Deltamethrin (EHC 97, 1990)

INTERNATIONAL PROGRAMME ON CHEMICAL SAFETY

ENVIRONMENTAL HEALTH CRITERIA 97

DELTAMETHRIN

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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chemicals.

WHO Library Cataloguing in Publication Data

Deltamethrin.

(Environmental health criteria ; 97)

1.Pyrethrins I.Series

ISBN 92 4 154297 7 (NLM Classification: WA 240)
ISSN 0250-863X

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CONTENTS

ENVIRONMENTAL HEALTH CRITERIA FOR TETRAMETHRIN, CYHALOTHRIN, AND
DELTAMETHRIN

INTRODUCTION

1. SUMMARY AND EVALUATION, CONCLUSIONS AND RECOMMENDATIONS

1.1. Summary and evaluation
1.1.1. Identity, physical and chemical properties,
analytical methods
1.1.2. Production and uses
1.1.3. Human exposure
1.1.4. Environmental exposure and fate
1.1.5. Uptake, metabolism, and excretion
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
1.3. Recommendations

2. IDENTITY, PHYSICAL AND CHEMICAL PROPERTIES, ANALYTICAL METHODS

2.1. Identity
2.2. Physical and chemical properties
2.3. Analytical methods

3. SOURCES OF ENVIRONMENTAL POLLUTION AND ENVIRONMENTAL LEVELS

3.1. Industrial production
3.2. Use patterns
3.3. Residues in food
3.4. Levels in the environment

4. ENVIRONMENTAL TRANSPORT, DISTRIBUTION, AND TRANSFORMATION

4.1. Transport and distribution between media
4.2. Abiotic degradation in air and water
4.3. Environmental fate
4.4. Bioaccumulation

5. KINETICS AND METABOLISM

5.1. Metabolism in experimental animals
5.2. Metabolism and fate in farm animals
5.3. Enzymatic systems for biotransformation
5.4. Metabolism in human beings

6. EFFECTS ON ORGANISMS IN THE ENVIRONMENT

6.1. Aquatic organisms
6.1.1. Acute toxicity for fish
6.1.2. Acute toxicity for other aquatic organisms
6.1.3. Field studies and community effects
6.1.4. Appraisal
6.2. Terrestrial organisms
6.2.1. Plants
6.2.2. Soil microorganisms
6.2.3. Soil fauna
6.2.3.1 Earthworms
6.2.3.2 Slugs
6.2.3.3 Soil arthropods
6.2.4. Beneficial insects
6.2.4.1 Honey-bees
6.2.4.2 Foliar insects
6.2.5. Birds
6.2.5.1 Laboratory studies
6.2.5.2 Field studies on birds

7. EFFECTS ON EXPERIMENTAL ANIMALS AND IN VITRO TEST SYSTEMS

7.1. Single exposures
7.1.1. Mouse
7.1.2. Rat
7.1.3. Rabbit
7.1.4. Dog
7.2. Irritation and sensitization
7.2.1. Skin irritation
7.2.2. Eye irritation
7.2.3. Sensitization
7.3. Short-term exposure
7.3.1. Rat
7.3.2. Dog
7.4. Long-term exposure and carcinogenicity
7.4.1. Mouse and rat
7.4.2. Dog
7.5. Mutagenicity
7.5.1. Microorganisms
7.5.2. Cultured cells
7.5.3. Mouse
7.5.4. Appraisal
7.6. Teratological and reproductive effects
7.6.1. Teratology
7.6.1.1 Mouse
7.6.1.2 Rat
7.6.1.3 Rabbit
7.6.2. Reproduction studies
7.7. Neurotoxicity and behavioural effects
7.8. Miscellaneous effects
7.9. Potentiation
7.10. Mechanism of toxicity (mode of action)
7.11. Experimental studies on antidotes

8. EFFECTS ON MAN

8.1. General population-poisoning incidents
8.2. Occupational exposure
8.2.1. Acute toxicity-poisoning incidents
8.2.2. Effects of short- and long-term exposure
8.3. Clinical studies

9. PREVIOUS EVALUATIONS BY INTERNATIONAL BODIES

REFERENCES

APPENDIX I

RESUME

RESUMEN

WHO TASK GROUP ON ENVIRONMENTAL HEALTH CRITERIA FOR TETRAMETHRIN,
CYHALOTHRIN, AND DELTAMETHRIN

Members

Dr V. Benes, Department of Toxicology & Reference Laboratory,
Institute of Hygiene and Epidemiology, Prague, Czechoslovakia

Dr A.J. Browning, Toxicology Evaluation Section, Department of
Community Services and Health, Woden, Australia

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

Dr K. Imaida, Section of Tumor Pathology, Division of Pathology,
National Institute of Hygienic Sciences, Tokyo, Japan

Dr P. Hurley, Office of Pesticide Programme, US Environmental
Protection Agency, Washington, DC, USA

Dr S.K. Kashyap, National Institute of Occupational Health,
(I.C.M.R.) Ahmedabad, India (Vice-Chairman)

Dr Yu. I. Kundiev, Research Institute of Labour, Hygiene and
Occupational Diseases, Kiev, USSR

Dr J.P. Leahey, ICI Agrochemicals, Jealotts Hill Research Station,
Bracknell, Berkshire, United Kingdom (Rapporteur)

Dr M. Matsuo, Sumitomo Chemical Company Limited, Biochemistry &
Toxicology Laboratory, Osaka, Japan

Observers

Mr M. L'Hotellier, International Group of National Associations of
Manufacturers of Agrochemical Products (GIFAP)

Dr N. Punja, International Group of National Associations of
Manufacturers of Agrochemical Products (GIFAP)

Secretariat

Dr K.W. Jager, Division of Environmental Health, International
Programme on Chemical Safety, World Health Organization, Geneva,
Switzerland (Secretary)

Dr R. Plestina, Division of Vector Biology and Control, World
Health Organization, Geneva, Switzerland

Dr J. Sekizawa, 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 publication. In the interest of all users of the
environmental health criteria documents, readers are kindly
requested to communicate any errors that may have occurred to the
Manager of the International Programme on Chemical Safety, World
Health Organization, Geneva, Switzerland, 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 -
7985850).

NOTE: 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 para. 82-84 and
recommendations para. 90 of the 2nd FAO Government Consultation
(1982).

ENVIRONMENTAL HEALTH CRITERIA FOR TETRAMETHRIN, CYHALOTHRIN, AND
DELTAMETHRIN

A WHO Task Group on Environmental Health Criteria for
Tetramethrin, Cyhalothrin, and Deltamethrin met at the World Health
Organization, Geneva, from 24 - 28 October 1988. Dr M. Mercier,
Manager of the IPCS, welcomed the participants on behalf of the
three IPCS cooperating organizations (UNEP/ILO/WHO). The Group
reviewed and revised the draft Criteria Documents and Health and
Safety Guides and made an evaluation of the risks for human health
and the environment from exposure to tetramethrin, cyhalothrin, and
deltamethrin.

The first drafts of the documents on tetramethrin and
deltamethrin were prepared by Dr J. MIYAMOTO and Dr M. MATSUO of
Sumitomo Chemical Co. Limited. Dr J. SEKISAURA of the National
Institute of Hygienic Sciences, Tokyo, Japan, assisted in the
finalization of the drafts. The first draft of the document on
cyhalothrin was prepared by the IPCS Secretariat based on material
made available by ICI Agrochemicals, United Kingdom.

The second drafts were prepared by the IPCS Secretariat,
incorporating comments received following circulation of the first
drafts to the IPCS contact points for Environmental Health Criteria
documents.

Dr K. JAGER of the IPCS Central Unit was responsible for the
scientific content of the deltamethrin document, and Mrs M.O. HEAD
of Oxford, England, for the editing.

The fact that Sumitomo Chemical Company Limited, Japan, ICI
Agrochemicals, United Kingdom, and Roussel Uclaf SA, France, made
available to the IPCS and the Task Group their proprietary
toxicological information on their products under discussion is
gratefully acknowledged. This allowed the Task Group to make their
evaluation on a more complete data base.

The efforts of all who helped in the preparation and
finalization of the documents is gratefully acknowledged.

INTRODUCTION

Synthetic pyrethroids-a profile

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
biological 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.

The pyrethroids constitute another group of insecticides in
addition to organochlorine, organophosphorus, carbamate, and other
compounds. Pyrethroids commercially available so far 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,
kadethrin, and tellallethrin (usually for household insects),
fenpropathrin, tralomethrin, cyhalothrin, lambda-cyhalothrin,
tefluthrin, cyfluthrin, flucythrinate, fluvalinate, and biphenate
(for agricultural insects).

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.

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,
the 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/l) 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).

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, choreo-athetosis, and paralysis. The signs disappear
fairly rapidly, 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 the sciatic nerves. They are not
considered to cause delayed neurotoxicity of the kind induced by
some organophosphorus compounds. The mechanism of toxicity of
synthetic pyrethroids, and their classification into two types, are
discussed in Appendix I.

Some pyrethroids (e.g., deltamethrin, fenvalerate,
flucythrinate, and cypermethrin) may cause a transient itching
and/or burning sensation in exposed human skin.

Synthetic pyrethroids are generally metabolized in mammals
through ester hydrolysis, oxidation, and conjugation, and there is
no tendency to accumulate in tissues. In the environment,
synthetic pyrethroids 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 are hardly eluted with
water. There is little tendency for bioaccumulation in organisms.

Because of low application rates and rapid degradation in the
environment, residues in food are generally low.

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 environment. The toxicity of synthetic pyrethroids in birds
and domestic animals is low.

In addition to the evaluation documents of FAO/WHO, there are
several good reviews and books on the chemistry, metabolism,
mammalian toxicity, environmental effects, etc., of synthetic
pyrethroids, including those by Elliot (1977), Miyamoto (1981),
Miyamoto & Kearney (1983), and Leahey (1985).

1. SUMMARY AND EVALUATION, CONCLUSIONS AND RECOMMENDATIONS

1.1 Summary and Evaluation

1.1.1 Identity, physical and chemical properties, analytical
methods

Deltamethrin was synthesized in 1974, and first marketed in
1977. Chemically, it is the [1R, cis; alphaS]-isomer of 8
stereoisomeric esters of the dibromo analogue of chrysanthemic
acid, 2,2-dimethyl-3-(2,2-dibromovinyl) cyclopropanecarboxylic acid
(Br₂CA) with alpha-cyano-3-phenoxybenzyl alcohol.

Technical grade deltamethrin is an odourless white powder with
a melting point of 98 - 101 °C and contains more than 98% of the
material. The vapour pressure is 2.0 x 10^-6Pa at 25 °C and it is
practically non-volatile. It is insoluble in water, but soluble in
organic solvents, such as acetone, cyclohexanone, and xylene. It
is stable to light, heat, and air, but unstable in alkaline media.

The determination of residues and analysis of environmental
samples were carried out by solvent extraction with n-hexane/
acetone, partitioning with n-hexane/acetone/water, clean-up with a
silica gel column chromatograph, and determination with a gas
chromatograph equipped with an electron capture detector with a
minimum detectable concentration of 0.01 mg/kg or less. High-
performance liquid chromatography with an UV-detector is used for
product analysis.

1.1.2 Production and uses

The consumption of deltamethrin in the world was about 250
tonnes in 1987. It is mostly used on cotton (45% of the
consumption) and on crops such as coffee, maize, cereals, fruit,
vegetables, and hops, and on stored products. Deltamethrin is also
used in animal health, in vector control, and in public health. It
is formulated as an emulsifiable concentrate, ultra-low-volume
concentrate, wettable powder, suspension concentrate, or dust
powder, alone, or in combination with other pesticides.

1.1.3 Human exposure

Exposure of the general population to deltamethrin is mainly
via dietary residues, but may also occur from its use in public
health. Residue levels in crops treated according to good
agricultural practice are generally very low, except for those
arising from post-harvest treatment. Extensive data have been
reviewed by FAO/WHO (see section 9).

Exposure of the general population is expected to be very low,
but actual data in the form of total diet studies are lacking.

1.1.4 Environmental exposure and fate

When ¹⁴C-(acid, alcohol, or cyano labelling)-deltamethrin-[1R,
cis; alphaS] was exposed to sunlight as a thin film for 4 - 8 h,
70% of it was transformed by cis/trans-isomerization to give the
[1R, trans; alphaS] and [1S, trans; alphaS] isomers, together with
ester cleavage products, including Br₂CA and alpha-cyano-3-
phenoxybenzyl alcohol.

Deltamethrin was degraded in cotton plants, under glasshouse
conditions, with an initial half-life of 1.1 weeks, and the time
needed for 90% loss was 4.6 weeks.

The major metabolites were free and conjugated Br₂CA, trans-
hydroxymethyl-Br₂CA, and 3-(4-hydroxyphenoxy)benzoic acid formed by
ester cleavage, oxidation, and conjugation.

Deltamethrin was incubated in sand and organic soil at 28 °C
under laboratory conditions. Approximately 52% and 74% of the
applied deltamethrin was recovered from sand and organic soil,
respectively, 8 weeks after treatment.

Deltamethrin is not mobile in the environment because of its
strong adsorption on particles, its insolubility in water, and very
low rates of application.

No data are available on actual levels in the environment, but
with the current use pattern and under normal conditions of use,
environmental exposure is expected to be very low. Degradation to
less toxic products is rapid.

1.1.5 Uptake, metabolism, and excretion

Deltamethrin is readily absorbed by the oral route, but less so
dermally; the rate of absorption is strongly dependent on the
carrier or solvent. Absorbed deltamethrin is readily metabolized
and excreted.

When rats were given ¹⁴C-(acid, alcohol, or cyano labelled)-
deltamethrin orally at the rate of 0.64 - 1.60 mg/kg, the
radiocarbon from the acid and alcohol moiety was almost completely
eliminated within 2 - 4 days. Tissue residue levels were generally
very low, except in fat, where slightly higher residues occurred.
However, the cyano portion was excreted more slowly, with total
recovery of 79% in 8 days. The major metabolic reactions were
oxidation (at the trans-methyl of the cyclopropane ring and at the
2'-, 4'-, and 5-positions of the alcohol moiety), ester cleavage,
and conversion of the cyano portion to thiocyanate. The resultant
carboxylic acids and phenols were conjugated with sulfuric acid,
glycine, and glucuronic acid.

When mice were fed ¹⁴C-(acid, alcohol, or cyano labelled)-
deltamethrin orally at rates of 1.7 - 4.4 mg/kg, the excretion of
the radiocarbon was rapid and almost complete, except for the cyano
portion. The major metabolic reactions in mice were generally
similar to those in rats.

In cows and poultry, degradation pathways are very close to
those in rodents.

1.1.6 Effects on organisms in the environment

Deltamethrin is highly toxic for fish, the 96-h LC₅₀ranging
between 0.4 and 2.0 µg/litre. It is also highly toxic for aquatic
invertebrates; the 48-h LC₅₀for Daphnia is 5 µg/litre. However,
extensive field studies, in experimental ponds, and field use have
shown that this high potential toxicity is not realized. Some
kills of aquatic invertebrates occur in the field, but these are
usually compensated for rapidly.

The toxicity of deltamethrin for birds is very low with LD₅₀
values for a single oral dose exceeding 1000 mg/kg. Under
laboratory conditions, it is highly toxic for honey-bees with a
contact LD₅₀of 0.051 µg/bee. Field trials and actual usage have
established that deltamethrin formulations have a repellent action,
which means that, in practice, the hazard for bees is low.

1.1.7 Effects on experimental animals and in vitro test systems

In a non-aqueous vehicle, the acute oral toxicity of
deltamethrin is high to moderate with LD₅₀values of 19 - 34 mg/kg
(mouse) and 31 - 139 mg/kg (rat). However, in a suspension in
water, the toxicity is much less with LD₅₀values exceeding
5000 mg/kg (rat). Deltamethrin is a Type II pyrethroid; clinical
signs of poisoning include tremor, salivation, and convulsion. The
onset of signs is rapid and they disappear within several days in
survivors. The electroencephalogram shows generalized spike and
wave discharges prior to choreo-athetosis.

Single applications of technical deltamethrin did not produce
any irritant effect on the intact and abraded skin of the rabbit.
However, transient irritating effects were produced in the eye of
the rabbit, with and without rinsing. Deltamethrin was not a skin
sensitizer in the guinea-pig.

When rats were dosed, by gavage, with deltamethrin levels of up
to 10.0 mg/kg body weight per day for 13 weeks, hyperexcitability
was observed at 6 weeks in males given the highest dose. Body
weight gain was lower in males given 2.5 and 10 mg/kg.

When beagle dogs were dosed orally with deltamethrin at levels
of up to 10 mg/kg body weight per day for 13 weeks, there were
various compound-related symptoms, such as vomiting, tremor,
salivation, and depressed gag-, patellar-, and flexor reflexes. In
a 2-year feeding study on dogs, 1 mg/kg body weight per day was the
no-observed-effect level (highest level tested).

When mice were fed deltamethrin at levels of up to 100 mg/kg
diet for 24 months, tumour incidence was unaffected. The no-
observed-effect level for systemic toxicity was 100 mg/kg diet.

When rats were fed deltamethrin at levels of up to 50 mg/kg
diet for 2 years, no compound-related tumours were observed. The
no-observed-effect level for systemic toxicity was 50 mg/kg diet.

Deltamethrin was not mutagenic in a variety of in vivo and in
vitro test systems, including: DNA repair, gene mutation,
chromosomal aberration, sister chromatid exchange, micronucleus
formation, and dominant lethal tests.

Teratology studies were conducted on pregnant rats and mice in
which deltamethrin was administered orally at levels of up to
10 mg/kg body weight per day during the period of major
organogenesis. There were no teratogenic or reproductive effects,
except for a dose-related decrease in mean fetal weight in the
mouse study and slightly delayed ossification in the rat study.

Rabbits received deltamethrin at levels of up to 16 mg/kg body
weight per day between days 6 and 19 of pregnancy. A decreased
average fetal weight was noted at the highest dose. No teratogenic
effects were observed in rabbits.

When rats were fed deltamethrin at levels of up to 50 mg/kg
diet in a 3-generation, 2-litter reproduction study, no effects on
reproduction were observed.

There are indications that potentiation of toxicity may occur
when deltamethrin is combined with some organophosphorus compounds.

1.1.8 Effects on human beings

Deltamethrin can induce skin sensations in exposed workers.
Several non-fatal cases of poisoning have been reported through
occupational exposure resulting from neglect of safety precautions.
Numbness, itching, tingling, and burning of the skin and vertigo
are symptoms that are frequently reported. Occasionally, a
transient papular or blotchy erythema has been described. Most of
these symptoms are transient and disappear within 5 - 7 days. No
long-term adverse effects have been reported. Three non-fatal
cases of deltamethrin poisoning have been described following
ingestion of several grams of the product.

1.2 Conclusions

General population: The exposure of the general population to
deltamethrin is expected to be very low and is not likely to
present a hazard under recommended conditions of use.

Occupational exposure: With good work practices, measures of
hygiene, and safety precautions, deltamethrin is unlikely to
present a hazard for those occupationally exposed.

Environment: It is unlikely that deltamethrin or its degradation
products will attain levels of adverse environmental significance
with recommended rates of application. Under laboratory
conditions, deltamethrin is highly toxic for fish, aquatic

arthropods, and honey-bees. However, under field conditions,
lasting adverse effects are not likely to occur under recommended
conditions of use.

1.3 Recommendations

Although dietary levels are considered to be very low following
recommended usage, confirmation of this through inclusion of
deltamethrin in monitoring studies should be considered.

Deltamethrin has been used for many years and several cases of
non-fatal poisoning and transient effects from occupational
exposure have been reported. Observations of human exposure should
be maintained.

2. IDENTITY, PHYSICAL AND CHEMICAL PROPERTIES, ANALYTICAL METHODS

2.1 Identity

Molecular formula: C₂₂H₁₉Br₂NO₃

Deltamethrin is the first pyrethroid composed of a single
isomer of 8 stereoisomers selectively prepared by the
esterification of [1R, 3R or cis]-2,2-dimethyl-3-(2,2-dibromovinyl)
cyclopropanecarboxylic acid with (alphaS)- or (+)-alpha-cyano-3-
phenoxybenzyl alcohol or by selective recrystallization of the
racemic esters obtained by esterification of the (1R, 3R or cis)-
acid with the racemic or [alphaR, alphaS, or alphaRS or ±]-alcohol
(Elliott et al., 1974). Thus, its stereospecific structure (4) is
the ester of [1R, 3R or cis]-acid with (alphaS)-alcohol.

The acid is a characteristic dibromo analogue of chrysanthemic
acid.

2.2 Physical and Chemical Properties

Technical grade deltamethrin contains more than 98% deltamethrin
(FAO/WHO, 1981). It is stable to heat (6 months at 40 °C), light,
and air, but unstable in alkaline media (FAO/WHO, 1981; Meister et
al., 1983; Worthing & Walker, 1983). Some physical and chemical
properties are listed in Table 1, and the chemical composition of
various stereoisomeric mixtures is shown in Table 2.

Table 1. Some physical and chemical properties of deltamethrin
-------------------------------------------------------------------
Physical state crystalline powder
Colour colourless
Odour odourless
Density (20 °C) 0.5 g/cm³
Relative molecular mass 505.24
Melting point (°C) 98-101
Boiling point decomposes above 300 °C
Water solubility (20 °C) < 0.002 mg/litre (practically insoluble)
Solubility in organic soluble^a
solvents
Vapour pressure (25 °C) 2.0 x 10^-6Pa
n-Octanol-water 5.43
partition coefficient
(Log Pow)
-------------------------------------------------------------------
^aAcetone (500 g/litre), ethanol (15 g/litre), cyclohexanone (750
g/litre), dioxane (900 g/litre), xylene (250 g/litre), ethyl
acetate.

2.3 Analytical Methods

Methods for the determination of deltamethrin residues and the
analysis of environmental samples, and products are summarized in
Table 3.

To analyse technical grade deltamethrin, a mixture of
deltamethrin and diphenylamine (an internal standard) was injected
in a high-performance liquid chromatograph equipped with a UV-
detector (Mourot et al., 1979).

The Joint FAO/WHO Codex Alimentarius Commission has published
recommendations for methods for the determination of deltamethrin
residues (FAO/WHO 1985b). A further review of analytical methods
for deltamethrin has been made by Vaysse et al. (1984).

Table 2. Chemical identity of deltamethrins of various stereoisomeric compositions
---------------------------------------------------------------------------------------------------------------
Common name CA Index name (9CI) Stereoisomeric Synonyms and trade names
CAS Registry No. composition^c
NIOSH Accession No.^a Stereospecific name^b
---------------------------------------------------------------------------------------------------------------
Deltamethrin Cyclopropanecarboxylic acid, (4) Decamethrin, Decis,
52918-63-5 3-(2,2-dibromovinyl)-2,2-dimethyl-, K-Othrine, NRDC 161,
GZ1233000^a alpha-cyano(3-phenoxyphenyl)methyl ester, WHO 1998, K-Obiol, Butox
[1R-[1 (S^*), 3 R]]-, Butoflin, Cislin, FMC 45498
RU 22974

(S)-alpha-cyano-3-phenoxybenzyl
(1R, cis)-2,2-dimethyl-3-(2,2-di-
bromovinyl)cyclopropanecarboxylate

d- cis-Deltamethrin same as deltamethrin - Decamethrin, Decis
52820-00-5
GZ1240000^a (S)-alpha-cyano-3-phenoxybenzyl
(d, cis)-2,2-dimethyl-3-(2,2-di-
bromovinyl)cyclopropanecarboxylate
---------------------------------------------------------------------------------------------------------------
^aRegistry of Toxic Effects of Chemical Substances (RTECS) (1981-82 edition).
^b(1R), d, (+) or (1S), 1, (-) in the acid part of deltamethrin signifies the same stereospecific conformation,
respectively.
^cThe number in the parenthesis identifies the structure shown in the figures of stereoisomers.

Table 3. Analytical methods for deltamethrin
---------------------------------------------------------------------------------------------------------------------------------
Sample Extraction Sample preparation Determination: MDC^b % Recovery Reference
solvent ----------------------------------- (mg/kg) (fortification
Partition Clean up GLC or HPLC level in
column elution condition; detector, mg/kg)
carrier flow, column,
temp, R.T.^a
---------------------------------------------------------------------------------------------------------------------------------
RESIDUE ANALYSIS

apple n-hexane/ ext.sol.^c/ silica gel CH₂Cl₂ ECD-GC; N₂; 0.01 105(0.1), 100(1.0) 1
acetone H₂O 50 ml/min; 1 m
(1/1) 3% OV-7; 235 °C
pear 0.01 125(0.1), 98(1.0)
cabbage 0.01 130(0.1), 118(1.0)
potato 0.01 126(0.1), 97(1.0)

apple, acetonitrile petroleum Florisil ether/ EDC-GC; 1.2 m 0.005 85-100(0.02-0.1) 2
peach, ether/H₂O n-hexane DC-200, OV-1 or
grape, (1/4) OV-101; 245 °C,
tomato 10-12 min

wheat methanol n-hexane alumina HPLC; 235 nm; 87(2.0) 3
grain 30 cm; uBondapak;
C 18; methanol/H₂O
(4/1); 2.5 ml/min

wheat n-hexane Florisil ether/ ECD-GC; N₂; 91 4
petroleum 75 ml/min; 0.6 m
ether (1/9) 5% SE-30; 215 °C

meat ethyl ether/ acetonitrile gel diisopropyl ECD-GLC; N₂; 0.001 90-95% at 0.01 5
petroleum permeation ether 40 ml/min; 1.8 m
ether column SE-30 1% on gas
(Styragel) Chrom. PAW

milk hexane acetonitrile Florisil + benzene/ ECD-GLC; N₂; 0.01 83-87% at 0.1 5
cellulose/ hexane 40 ml/min; 1.8 m
charcoal (1/1) SE-30 1% on gas
Chrom. PAW
---------------------------------------------------------------------------------------------------------------------------------

Table 3. (contd.)
-----------------------------------------------------------------------------------------------------------------------------------
Sample Extraction Sample preparation Determination: MDC^b % Recovery Reference
solvent ----------------------------------- (mg/kg) (fortification
Partition Clean up GLC or HPLC level in
column elution condition; detector, mg/kg)
carrier flow, column,
temp, R.T.^a
-----------------------------------------------------------------------------------------------------------------------------------
ENVIRONMENTAL ANALYSIS

locust n-hexane Florisil ether/ ECD-GC; N₂; 92 4
petroleum 75 ml/min; 0.6 m 5%
ether (1/9) SE-30; 215 °C

sea water XAD-2 ext.sol.^c/ alumina ECD-GC; N₂; 6
resin n-hexane 70 ml/min; 1.5 m
acetone 4% SE-30; 207 °C

water n-hexane alumina ECD-GC; N₂; 6
70 ml/min; 1.5 m
4% SE-30; 207 °C

water petroleum Florisil petroleum ECD-GLC; 1 m OV 0.0001 97 at 0.010 8
ether/ ether/ 1-3% on Chromosorb
diethyl- diethyl- W.A.W. HMDS 60/80
ether (1/1) ether
(80/20)

soil acetone, acid hexane ECD-GLC; 5.2% 0.001 > 91% 9
acetone/ alumina ether OV-210 with AR/CH4
hexane (1/1) hexane
hexane (5-10%)

acetone, acid hexane/ ECD-GLC; N₂; 0.0001 > 91% 5
acetone/ alumina ethyl ether 40 ml/min; 1.8 m
hexane (1/1) (90/10) SE-30 1% on gas
hexane Chrom. PAW

cotton n-hexane transesterification 7
foliage followed by ECD-GC;
(dislodgeable 31 ml/min; 0.45 m
residue) 5% SE-30; 120 °C
-----------------------------------------------------------------------------------------------------------------------------------

Technical HPLC, 230 nm; 15 cm 10
grade Lichrosorb Si-60;
n-hexane/diisopropyl
ether (93/7); 80 ml/h;
7.6 min

isoctane/ HPLC - UV detector 5
dioxane 254 nm (230 nm for
(80/20) conc. <0.5%) Silica-60;
100ml/h; isooctane/
dioxane (95/5)
-----------------------------------------------------------------------------------------------------------------------------------
^aR.T.: retention time;
^bMDC: minimum detectable concentration;
^cext .sol.: extraction solvent.

References

1. Baker & Bottomley (1982); 2. Mestres et al. (1978a); 3. Noble et al. (1982); 4. Pansu et al. (1981); 5. Vaysse et al. (1984);
6. Zitko et al. (1979); 7. Estesen et al. (1979); 8. Mestres et al. (1978b); 9. Hill (1982); 10. Mourot et al. (1979).
3. SOURCES OF ENVIRONMENTAL POLLUTION AND ENVIRONMENTAL LEVELS

3.1 Industrial Production

Deltamethrin was first marketed in 1977. Production volumes in
recent years are shown in Table 4.

Table 4. Worldwide production of deltamethrin
-------------------------------------------------
Year Production Reference
(tonnes)
-------------------------------------------------
1979 75 Wood Mackenzie (1980)
1980 100 Wood Mackenzie (1981)
1981 100 Wood Mackenzie (1982, 1983)
1982 115 Wood Mackenzie (1983)
1987 250 Information from Roussel Uclaf
-------------------------------------------------

3.2 Use Patterns

After an initial period when the product was mainly used on
cotton, several major crops were treated with deltamethrin from
1980 to 1987. Some 85% of the total production is used for crop
protection. Within this, 45% is used on cotton, 25%, on fruit and
vegetable crops, 20% on cereals, corn, and soybean, and the
remaining 10% on miscellaneous crops.

Deltamethrin is used to protect stored commodities (mainly
cereals, grains, coffee beans, dry beans), in forestry, and in
public health (e.g., Chagas disease control in South America, and
malaria control in Central America and on the African continent).
It is also used in animal facilities and against cattle
infestation.

It is formulated as an emulsifable concentrate (25 - 100
g/litre), an ultra-low-volume concentrate (1.5 - 30 g/litre), a
wettable powder (25 - 50 g/kg), a flowable powder (7.5 - 50
g/litre), or a dust powder (0.5 - 2.5 g/kg). It is also used in
combination with other pesticides and with piperonyl butoxide
(unpublished information from Roussel Uclaf to the IPCS, 1988).

3.3 Residues in Food

Supervised trials have been carried out on a wide variety of
crops and comprehensive summaries of analyses for residues in these
trials can be found in the evaluation reports of the Joint FAO/WHO
Meeting on Pesticide Residues (JMPR) (FAO/WHO 1981, 1982, 1983,
1985a, 1986a, 1986b, 1988b). A comprehensive list of maximum
residue limits (MRLs) for a large number of commodities resulted
from these evaluations (FAO/WHO, 1986c, 1988a,c) (see section 9).

Residues were determined in stored products, e.g., wheat,
maize, and coffee. The residue level in wheat grains treated with
deltamethrin at the rate of 2 mg/kg was 1.08 mg/kg after storage

for 9 months. When the wheat was subjected to milling and baking,
the residue levels in white bread were 0.11 mg/kg (Halls & Periam,
1980).

Mestres et. al. (1986) reviewed the changes in deltamethrin
residues in edible crops resulting from processing and cooking and
found that, depending on the commodity, pre- or post-harvest
residues were reduced by 20 - 98% by processing, and especially by
cooking.

When 0.27 g of ¹⁴C-(alcohol labelling)-deltamethrin was
injected intrarumenally in a lactating Jersey cow, in solution in a
sesame oil/alcohol mixture, only 0.4% of the compound was found in
whole milk. Peak residue levels of 0.045 and 0.92 mg/kg were found
in whole milk and rendered butter fat, respectively, 1 day after
administration. Residues in omental fat and leg muscle were 0.088
and 0.008 mg/kg, respectively, 2 days after treatment (Wellcome
Foundation, 1979).

3.4 Levels in the Environment

No information is available.

4. ENVIRONMENTAL TRANSPORT, DISTRIBUTION, AND TRANSFORMATION

4.1 Transport and Distribution Between Media

Using three different soils (silty clay, silty clay loam, and
loamy sand), Kaufman et al. (1981) found that deltamethrin was
practically immobile in soil columns. Approximately 96 - 97% of
the ¹⁴C activity remained in the upper 0 - 2.5 cm layer of the
columns with only 1.3 % in the 2.5 - 5.1 cm layer and no ¹⁴C in the
leachate. Soil thin layer chromatography (soil TLC) was also used
to evaluate the mobility of deltamethrin. According to the
pesticide mobility classification system developed by Helling &
Turner, deltamethrin is classified as a low-mobility to immobile
compound in soils.

The immobility of deltamethrin in soil was also studied by
Hascoet (1977) using a French Fontainebleau sand column leached
with a very high volume of water (equivalent to 1030 mm of rain).
In this experiment, approximately 97% of the applied ¹⁴C-
deltamethrin remained in the upper 0 - 2.5 cm layer and only 2% was
found in the leachate. The author concluded that deltamethrin was
unlikely to leach in cultivated soil that had a higher organic
matter content and/or higher clay contents than sand (organic
matter 0.03%), which has especially good filtration and low
adsorption properties.

The leaching of deltamethrin was also studied in three
different German soils the organic contents of which ranged from
0.8 to 2.6%. The study was carried out using the commercial
product Decis EC 25 at a rate equivalent to 1 litre/ha (i.e., 25 g
deltamethrin/ha). Each column was leached with 370 ml of water,
which was equivalent to a rainfall of 200 mm for 2 days. Under
these conditions, the amount of active ingredient (a.i.) detected
in seepage water was found to be less than 1 µg/ml, which was less
than 2% of the original applied dose (Thier & Schmidt, 1976).

The mobility of the primary deltamethrin degradation products
3-phenoxybenzoic acid (PBacid) and 3-phenoxybenzyl alcohol (PBalc)
was also investigated by Kaufman et al. (1981) using soil TLC and
soil columns. PBacid was found to be relatively mobile, whereas
PBalc was only slightly mobile. 2,2-Dimethyl-3-(2,2-dibromovinyl)
cyclopropanecarboxylic acid (Br₂CA) was not studied in this
experiment, but Cl₂CA, the chloride substituted analogue, was
evaluated and also found to be relatively mobile. However, these
metabolites did not accumulate in the soil to any extent, since
they were never in excess of 3% of the applied dose under the
aerobic conditions reported by Kaufman & Kayser (1979a,b). The
very significant production of ¹⁴CO₂during the incubation period
confirmed that they were further degraded.

4.2 Abiotic Degradation in Air and Water

Degradation pathways for deltamethrin are summarized in Fig. 1.

When ¹⁴C-deltamethrin-[1R, 3R; alphaS] (9) labelled at the
cyano, benzylic, or dibromo-substituted carbon was exposed to
sunlight as a thin film (40 µg/cm²) for 4 - 8 h, the trans-[1R,
3S; alphaS] and -[1S, 3R; alphaS] isomers were formed. They
accounted for approximately 70% of the applied radioactivity.
Smaller amounts of ester cleavage products including the
2,2-dimethyl-3-(2,2-dibromovinyl) cyclopropanecarboxylic acid
(Br₂CA) (18) and the cyanohydrin component, and 18% of
unidentified products were also formed (Fig. 1). In a thick film (3
mg/cm²), small amounts of other products including
alpha-cyano-3-phenoxybenzyl 3,3-dimethylacrylate (13) and 3-phenoxy
2,2-dimethyl-3-(2,2- dibromovinyl)cyclopropan-1-yl-benzylcyanide
(14) (decarboxydeltamethrin) were also detected. In contrast, the
predominant products in methanol were the trans mixtures, which
amounted to approximately 35% of the applied radioactivity. Under
UV radiation (peak output 290 - 320 nm), the photodegradation rate
of deltamethrin in alcohols decreased in the order of methanol,
ethanol, and 2-propanol, as the solvent viscosity increased. The
relative photolysis rates in hexane and cyclohexane, with respective
relative viscosities of 0.33 and 1, were 1.5 and 1. There was no
difference in the extent of the reaction on flushing the hexane with
O₂or N₂, while the triplet quenchers piperilene and
1,3-cyclohexadiene reduced the reaction rate in hexane.

At 30 - 50% conversion, the trans-[1R, 3S; alphaS] and -[1S,
3R; alphaS] isomers were the major photoproducts in aqueous
acetonitrile, whereas they were observed in only minor amounts in
methanol and were absent in hexane. The mono-debrominated esters
(16) were the major ester products in methanol and hexane. The
cis-acid (18) was always the major photoproduct from the acid
moiety, with smaller amounts of the two isomeric debrominated acids
(17).

Major products from the alcohol moiety were 3-phenoxybenzoic
acid (25) (PBacid) in aqueous acetonitrile, 3-phenoxybenzyl cyanide
(15) in hexane, and methyl 3-phenoxybenzoate (22) in methanol.
Photolysis of 3-phenoxybenzoyl cyanide (21) gave methyl
3-phenoxybenzoate and the methyl ester of Br₂CA (19) in methanol
and PBacid in aqueous acetonitrile. Thus, it appears that the
photoproducts obtained originated from cyclopropane ring opening
and various recombinations, scission of the ester oxygen-benzyl
carbon bond, scission of the acyl-oxygen bond, and/or reductive
debromination (Ruzo et al., 1976, 1977).

A photodegradation study with ¹⁴C-deltamethrin in aqueous
solution showed that such a solution, at pH 5, is hydrolytically
stable. When exposed to simulated sunlight, degradation was
induced. The primary product observed was PBacid. A half-life of
47.7 days was calculated for the non-sensitized system, but this
was reduced to 4.03 days when sensitized with 1% acetone.
Practically no volatile degradation products were observed (Bowman
& Carpenter, 1987).

4.3 Environmental Fate

The degradation and persistence of ¹⁴C-cyano- and ¹⁴C-phenoxy-
deltamethrin was examined in a Dubbs fine sandy loam and a Memphis
silt loam under aerobic laboratory conditions at 25 °C (Kaufman &
Kayser 1979a); ¹⁴C-deltamethrin was applied at final concentrations
equivalent to 0.02 and 0.2 kg/ha. Deltamethrin degradation
occurred rapidly in both soils with 62 - 77% and 52 - 60% of the
¹⁴C-cyano- and ¹⁴C-phenoxy-labels, respectively, being evolved as
¹⁴CO₂during the 128-day incubation period. The half-life of
deltamethrin varied from 11 to 19 days in the two soil types.

The effect of soil temperature on the degradation of
deltamethrin was also examined in Dubbs fine sandy loam under
laboratory conditions using ¹⁴C-cyano- and ¹⁴C-vinyl-labelled
deltamethrin (Kaufman & Kayser 1979b). Degradation and evolution
of ¹⁴C-labelled forms of deltamethrin occurred most rapidly at
25 °C and most slowly in soils incubated at 10 °C. The half-life
of deltamethrin was 46, 13, and 27 days in soils incubated at 10,
25, and 40 °C, respectively.

The results of these two studies indicate that deltamethrin
degradation occurs by two principal pathways (Fig. 2): hydrolysis
of the ester linkage to yield Br₂CA (18) and 3-phenoxybenzoic acid;
and hydrolysis of the cyano group to yield first the amide, and
subsequently the carboxylic acid (DCOOH) analogues of deltamethrin.

Br₂CA accumulated to a maximum of 5.7% of the original ¹⁴C in soil
incubated at 40 °C, whereas DCOOH accumulated at 10 °C (to a
maximum of 5.3%). However, both products decreased in
concentration by the end of the 64-day incubation period. In the
first experiment, DCOOH was also identified as the major
degradation product to reach a maximum concentration of 6 - 9% of
the original ¹⁴C. But it ultimately dissipated to less than 2% at
the end of the 128-day incubation period.

From the ¹⁴C-phenoxy label, 3-phenoxybenzoic acid (PBacid) was
identified as the main degradation product resulting from
hydrolysis of the ester bond. This product was further degraded to
yield both 3-(2-hydroxyphenoxy)-benzoic acid and 3-(4-hydroxyphenoxy)
benzoic acid. In this experiment, DCOOH was the only deltamethrin
degradation product detected in excess of 3% of the original material
applied.

Although essentially no radiolabel was detected in the leachate
from soil columns treated with ¹⁴C-deltamethrin, PBacid produced by
degradation of deltamethrin was fairly mobile in the soil columns
(Kaufman et al., 1981).

The degradation pathways are proposed in Fig. 2.

The degradation of deltamethrin was also examined under
anaerobic conditions using ¹⁴C-cyano-, ¹⁴C-phenoxy-, and
¹⁴C-vinyl-labelled materials for the tests (Kaufman & Kayser,
1980). Under anaerobic conditions, ¹⁴CO₂evolution varied
according to the ¹⁴C label position and the time of flooding.
Generally, flooding reduced or initially inhibited the rate of
¹⁴CO₂dissipation. However, after one month, ¹⁴CO₂dissipation
started again, which suggested the presence of a unique microbial

flora. It was also shown that all three carboxylic acids that
accumulate initially in flooded soils are subsequently further
degraded. Some reduction of PBacid to 3-phenoxybenzyl alcohol
(PBalc) was also observed in these flooded soils.

When deltamethrin was applied to a sandy clay loam soil at
17.5 g/ha in an indoor incubation study and in two field
experiments, the half-lives of deltamethrin were found to be 4.9
and 6.9 weeks under indoor and field conditions, respectively
(Hill, 1983). This difference in the rate of decrease in the
residue was attributed to climatic effects.

This was further confirmed by Hill & Schaalje (1985) who
pointed out a first-order dissipation, if degree-days above 0 °C
rather than days was used as the independent variable, when
deltamethrin was applied by pipette to soils. When deltamethrin
was boom-sprayed, a biphasic first-order plot was observed. A two-
compartment model that predicts an initial fast loss of residue
followed by a slower first-order degradation gave a good fit of the
data.

Chapman & Harris (1981) examined the relative persistence of
five pyrethroids, permethrin, cypermethrin, deltamethrin,
fenpropathrin, and fenvalerate, in sand and organic soil at 28 °C,
under laboratory conditions. All of the insecticides (1 mg/kg) were
degraded more rapidly in natural soils than in sterilized soils,
suggesting the importance of microbial degradation. The rate of
degradation under non-sterilized conditions decreased as follows:
fenpropathrin > permethrin > cypermethrin > fenvalerate >
deltamethrin. Amounts of approximately 52% and 74% of the
deltamethrin applied were recovered from the sand and organic soil,
respectively, 8 weeks after treatment.

It was pointed out by Chapman et al. (1981) that biological
processes played a major role in the degradation of deltamethrin in
soils.

The degradation of deltamethrin was also investigated by Zhang
et al. (1984) in an organic soil over a 180-day period. The half-
life of deltamethrin was found to be 72 days, indicating that
deltamethrin is likely to be less susceptible to degradation in
organic soils than in mineral soils. Identification of metabolites
present in the extractable phase confirmed the metabolic pathways
previously reported by Kaufman. Levels of bound ¹⁴C residues
increased with the incubation period to reach 19% of the original
¹⁴C after 180 days. Most of these bound ¹⁴C residues were in the
humic fraction. Bacterial and actinomycete populations increased
in the treated soil, but fungal populations remained relatively
stable during the incubation period.

The degradation of deltamethrin was also studied in two German
soils. Half-lives for sandy soil and sandy loam soil were 35 and
60 days, respectively (Thier & Schmidt, 1977).

All these studies demonstrate that deltamethrin is readily and
quickly degraded in the soil. The half-life of the compound
depends on the nature of the soil as well as the temperature.

Generally speaking, the half-life ranges from 11 to 72 days, under
aerobic conditions. Deltamethrin degradation is slower under
anaerobic or sterile conditions, indicating that microorganisms and
other biological processes play a very important role.

The metabolism of deltamethrin in cotton plants was studied
using material ¹⁴C-labelled at the dibromovinyl, benzylic, and
cyano carbons. Under glasshouse conditions, the initial half-life
of deltamethrin was 1.1 weeks and the time needed for 90% loss was
4.6 weeks. Conversion of deltamethrin to the trans-isomer occurred
via photochemical reactions and, after 6 weeks, the trans/cis ratio
was 0.44:1. Deltamethrin degraded more rapidly under field
conditions to give a higher proportion of trans- to cis-isomers and
large amounts of unextractable products. Trace amounts of three
deltamethrin derivatives hydroxylated either at the 4'-position
(10), or at the trans-methyl relative to the carboxy group in the
acid moiety (7), or at both sites (12) were detected with all three
¹⁴C preparations (Fig. 1). However, the major metabolites were
free and conjugated Br₂CA together with small quantities of the
trans-hydroxymethyl derivatives (20) of Br2CA and 3-(4-
hydroxyphenoxy) benzoic acid (26). The above compounds were
analogues of those formed from permethrin and cypermethrin in
plants. Several types of conjugated metabolites were isolated, but
they were not fully characterized. One type was cleaved readily
with beta-glucosidase or hydrogen chloride to yield Br₂CA and
PBacid. Two other types were resistant to beta-glucosidase, but
cleaved readily with hydrogen chloride to yield Br₂CA (from the
dibromovinyl label) and 3-phenoxybenzoic acid, 3-phenoxybenzyl
alcohol (from the alcohol label), and alpha-cyano-3-phenoxybenzyl
alcohol (from the cyano and alcohol labels). The metabolites of
deltamethrin identified in plants were analogous to those in
mammals, except for the conjugated products.

The metabolism of deltamethrin and its degradation products in
cotton and bean leaf disks has also been studied. Limited
conversion (approximately 6%) of deltamethrin occurred to give
Br₂CA and 3-phenoxybenzyl alcohol (27) (PBalc) conjugates. The
ester cleavage products used as substrates underwent more extensive
metabolism, and two to three types of glucosides were formed from
Br₂CA and four from PBalc. 3-Phenoxybenzaldehyde (24),
administered directly or as the cyanohydrin (23), was reduced to
PBalc, though part was oxidized to PBacid (Ruzo & Casida, 1979).

4.4 Bioaccumulation

Bioaccumulation studies with fish, have shown that pyrethroids
have bioconcentration factors (BCFs) that are far lower than those
predicted from the correlation between the K_owpartition
coefficient and BCF. The low accumulation can be attributed to
metabolism by the fish and to the reduced bioavailability to fish
of deltamethrin bound by dissolved organic carbon and suspended
colloids. Metabolic kinetics were assessed by Cary (1978) in
Ictalurus punctatus maintained for 30 days in the water of a
hydrosoil system, in which the soil was treated with a dose of
125 g a.i./ha (10 times the normal agricultural dose) and then
flooded after 31 days. During the exposure period, none of the

300 fish died or behaved abnormally despite a final deltamethrin
concentration of 2.19 µg/litre, which is more than 3 times the
acute 96-h LC₅₀of 0.63 µg/litre (Table 6). During a third phase,
fish were introduced into an uncontaminated liquid medium,
continuously renewed, to monitor elimination of deltamethrin or its
metabolites. The main results are given in Table 5.

Table 5. Bioaccumulation factors after exposure of Ictalurus
punctatus and depuration kinetics^a
----------------------------------------------------------------
Organ Value of bioconcentration ¹⁴C elimination (%)
factor (BCF)^bduring after depuration of
exposure, 30 days -------------------
1 day 14 days
----------------------------------------------------------------
muscles 25 <50 77
viscera 972 67 86
carcasses 41 >50 93
body as a whole 144 >50 93
----------------------------------------------------------------
^aFrom: Cary (1978).
^bBCF: µg/kg concentration in fish/µg/litre concentration in
water.

Muir et al. (1985) monitored the fate and uptake of
¹⁴C-labelled deltamethrin in organisms in experimental ponds over
306 days. Initial concentrations of the pyrethroid ranged from 1.8
to 2.5 µg/litre. The deltamethrin rapidly became distributed in
suspended solids, plants, sediment, and air with a half-life of
2 - 4 h in the water. Aquatic plants (the floating duckweed Lemna
sp. and a submerged/floating weed (Potomageton berchtoldi)
accumulated deltamethrin at concentrations of between 253 and
1021 µg/kg, respectively, 24 h after treatment, but the compound
had all disappeared within 14 days. Fathead minnows, Pimephales
promelas, showed bioconcentration factors of 248 - 907. Although
radioactivity remained in the fish throughout the experimental
period, presumably in the fat, the levels fell steadily and no
effects were seen on the fish.

5. KINETICS AND METABOLISM

5.1 Metabolism in Experimental Animals

Metabolic pathways of deltamethrin in mammals are summarized in
Fig. 3.

After oral administration to male rats at 0.64 - 1.60 mg/kg,
the acid and alcohol moieties of deltamethrin were almost
completely eliminated from the body within 2 - 4 days (Ruzo et al.,
1978). On the other hand, the cyano group was eliminated more
slowly, the total recovery during 8 days being 79% of the
radiocarbon dose (43% and 36% in the urine and faeces,
respectively). Tissue residues of deltamethrin labelled with ¹⁴C
at the dibromovinyl carbon in the acid moiety and the benzylic
carbon in the alcohol moiety were generally very low, whereas
residue levels in the fat were somewhat higher (0.1 - 0.2 mg/kg).
Residue levels of the radiocarbon derived from the cyano group were
relatively high, especially in the skin and stomach. Essentially,
all the radiocarbon in the stomach was thiocyanate. No noticeable
¹⁴CO₂was evolved from any of the radioactive preparations,
including the CN-labelled group, in contrast to the CN group from
fenvalerate, which yielded ¹⁴CO₂in considerable amounts.

The major metabolic reactions of deltamethrin were oxidation
(at the trans methyl relative to carbonyl group of the acid moiety
and at the 2'-, 4'-, and 5-positions of the alcohol moiety),
cleavage of the ester linkage, and conversion of the cyano portion
to thiocyanate and 2-iminothiazolidine-4-carboxylic acid (31)
(ITCA) (see Fig. 3). These carboxylic acid and phenol derivatives
were conjugated with sulfuric acid, glycine, and/or glucuronic
acid.

The major faecal metabolites were unchanged deltamethrin (9),
accounting for 13 - 21% of the dose, followed by 4'-OH- (10) and
5-OH-deltamethrin (28), and a trace amount of 2'-OH-deltamethrin
(29). Intact deltamethrin and the 4'-OH-derivative appeared not
only as the administered S-epimer, but also in parts as the
R-epimer, probably due to artefactural racemization on exchange of
the alpha-position hydrogen in methanol solution. The metabolites
from the acid moiety were mostly 3-(2,2-dibromovinyl)-2,2-
dimethylcyclopropanecarboxylic acid (18) (Br₂CA) in free form
(10% of the dose), glucuronide (51%) and glycine (trace level)
conjugates, and OH-Br₂CA (20) in free form and glucuronide
conjugate (<1%).

The major metabolites of the aromatic portion of the alcohol
moiety were 3-phenoxybenzoic acid (25) (PBacid) in free form (5%),
and glucuronide (13%) and glycine (4%) conjugates and its
4'-hydroxy derivative (26) (4'-OH-PBacid).

Sulfate of 4'-OH-PBacid accounted for about 50% of the dose,
together with small amounts of free (4%) and glucuronide forms
(2%). The CN group was converted mainly to thiocyanate (30) and,
in small amounts, to ITCA (31) (Ruzo et al., 1978). The trans-
isomer of deltamethrin was also rapidly metabolized and yielded
almost the same metabolites as deltamethrin, though 5-OH-derivative
was found in the cis-isomer, but not in the trans-isomer (Ruzo et
al., 1978).

When a single oral dose of ¹⁴C-(acid-, alcohol-, or cyano-
labelled) deltamethrin was administered to male mice at 1.7 - 4.4
mg/kg, the acid moiety and the aromatic portion of the alcohol
moiety were rapidly and almost completely excreted, whereas the CN
group was excreted relatively slowly (Ruzo et al., 1979).

Gray & Rickard (1982) followed the distribution of ¹⁴C-acid-,
¹⁴C-alcohol-, and ¹⁴C-cyano-labelled deltamethrin and selected
metabolites in the liver, blood, cerebrum, cerebellum, and spinal
cord after iv administration of a toxic, but non-lethal, dose
(1.75 mg/kg) to rats. Approximately 50% of the dose was cleared
from the blood within 0.7 - 0.8 min, after which the rate of
clearance decreased. 3-Phenoxybenzoic acid (PBacid) was isolated
from the blood in vivo, and was also the major metabolite when
¹⁴C-alcohol-labelled deltamethrin was incubated with blood in
vitro. Deltamethrin levels in the liver peaked at 7 - 10 nmol/g at
5 min and then decreased to 1 nmol/g by 30 min. In contrast, peak
central nervous system levels of deltamethrin were achieved within
1 min (0.5 nmol/g), decreasing to 0.2 nmol/g at 15 min, and

remaining stable until 60 min. Peak levels of deltamethrin were
not related to the severity of toxicity, though the levels of
unextractable pentane radiolabel did appear to be correlated with
signs of motor toxicity. Experiments with brain homogenates from
animals injected iv with deltamethrin failed to reproduce the
pentane-unextractable radioactivity in vitro and metabolism of the
compound was not demonstrated.

The major metabolic pathways of deltamethrin in mice were
similar to those in rats, though there were some differences. These
included the presence of more unchanged deltamethrin in mouse faeces
than in rat faeces. In mouse faeces, there were 4 monohydroxy ester
metabolites (2'-OH-, 4'-OH-, 5-OH-, and trans-OH- deltamethrin
(11)) and one dihydroxy metabolite (12) (4'-OH- trans-
OH-deltamethrin) that were not found in mouse urine. Major
metabolites from the acid moiety in mice were Br₂CA,
trans-OH-Br₂CA (20), and their glucuronide and sulfate
conjugates. Among them, trans-OH-Br₂CA-sulfate was detected
only in mice, but not in rats. Compared with rats, much larger
amounts of trans-OH-Br₂CA and its conjugates were formed in
mice. A major metabolite of the alcohol moiety in mice was the
taurine conjugate of PBacid in the urine, which was not detected in
rats. Generally, mice produced smaller amounts of phenolic
compounds compared with rats. Also, 3-phenoxybenzaldehyde (24)
(PBald), 3-phenoxybenzyl alcohol (32) (PBalc), and its glucuronide,
and glucuronides of 3-(4- hydroxyphenoxy)benzyl alcohol (33)
(4'-OH-PBalc) and 5-hydroxy-3- phenoxybenzoic acid (34)
(5-OH-PBacid) were found in mice, but not in rats. When mice were
given an ip dose of ¹⁴C-deltamethrin, with or without piperonyl
butoxide (PBO) and/or S,S,S-tributyl- phosphorotrithioate (DEF),
the same metabolites were obtained as with oral administration.
However, DEF decreased the hydrolytic products relative to the
controls, while PBO decreased the oxidation products (Ruzo et al.,
1979).

The comparison between the excreted radioactivity of
¹⁴C-deltamethrin in rats treated by the percutaneous route and iv
(controls) showed that only 3.6% of the dosage applied on the skin
was absorbed and excreted in 24 h with 1.1% excreted during the
first 6 h. Since the rat skin is more permeable than human skin,
the uptake of deltamethrin through the human skin should be
relatively weak (Pottier et al., 1982).

5.2 Metabolism and Fate in Farm Animals

In a metabolic study, ¹⁴C-deltamethrin was administered orally
to lactating dairy cows at the rate of 10 mg/kg body weight per day
for 3 consecutive days. It was poorly absorbed and mainly
eliminated in the faeces as unchanged deltamethrin. Only 4 - 6% of
the administered ¹⁴C was eliminated in the urine, and 0.42 - 1.62%
was secreted in the milk. The radiocarbon contents of various
tissues were generally very low with the exception of those of the
liver, kidney, and fat, which were higher (Akhtar et al. 1986).
Deltamethrin degradation occurred by cleavage of the ester bond, as
already reported in rats and mice (Ruzo et al. 1978, 1979). The
enzymes responsible for the ester bond cleavage were located in cow

liver homogenate, mainly in the microsomal fraction, as seen in an
in vitro study (Akhtar, 1984). Metabolites resulting from ester
bond cleavage were further metabolized and/or conjugated, resulting
in a large number of compounds excreted in the urine (see Fig. 3).
In milk, the major identifiable radiolabelled compound was
deltamethrin.

In a feeding study by Akhtar et al. (1987), deltamethrin was
administered twice daily to lactating dairy cows in portions of
their daily feed at the rate of 2 or 10 mg/kg diet for 28
consecutive days. The level of 2 mg/kg diet was the residue level
found in a recently treated pasture (Hill & Johnson, 1987), whereas
10 mg/kg diet was five times this level. Deltamethrin residues in
the milk were dose-dependent and appeared to reach a plateau
between 7 and 9 days after the start of treatment. At the high
deltamethrin intake of 10 mg/kg diet, the deltamethrin residue in
milk was about 0.025 mg/litre. Deltamethrin residues in tissues
were measured 1, 4, and 9 days after the last dose. At the
10 mg/kg diet intake, very small amounts of deltamethrin residues
were found in the liver (<0.005 mg/kg), kidney (<0.002 mg/kg),
and muscle (0.002 - 0.014 mg/kg). Residues in fat were about
0.04 mg/kg and 0.2 mg/kg for the 2 and 10 mg/kg intake,
respectively. Depletion of deltamethrin residues in milk was very
rapid (estimated half-life was about 1 day); while in fat (renal
and subcutaneous) the half-life was 7 - 9 days. Br₂CA (3-(2,2-
dibromovinyl)-2,2-dimethylcyclopropanecarboxylic acid) and PBacid
(3-phenoxybenzoic acid) were the only metabolites detected in the
milk and tissues of treated cows. In all cases, they were found at
trace levels of < 0.0235 mg/litre and < 0.034 mg/litre,
respectively. These two metabolites were also previously
identified in rats and mice as the major degradation products of
deltamethrin (Ruzo et al., 1978, 1979).

The fate of ¹⁴C-deltamethrin was examined in Leghorn hens
(Akhtar et al., 1985). When laying hens were administered 7.5 mg
of ¹⁴C-labelled deltamethrin/hen per day orally for 3 consecutive
days, about 83% and 90% of the administered ¹⁴C was eliminated
during the first 24 h and 48 h after dosing, respectively. Tissue
residues were generally very low with the exception of those in the
liver and kidney. Very low levels of residues were found in eggs
obtained within the first 24 h after dosing, but levels increased
reaching a peak within 48 h of the last dose. Residue levels were
higher in the yolk (up to 0.6 mg/kg) than in the albumen (up to
0.2 mg/kg), which is probably related to the lipid content of
yolks. Metabolites were the same as those found in rats and mice.

These studies showed that feeding domestic animals on
deltamethrin-treated feed resulted in very low levels of residues
(if any) in products of animal origin and is unlikely to present a
hazard for the consumer.

5.3 Enzymatic Systems for Biotransformation

Deltamethrin (1 µg) was incubated at 37 °C for 30 min with each
of the following mouse microsome preparations; a) tetraethyl
pyrophosphate (TEPP)-treated microsomes (no esterase and oxidase
activity); b) normal microsomes (esterase activity); c) TEPP-
treated microsomes plus NADPH (oxidase activity); and d) normal
microsomes plus NADPH (esterase plus oxidase activity) (Shono et
al., 1979). Deltamethrin was more rapidly metabolized under the
oxidase system than under the esterase system. The major site of
ring hydroxylation was the 4'-position and the secondary site was
the 5-position. The trans methyl group was an important site of
hydroxylation of the esters and cis methyl oxidation was evident in
the metabolites of the cleaved acid moiety. The preferred sites of
hydroxylation were as follows; trans of dimethyl group,
4'-position in the phenol group, and cis of the dimethyl group,
which was equal to the 5-position in the phenoxy group. Cleavage
of deltamethrin to cyanohydrin may result from both esterase and
oxidase enzyme activities, since larger amounts of the cleaved
products were evident in the oxidase system.

However, at a much higher (approximately 35-fold) concentration
of deltamethrin than that in the above study, it was not detectably
hydrolysed (Miyamoto, 1976; Soderlund & Casida, 1977).

Deltamethrin was hydrolysed by esterases in the blood, brain,
kidney, and stomach of mice yielding PBald and PBacid (Ruzo et al.,
1979).

5.4 Metabolism in Human Beings

Three young male human volunteers underwent a complete medical
check-up one week prior to the morning of the study. Each of them
received a single dose of 3 mg of ¹⁴C-deltamethrin mixed in 1 g
glucose and diluted first in 10 ml PEG 300 and again in 150 ml
water. Total radioactivity was 1.8 ± 09 mBq. Samples of blood,
urine, saliva, and faeces were taken at intervals over 5 days.
Clinical and biological examinations were performed every 12 h
during the trial and one week after its termination. Radioactivity
in the biological samples was measured with a liquid scintillation
spectrometer. The clinical and biological checks did not detect
any abnormal findings. There were no signs of side effects or
intolerance reactions, either during or after the trial period.
The maximum plasma radioactivity appeared between 1 and 2 h after
administration of the product, and remained over the detection
limit (0.2 KBq/litre) during the 48 h. The apparent elimination
half-life was between 10.0 and 11.5 h. The radioactivity of blood
cells, as well as the saliva, was extremely low. Urinary excretion
was 51 - 59% of the initial radioactivity; 90% of this
radioactivity was excreted during the 24 h following absorption.
The apparent half-life of urinary excretion was 10.0 - 13.5 h,
which is consistent with the plasma data. Faecal elimination at
the end of the observation period represented 10 - 26% of the dose.
The total faecal plus urine elimination was around 64 - 77% of the
initial dose after 96 h (Papalexiou et al., 1984).

6. EFFECTS ON ORGANISMS IN THE ENVIRONMENT

6.1 Aquatic Organisms

6.1.1 Acute toxicity for fish

Acute toxicity data for deltamethrin in fish have been
summarized by L'Hotellier & Vincent (1986) (Table 6). From this,
it appears that deltamethrin is highly toxic for fish, though the
toxicity varies with the formulation tested.

Table 6. Acute toxicity of deltamethrin tested as the technical or formulated product on
fish; lethal concentrations all expressed as µg active ingredient (a.i.)/litre (96-h)
------------------------------------------------------------------------------------------
Species System^a LC₅₀(µg/litre) Ref. LC₅₀(µg/litre) Ref.
(Common name) tested as No. tested as No.
technical formulated
product product^b
------------------------------------------------------------------------------------------
Alburnus alburnus S 0.69 4 82 (ULV) 4
(Bleak)
Brachydanio rerio F,S 2.0 10 -
(Zebra fish)
Cyprinodon macularius S - 0.6^c (EC) 13
(Desert pupfish)
Cyprinodon S - 0.9 (EC) 19
variegatus^d
(Sheepshead minnow)
Cyrpinus carpio F, S 1.84 4 0.65 (EC) 4
(Common carp) 0.86 3 210.0 (ULV)
Gambusia affinis F, S - 1.0^c (EC) 13
(Mosquito fish)
Ictalurus nebulosus F, S 1.2 7 2.3 (EC) 15
(Brown bullhead)
Ictalurus punctatus F, S 0.63 8 -
(Hannel catfish)
Idus idus melanotus S - 1.2 (EC) 16
(Golden orfe)
Lebistes reticulatus F, S - 1.8 (EC) 17
(Guppy)
Lepomis gibbosus F, S 0.58 5 0.87 (EC) 14
(Pumpkinseed sunfish)
Lepomis machrochirus F 1.2 6 -
(Bluegill sunfish)
Osteochilus hasselti^e S - 1.2 (EC) 20
(Nilem carp)
Puntius gonionotus^e F,S - 0.87 (EC) 18
(Jawa carp)
Rhodeus sericeus S 1.12 4 140 (ULV) 4
amarus
Salmo gairdneri F, S 0.39 1 2.2 (EC) 12
(Rainbow trout)
Salmo salar 1.97 2 0.59 (EC) 2
------------------------------------------------------------------------------------------

Table 6. (contd.)
------------------------------------------------------------------------------------------
Species System^a LC₅₀(µg/litre) Ref. LC₅₀(µg/litre) Ref.
(Common name) tested as No. tested as No.
technical formulated
product product^b
------------------------------------------------------------------------------------------
Salmo trutta F, S - 4.7^c (EC) 11
(Brown trout)
Sarotherodon F, S 3.5 9 2.0 (EC) 9
mossambicus^e
Tilapia mossambica^e F, S - 0.8^c (EC) 13
------------------------------------------------------------------------------------------
^aF: Flow system, S: Static condition.
^bEC: 25 g a.i./litre; ULV: 1 g a.i./litre; values in a.i. equivalent obtained by
calculation.
^cLC₅₀(48-h)
^dMarine fish.
^eRiver or pond fish from tropical areas (water temperature > 24 °C).

References

(1) Knauf & Horlein (1979); (2) Zitko et al. (1979); (3) Knauf & Schulze (1977a);
(4) Gulyas & Csanyi (undated); (5) Waltersdorfer & Schulze (1976a); (6) Buccafusco et al.
(1977a); (7) Knauf & Schulze (1977b); (8) Buccafusco et al. (1977b); (9) Adeney et al.
(1980); (10) Lepailleur & Chambon (1984); (11) Lhoste et al. (1979); (12) Waltersdorfer &
Schulze (1976c); (13) Mulla et al. (1978); (14) Waltersdorfer & Schulze (1976d); (15) Knauf
& Schulze (1977b); (16) Waltersdorfer & Schulze (1976b); (17) Waltersdorfer & Schulze
(1976a); (18) Santosa & Hadi (1980); (19) Heitmuller et al. (1978); (20) Santosa (1983)

Zitko et al. (1979) established a 96-h lethal threshold for
Atlantic salmon (Salmo salar) of 1.97 µg/litre.

6.1.2 Acute toxicity for other aquatic organisms

Data on aquatic organisms other than fish are presented in
Table 7 and are of the same order as those for fish, although the
oyster (Crassostrea virginica) is somewhat more tolerant and the
Northern lobster (Homarus americanus) (96-h lethal threshold
0.0014 µg/litre) is far more sensitive (Zitko et al., 1979).

Mohsen & Mulla (1981) exposed aquatic insect larvae to
deltamethrin (as a 2.5% emulsifiable concentrate) for 1 h under
flow-through conditions, and calculated the LC₅₀after a 24-h
holding period. For the target species blackfly (Simulium
virgatum) an LC₅₀of 0.9 µg/litre was calculated. Non-target
species tested, mayfly (Baetis parvus) and caddisfly (Hydropsyche
californica), were found to be more susceptible, with LC₅₀values
of 0.4 µg/litre.

Varanka, (1987) investigated the effects of deltamethrin on
three species of freshwater mussels. Results presented in Table 8
show that the mussels are very insensitive to the pyrethroid.

Table 7. Acute toxicity of deltamethrin tested as technical or
formulated product on other aquatic organisms-lethal concentrations
expressed as µg active ingredient (a.i.)/litre (96-h)^a
-------------------------------------------------------------------
Species LC₅₀(µg/litre) LC₅₀(µg/litre)
tested as technical tested as formulated
product product^b
-------------------------------------------------------------------
Crassostrea virginica - 12.0
(Eastern oyster)
Daphnia magna 5^c -
(Water flea)
Gammarus pulex - 0.03^c
(Scud)
Penaeus duorarum - 0.35
(Pink shrimp)
Uca pugilatorulosus - 1.1
(Fiddler crab)
Bufo bufo (larvae) - 0.93
(Common toad)
-------------------------------------------------------------------
^aAdapted from: L'Hotellier & Vincent (1986).
^bEC: 25 g a.i./litre; ULV: 1 g a.i./litre; values in a.i.
equivalent obtained by calculation.
^cLC₅₀(48-h).

Table 8. Acute toxicity^aof deltamethrin formulation^bin
freshwater mussels, under static conditions at 21 - 23 °C^c
-------------------------------------------------------------------
Species 24-h 48-h 72-h 96-h 7-day
-------------------------------------------------------------------
Anodonta cygnea nd nd ~24.6 12.0 7.6

Anodonta anatina nd nd nd ~23.4 10.3

Unio pictorum nd ~31.8 9.7 7.0 6.0
-------------------------------------------------------------------
^aLC₅₀µg active ingredient (a.i.)/litre): values in a.i.
equivalent obtained by calculation.
^bULV 0.12%.
^cFrom: Varanka (1987).

6.1.3 Field studies and community effects

Two experimental pond studies have been performed. Tooby et
al. (1981) reported that application of deltamethrin to static
water at 10 g a.i./ha did not have any lethal effects on two fish
species (Canassius auratus, Rutilus rutilus) or on molluscs.
Aquatic insects and crustaceans present were killed. Rawn et al.
(1985) applied deltamethrin at a similar rate and also reported
that no fish were killed. The half-life of deltamethrin in the
pond was 2 - 4 h for water and 2 - 14 days for bottom sediment.

Neto et al. (1983) sprayed-flooded fields in Brazil, at
intervals of 2 days, with rates of deltamethrin progressively
increased at 5, 10, 12, and 13 g a.i./ha. The expected
concentrations in water from these applications were between 3 and
7 µg/litre. No mortality was recorded in fish placed in the
sprayed area in experimental cages. Slight "agitation" was
reported after exposure to the highest dose.

Impact assessments on the use of deltamethrin on paddy fields
have been made in the field in various countries throughout the
world. The maximum normal usage rate of the compound was 6.5 g
a.i./ha. In these studies, fish ( Tilapia spp., Cyprinus carpio,
Gambusia spp.) tolerated deltamethrin up to 18.75 g a.i./ha without
any adverse effects. The compound is known to be toxic for aquatic
organisms and is not recommended for use over water under any but
exceptional circumstances. However, it has been used to control
vectors of major human diseases, i.e., mosquitos and blackfly
( Elossina spp.), where benefit outweighed potential risk. In these
cases, extensive field evaluations of the environmental impact have
been made. While there have not been any instances of fish kills
from these applications, there are reports of large numbers of
deaths of aquatic invertebrates. The populations usually recovered
rapidly and all studies have shown numbers back to normal before
the compound was applied again in the following season. It is
suggested that relatively resistant parts of the population soon
recolonize the area; immigration also occurs (Takken et al., 1978;
Smies et al., 1980; Baldry et al., 1981; Everts et al., 1983).

6.1.4 Appraisal

Notwithstanding its high toxicity for fish and crustacea, the
results of many studies, as well as the wide use of deltamethrin
for several years, have confirmed that its normal use does not
cause significant mortality in fish populations. This difference
is due to its strong adsorption on soil and its rapid breakdown,
decreasing its bioavailability under field conditions.

6.2 Terrestrial Organisms

6.2.1 Plants

Hargreaves & Cooper (1979) sprayed glasshouse-grown tomato
seedlings with 50 mg deltamethrin/litre (2.5% emulsifiable
concentrate) 3 weeks after emergence and again 7 days later. Three
days after the second application, plants were examined for damage.
No damage was found and, at this rate of use, deltamethrin was not
phytotoxic.

6.2.2 Soil microorganisms

In a study by Tu (1980) on the effects of 5 pyrethroids on
microbial populations and their activity in soil, 0.5 mg
deltamethrin/kg incorporated into sandy loams (residues under
normal use conditions would be of the order of < 0.001 mg/kg)
produced only a few transient effects. No effects were noted on

the nitrifying microorganisms and their capacity to produce nitrate
and there were no inhibitory effects on deshydrogenase or urease
activity. Deltamethrin induced an increase in oxygen consumption
because of an increase in microbial respiration (probably linked
with the microbial degradation of deltamethrin). It also
stimulated the growth of soil fungi and inhibited the development
of bacteria. Four weeks after treatment, deltamethrin-treated soil
recovered completely and microorganism activity was equal to that
in untreated soil.

6.2.3 Soil fauna

6.2.3.1 Earthworms

When deltamethrin at 12.5 g a.i./ha (high agricultural dose)
was incorporated into the soil to a depth of 1 cm, there were no
toxic effects on earthworms (Lumbricus terrestris) during an
observation period of 28 days (Bouche & Fayolle, 1979). However,
significant toxic effects on earthworms were observed at levels of
60 - 125 g a.i./ha (5 - 10 times the highest rates applied in
agriculture).

In another study with Eisenia foetida andrei, deltamethrin
incorporated in artificial soil at concentrations of 1.7 mg/kg and
10 mg/kg did not produce any lethal effects (Chambon & Lepailleur,
1984).

6.2.3.2 Slugs

Lettuce leaves treated with 4 times normal dosage rates, were
fed to slugs ( Agrolimax sp.). Leaves were quickly consumed but no
toxic effects (mortality or activity) were observed (Ricou, 1978).

6.2.3.3 Soil arthropods

Under laboratory conditions, deltamethrin, applied topically
and by immersion, was very toxic for the carabid beetle
Pterostichus melanarius (Illiger). Under natural conditions in the
field, deltamethrin applied at normal dose rates was not toxic for
these organisms (Dunning et al., 1981).

Everts et al. (1985) monitored the effects, on non-target
organisms, of various compounds when used for the control of tsetse
fly in the Ivory Coast in Africa. Deltamethrin was the most
effective compound against the tsetse and also killed non-target
musca flies. After deltamethrin spraying, Orthoptera and
Proctotrupoidea were also significantly decreased while Nematocera
increased in number. The results of this study suggest that ground
spraying of the pyrethroid had greater effects on terrestrial
arthropods than aerial applications.

Concurrent laboratory and field studies were conducted on the
effects of deltamethrin on beneficial predatory spiders in a polder
area of the Netherlands (Everts et al., 1988). During two growing
seasons, 2800 samples were taken over an area of 17 different

fields. The authors found that effects on spiders were eliminated
when it rained soon after application, since the effect of the
pyrethroid appeared to be indirect, causing the dehydration of
spiders. This different response under dry and damp conditions was
confirmed in the laboratory. However, reduction of spider numbers
in the field was much greater than predicted from laboratory tests
and recovery was more rapid in laboratory populations than in field
populations. The uptake and effects of deltamethrin were greater
through exposure to residues than through contact or oral exposure.
There was a positive correlation between temperature and the
toxicity of deltamethrin for spiders in the field. This contrasted
with reports of a negative correlation for target insects reported
in the literature. Laboratory studies showed that the negative
temperature effect only occurred when spiders could not drink. It
appeared that qualitative prediction from laboratory to field was
possible but that quantitative prediction was not.

6.2.4 Beneficial insects

6.2.4.1 Honey-bees

Single applications of deltamethrin are highly toxic for honey-
bees (Apis mellifera). Stevenson et al (1978) found a contact LD₅₀
of 0.051 µg/bee and an oral LD₅₀of 0.079 µg/bee.

Arzone & Vidano (1978) did not find any difference in mortality
between controls and bees fed on sugar solutions containing 0.2 µg
deltamethrin/litre. Increased mortality was recorded at all higher
exposures reaching 100% within 1 h at a concentration of 12.5
µg/litre.

In the field, direct treatment of caged bees caused a high
mortality rate with doses of from 11.2 g/ha upwards (Atkins et al.,
1976). Rape flowers were treated at a rate of 0.75 g a.i./100
litre and 1.5 g a.i./100 litre with an emulsifiable concentrate
formulation, 25 g/litre; control plots were treated with water.
Cages (3 x 2 x 2 m) containing a small hive (2 frames + open brood)
were put over the treated flowers once the spray had dried. The
mortality of the bees was then assessed over 7 days. The average
mortalities were not significantly higher in the treated plots than
in water-sprayed control plots (Louveaux et al., 1977).

However, Bocquet et al. (1980, 1983) demonstrated, after 3
years of field experiments, that deltamethrin under field
conditions was innocuous at doses up to 12.5 g/ha. They also noted
a repellant effect by the formulating materials, which lasted for
2 - 3 h. Further studies have been reported by Florelli et al.
(1987a,b).

6.2.4.2 Foliar insects

Deltamethrin was 70 times more toxic to the tobacco budworm
(Heliothis virescens) than to its predator, green lacewing

(Chrysopa carnea), but it was only 1.25 times more toxic to the
tobacco budworm than to its parasite (Campoletis sonorensis) (Plapp
& Bull, 1978).

In an apple orchard, where deltamethrin was applied at
12.5 mg/kg, no predatory mites (Typhlodromus pyri) were found
during 10 weeks of observation, but spider mites (Paponychus ulmi)
were not affected. The elimination of the predatory mite led to a
marked increase in spider mite populations, later in the same
season (Aliniazee & Cranham, 1980).

The impact of deltamethrin used against the English grain aphid
(Sitobion avenae) was studied in 1983, 1984, and 1985 in the Paris
basin. This study was carried out on wheat with pitfall traps,
yellow water traps, suction sampling (D-vac), and sampling of ears.
Effects were noted on: S. avenae, phytophagous Diptera (Opimyza
florum, Phytomyza nigra, and Oscinella frit), Homoptera (Zyginidia
scutellaris, Metopolophium dirhodum), Thysanoptera (Limothrips
cerealium, Acolothrips intermedius), predatory Diptera (Empididae,
Dolichopodidae), and on spiders (Erigonidae, Lycosidae,
Linyphiidae, Theridiidae). The detritiphagous insects (Sciaridae,
Chironomidae), the Carabidae and Staphylinidae and most
microhymenoptera showed little or no difference after treatment.
During the 3 years, no differences were observed from year to year
as a result of field treatment, populations appearing homogeneous
at the beginning of each trial (Fischer & Chambon, 1987).

A large-scale field trial was carried out in 1984 in southern
England to investigate the side-effects of deltamethrin on non-
target arthropods in winter wheat. The insecticides were applied
in June and two methods, suction sampling (D-vac) and quadrats,
were used to sample the arthropods for up to 75 days after
treatment. During the post-treatment period, the numbers of
Carabidae and Staphylinidae adults found in D-vac samples were
reduced by 22% and 20%, respectively, compared with the controls
(Vickerman et al., 1987a).

In the same field trial, arthropods were sampled with a D-vac
for 11 weeks. Total numbers were similar in the control and
deltamethrin-treated plots. The numbers of Empididae were reduced
by deltamethrin, but Dolichopodidae were more numerous in treated
than in control plots. The numbers of Aphidius spp. were higher in
the deltamethrin-treated plots than in the control plots. The
numbers of Coccinellidae larvae were reduced (Vickerman et al.,
1987b).

6.2.5 Birds

6.2.5.1 Laboratory studies

Data on the acute toxicity of deltamethrin for birds are given
in Table 9.

Table 9. Acute toxicity of deltamethrin for birds
---------------------------------------------------------------------------
Species Sex Application LD₅₀(mg/kg) Reference
---------------------------------------------------------------------------
Red partridge male & oral >3000 Grolleau & Griban,
(Alectonis tufa) female 1976b
Grey partridge male & oral >1800 Grolleau & Griban,
(Perdix perdix) female 1976b
Chicken oral >1000 Grandadam, 1976
(Gallus domestica)
Hen adult oral >2500 Ross et al., 1978
female
Mallard duck oral >4640 Beavers & Fink,
(Anas platyrhynchos) 1977a
Game duck oral >4000 Grolleau & Griban,
1976a
---------------------------------------------------------------------------

The toxicity of deltamethrin for birds is very low. Both
technical grade and commercially formulated deltamethrin
administered in feed at 100 mg/kg diet was not palatable to
Japanese quail (Coturnix coturnix japonica), with strong individual
variations. Unpalatability diminished after repeated exposure and
even became reversed in the case of the purified deltamethrin,
which attracted quail already suffering from toxic effects (David,
1981).

Groups of 39 female Japanese quail (Coturnix coturnix japonica)
were given daily doses of 0, 0.2, or 1 mg technical deltamethrin
per animal, by gavage, over 34 days. No significant effects were
observed on reproduction (De Lavaur et al., 1985).

6.2.5.2 Field studies on birds

The low toxicity of deltamethrin for birds, indicated by
laboratory studies, has been confirmed in the field. In studies on
the ecological consequences of the use of the compound to control
tsetse fly (Takken et al., 1978) and blackfly (Smies et al., 1980)
in West Africa, populations of various species of insectivorous,
granivorous, and piscivorous birds were examined before and after
spraying. There were no indications of any effects on either
numbers or species diversity.

7. EFFECTS ON EXPERIMENTAL ANIMALS AND IN VITRO TEST SYSTEMS

7.1 Single Exposures

Tables 10 and 11 show the results of acute toxicity studies on
various animal species. From these tables, it is clear that the
vehicle has a great influence on the LD₅₀, probably by influencing
absorption. Powder formulations and aqueous suspensions are
significantly less toxic than formulations in oils or organic
solvents (Pham Huu Chanh et al., 1984).

The acute oral toxicity of deltamethrin for rats produced such
symptoms as: staining of the fur, excessive grooming, salivation,
diarrhoea, drowsiness, weakness, dyspnoea, piloerection, ptosis,
difficulty in walking, general motor incoordination, hypotonia,
choreoathetosis, clonic seizures, and death (Glomot, 1979; Glomot
et al., 1979, 1981a; Kavlock et al., 1979; Ray & Cremer, 1979; Pham
Huu Chanh et al., 1984). Electroencephalogram (EEG) records showed
generalized spike discharges prior to choreoathetosis (Ray &
Cremer, 1979; Ray, 1980).

Mice presented far fewer symptoms than rats after oral dosing
at comparable levels, diarrhoea being the only reportable
observation (Glomot et al., 1980a).

Rats were injected intraperitoneally with ¹⁴C-labelled
deltamethrin at the threshold doses required to produce the motor
symptoms of toxicity of tremor and choreoathetosis. Blood and brain
samples were analysed for their total radiolabel content, and were
also extracted with ethyl acetate to determine the levels of
extractable parent deltamethrin and 3-phenoxybenzyl-derived acid and
the residual radiolabel after this extraction. There was a clear
correlation between onset of symptoms and blood and brain levels of
deltamethrin. It was found that certain threshold levels of parent
deltamethrin in the blood and brain were required for symptoms
development, and that the symptoms persisted for as long as this
threshold was maintained (Rickard & Brodie, 1985).

7.1.1 Mouse

Mice intravenously injected with deltamethrin showed intense
tremors, convulsions, and ataxia, immediately after administration.
Tachycardia and respiratory defects were also observed at higher
dosages. Surviving animals appeared normal after 4 - 5 h.
Immediately after intraperitoneal injection, jumping movements,
slight convulsions and prostration, ptosis, tail hypertonicity, and
cyanosis were observed. These toxic signs disappeared after 72 h
in surviving animals.

Animals administered deltamethrin by gavage showed muscular
stiffening and convulsions, 1 h after dosing. After 24 h,
hypermotility, stereotype movements of the head, tachycardia,
hypertonicity of the tail, and a few convulsions were observed.
Behaviour and appearance were normal again after 48 h (Glomot &
Chevalier, 1976a,c).

Table 10. Acute toxicity of technical grade deltamethrin
--------------------------------------------------------------------------------------------------------------
Species Sex Route Vehicle LD₅₀(mg/kg Reference
body weight)
--------------------------------------------------------------------------------------------------------------
Rat male oral sesame oil 128 Glomot & Chevalier (1976a)
female 139
male PEG 200 67
female 86

Rat male adult peanut oil 52 Kavlock et al. (1979)
female adult 31
female weanling 50

Rat male adult peanut oil 53 Gaines & Linder (1986)
female adult 30
female weanling 48

Rat male + female aqueous suspension > 5000 Audegond et al. (1981)
with carboxy- (no mortality)
methylcellulose

Rat dermal - 700 Panshina & Sasinovich (1983)

Rat male methylcellulose (1%) > 2940 Kynoch et al. (1979)
female

Rat female adult xylene > 800 Kavlock et al. (1979)

Rat male + female inhalation (6 h) dust 600 mg/m³ Coombs & Clark (1978)

Rat male adult (2 h) DMSO 10% aerosol 940 mg/m³ Kavlock et al. (1979)
female adult > 785 mg/m³

Rat male + female (1 h) micronized powder > 4620 mg/m³ Jackson & Hardy (1986)

Rat intraperitoneal - 58.8 Panshina & Sasinovich (1983)

Rat male intraperitoneal sesame oil 209 Glomot & Chevalier (1976b)
female 186
male PEG 200 24 Glomot & Chevalier (1976b)
female 25
--------------------------------------------------------------------------------------------------------------

Table 10. (contd.)
--------------------------------------------------------------------------------------------------------------
Species Sex Route Vehicle LD₅₀(mg/kg Reference
body weight)
--------------------------------------------------------------------------------------------------------------
Rat male intravenous PEG 200 3.3 Glomot & Chevalier, (1976c)
female 3.3
Rat female adult acetone 4 Kavlock et al. (1979)
female weanling 1.8

Mouse male oral sesame oil 33 Glomot & Chevalier (1976a)
female 34
male PEG 200 21 Glomot & Chevalier (1976a)
female 19

Mouse intraperitoneal - 33 Panshina & Sasinovich (1983)

Mouse male intraperitoneal sesame oil 171 Glomot & Chevalier (1976b)
female 166

Mouse male PEG 200 18 Glomot & Chevalier (1976b)
female 12

Mouse male PEG 200 4.1 Glomot & Chevalier (1976c)
female 4.0

Mouse male glycerol formal 5 Glomot & Chevalier (1976c)
female 5.8

Dog male + female oral in capsules >300 Glomot et al. (1977)
no mortality

Dog male + female PEG 200 2 Glomot & Chevalier (1976c)

Rabbit male dermal PEG 400 > 2000 Clair (1977)
female > 2000
--------------------------------------------------------------------------------------------------------------

Table 11. Acute toxicity of some formulations
--------------------------------------------------------------------------------------------------------------
Species Sex Route Formulation LD₅₀(mg/kg Reference
body weight)
--------------------------------------------------------------------------------------------------------------
Rat male, female oral 2.5% flowable formulation 22 000 Glomot et al. (1979)

Rat male, female oral 2.5% wettable powder >15 000 Glomot (1979)

Mouse male, female oral 2.5% wettable powder >15 000 Glomot et al. (1980a)

Dog male, female oral 2.5% wettable powder >10 000 Glomot et al. (1980b)

Rat male, female oral 2.5% emulsifiable concentrate 535 Coquet (1977)

Rat male, female oral 10 g/litre ULV >6 470 Coquet (1977)

Rat male, female inhalation (4 h) aerosol-2.5% wettable powder >2 800 mg/m³ Clark et al. (1980)
--------------------------------------------------------------------------------------------------------------
7.1.2 Rats

Rats intravenously injected with deltamethrin showed muscular
contractions, piloerection, respiratory defects, convulsions, and
paresis of the hind quarters, immediately following treatment.
Surviving animals showed normal behaviour after 48 h. Immediately
after intraperitoneal injection, tremor, convulsions, prostration,
and cyanosis were observed. These toxic signs disappeared after
48 h in surviving animals. Animals administered deltamethrin by
gavage showed motor incoordination, convulsions, respiratory
defects, and hypomotility, shortly after dosing. Normal behaviour
was observed after 3 days (Glomot & Chevalier, 1976c).

In an inhalation study (whole body exposure for 6 h),
hyperactivity, grooming, and irritation were observed during
exposure. The animals were hypersensitive to touch and noise and
showed uncoordinated movements. Gross pathological investigation
showed a gas-filled stomach and small intestine, and massive
haemorrhage and degeneration in the lung (Coombs & Clark, 1978).

Rats were exposed (whole body exposure) for 4 h to an aerosol
concentration of deltamethrin equal to 2.8 g/m³, the highest
attainable airborne concentration of a 2.5% wettable powder
formulation. Approximately 80% of the total aerosol had a mean
aerodynamic diameter of less than 5.5 µm. Dyspnoea and gasping
were observed in exposed rats. Relative lung weights and
macroscopic pathology were normal. There was no mortality (Clark
et al., 1980).

7.1.3 Rabbit

Rabbits (10 males and 10 females) were treated with 2 g
deltamethrin in 2 ml PEG 400 per kg body weight on 80 cm²of
occluded shaved skin for 24 h. The animals were observed for 14
days. Two animals showed obvious erythema. No body weight changes
or abnormal behaviour were observed. On histological observation
of the liver, kidneys, and skin, small changes were observed, but
these were common for this strain of rabbit and not related to
treatment (Clair, 1977).

7.1.4 Dog

Dogs given oral doses of 100 mg deltamethrin/kg body weight or
more showed transient hyperexcitability, akinesia, vomiting, and
stiffness of the hind legs (Glomot et al., 1977).

Dogs orally dosed with 10.0 mg deltamethrin/kg body weight did
not display any clinical signs related to treatment (Glomot et al.,
1980b).

7.2 Irritation and Sensitization

7.2.1 Skin irritation

Male albino rabbits (12 per group) weighing 2.5 - 3.5 kg were
administered 0.5 g deltamethrin on either shaved intact or abraded
skin. The occlusive patch was fixed on the skin for 23 h.

Technical deltamethrin (98% purity) did not produce any irritant
effects (Coquet, 1976a).

Male albino rabbits (6) weighing 2.5 - 2.9 kg were administered
0.5 ml of formulated deltamethrin (25 g/litre flowable suspension
concentrate) to both shaved intact and abraded skin. The Primary
Irritation Index after 24 h exposure of occluded sites was 1.2,
i.e., slightly irritating (Glomot et al., 1981b).

An evaluation similar to the one described above was carried out
for a 2.5% wettable powder concentrate deltamethrin formulation.
Rabbits had a Primary Irritation Index of 2.41, i.e., moderately
irritating. Moderate erythema continued for 72 h, while the oedema
generally diminished, with the exception of scarified skin sites
(Glomot et al., 1981c).

The skin irritation potentials of Decis emulsifiable
concentrate 2.5% and Decis Flowable 2.5% were studied on rabbits
and guinea-pigs with 0.05, 0.10, 0.5, 1, and 2.5% deltamethrin.
The threshold irritative levels were 0.05% for Decis emulsifiable
concentrate and 2.5% for Decis Flowable. The intensity of
irritation depended on the relative content of organic solvents and
emulsifiers in the trade products. The water-soluble concentrate
of Decis 2.5% caused negligible risk of contact irritative
dermatitis (Bainova & Kaloyanova, 1985).

7.2.2 Eye irritation

Deltamethrin (0.1 g/animal) was administered into the
conjunctival sac of the eyes of 6 male albino rabbits, weighing
2.5 kg, with or without rinsing 60 seconds after instillation.
Deltamethrin produced transient irritating effects, both with and
without rinsing (Coquet, 1976b).

Male albino rats (9) weighing between 2 and 3 kg were
administered 0.1 ml of formulated deltamethrin (25 g/litre flowable
suspension concentrate) in the conjunctival sac. Six of the
treated eyes remained unwashed, while the remaining three were
rinsed with lukewarm water 20 - 30 seconds after instillation.
There was only transient clouding of the cornea in 2 animals 1 h
after dosing (1 washed, 1 unwashed), which cleared by day 2. Low
grade conjunctival irritation was noted among all animals
initially, which disappeared following day 2 of observations
(Glomot et al., 1981d).

A 2.5% deltamethrin formulation diluted 1/10 in distilled water
(0.1 ml per rabbit) elicited a similar pattern of initial transient
corneal clouding in 3 out of 9 rabbits examined, which cleared by
day 4. The undiluted formulation (100 mg) administered in the
conjunctival sac of rabbits produced increased involvement of the
conjunctiva, iris, and cornea in all animals, generally moderate in
severity, with low grade corneal opacity persisting in 2 rabbits
until day 7 (1 washed, 1 unwashed) (Glomot et al., 1981e).

7.2.3 Sensitization

Deltamethrin (0.5 g/animal) was applied topically to the skin
of albino guinea-pigs (10 male and female) 3 times per week, with a
2-day interval for 3 weeks, and once at the start of the fourth
week. The preparation was covered with an occlusive patch for
48 h. On days 1 and 10, the guinea-pigs received an intradermal
injection of 0.1 ml of Freund's adjuvant. The animals were
challenged 12 days after the last application with 0.5 g
deltamethrin. No sensitization was found (Guillot & Guilaine,
1977).

7.3 Short-Term Exposure

7.3.1 Rat

Male and female weanling Sprague-Dawley rats (20 of each sex
per group) were dosed (by gavage) with 0, 0.1, 1, 2.5, or 10 mg
deltamethrin in PEG 200/kg body weight per day for 13 weeks. No
treatment-related effects were observed on food and water
consumption, mortality, urinalysis, and haematology. Neurological
examinations and ophthalmoscopy did not reveal any abnormalities.
At the highest dose level, a slight hyperexcitibility was observed
among some rats in week 6. Lower body weight gain was noted in
males at 2.5 and 10 mg/kg. No clear treatment-related effects were
noted in the results of laboratory investigations or on the weights
of the organs. Gross and microscopic examination of a variety of
tissues and organs did not show any treatment-related findings.
Following the 13-week dosage period, 5 males and 5 females per
group were allowed to recover for 4 weeks. No evidence of
hyperexcitability was observed among the rats; body weight gain was
slightly higher in the treated groups than in the controls. The
no-observed-effect level was 1 mg/kg body weight (Hunter et al.,
1977).

Four groups of CD rats (8 of each sex per group) were exposed to
aerosolized deltamethrin (technical grade powder) for 6 h per day, 5
days a week, for 2 weeks, and for 4 days during a third week. Mean
aerosol concentrations were 3, 9.6, and 56.3 mg a.i./m³ with
about 87% of respirable particles (diameter lower than 5.5 µm). No
rats died as a result of exposure. Signs of irritation (agitated
grooming and ptyalism due to the powder were noted in all groups
during exposure, with more pronounced toxic signs (ataxia and
walking with arched backs) in the group receiving the highest dose
tested. Male rats also showed a reduced body weight (-5%) in all
groups. An elevation of the serum sodium ion content was noted at
the two highest doses. No increased incidence of any particular
lesion was observed in the high-dose group compared with the control
group. Irritation and weight loss were only slight at 3 mg/m³and
this can be considered as a no-effect level (Coombs et al., 1978).

7.3.2 Dog

Male and female beagle dogs (3 - 5/sex per group), 25 weeks of
age, received a daily oral dose of 0, 0.1, 1, 2.5, or 10 mg
deltamethrin/kg body weight in PEG 200 in gelatin capsules over 13
weeks. All treated groups showed reduced body weight gain, but
this was not dose-related. Liquid faeces were associated with all
groups of treated dogs throughout the dosing period. Dilatation of
the pupils was seen in dogs receiving 2.5 and 10 mg/kg per day.
The sign was first seen 4 - 7 h after dosing and persisted
throughout the day. The incidence of vomiting increased dose-
dependently in all treated groups, except the group receiving
0.1 mg/kg. In the highest dose group, unsteadiness, body tremors,
and jerking movements were seen, particularly in males, in weeks 2,
3, and 4. Excessive salivation was seen initially and diminished
during the dosing period. After 5 and 12 weeks, depression of the
gag reflex was noted in a proportion of animals in all treated
groups. However, this was not considered to be of toxicological
significance. Exaggeration or depression of the patellar reflex
was observed in some animals in all treated groups after 5 and 12
w