilized. The highest rates (0.21-0.22% per day) were
observed in soils amended with either dairy manure or sewage sludge at
100 tonnes/ha. The rate of 14CO2 formation correlated directly with
the total microbial activity, as measured by total CO2 production.
In studies by Williams & Brown (1979), the persistence of per-
methrin in six soils was compared with that of fenvalerate under lab-
oratory conditions. The soils were treated with one of the insecticides
at 1 mg/kg and incubated under aerobic conditions for 16 weeks at a
temperature alternating between 20°C for 15 h and 10°C for 9 h to simu-
late the actual field conditions. With the exception of organic soil
from Cloverdale, degradation of permethrin was rapid in all soils, with
half-lives of 3 weeks or less. Under identical conditions, the half
life for fenvalerate was about 7 weeks. Again, trans-permethrin was
lost more rapidly than the cis isomer, and there was very little loss
of either insecticide in the sterilized soils. With Cloverdale organic
soil, a greater degree of adsorption onto the soil organic fraction
might have contributed to the slower degradation rate.
When soil was treated with [14C-cyclopropyl]-permethrin, sugar
beet grown on the treated soil was found to contain radiolabelled
conjugates of Cl2CA and 3-(2,2-dichlorovinyl)-2-methylcyclopropane-
1,2-dicarboxylic acid (21) (Leahey & Carpenter, 1980). It was possible
that both carboxylic acids were formed in the soil and were sub-
sequently taken up by the plants (see section 4.1).
5. KINETICS AND METABOLISM
5.1 Metabolism in Mammals
Appraisal
The metabolic pathways of permethrin in mammals are summarized in
Fig. 3.
The metabolism of permethrin has been studied in great detail in
various species of mammals, using a variety of radiolabelled isomers.
Permethrin administered to mammals was rapidly metabolized and almost
completely eliminated from the body within a short period of time. The
trans isomer of permethrin was eliminated more rapidly that the cis
isomer. Radiocarbon from trans- permethrin was excreted mostly in
urine, whereas that from the cis isomer was eliminated both in urine
and faeces to a similar extent. Expiration as CO2 contributed little
to its elimination in mammals. Major routes of metabolism for both
trans and cis isomers were ester cleavage and oxidation of the 4'-
position of the terminal aromatic ring. A less important reaction in
mammals was hydroxylation of the geminal dimethyl group of the cyclo-
propane ring. Major metabolites thus formed were Cl2 CA in free and
glucuronide form, sulfate conjugate of 4'-hydroxy-3-phenoxybenzoic
acid, PBacid in free and conjugate form, and hydroxymethyl-Cl2 CA as a
glucuronide conjugate. This latter compound was also isolated as a
lactone where the hydroxymethyl group and the carboxy group had a cis
configuration.
5.1.1 Mouse
In studies by Shah et al. (1981), 14C- cis-permethrin was applied
to the clipped skin of mice at a level of 1 mg/kg body weight in 0.1 ml
of acetone. The mice were restrained until the solvent had evaporated
and then placed in mouse metabolism cages. They were sacrificed at 1,
5, 15, 50, 480, and 2880 min after treatment and examined for absorp-
tion, distribution, and excretion of the insecticide. About 40% of the
applied permethrin had moved from the site of application within 5 min
and appeared to move rapidly to other parts of the body.
5.1.2 Rat
When a preparation of [1RS, trans ]- or [1RS, cis]-permethrin (14C-
labelled in the alcohol or acid moiety) was administered orally to male
rats at levels of 1.6-4.8 mg/kg, the compounds were rapidly metabolized
and labels in the acid and alcohol fragments were almost completely
eliminated from the body within a few days. The radiocarbon (alcohol
or acid label) from the cis isomer was eliminated in the urine (52-54%
of the dose) and the faeces (45-47%), whereas 79-82% of the radiocarbon
from the trans isomer appeared in the urine and 16-18% in the faeces
within 12 days after administration. The 14CO2 contained in the ex-
pired air corresponded to less than 0.5% of the dose. The tissue
residues were very low, although the cis isomer showed relatively
higher residue levels (0.46-0.62 mg/kg tissue) in the fat (Gaughan et
al., 1977). The major metabolite from the acid moiety was Cl2CA (17),
which was mostly excreted in the urine, conjugated with glucuronic
acid. This accounted for 50-63% of the dose from trans-permethrin and
15-22% from cis-permethrin. Oxidation at either of the geminal di-
methyl groups occurred to the extent of 4.3-10.4% (trans) or 12.2-14.9%
(cis), and these oxidised products were eliminated in the urine and
faeces as such or as the lactone or glucuronide. The major metabolite
from the alcohol moiety was 3-(4'-hydroxyphenoxy)benzoic acid (4'-OH-
PBacid) sulfate, accounting for 30.7-42.8% of the dose (trans) and
19.5-29.3% (cis). From cis-permethrin, 2'-OH-PBacid sulfate (about 3%)
was identified. Another significant metabolite was PBacid, which oc-
curred free and as glucuronide or glycine conjugates, and accounted for
25-31% (trans) and 5.7-10.1% (cis) of the dosed radiocarbon. Except for
a trace of PBacid, all the above metabolites from the alcohol moiety
were excreted entirely in the urine. However, the faeces of rats dosed
with trans-permethrin contained 1-2% of the radioactive dose as PBalc.
Thus substantial portions of the radioactive metabolites in the
recovered excreta were identified. The proposed metabolic pathways for
cis- and trans-permethrin are shown in Fig. 2. The five principle
sites of metabolic attack in both permethrin isomers were ester
cleavage, oxidation at the trans- and cis-methyl of the geminal
dimethyl group of the acid moiety, and oxidation at the 2'- and 4'-
positions of the phenoxy group. Conjugation of the resultant car-
boxylic acids, alcohols, and phenols with glucuronic acid, glycine, and
sulfuric acid occurred to varying extent. cis-Permethrin (29) was more
stable than trans-permethrin (30), and the cis isomer yielded four
faecally excreted ester metabolites that resulted from hydroxylation at
the 2'- or 4'-position of the phenoxy group or at the trans- or cis-
methyl group on the cyclopropane ring (e.g., (35'), (36')). The ester-
cleaved metabolites were extensively excreted into the urine whereas
the metabolites retaining an ester bond were found only in the faeces.
The major metabolite from the acid moiety of both isomers was Cl2CA
(31,31') in free (1-8%) and glucuronide (14-42%) forms. Other signifi-
cant metabolites were trans-OH-Cl2CA (32,32') (1-5%) and cis-OH-
Cl2CA (33,33') in the free (3-5%), lactone (34,34') (0-4%) and
glucuronide (1-2%) forms. On the other hand, the alcohol moiety
released after cleavage of the ester bond of both isomers was converted
mainly to the sulfate of 3-(4'-hydroxyphenoxy)benzoic acid (4'-OH-
PBacid) (13) (29-43% of the dose) and PBacid (12) in the free (1-10%)
and glucuronide (7-15%) forms. Other significant metabolites of the
alcohol moiety were PBalc (6), PBacid-glycine and the sulfate of 3-(2'-
hydroxyphenoxy) benzoic acid (2'-OH-PBacid) (14). [1RS, trans ]- and
[1RS, cis ]-permethrin showed no significant differences in metabolic
fate in the rat from [1R, trans ]- and [1R, cis ]-permethrin, respect-
ively (Elliott et al., 1976; Gaughan et al., 1977).
5.1.3 Goat
When ten consecutive oral doses of 14C- trans- or 14C- cis-permethrin
(labelled in the acid or alcohol moieties) at 0.2-0.3 mg/kg body
weight/day were given to lactating goats, they excreted 72-79% and 25-
36% of the trans and cis isomer doses, respectively, in urine and 12-
15% and 52-68%, respectively, in the faeces. The amounts of the
radiocarbon appearing in the milk were less than 0.7% with any one of
the four 14C-labelled preparations. Concerning the tissue residues 24h
after the last dose, detectable levels of radiocarbon were found in
most tissues, but none was higher than 0.04 mg/kg for the trans isomer
or 0.25 mg/kg for the cis isomer (Hunt & Gilbert, 1977).
The permethrin metabolites in goats were formed through cleavage of
the ester linkage, hydroxylation at the cis- or trans-methyl of the
geminal dimethyl group, and hydroxylation at the 4'-position of the
phenoxybenzyl moiety. Some of these metabolic products were further
oxidized and/or conjugated with glycine, glutamic acid and glucuronic
acid. The major compounds found in faeces after dosing with cis-per-
methrin were unmetabolized parent compound, 4'-OH-permethrin (35'),
trans-OH-permethrin (36'), PBalc, cis-OH- cis-Cl2CA-lactone (34') and
eight unidentified ester metabolites (Fig. 2). The faeces of goats
treated with the trans isomer contained large amounts of the parent
compound (41-79% of the faecal 14C) and of PBalc (8-25%) and cis-OH-
trans-Cl2CA-lactone (34). Also, three unidentified ester metab-
olites were found (8-23%). On the other hand, major urinary metab-
olites from the alcohol moiety of both isomers were PBacid-glycine (7-
9% of the urinary 14C) and 4'-OH-PBacid-glycine (4-12%). PBalc,
PBacid, 4'-OH-PBalc (7), 4'-OH-PBacid, PBacid-glutamic acid and 4'-OH-
PBacid-glutamic acid were also identified as minor metabolites. The
urine of goats treated with both isomers contained, as major compo-
nents, Cl2CA in the free form (2-47% of the urinary 14C) and as a
glucuronide (27-71%). Cl2CA-glucuronide was obtained to a larger
extent with the trans isomer than with the cis isomer. Other major
metabolites of the cis isomer were cis-OH-Cl2CA (33') (9-11%) and
cis-OH- cis-Cl2CA-lactone (34') (11-16%). trans-OH-Cl2CA (32,32') was
detected as a minor metabolite of both isomers. The milk of goats con-
tained the parent compounds, PBacid-glycine, and 4 -OH-PBacid-glycine.
On administration of the cis isomer, a larger amount of the parent
compound was excreted in the milk than in the case of the trans isomer.
Comparatively, when the trans isomer was administered, PBacid-glycine
was detected in the milk to a larger extent than with the cis isomer.
Most of the radioactivity in the fat was attributable to the parent
compound, or ester metabolites such as trans-OH-permethrin (36,36')
and trans-OH-permethrin conjugate (Ivie & Hunt, 1980).
5.1.4 Cow
When four lactating Jersey cows were orally administered 14C- trans- or
cis-permethrin preparations (labelled either in the alcohol or acid
moiety; three doses of ca. 1 mg/kg body weight at 24-h intervals), the
radiocarbon was almost completely eliminated in the faeces and urine 12
or 13 days after the initial dose. There was more faecal elimination of
the radiocarbon and higher tissue residue levels in the fat with the
cis isomer than the trans isomer. The 14C blood level reached a tran-
sient peak shortly after each dose and decreased to an insignificant
level within 2 to 4 days after the last dose. Higher blood levels were
attained with 14C- trans-permethrin labelled in the acid moiety than
when labelled in the alcohol moiety. This difference arising from
labelling positions was not evident with cis-permethrin. The radio-
carbon excreted in the milk was less than 0.5% of the dose. The lowest
14C level in milk was obtained from 14C- trans-permethrin (acid
moiety labelling) and the highest with 14C-trans-permethrin (alcohol
moiety labelling). With all labelled preparations, however, the radio-
carbon levels in milk decreased to <100 µg/litre within 2 to 4 days
after treatment ceased. The only radiolabelled compound recovered from
milk, in the case of the trans isomer, was unmetabolized permethrin,
whereas with the cis isomer 85% of the radiocarbon was as parent com-
pound and 15% as trans-OH- cis-permethrin (36 ). The metabolic reac-
tions of permethrin in cows were similar to those in rats and hens. In
cows, the permethrin isomers, their mono- and dihydroxy derivatives,
and PBalc, appeared only in the faeces, while the cis-OH-Cl2CA-
lactones (34,34') appeared in both faeces and urine. The remaining
metabolites appeared only in the urine. Although a slightly larger
portion of cis-permethrin than trans-permethrin was excreted un-
changed, there were similar amounts of ester metabolites with both iso-
mers. These ester metabolites were hydroxylated at the trans- or cis-
methyl positions of the geminal dimethyl group, at the 4'-position of
the phenoxybenzyl group, or at both the geminal dimethyl and phenoxy
groups. The preferred hydroxylation site with both isomers was the
trans-methyl group. The major metabolites from the acid moieties of
both isomers was the corresponding cis-OH-Cl2CA (33,33') and its
lactone and Cl2CA-glucuronide, while trans-OH- cis-Cl2CA (32') was also
a major metabolite from cis-permethrin. On the other hand, the major
metabolites from the alcohol moiety of both isomers were PBacid-glycine
(3-11% of the dose), PBalc (8-10%), and PBacid-glutamic acid (12-28%)
(Gaughan et al., 1978a).
5.1.5 Man
Two human volunteers, who consumed about 2 and 4 mg of permethrin
(25:75), respectively, excreted 18-37% and 32-39% of the administered
dose, detected as the metabolite Cl2CA, after acid hydrolysis of
their urine collected over 24 h (Cridland & Weatherley, 1977a,b).
5.2 Metabolism in Hens
A mixture (cis:trans = 25:75) of permethrin labelled with 14C in
the alcohol moiety was sprayed on 28 hens at doses of 3.77 or 11.94
mg/hen. The hens treated with the low dose showed no detectable levels
of radiocarbon in the gizzard, heart, lung, muscle, or egg white 24 h
after spraying, but the radiocarbon in the egg yolk reached a maximum
level of 0.049 mg/kg 5 days after treatment. The concentration of per-
methrin residues in the fat reached a peak 7 days after treatment and
no significant radioactivity was detectable after 4 weeks. With the
high dose, the radiocarbon in the skin had reached 6.69 mg/kg after 3
days. Small quantities of the radiocarbon were found in the egg yolks
(0.121 mg/kg) after 5 days and fat (0.110 mg/kg) after 1 day (Hunt et
al., 1979).
When White Leghorn hens were treated orally three consecutive days
with one of four 14C- trans- and cis-permethrin isomers labelled in
the alcohol or acid moieties at 10 mg/kg body weight, they showed no
signs of poisoning. More than 87% of the radiocarbon from the four
labelled preparations was found in the excreta 9 days after the initial
dose, 0.7-4.7% of the dose was exhaled as 14CO2, and 0.12-0.47% and
0.06-0.66% of the radiocarbon was recovered in egg yolk and fat (sub-
cutaneous and visceral fat), respectively. Both the cis isomers
labelled in the alcohol and acid moieties showed recoveries 3 to >10
times higher in the fat and egg yolk than those shown by the corre-
sponding trans isomers. The excreta (0-72 h) contained 1.7 times more
cis-permethrin than trans-permethrin. Hydroxylated ester metab-
olites of trans-permethrin were not excreted, but four monohydroxy and
dihydroxy esters (i.e., trans-OH-permethrin, 4'-OH-permethrin, 4'-OH,
trans-OH-permethrin (37) and trans-OH-permethrin sulfate) of cis-per-
methrin were found. Metabolites from the acid moieties of both isomers
were the Cl2CA isomers in free, glucuronide, and taurine conjugate
forms, trans-OH-Cl2CA (32,32'), cis-OH-Cl2CA (33,33'), cis-OH-Cl2CA
lactone (34,34'), and cis-OH-Cl2CA sulfate. trans-OH-Cl2CA (32,32')
was obtained from the cis isomer to larger extents than from the trans
isomer, whereas the amounts of cis-OH-Cl2CA (33,33') were larger with
the trans isomer than with the cis isomer. The metabolites from the
alcohol moiety included PBalc, PBacid, their 4'-hydroxy-derivatives and
the corresponding sulfate, the glucuronide of PBalc, and a variety of
unidentified conjugates of 4'-OH-PBalc (7) and 4'-OH-PBacid (13). The
taurine conjugate of PBacid was not detected. The metabolites produced
in largest amounts were the unidentified conjugates of 4'-OH-PBalc (6-
13% of the dose) and 4'-OH-PBacid (2-11%). The yolk of eggs 5 and 6
days after initial dosing contained 4.4 times more cis-permethrin than
trans-permethrin in unchanged form and the same ester metabolites of
cis-permethrin as those found in the excreta. Other metabolites in
the yolk were generally the same as those in the excreta. Overall,
cis-permethrin appeared at higher levels than trans-permethrin in
the egg yolk, fatty tissues, and excreta. Radiocarbon from cis-permethrin
preparations also persisted longer in the blood than that from trans-per-
permethrin preparations. It probably resulted from more rapid ester
cleavage of the trans isomer than the cis isomer, based on the relative
amounts of hydrolysis products from the two isomers in hen excreta
(Gaughan et al., 1978b).
5.3 Enzymatic Systems for Biotransformation
In studies by Shono et al. (1979), 1 µg each of [1RS, trans ]-permethrin
or [1RS, cis ]-permethrin was incubated at 37°C for 30 min with 2.2 ml
of ca. 10% rat and mouse liver microsomes under the following
conditions:
* microsomes treated with tetraethyl pyrophosphate (TEPP) (no ester-
ase and oxidase activity),
* normal microsomes (esterase activity),
* TEPP-treated microsomes plus NADPH (oxidase activity),
* normal microsomes plus NADPH (esterase plus oxidase activity).
Each esterase preparation hydrolyzed trans-permethrin to a much
greater extent than the corresponding cis isomer. In contrast, oxidat-
ive metabolism was greater for cis-permethrin than for trans-permethrin
except with the mouse microsomes, where the reactions of both isomers
proceeded to a similar extent. Aryl hydroxylation occurred at the 4'-
and 6-positions with the mouse enzymes but only at the 4'-position with
the rat enzymes. Hydroxylation at the 2'-position was observed only
with the cis-permethrin and mouse oxidase system. The amount of trans-
hydroxymethyl ester metabolites exceeded that of the corresponding
cis-hydroxymethyl compounds except with rat enzymes acting on trans-
permethrin. In general, oxidative activity with rat microsomes was
weaker than that with mouse microsomes. The dihydroxy ester metabolite
was evident only with cis-permethrin. The cis-hydroxymethyl ester
derivatives of trans-permethrin were further oxidized to the corre-
sponding aldehyde and carboxylic acid by the mouse enzymes. The pre-
ferred sites of hydroxylation, based on all identified metabolites in
the oxidase and esterase-plus-oxidase systems, were as follows (Shono
et al., 1979):
trans-permethrin
mouse: cis-methyl > trans-methyl > 4'-carbon = 6-carbon
rat: 4'-carbon = cis-methyl > trans-methyl
cis-permethrin
mouse: trans-methyl > cis-methyl = 4'-carbon > 6-carbon
> 2'-carbon
rat: 4'-carbon = trans-methyl > cis-methyl
When 100 nmol each of [1R, trans]-, [1S, trans]-, [1RS, trans]-, [1R, cis]-,
[1S, cis ]-, or [1RS, cis ]-permethrin were incubated individually with
2.5 ml of mouse liver microsome (1.5-2.0 mg of protein), the trans iso-
mers were much more rapidly hydrolyzed than the corresponding cis iso-
mers. Of the trans isomers, [1S,trans] isomer was hydrolyzed to a
greater extent than the other trans isomers. On the other hand, when
esterase activity was suppressed, there were no distinct differences in
the oxidative metabolic rates between trans and cis isomers (Soderlund
& Casida, 1977).
The persistence of isomers of permethrin, cypermethrin, delta-
methrin, and fenvalerate in the fat and brain after oral or intraper-
itoneal administration of these pesticides to rats was compared by
Marei et al. (1982). Residues in fat and brain were much higher and more
persistent with cis-permethrin than with trans-permethrin or the
alpha-cyano phenoxybenzyl pyrethroids (cypermethrin, fenvalerate, delta-
methrin). Brain levels of trans-permethrin (but not of cis-permethrin)
were greatly elevated after pretreatment with pyrethroid esterase and
oxidase inhibitors (i.e. tri- o-cresyl phosphate, S,S,S-tributyl phosph-
orotrithioate, phenyl saligenin cyclic phosphanate as esterase inhibit-
ors and piperonyl butoxide as oxidase inhibitor).
Pyrethroid carboxyesterase(s) that hydrolyze esters of chrysan-
themic acid were purified by Suzuki & Miyamoto (1978) from rat liver
microsomes by cholic acid solubilization, ammonium sulfate fraction-
ation, heat treatment, and DEAE-Sephadex A-50 column chromatography.
The 45-fold purified enzyme (38% yield) was thought to consist of a
single protein with a relative molecular mass of approximate 74 000, a
Michaelis constant (Km) of 0.21 mmol/litre for [1R, trans ]-phenothrin,
and an optimum pH of 7-9. It was susceptible to inhibition by organo-
phosphate and carbamate insecticides and insensitive to p-chloromerc-
urybenzoic acid and to mercuric and cupric ions. The enzyme seemed
to require neither coenzymes nor cofactors and hydrolysed trans isomers
of several synthetic pyrethroids (tetramethrin, resmethrin, trans- or
cis-phenothrin and permethrin) well, at more or less similar rates. On
the other hand, the cis isomers were hydrolysed at rates one-fifth to
one-tenth of those of the trans counterparts. The purified pyrethroid
carboxyesterase was apparently identical in nature to malathion carbox-
yesterase and p-nitro phenyl acetate carboxyesterase (Suzuki &
Miyamoto, 1978).
6. EFFECTS ON THE ENVIRONMENT
Acute toxicity data of permethrin on aquatic and terrestrial non-
target organisms are summarized in Tables 5 and 6, respectively.
6.1 Toxicity to Aquatic Organisms
6.1.1 Aquatic microorganisms
Stratton & Corke (1982) investigated the toxicity of permethrin and
ten of its degradation products on the growth, photosynthesis, and
acetylene-reducing activity of two species of green algae ( Chlorella
pyrenoidosa and Scenedesmus quadricaudata ) and three species of cyano-
bacteria ( Anabaena spp.). Permethrin itself was relatively non-toxic
to photosynthesis (EC50 values >100 mg/litre) and to acetylene re-
duction (EC50 values >100 mg/litre). Its degradation products were
similarly non-toxic to green algae. However, the cyanobacteria were
susceptible to some of the breakdown products of permethrin. Growth
was the most sensitive parameter with growth yield showing EC50 values
of 2.5, 2.2, and 1.4 mg/litre for the cyanobacteria and 2.8 and 4.3 mg/
litre for the green algae with PBalc and similar values for three of
the five test species with PBald. A complex test system found interac-
tions between the various metabolites and the parent compound which
were sometimes additive and sometimes synergistic. The authors con-
cluded that it is difficult to assess the true toxicity of compounds to
soil and water microorganisms without considering the breakdown prod-
ucts. The cyanobacteria are significant nitrogen-fixing organisms in
wet tropical soils.
6.1.2 Aquatic invertebrates
Non-target invertebrates, except molluscs, are more sensitive to
permethrin than fish, as shown in Table 5.
During exposure of permethrin for up to 28 days, the caddisfly
(Brachycentrus americanus) and the stonefly (Pteronarcys dorsata)
showed behavioural changes or death at concentrations as low as 0.022
µg/litre (Anderson, 1982).
A 3-h exposure to permethrin, at 50 mg/litre, was not lethal to
Daphnia pulex. The no-effect levels were 1 µg/litre for racemic, 1R
or (+)-trans, and 1R or (+)-cis, and 50 µg/litre for 1S or (-)-trans
and 1S or (-)-cis isomers (Miyamoto, 1976).
Zitko et al. (1979) established lethal threshold values for the
lobster Homarus americanus of 7.00 µg/litre for technical permethrin
and 0.40 µg/litre for [1R, cis ]-permethrin.
Larval oyster and bullfrog (tadpole) are highly tolerant to the
insecticide, with LC50 values of >1000 and 7000 µg/litre, respect-
ively.
Stratton & Corke (1981) reported that the 48-h LC50 of permethrin
to juvenile and adult waterfleas Daphnia magna was 0.2-0.6 µg/litre. A
further series of experiments involved the addition of algae or
bacteria to the cultures of daphnids, since feeding of daphnids during
these tests had been reported to reduce the toxicity of several
chemicals to the animals. With permethrin, however, algae in the test
vessel increased the lethal effect of the compound. Algae, bacteria,
and also inert silica powder adhered to the swimming antennae of the
daphnids, causing the daphnids to sink and die on the bottom of the
flasks. The effect was greatest with adults; the shed carapaces of
juvenile showed the same adhesion of particulates but moulting pro-
tected the juveniles to some degree. This raised toxicity was due to a
direct effect of the permethrin on the daphnids and not to a tendency
for the compound to cause flocculation of the suspended material.
Friesen et al. (1983) tested the toxicity of permethrin to
sediment-living nymphs of the mayfly Hexagenia rigida. In test vessels
containing water without sediment, the 6-h LC50 was estimated to lie
between 0.58 and 2.06 µg/litre; no nymphs survived exposure to water
concentrations of 7.63 µg/litre. In the presence of sediment,
lethality was reduced; there was 88% mortality of nymphs exposed to
permethrin in water at 7.63 µg/litre after 24-h exposure. Mortality
reached 100% only after 7 days exposure with sediment. Maximum concen-
trations of permethrin in the sediment over the 7 days were estimated
to be 50 µg/kg dry weight. The authors also exposed nymphs to sedi-
ment previously exposed to permethrin. The initial water concentration
was again 7.63 µg/litre, and the sediment was left for 8 days to take
up the insecticide before the water was decanted off. Nymphs were
introduced along with clean water over the contaminated sediment. There
was 100% mortality in the exposed nymphs. Long-term exposure to both
water and sediment contaminated with permethrin led to increasing
mortality up to 4 weeks; there was little further mortality between 4
and 10 weeks. Lethality reached 100% after exposure to either water or
sediment at a simulated application rate of 7.3 g/ha over 10 weeks (95%
at 4 weeks), whereas a simulated exposure equivalent to 0.6 g/ha led to
74% mortality after a 10-week exposure of the nymphs in water and 45%
after exposure of the nymphs to sediment. The authors comment that it
is not yet possible to state a concentration of permethrin in sediment
which is sufficiently low to permit successful recolonization of con-
taminated sediment.
6.1.3 Fish
Permethrin is highly toxic to fish, as shown in Table 5. Prep-
arations using an emulsifiable concentrate of permethrin enhanced its
toxicity twofold (Coats & O'Donnell-Jeffery, 1979).
The lethal toxicity of permethrin varied inversely with water
temperature, particularly between 10 and 20°C, and with body weight
between 1 and 50 g. There was a 10-fold difference between the 96-h
LC50 values at 10 and 20°C. At 15°C, a large trout (200 g) was con-
siderably more (about 100 times) tolerant than a small fish (1 g)
(Kumaraguru & Beamish, 1981).
Toxicity to fish is linked more with the nature of the optical iso-
mers than with that of the stereoisomers; i.e. 1R isomers are more
toxic than 1S isomers. Trans and cis isomers are of similar toxicity
(Miyamoto, 1976).
Zitko et al. (1979) established lethal threshold values for the
Atlantic salmon Salmo salar of 8.8 µg/litre for technical permethrin
and 1.34 µg/litre for [1R, cis ]-permethrin.
Hansen et al. (1983) exposed embryos and the hatched fry of
sheepshead minnow (Cyprinodon variegatus), continuously over 28 days,
to concentrations of permethrin of 1.25, 2.5, 5.0, 10, 20, or 40 µg/
litre. The survival of embryos was unaffected by any of the test
concentrations. Fry were affected by exposure to 20 µg/litre or more
but unaffected by 10 µg/litre. The toxicity curve was steep; 99% of fry
survived at 10 µg/litre but only 1% at 20 µg/litre. The authors
estimated the ratio between the 96-h LC50 and the NOEL to be 0.8.
Holdway & Dixon (1988) exposed larval fish (white sucker,
Catastomus commersoni, and flagfish, Jordanella floridae ) to per-
methrin in a single 2-h pulse and examined lethality over the following
96-h. They examined the effect of age, and whether or not the fish were
fed, upon the toxic effect of the insecticide. Feeding decreased the
toxicity of permethrin to flagfish at 2 and 4 days of age but not at 8
days. Age was the most important factor affecting toxicity. The 96-h
LC50 (from exposure for 2 h) was 5.55 mg/litre, 7.91 mg/litre, and
0.57 mg/litre for flagfish of age 2, 4, and 8 days, respectively.
White suckers were most susceptible to permethrin at 20 days of age,
with a 2-h LC50 of 10.0 µg/litre. Unfed white suckers at 13 and 20
days of age were highly susceptible to permethrin, with LC50 values of
2.0 and 1.0 µg/litre, respectively. The authors pointed out that
permethrin is toxic to cladocerans (waterfleas) at levels of 0.5 µg/
litre and that fish could suffer both from the direct toxic effect of
the insecticide and the added effect experienced during food deprivation.
When used for mosquito control, the safety margins (LC50 fish/LC50
mosquito larvae) for permethrin and cis-permethrin are 2-40 and 25-65,
respectively (Mulla et al., 1978a). When intraperitoneally injected
into rainbow trout, the trans- and cis-permethrin isomers were about
110 and 5 times, respectively, more toxic to trout than to mice,
(Glickman et al., 1981).
Rainbow trout exposed to sublethal concentrations of permethrin in
water (0.09-0.35 µg/litre) or in food (85-350 µg/kg) in 20-40-day
experiments showed similar branchial changes, i.e. epithelial separa-
tion or necrosis, mucus cell hyperplasia, clubbing of epithelial cells,
or hyperplasia and fusion of adjacent secondary lamellae (Kumaraguru et
al., 1982).
6.1.4 Field studies and community effects
In studies by Mulla et al. (1975), permethrin was applied to ponds
at rates of 56 g/ha and 112 g/ha in field trials. The numbers of
Tanypodinae (mostly Pentaneura and Tanypus ) and Chironominae (mostly
Tanytarsus and Chironomus ) midge larvae were slightly depressed by
the 56 g/ha treatment. Mayfly (mostly Baetis sp.) naiads and diving
beetle ( Hydrophilidae and Dytiscidae ) larvae and adults were also
affected. However, Copepoda (mostly Cyclops and Diaptomus ) and
Ostracoda (mostly Cypricercus and Cyprinotus ) were not greatly affec-
ted. The effect on these non-target organisms was much greater at the
higher dose level of permethrin, except for the ostracods. It was con-
cluded that permethrin affected mayfly naiads severely during the
exposure period. Most populations recovered within 2 weeks following
exposure.
Mayfly naiads (mostly baetids) were also adversely affected by per-
methrin at 5.6-28 g/ha and by its cis isomer at 2.8-28 g/ha. There was
a slight recovery within 1-3 weeks after treatment (Mulla et al.,
1978b).
Permethrin was applied weekly for 6 or 8 successive weeks at the
mosquito larvicidal rate of 28 g/ha (and at a rate 5 times higher) to
ponds where 20 individuals of mosquito fish or desert pupfish were
maintained. The insecticide produced no adverse effects on the two
species of fish, and the number of fish in the treated ponds increased
markedly during the experiment. At the higher rate, mats of algae were
formed, probably as the result of elimination by permethrin of her-
bivorous arthropods that feed on the algae (Mulla et al., 1981).
Kaushik et al. (1985) investigated the effect of permethrin on the
pelagic zooplankton of a 10-ha lake in southern Ontario, Canada. The
insecticide was applied to give nominal water concentrations of 0.5,
5.0, or 50 µg/litre in in situ aquatic enclosures of 5 x 5 x 5 m.
Macrozooplankton (daphnids and copepods) were most susceptible to the
insecticide. The numbers, which in untreated enclosures were 100-1000
organisms per litre of water, fell in the days immediately following
treatment to 1-10 at 0.5 µg/litre, 0.1-1.0 at 5.0 µg/litre, and
0.01-0.1 organisms per litre at 50 µg/litre of permethrin (nominal).
Microzooplankton (mainly rotifers) were unaffected by all doses except
the highest. At this dose, numbers fell transitorily to about one tenth
of their control levels (about 1000 organisms per litre). In all cases
of treatment, rotifer numbers increased between 5- and 10-fold 20 to
100 days after treatment. The authors attributed this rise in numbers
to the resistance of the organisms to the insecticide coupled with a re-
duction in the predator organisms that normally feed on the rotifers.
Populations of macrozooplankton had returned to normal within 250 days
of treatment (after the winter freeze) even with the highest dose of
50 µg/litre. Recovery was quicker with the lower doses (about 60 days
for treatment at 5 µg/litre and 30 days for most species at 0.5 µg/
litre). Despite this recovery in overall numbers of zooplankton, there
was a decrease in the species diversity of the larger, predator organ-
isms at all treatment levels. The enclosures, of course, prevented
immigration from the surrounding areas of water.
Helson et al. (1986) placed two species of aquatic arthropods (the
amphipod Gammarus pseudolimnaeus and the mosquito Aedes aegypti ) in
open containers of different sizes downwind from the application of
permethrin to young spruce trees for control of defoliators. The insec-
ticide was applied to trees 0.75-0.8 m tall in a single swath from a
mistblower backpack. Nominal application rates of 36 g ai/ha were used
with a swath width of 10 m, and standard and ultra-low volume appli-
cations were made. The mortality of Gammarus after 48 h averaged 95%
(range 76-100%) in the first trial and 85% (range 37-100%) in a dupli-
cate trial in containers 10 m downwind from the spraying. The effect
was reduced to 12% and 18% at a distance of 30 m from the spraying and
further reduced to an average of 5% 50 m from the spray. Mosquito
larvae were examined only in the second trial and showed 76% (37-100%)
at 10 m falling to 6% and 2% at 30 and 50 m, respectively, from the
spray. Mortality increased over the following 9 days. The authors also
determined 48-h LC50 values for the two organisms in containers simi-
larly placed in the field. These were 0.37 µg/litre and 0.69 µg/litre for
Gammarus and mosquito larvae, respectively, while LC95 values were
0.61 µg/litre for Gammarus and 1.14 µg/litre for mosquito larvae.
The authors regarded these data as a "worst case" , since sediment in
natural water and flowing water in streams could be expected to reduce
the toxic effect of the permethrin. They concluded that a 30-m safety
zone needs to be left using this application method between a spraying
area and natural waters to avoid killing aquatic arthropods.
When permethrin was applied by airplane to the surface of a creek
at a nominal rate of 70 g ai/ha, the actual concentration that reached
the ground was 13.4 g ai/ha. Dramatic, but short-lived, increases in
the drift of aquatic insects (particularly large catches of springtail
(Collembola), mayfly nymphs (Ephemeroptera heptageniidea), water
scavenger beetle larvae (Coleoptera hydrophilidae), midge larvae and
pupae, water boatmen (Hemiptera corixidae), predaceous diving beetles
(Coleoptera dytiscidae), and caddisfly larvae (Trichoptera)) occurred
after treatment. No effects on populations of organisms that inhabited
the bottom layer of the creek were noticeable. The permethrin sprayed
had little effect on caged or native fish and no fish mortality was re-
corded due to the treatment. From these data, it could be inferred that
permethrin had no significant impact on the aquatic system (Kingsbury,
1976).
After an aerial application of permethrin at 17.5 g ai/ha, residues
attained peak concentrations of 147.0 µg/litre in ponds and 2.5 µg/litre
in streams, but accumulations and persistence of the pesticide in
bottom sediment were negligible. Noticeable increases in the number of
drifting organisms occurred in the treatment block ( Ephemeroptera hepta-
geniidae, Baetidae, and Plecoptera nymphs ) and 2.1 km