Aldrin and Dieldrin (EHC 91, 1989)

INTERNATIONAL PROGRAMME ON CHEMICAL SAFETY

ENVIRONMENTAL HEALTH CRITERIA 91

ALDRIN AND DIELDRIN

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, 1989

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WHO Library Cataloguing in Publication Data

Aldrin and Dieldrin.

(Environmental health criteria ; 91)

1.Aldrin 2.Dieldrin I.Series

ISBN 92 4 154291 8 (NLM Classification: WA 240)
ISSN 0250-863X

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CONTENTS

ENVIRONMENTAL HEALTH CRITERIA FOR ALDRIN AND DIELDRIN

1. SUMMARY

1.1. General
1.2. Environmental transport, distribution, and transformation
1.3. Environmental levels and human exposure
1.4. Kinetics and metabolism
1.5. Effects on organisms in the environment
1.5.1. Accumulation
1.5.2. Toxicity for microorganisms
1.5.3. Toxicity for aquatic organisms
1.5.4. Toxicity for terrestrial organisms
1.5.5. Population and ecosystem effects
1.6. Effects on experimental animals and in vitro test systems
1.7. Effects on man

2. IDENTITY, PHYSICAL AND CHEMICAL PROPERTIES, ANALYTICAL METHODS

2.1. Identity
2.1.1. Primary constituent: aldrin
2.1.2. Primary constituent: dieldrin
2.2. Physical and chemical properties
2.2.1. Aldrin
2.2.2. Dieldrin
2.3. Analytical methods
2.3.1. Sampling methods
2.3.2. Analytical methods

3. SOURCES OF HUMAN AND ENVIRONMENTAL EXPOSURE

3.1. Natural occurrence
3.2. Man-made sources
3.2.1. Production levels and processes; uses
3.2.1.1 World production figures
3.2.1.2 Manufacturing processes
3.2.1.3 Release into the environment during
normal production
3.2.2. Uses
3.2.2.1 Aldrin
3.2.2.2 Dieldrin

4. ENVIRONMENTAL TRANSPORT, DISTRIBUTION, AND TRANSFORMATION

4.1. Transport and distribution between media
4.1.1. Leaching of aldrin and dieldrin
4.1.2. Surface run-off

4.1.3. Loss of aldrin and dieldrin from soils -
volatilization
4.1.3.1 Movement within the soil profile - mass
flow
4.1.3.2 Movement within the soil profile -
diffusion
4.1.3.3 Actual volatilization losses - laboratory
studies
4.1.3.4 Actual volatilization losses - field
studies
4.1.4. Losses of residues following treatment of soil
with aldrin
4.1.5. Losses of residues from water
4.1.6. Aldrin and dieldrin in the atmosphere
4.1.7. Aldrin and dieldrin in water
4.2. Translocation from soil into plants
4.3. Models of the behaviour of water and chemicals in soil
4.4. Biodegradation of aldrin and dieldrin
4.4.1. Epoxidation of aldrin
4.4.2. Other metabolic pathways of aldrin
4.4.3. Biotransformation of dieldrin
4.4.4. Conclusions
4.5. Abiotic degradation
4.5.1. Photochemistry
4.5.1.1 Photochemistry of aldrin and dieldrin in
water
4.5.1.2 Photochemistry of aldrin and dieldrin in
air
4.5.1.3 Photochemistry of aldrin and dieldrin on
plant surfaces
4.5.1.4 Photochemistry of aldrin and dieldrin in
soils
4.5.1.5 Conclusions
4.5.2. Other abiotic processes
4.5.2.1 Reaction with ozone
4.5.2.2 Clay-catalysed decomposition
4.6. Bioaccumulation
4.7. The fate of aldrin and dieldrin in the environment
4.7.1. Aldrin and dieldrin in soils
4.7.2. Aldrin and dieldrin in the atmosphere
4.7.3. Conclusion

5. ENVIRONMENTAL LEVELS AND HUMAN EXPOSURE

5.1. Environmental levels
5.1.1. Air and rainwater
5.1.1.1 Aldrin
5.1.1.2 Dieldrin
5.1.2. Concentrations in houses
5.1.2.1 Aldrin used for subterranean termite
control
5.1.2.2 Aldrin and dieldrin used for remedial
treatment of wood
5.1.3. Aquatic environment
5.1.4. Soil

5.1.5. Drinking-water
5.1.6. Food and feed
5.1.6.1 Joint FAO/WHO food contamination
monitoring programme
5.1.6.2 Information summarized by GIFAP (1984)
5.1.6.3 United Kingdom (UK MAFF, 1983-1985)
5.1.6.4 USA
5.1.6.5 Appraisal of intake studies
5.1.7. Concentrations of dieldrin in non-target species
5.1.7.1 Occurrence of dieldrin in birds of prey
and fish-eating birds
5.2. General population exposure
5.2.1. Adults
5.2.1.1 Aldrin
5.2.1.2 Concentrations of dieldrin in adipose
tissue
5.2.1.3 Concentrations of dieldrin in blood
5.2.1.4 Concentrations of dieldrin in other
tissues
5.2.2. Babies, infants, and mother's milk

6. KINETICS AND METABOLISM

6.1. Absorption
6.1.1. Aldrin
6.1.1.1 Ingestion
6.1.1.2 Inhalation
6.1.2. Dieldrin
6.1.3. Photodieldrin (and other metabolites of dieldrin)
6.2. Distribution
6.2.1. Aldrin
6.2.1.1 Mouse
6.2.1.2 Rat
6.2.1.3 Dog
6.2.1.4 Human studies
6.2.2. Dieldrin
6.2.2.1 Laboratory animals
6.2.2.2 Transplacental transport
6.2.2.3 Domestic animals
6.2.2.4 Human volunteers
6.2.2.5 General population
6.2.3. Photodieldrin (and major metabolites of dieldrin)
6.2.3.1 Laboratory animals
6.2.3.2 Human beings
6.3. Metabolic transformation
6.3.1. Aldrin and dieldrin
6.3.1.1 Laboratory animals
6.3.1.2 Human studies
6.3.1.3 Non-domestic organisms
6.3.2. Photodieldrin (and major metabolites of dieldrin)
6.3.2.1 Rat
6.3.2.2 Monkey
6.4. Elimination and excretion
6.4.1. Aldrin
6.4.1.1 Rat

6.4.2. Dieldrin
6.4.2.1 Laboratory animals
6.4.2.2 Human studies
6.4.3. Photodieldrin (and major metabolites of dieldrin)
6.4.3.1 Rat
6.4.3.2 Monkey
6.5. Retention and turnover
6.5.1. Non-domestic organisms
6.5.2. Biological half-life in human beings
6.5.3. Body burden and (critical) organ burden; indicator
media
6.6. Appraisal

7. EFFECTS ON ORGANISMS IN THE ENVIRONMENT

7.1. Microorganisms
7.2. Aquatic organisms
7.2.1. Aquatic invertebrates
7.2.1.1 Acute toxicity
7.2.1.2 Short-term toxicity, reproduction, and
behaviour
7.2.2. Fish
7.2.2.1 Acute toxicity
7.2.2.2 Long-term toxicity
7.2.2.3 Reproduction
7.2.3. Amphibia and reptiles
7.3. Terrestrial organisms
7.3.1. Higher plants
7.3.2. Earthworms
7.3.3. Bees and other beneficial insects
7.3.4. Birds
7.3.4.1 Acute toxicity
7.3.4.2 Short- and long-term toxicity
7.3.4.3 Reproductive studies
7.3.4.4 Eggshell thinning
7.3.4.5 Concentrations of dieldrin in tissues of
experimentally poisoned birds
7.3.5. Mammals
7.4. Effect on populations and ecosystems
7.4.1. Exposure to dieldrin
7.4.2. Effects on populations of birds
7.4.3. Effects on populations of mammals

8. EFFECTS ON EXPERIMENTAL ANIMALS AND IN VITRO TEST SYSTEMS

8.1. Single exposures
8.1.1. Aldrin and dieldrin
8.1.1.1 Oral
8.1.1.2 Dermal
8.1.1.3 Inhalation
8.1.1.4 Parenteral
8.1.2. Formulated materials
8.1.2.1 Oral and dermal
8.1.2.2 Inhalation

8.2. Short-term exposures
8.2.1. Oral
8.2.1.1 Rat
8.2.1.2 Dog
8.2.1.3 Domestic animals
8.2.2. Dermal
8.2.3. Inhalation
8.3. Skin and eye irritation; sensitization
8.3.1. Skin and eye irritation
8.3.2. Sensitization
8.4. Long-term toxicity and carcinogenicity
8.4.1. Mouse
8.4.1.1 Appraisal
8.4.2. Rat
8.4.2.1 Appraisal
8.4.3. Hamster
8.4.4. Monkey
8.4.5. Mode of action
8.5. Reproduction, embryotoxicity, and teratogenicity
8.5.1. Reproduction
8.5.1.1 Mouse
8.5.1.2 Rat
8.5.1.3 Dog
8.5.1.4 Appraisal
8.5.2. Embryotoxicity and teratogenicity
8.5.2.1 Mouse
8.5.2.2 Rat
8.5.2.3 Hamster
8.5.2.4 Rabbit
8.5.2.5 Appraisal
8.6. Mutagenicity and related end-points
8.6.1. Microorganisms
8.6.2. Mammalian cell point mutations
8.6.3. Dominant lethal assays and heritable translocation
assays in mice
8.6.4. Micronucleus test
8.6.5. Chromosome and cytogenicity studies
8.6.6. Host-mediated assays
8.6.7. Cell transformation in mammalian cell systems
8.6.8. Drosophila melanogaster and other insect systems
8.6.9. Effects on DNA
8.6.10. Cell to cell communication
8.6.11. Appraisal
8.7. Special studies
8.7.1. Liver enzyme induction
8.7.2. Nervous system
8.7.2.1 Rat
8.7.2.2 Dog
8.7.2.3 Monkey
8.7.3. Weight loss and stress
8.7.3.1 Rat
8.7.4. Immunosuppressive action
8.8. Toxicity of photodieldrin and major metabolites

8.8.1. Photodieldrin
8.8.1.1 Acute toxicity
8.8.1.2 Short-term toxicity
8.8.1.3 Long-term toxicity
8.8.1.4 Reproduction, embryotoxicity, and
teratogenicity
8.8.1.5 Appraisal
8.8.2. Major metabolites of dieldrin
8.8.2.1 Acute toxicity
8.8.2.2 Short-term toxicity
8.9. Mechanisms of toxicity; mode of action
8.9.1. Central nervous system
8.9.2. Liver

9. EFFECTS ON HUMAN BEINGS

9.1. General population exposure
9.1.1. Acute toxicity - poisoning incidents
9.1.2. Effects of short- and long-term exposure -
controlled human studies
9.1.2.1 Accidental poisoning
9.1.2.2 Controlled human studies
9.1.3. Tissue concentrations of dieldrin in hospitalized
people
9.1.3.1 Pathological findings
9.1.3.2 Influence of weight loss and stress on
dieldrin concentrations in tissues
9.1.4. Exposure in treated homes
9.2. Occupational exposure
9.2.1. Acute toxicity - poisoning incidents
9.2.1.1 Blood levels diagnostic of
aldrin/dieldrin poisoning
9.2.1.2 Electroencephalography
9.2.2. Effects of short- and long-term exposure
9.2.3. Epidemiological studies

10. EVALUATION OF HUMAN HEALTH RISKS AND EFFECTS ON THE
ENVIRONMENT

10.1. Evaluation of human health risks
10.2. Evaluation of effects on the environment
10.3. Conclusions

11. RECOMMENDATIONS

12. PREVIOUS EVALUATIONS BY INTERNATIONAL BODIES

REFERENCES

APPENDIX I. NOMENCLATURE

FRENCH TRANSLATION OF SUMMARY, EVALUATION, AND RECOMMENDATIONS

WHO TASK GROUP ON ALDRIN AND DIELDRIN

Members

Dr G. Burin, Office of Pesticide Programs, US Environmental
Protection Agency, Washington DC, USA

Dr I. Desi, Department of Hygiene and Epidemiology, University
Medical School, Szeged, Hungary (Vice-Chairman)

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

Dr R. Goulding, Guy's Hospital, London, United Kingdom (Chairman)

Dr A. Furtado Rahde, Ministry of Public Health, Porto Alegre,
Brazil

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

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

Dr H.G.S. Van Raalte, The Hague, Netherlands

Observers

Dr R. Rimpau, European Chemical Industry, Ecology and Toxicology
Centre, Brussels, Belgium

Dr R.C. Tincknell, International Group of National Associations of
Agrochemical Manufacturers, Brussels, Belgium

Dr H.G.S. Van Raalte, International Commission on Occupational
Health, Geneva

Secretariat

Dr J.R.P. Cabral, International Agency for Research on Cancer,
Lyons, France

Dr J. Copplestone, Pesticide Development and Safe Use Unit, World
Health Organization, Geneva, Switzerland

Dr M. Gilbert, International Programme on Chemical Safety, World
Health Organization, Geneva, Switzerland

Ms B. Goelzer, Office of Occupational Health, World Health
Organization, Geneva, Switzerland

Dr H. Galal Gorchev, Food Safety Unit, World Health Organization,
Geneva, Switzerland

Secretariat (contd.)

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

Dr G.J. van Esch, Bilthoven, Netherlands (Rapporteur)

Dr N. Watfa, Safety and Health Branch, International Labour Office,
Geneva, Switzerland

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).

* * *

The proprietary information contained in this document cannot
replace documentation for registration purposes because the latter
has to be closely linked to the source, the manufacturing route,
and the purity/impurities of the substance to be registered. The
data should be used in accordance with paragraphs 82 - 84 and
recommendations paragraph 90 of the Second FAO Government
Consultation (FAO, 1982).

ENVIRONMENTAL HEALTH CRITERIA FOR ALDRIN AND DIELDRIN

A WHO Task Group on Environmental Health Criteria for Aldrin
and Dieldrin met in Geneva from 13 to 17 July 1987. Dr K.W. Jager,
IPCS, opened the meeting and welcomed the participants on behalf
of the heads of the three IPCS cooperating organizations
(UNEP/ILO/WHO). The group reviewed and revised the draft criteria
document and made an evaluation of the risks for human health and
the environment from exposure to aldrin and dieldrin.

The first draft of this document was prepared by Dr G.J. VAN
ESCH of the Netherlands on the basis of a review of all studies on
aldrin and dieldrin including the proprietary information, made
available to the IPCS by Shell International Chemical Company
Limited, London, United Kingdom.

The second draft was also prepared by Dr van Esch,
incorporating comments received following the circulation of the
first draft to the IPCS contact points for Environmental Health
Criteria documents.

Dr K.W. Jager and Dr P.G. Jenkins, both members of the IPCS
Central Unit, were responsible for the technical development and
editing, respectively, of this monograph.

The assistance of Shell in making available to the IPCS and the
Task Group its toxicological proprietary information on aldrin and
dieldrin is gratefully acknowledged. This allowed the Task Group
to make its evaluation on a more complete data base.

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

* * *

Partial financial support for the publication of this criteria
document was kindly provided by the United States Department of
Health and Human Services, through a contract from the National
Institute of Environmental Health Sciences, Research Triangle Park,
North Carolina, USA - a WHO Collaborating Centre for Environmental
Health Effects. The United Kingdom Department of Health and Social
Security generously supported the cost of printing.

INTRODUCTION

Aldrin and dieldrin are the common names of insecticides
containing 95% HHDN and 85% HEOD, respectively.

Throughout this monograph the names aldrin and dieldrin are
used, although concentrations determined in the different matrices
are actually those of the active molecules HHDN and HEOD.

Aldrin is readily metabolized to dieldrin (HEOD) in plants and
animals. Only rarely are aldrin residues present in food or in the
great majority of animals, and then only in very small amounts.
Therefore, national and international regulatory bodies have
considered these two closely related insecticides together. The
practicality of considering them jointly is further emphasized by
the lack of significant difference in their acute and chronic
toxicity and by their common mode of action.

1. SUMMARY

1.1. General

Aldrin and dieldrin, both organochlorine pesticides and
manufactured commercially since 1950, were used throughout the
world up to the early 1970s. Both compounds were used as
insecticides in agriculture for the control of many soil pests and
in the treatment of seed. Insects controlled by these compounds
include termites, grasshoppers, wood borers, beetles, and textile
pests. Dieldrin has also been used in public health for the
control of tsetse flies and other vectors of debilitating tropical
diseases. Both aldrin and dieldrin act as a contact and stomach
poison for insects.

Since the early 1970s, both compounds have been severely
restricted or banned, in a number of countries, from use,
especially in agriculture. Nevertheless, the use for termite
control continues in other countries. Global production, which was
estimated to be 13 000 tonnes/year in 1972, decreased to less than
2500 tonnes/year in 1984.

The purity of technical grade aldrin and dieldrin is 90%
and > 95%, respectively. Impurities for aldrin include
octachlorocyclopentene, hexachlorobutadiene, and polymerization
products, and for dieldrin polychloroepoxyoctahydrodimethano-
naphthalenes.

Both compounds are practically insoluble in water and
moderately to highly soluble in most paraffinic, aromatic, and
halogenated hydrocarbons, and in esters, ketones, and alcohols.
The vapour pressure of aldrin is 6.5 x 10^-5mmHg at 25 °C and that
of dieldrin is 3.2 x 10^-6 mmHg at 25 °C.

Analytical methods for the determination of aldrin and dieldrin
in food, feed, and the environment are described in section 2.

1.2. Environmental Transport, Distribution, and Transformation

A major use of aldrin is as a soil insecticide. Hence, aldrin-
treated soil is an important source of aldrin and its reaction
product dieldrin in the environment.

Aldrin has a low propensity for movement away from treated
areas, either through volatilization or by leaching. It is mainly
and rapidly adsorbed on soils with a high organic matter content,
but only moderately adsorbed by clay soils. Aldrin and dieldrin
rarely penetrate more than 20 cm beneath the top treated layer of
soil. Aldrin adheres to soil particles to such an extent that only
traces can be removed by water. For this reason, contamination of
ground water does not generally occur.

The disappearance of aldrin from soil resembles a first-order
reaction. Immediately after application, there is a short period
of rapid loss due to volatilization and thereafter a second longer

exponential period of decline, mainly due to conversion to
dieldrin, which is slower to dissipate. However, there is the
possibility of migration by way of soil erosion, as wind drift,
sediment transport, and surface run-off. From data on residues of
aldrin in the environment, it appears that it is mainly retained in
the soil and that 97% of the primary residue is not the parent
compound but its epoxide, dieldrin.

Photodieldrin is a photodegradation product of dieldrin and
does not occur widely in the environment.

Aldrin applied to soils is lost slowly in temperate areas,
three-quarters of the applied aldrin being lost during the first
year in a typical case. The rate of loss slows later as aldrin is
converted to dieldrin. There is some evidence that the rate of loss
is greater under the anaerobic conditions of rice paddies than under
aerobic conditions. Dieldrin is lost from the soil very rapidly in
tropical areas, up to 90% disappearing within 1 month, whereas the
half-life of dieldrin in temperate soils is approximately 5 years.
Volatilization appears to be the principal route of loss from the
soil, though atmospheric levels of dieldrin and aldrin are generally
low. Some dieldrin is washed from the atmosphere by rain, but
levels in ground water are very low because of strong adsorption to
soil particles. Dieldrin has been detected, in small amounts, in
surface water contaminated by run-off from agricultural land.

1.3. Environmental Levels and Human Exposure

Aldrin and dieldrin have been found in the atmosphere, in the
vapour phase, adsorbed on dust particles, or in rainwater at
variable levels according to the situation. They have been
detected mainly in agricultural areas, where the mean level in the
air has been of the order of 1 - 2 ng/m³, with maximum levels of
about 40 ng/m³. In rainwater, concentrations of the order of
10 - 20 ng/litre, or occasionally higher, have been found.

Concentrations found in the air in houses treated for the
control of termites were much higher, ranging from 0.04 to 7 µg/m³,
depending on the time of sampling (i.e., the number of days of
after application) and the type of house. Within 8 weeks, the
concentrations decreased rapidly. Treatment of internal wood in
houses resulted in dieldrin concentrations in the air ranging from
0.01 to 0.5 µg/m³. Aldrin and dieldrin migrated into food from
treated laminated timber and plywood, and by direct contact and/or
sorption from the atmosphere.

The occurrence of dieldrin in the aquatic environment has been
reported. However, the concentrations were very low, mainly less
than 5 ng/litre. Higher levels have been generally attributed to
industrial effluents or soil erosion during agricultural usage.
River sediments may contain much higher concentrations (up to 1 mg/kg).

Aldrin is found only rarely in food, but dieldrin is more
common, especially in dairy products, meat products, fish, oils and
fats, potatoes, and certain other vegetables (especially the root
vegetables). Maximum residue limits (MRLs) in the range of 0.02 to
0.2 mg/kg product have been recommended over the years by the
FAO/WHO Joint Meetings on Pesticide Residues. Recent studies in
different countries have shown that the actual concentrations of
dieldrin in these food commodities are generally lower. Studies
from the United Kingdom indicate this decrease clearly. In
1966 - 67, the mean level of dieldrin residues in a total diet
study was 0.004 mg/kg food, whereas in the period 1975 - 77 it was
0.0015 mg/kg, and in 1981, 0.0005 mg/kg. This downward trend has
been confirmed in other countries, for instance in the USA. This
may be due to the restriction or banning of the use of these
compounds.

A large number of investigations has been reported in which the
adipose tissue, organs, blood, or other tissues of the general
population have been examined for the presence of dieldrin. Over
the last 25 years, surveys have been carried out in many countries
all over the world. Most of the mean values for adipose tissue
have been in the range of 0.1 - 0.4 mg/kg. Surveys in the
Netherlands, the United Kingdom, and the USA have indicated a
decline in concentrations in adipose tissue, since the mid-1970s.
Blood concentrations range from 1 to 2 µg/litre. Levels in the
liver are below 0.4 mg/kg, while those in other tissues, including
the kidneys, brain, and gonads, are below 0.1 mg/kg tissue.

As a result of transplacental exposure, dieldrin is present in
the blood, adipose tissue, and other tissues of the fetus and
newborn infants. The concentrations are one tenth to one half of
those of their mothers. There is no difference between infants and
adults in the brain/liver/fat ratio of dieldrin concentrations.
Dieldrin is also excreted in mother's milk. Over the last 15
years, samples of mother's milk have been analysed for the presence
of organochlorine pesticides, including dieldrin, in various
countries. In most countries, the dieldrin concentration in milk
amounts to 6 µg/litre, though higher levels have occasionally been
found.

1.4. Kinetics and Metabolism

In both animals and human beings, aldrin and dieldrin are
readily absorbed into the circulating blood from the
gastrointestinal tract, through the skin, or through the lungs
following inhalation of the vapour. A study on human volunteers
showed that absorption through the intact skin amounts to 7 - 8% of
the applied dose. Inhalation studies with human volunteers
suggested that up to 50% of inhaled aldrin vapour is absorbed and
retained in the human body. After absorption, it is rapidly
distributed throughout the organs and tissues of the body and a
continuous exchange between the blood and other tissues takes
place. In the meantime, aldrin is readily converted to dieldrin,
mainly in the liver but also to a much lesser extent in some other
tissues, such as the lungs. This conversion proceeds very rapidly.

When 1-day-old rats were given oral doses of 10 mg aldrin/kg
body weight, their livers contained dieldrin 2 h after treatment.
Over the course of the next few hours, dieldrin concentrated to a
greater extent in the lipid tissues.

Numerous studies carried out with ¹⁴C-labelled aldrin and
dieldrin have shown that part of the ingested material is passed
unabsorbed through the intestinal tract and eliminated from the
body, part is excreted unchanged from the liver into the bile, part
is stored in the various organs and tissues particularly in the
adipose tissue, and part is metabolized in the liver to more polar
and hydrophilic metabolites. In human beings and most animals, the
metabolites are excreted primarily via the bile in the faeces. It
has also been shown that both aldrin and dieldrin are biodegraded
into the same metabolites.

Most of the currently available information on the
biodegradation metabolism in mammals is based on studies on
dieldrin in the mouse, rat, rabbit, sheep, dog, monkey, chimpanzee,
and in human beings. The overall picture shows only quantitative
variations between species, and the mechanisms in rats seem to be
similar to those in primates.

The major metabolite, except in the case of the rabbit, is the
9-hydroxy derivative. This metabolite is found in the faeces and
in a free or conjugated form in the urine. Small amounts of three
other metabolites have been found and identified in experimental
animals. These are the trans-6,7-dihydroxy derivative,
dicarboxylic acid derived from the dihydroxy compound, and the
bridged pentachloroketone.

Only the 9-hydroxy compound has been demonstrated in the faeces
of human beings and neither this nor the other metabolites have
been found in human blood or other tissues. Dieldrin was found to
be present in the faeces of occupationally exposed workers, whereas
the concentrations in the samples from the general population were
below the limits of detection. Examination of the urine of five
workers indicated that urinary excretion of dieldrin and its four
metabolites was minor compared to the elimination of the 9-hydroxy
metabolite via the faeces.

The conversion of aldrin to dieldrin by mixed-function
monooxygenases (aldrin-epoxidase) in the liver and the distribution
and the subsequent deposition of dieldrin (mainly in lipid-
containing tissues, such as adipose tissue, liver, kidneys, heart,
and brain) proceed much more rapidly than the biodegradation and
ultimate elimination of unchanged dieldrin and its metabolites from
the body. Thus, at a given average daily intake of aldrin and/or
dieldrin, dieldrin slowly accumulates in the body. However, this
accumulation does not continue indefinitely. As dosing continues,
a "steady state" is eventually reached at which the rates of
excretion and intake are equal. The upper limit of storage is
related to the daily intake. This has been demonstrated in rats,
dogs, and human beings.

When the intake of aldrin/dieldrin ceases or decreases, the
body burden decreases. The biological half-life in man is
approximately 9 - 12 months. Significant relationships have been
found between the concentrations of dieldrin in the blood and those
in other tissues in rats, dogs, and human beings.

Numerous investigations of the concentrations of dieldrin in
the blood, adipose tissue, and other tissues of members of the
general population and from special groups, carried out in several
different countries, have shown that at equilibrium the ratio of
dieldrin concentrations in the adipose tissue, liver, brain, and
blood is about 150:15:3:1.

Dieldrin is transported via the placenta and reaches the fetus.
Accumulation takes place in the same organs and tissues as in the
adult, but to a much lower level. There seems to be an equilibrium
between the levels in the mother and the fetus.

Photodieldrin is also metabolized into bridged pentachloroketone
in the rat and dog. Both compounds were found in the adipose
tissue, liver, and kidneys when animals were administered high
levels of photodieldrin. No residues of these compounds could be
detected in human adipose tissue, kidneys, or breast milk. The
accumulation of photodieldrin in the adipose tissue of experimental
animals was much less than that of dieldrin.

1.5. Effects on Organisms in the Environment

1.5.1. Accumulation

Most residues in organisms are of dieldrin, since aldrin is
readily converted to dieldrin in all organisms.

The uptake of dieldrin from medium into fungi, streptomycetes,
and bacteria over 4 h has yielded concentration factors ranging
from 0.3 to >100. Protozoa take up more dieldrin than algae.
Algae take up dieldrin from the culture medium very rapidly, maxima
often being reached within a few hours.

Many species of aquatic invertebrates concentrate dieldrin from
very low water concentrations, yielding high concentration factors.
A steady state is reached within a few days. On transfer to clean
water, the loss of dieldrin is rapid, the half-life being 60 - 120 h.

Bioconcentration factors for whole fish are greater than
10 000. The half-life for loss of accumulated dieldrin was found
to be 16 days for one species of fish.

The bioconcentration of dieldrin in aquatic organisms is
principally from the water rather than by ingestion of food.

Earthworms take up dieldrin from the soil and concentrate it to
a maximum of about 170 times. There is little correlation between
levels in earthworms and levels in most types of soil.

Many investigations have been carried out to estimate the
occurrence of dieldrin in the tissues or eggs of non-target
species. The concentrations found cover a wide range from 0.001
mg/kg up to 100 mg/kg tissue, but most are below 1 mg/kg tissue.

Both the body tissues and eggs of birds accumulate dieldrin
readily. Similarly, various mammal species have been shown to
accumulate dieldrin, particularly in the fatty tissues.

1.5.2. Toxicity for microorganisms

The effects of dieldrin on unicellular algae are very variable,
some species being markedly affected by 10 µg/litre and others
unaffected even by 1000 µg/litre. Aldrin and dieldrin have only
minor effects on soil bacteria, even at levels far exceeding those
normally encountered. Most studies have shown no effects at
exposure levels of 2000 mg/kg soil. Effects on photosynthesis have
been reported in several different species of algae, with aldrin
showing a more marked effect than dieldrin at the same
concentration. However, these slight effects on the biochemical
processes of soil algae were only transitory.

1.5.3. Toxicity for aquatic organisms

Aldrin and dieldrin are highly toxic for aquatic crustaceans,
most 96-h LC₅₀values being below 50 µg/litre. However, a few
reported results of up to 4300 µg/litre illustrate species
variability. Daphnids are less sensitive to dieldrin than aldrin,
with 48-h tests yielding LC₅₀values of 23 - 32 µg/litre for aldrin
and 190 - 330 µg/litre for dieldrin. Molluscs are significantly
more resistant, with 48 h values ranging up to >10 000 µg/litre.
The results of studies over several weeks have confirmed the
relative resistance of daphnids and molluscs. The most susceptible
aquatic invertebrates are the larval stages of insects with 96-h
values of 0.5 - 39 µg/litre for dieldrin and 1.3 - 180 µg/litre for
aldrin.

Both aldrin and dieldrin were highly toxic in acute tests on
fish. Values for 96-h LC₅₀s in various fish species varied from
2.2 to 53 µg/litre for aldrin, and from 1.1 to 41 µg/litre for
dieldrin. Several studies have revealed that toxicity increases
with increasing temperature. In a long-term study on Poecilia
latipinna, there was 100% mortality at dieldrin concentrations of
3 µg/litre or more. Dieldrin administered in the food of rainbow
trout at up to 430 µg/kg body weight per day did not have any
effects on mortality, but enzymic changes were reported.
Morphological changes in liver mitochondria were seen using the
electron microscope. The ammonia-detoxifying mechanism of fish is
sensitive to dieldrin, the no-observed-adverse-effect level being
less than 14 µg/kg body weight per day. Different life stages of
fish have been found to have different susceptibilities to
dieldrin. Eggs were resistant and juvenile stages were less
susceptible than adults.

The acute toxicity of both aldrin and dieldrin is high for
larval amphibia with 96-h LC₅₀s of the order of 100 µg/litre.

1.5.4. Toxicity for terrestrial organisms

The toxicity of dieldrin for higher plants is low, crops only
being affected at application rates greater than 22 kg/ha. Aldrin
is more phytotoxic, to tomatoes and cucumbers particularly, but
only at application rates many times greater than those
recommended. Cabbage is the most sensitive crop to aldrin.

Oral LD₅₀s for honey bees ranging from 0.24 to 0.45 µg/bee for
aldrin and from 0.15 to 0.32 µg/bee for dieldrin have been reported.
Contact toxicity ranged from 0.15 to 0.80 µg/bee for aldrin and from
0.15 to 0.41 µg/bee for dieldrin. Two studies have indicated that
dieldrin is relatively non-toxic for predatory insects eating pest
species.

In laboratory studies, earthworms tolerated aldrin at a level
of 13 mg/kg of artificial soil with <1% mortality. The 6-week
LC₅₀was 60 mg aldrin/kg soil.

The acute toxicities of aldrin and dieldrin have been found to
vary by more than an order of magnitude for 13 species of birds,
ranging from 6.6 to 520 mg/kg body weight for aldrin and from 6.9
and 381 mg/kg body weight for dieldrin. In four bird species,
subacute oral toxicity varied between 34 and 155 mg/kg for aldrin
and 37 and 169 mg/kg for dieldrin. Repeated testing over a period
of time did not indicate the development of resistance in these
species. Reproductive studies on several species of domestic birds
have indicated that levels of dieldrin in the diet of more than
10 mg/kg cause some adult mortality. There are no reproductive
effects on egg production, fertility, hatchability, or chick
survival at levels of dietary dieldrin not causing maternal
toxicity. Eggshell thickness is not directly affected by dieldrin.
However, reduced food consumption is a symptom of dieldrin
poisoning, and eggshell thickness can be reduced by decreased food
intake.

Among non-laboratory mammals, the response to dieldrin varies
from species to species. Four vole species showed acute LD₅₀s
ranging from 100 to 210 mg/kg body weight, making them less
susceptible to dieldrin than laboratory species. Shrews survived a
diet containing 50 mg dieldrin/kg but died with a dietary level of
200 mg/kg. Blesbuck (antelope) survived for 90 days at 5 and 15
mg/kg diet but all died within 24 days at levels of 25 mg/kg or
more. All blesbuck in an area sprayed with dieldrin at 0.16 kg/ha
died, the calculated dietary intake being 1.82 mg/kg per day. Thirty
percent of springbok survived the spray with no after-effects.
Toxicological signs of dieldrin poisoning were similar to those of
laboratory mammals.

1.5.5. Population and ecosystem effects

It has been suggested that some mammal populations have been
affected by dieldrin. Small mammals were probably killed by eating
dieldrin-dressed seed, but populations were replenished by
immigration. Bats have been killed by dieldrin in wood preservatives.

Residues of dieldrin have been reported in many species of
birds. Throughout the world, the highest residues have been found
in birds of prey at the top of foodchains. The dieldrin content of
bird tissues and eggs has paralleled usage patterns and decreased
with restrictions in the use of aldrin and dieldrin. It is not
easy to identify the effects of dieldrin, because residues occur
together with residues of other organochlorines. Dieldrin is more
toxic to birds than DDT and probably has been responsible for more
adult deaths that DDT. However, the reproductive effects of
dieldrin in the field are more difficult to prove. There are
seasonal changes in the contents of dieldrin in bird tissues.
Furthermore, effects can occur long after exposure to the source of
the pollutant.

1.6. Effects on Experimental Animals and In Vitro Test Systems

Aldrin and dieldrin are of a high order of toxicity; the oral
LD₅₀s for both compounds in the mouse and rat range from 40 to 70
mg/kg body weight. The dermal toxicity is in the range of 40 - 150
mg/kg body weight, depending on the animal species and the solvent
used. Technical aldrin and dieldrin were found to produce slight
to severe irritation in the rabbit skin, but this effect was mainly
caused by the solvent. In the Magnusson & Kligman guinea-pig
maximization test, aldrin produced a sensitization effect.
However, during 20 years of manufacture and formulation, no cases
of skin sensitization occurred in a group of over 1000 workers.

The vapour pressures of both aldrin and dieldrin are low and
acute inhalation effects do not normally arise. The effects
observed in acute toxicity studies by all routes involve the
central nervous system and include hyperexcitability, tremors, and
convulsions.

Short- and long-term oral studies have been carried out with
aldrin and dieldrin on the mouse, rat, dog, hamster, and monkey.
The liver is the major target organ in the rat and mouse, with an
increased liver/body weight ratio and hypertrophy of the
centrilobular hepatocytes occurring, which in the early stages may
be reversible. Microscopically these changes include increased
cytoplasmatic oxyphilia and peripheral migration of basophilic
granules. These changes were not found in the liver of the hamster
and the monkey. In the dog, mild liver changes (fatty changes and
slight hepatic cell atrophy) were accompanied by kidney changes
consisting of vacuolization in the epithelia of distal renal
tubules and tubular degeneration. In the rat, the overall no-
observed-adverse-effect level from the available short-term and
long-term studies is 0.5 mg/kg diet, equivalent to 0.025 mg/kg body

weight. With feeding levels equivalent to 0.05 mg/kg body weight
or more, an increasing dose-related hepatomegaly and histological
changes occurred. In the dog, no-effect levels of 0.04 - 0.2 mg/kg
body weight were found.

A number of long-term carcinogenicity studies on mice of
different strains were carried out with aldrin or dieldrin. In all
studies, benign and/or malignant liver cell tumours were found.
Females seemed to be less sensitive than males. No other types of
tumours were induced.

Long-term studies on the other animal species (rat, hamster)
did not show any increase in tumour incidence. Photodieldrin, fed
at concentrations up to 7.5 mg/kg diet, did not induce tumours.

In addition, a number of special studies have been published
that have so far failed to elucidate the mechanism of the induction
of the liver tumours in mice.

In most of the reproduction studies (over 1 - 6 generations)
carried out with aldrin or dieldrin on mice and rats, the major
effect was an increased mortality rate in pre-weaning pups.
Reproductive performance was only affected at doses causing
maternal intoxication. Studies on dogs were too limited to draw
firm conclusions, apart from a consistent increase in pre-weaning
pup mortality.

It can be concluded from the results of these reproduction
studies that 2 mg dieldrin/kg in the rat diet and 3 mg dieldrin/kg
in the mouse diet, equivalent to 0.1 and 0.4 mg/kg body weight per
day, respectively, are no-observed-adverse-effect levels for
reproduction.

No evidence of teratogenic potential was found in studies on
the mouse, rat, or rabbit using oral doses of aldrin and dieldrin
of up to 6 mg/kg body weight. Single doses of aldrin and dieldrin,
equal to about half the LD₅₀, caused severe fetotoxicity and an
increased incidence of teratogenic abnormalities in the mouse and
hamster. The significance of these findings in the presence of
likely maternal toxicity is doubtful.

Many in vivo and in vitro mutagenicity studies have been
carried out, but the results of nearly all these studies were
negative.

The acute oral toxicity of photodieldrin is higher than that of
dieldrin in the mouse, rat, and guinea-pig. In acute and short-
term toxicity studies, the symptoms of intoxication and the effects
on target organs are quantitatively and qualitatively similar to
those of dieldrin. Photodieldrin did not induce tumours in mice
and rats.

Like most other chemical substances, aldrin and dieldrin do not
have a single mechanism of toxicity. The target organs are the
central nervous system and the liver. In human beings and other

vertebrates, intoxication following acute or long-term overexposure
is characterized by involuntary muscle movements and epileptiform
convulsions. Survivors recover completely after a short period of
time of residual signs and symptoms. In the liver there is an
increased activity of microsomal biotransformation enzymes,
particularly of the monooxygenase system with cytochrome P-450.
This induction of the microsomal enzymes is reversible and, if it
exceeds a certain level, it appears to be linked to cytoplasmic
changes and hepatomegaly in the liver of rodents.

All the available information on aldrin and dieldrin taken
together, including studies on human beings, supports the view that
for practical purposes these chemicals make very little
contribution, if any, to the incidence of cancer in man.

1.7. Effects on Man

Aldrin and dieldrin are highly toxic for human beings. Severe
cases of both accidental and occupational poisoning have occurred
but only rarely have fatalities been reported. The lowest dose
with a fatal outcome has been estimated to be 10 mg/kg body weight.
Survivors of acute or subacute intoxications recovered completely.
Irreversible effects or residual pathology have not been reported.

Adverse effects from aldrin and dieldrin are related to the
level of dieldrin in the blood. Determination of the level of
dieldrin in the blood provides a specific diagnostic test of
aldrin/dieldrin exposure. The level of dieldrin in the blood of
male workers below which adverse effects do not occur, (the
threshold no-observed-adverse-effect level) is 105 µg/litre blood.
This corresponds to a daily intake of 0.02 mg dieldrin/kg body
weight per day.

Environmental exposure (mainly dietary though also, to a small
extent, respiratory) leads to the presence of dieldrin at very low
levels in organs, adipose tissue, blood, and mother's milk. As far
as can be judged from the extensive clinical and epidemiological
studies, there is no reason to believe that these prevailing body
burdens constitute a health hazard for the general population. In
a continuing study lasting more than 20 years, involving more than
1000 industrial workers in an aldrin/dieldrin insecticide-
manufacturing plant, no increase in cancer incidence occurred among
workers who had been exposed to high levels of aldrin and dieldrin.
More significantly, there were no signs of any premonitory change
in liver function in these workers.

An epidemiological mortality study was carried out at a
manufacturing plant in the USA on a cohort of 870 workers exposed
to aldrin, dieldrin, and endrin. With almost 25 000 man-years of
observation, no specific cancer risk associated with employment at
this plant could be identified.

2. IDENTITY, PHYSICAL AND CHEMICAL PROPERTIES, ANALYTICAL METHODS

2.1. Identity

2.1.1. Primary constituent: aldrin^a

Chemical formula: C₁₂H₈Cl₆

Relative molecular mass: 364.9

IUPAC chemical name^b: (1 R,4 S,4a S,5 S,8 R,8 R,a R)-1,2,3,4,10,
10-hexachloro-1,4,4a,5,8,8a-hexahydro-1,
4:5,8-dimethanonaphthalene or 1,2,3,4,10,
10-hexachloro-1,4,4a,5,8,8a-hexahydro-
exo-1,4- endo-5,8-dimethanonaphthalene

Common synonyms
and trade names: ENT 15 949 (compound 118), HHDN,
Octalene, OMS 194

CAS registry number: 309-00-2

RTECS registry number: I02100000

Technical product

Common trade name: Aldrin. This is the common name of an
insecticide containing 95% of HHDN.

Purity: The minimum content of aldrin (as defined
above) in technical aldrin is 90%.

Impurities: octachlorocyclopentene (0.4%),
hexachlorobutadiene (0.5%), toluene (0.6%),
a complex mixture of compounds formed by
polymerization during the aldrin reaction
(3.7%) and carbonyl compounds (2%)
(FAO/WHO, 1968b)

-------------------------------------------------------------------
^aFrom: Worthing & Walker (1983).
^bOther chemical names are given in Appendix I.

2.1.2. Primary constituent: dieldrin^a

Chemical formula: C₁₂H₈OCl₆

Relative molecular mass: 380.9

IUPAC chemical name^b: (1 R,4 S,4a S,5 R,6 R,7 S,8 S,8a R)-1,2,3,
4,10,10-hexachloro-1,4,4a,5,6,7,8,8a-
octahydro-6,7-epoxy-1,4:5,8-
dimethanonaphthalene or 1,2,3,4,10,10-
hexachloro-6,7-epoxy-1,4,4a,5,6,7,8,8a-
octahydro- endo-1,4- exo-5,8,-
dimethanonaphthalene

Common synonyms ENT 16 225 (compound 497), HEOD, Alvit,
and trade names: Octalox, OMS 18, Quintox

CAS registry number: 60-57-1

RTECS registry number: I01750000

Technical product

Common trade name Dieldrin. This is the common name of an
insecticide containing 85% of HEOD.

Purity: Technical dieldrin contains not less than
95% of dieldrin, as defined above.

Impurities: other polychloroepoxyoctahydrodimethano-
naphthalenes, endrin 3.5% (FAO/WHO,
1968b)

-------------------------------------------------------------------
^aFrom: Worthing & Walker (1983).
^bOther chemical names are given in Annex I.

2.2. Physical and Chemical Properties

2.2.1. Aldrin

Pure aldrin is a colourless crystalline solid. It has a
melting point of 104 - 104.5 °C.

Technical aldrin (90%) is a tan to dark brown solid with a
melting point of 49 - 60 °C. Its vapour pressure is 8.6 mPa at
20 °C (6.5 x 10^-5mmHg at 25 °C). Its density is 1.54 g/ml at
20 °C. Its solubility in water is 27 µg/litre at 27 °C
(practically insoluble), and in acetone, benzene, and xylene
is > 600 g/litre. Aldrin is stable at < 200 °C and at pH 4 - 8,
but oxidizing agents and concentrated acids attack the
unchlorinated ring. Aldrin is non-corrosive or slightly corrosive
to metals because of the slow formation of hydrogen chloride on
storage (Shell, 1976, 1984; Worthing & Walker, 1983).

2.2.2. Dieldrin

Technical dieldrin (95%) consists of buff to light tan flakes
(setting point > 95 °C) with a mild odour. Its melting point is
175 - 176 °C. Its vapour pressure is 0.4 mPa at 20 °C (3.2 x 10^-6
mmHg at 25 °C). Its density is 1.62 g/ml at 20 °C. Its solubility
in water is 186 µg/litre at 20 °C (practically insoluble), but it
is moderately soluble in most paraffinic and aromatic hydrocarbons,
halogenated hydrocarbons, ethers, esters, ketones, and alcohols.
Dieldrin is stable to alkali, mild acids, and to light. It reacts
with concentrated mineral acids, acid catalysts, acid oxidizing
agents, and active metals (iron, copper). It is non-corrosive or
slightly corrosive to metals in the same way as aldrin (Shell,
1976; Worthing & Walker, 1983).

2.3. Analytical Methods

2.3.1. Sampling methods

Methods of sampling and storage have been reviewed by Beynon &
Elgar (1966). Sample collection is broadly divisible into two types:
adventitious sampling (particularly of wildlife) and systematic
sampling (soil, total diet surveys) in which samples are collected
in accordance with the principles of statistical design. Surveys
of dieldrin in human blood and adipose tissue are a partial
combination of these two classes of sample collection. The
sampling methods for total diet surveys were reviewed by Cummings
(1966), and the sampling of air for pesticide residues has been
discussed in detail by Lewis (1976).

2.3.2. Analytical methods

Since the introduction of the method of gas-liquid
chromatography with electron capture detection (GLC/EC) (Goodwin et
al., 1961), old methods, based on, for instance, total organic
chlorine or the colorimetric phenyl azide procedure, have been
abandoned. The great majority of analytical data relating to the

occurrence of residues of aldrin or dieldrin since that time have
been based on GLC/EC procedures. There has been considerable
evolution of various aspects (especially extraction and clean up
procedures) of the methodology. The many publications on specific
procedures are reviewed in the Codex Publication "Recommendations
for methods of analysis of pesticide residues", CAC/PR 8-1986,
(FAO/WHO, 1986b). This review lists 22 individual publications,
four of which refer to simplified methods. It also lists the
following compendia of methods which may also be consulted.

- Official methods of analysis of the Association of Official
Analytical Chemists, 14th Edition 1984.

- Pesticide analytical manual, Food & Drug Administration,
Washington DC, USA.

- Manual on Analytical methods for pesticide residues in foods,
Health Protection Branch, Health and Welfare, Ottawa, Canada,
1985.

- Methodensammlung zur Rueckstandsanalytik von
Pflanzenschutzmitteln (Methods for analysing residues of plant
protective agents) 1984 Verlag Chemie GmbH, Weinheim, Federal
Republic of Germany.

- Chemistry Laboratory Guidebook, USDA.

Whatever procedure is adopted should be carried out within the
requirements of the CAC publication "Codex Guidelines on Good
Laboratory Practice in Pesticide Residue Analysis", CAC/PR 7-1984,
(FAO/WHO, 1984).

It is important to recognize that the electron capture detector
is not specific for aldrin and dieldrin and in the analysis of
samples without a precise history of treatment, confirmation of the
identity of the residue is an essential part of the analysis.
Reports of the occurrence of aldrin in environmental samples in the
past, are now thought, in many cases, to have been instances of
misidentification. The occurrence of PCBs in the same sample has
been a particularly troublesome source of interference. Many
procedures for the confirmation of identity are available and
include comparison of the position of the peak on different
chromatographic columns, thin-layer chromatography, and
derivatization. The most definitive method, however, involves the
uses of mass spectrography as the detector. With this procedure,
much of the uncertainty with regard to the identification of the
residue has been eliminated. The mass spectrography procedure
described by Hargesheimer (1984) is effective for the determination
of chlorinated hydrocarbon residues in the presence of PCBs. The
limit of determination of individual methods depends to a
considerable extent on the amount of effort the analyst devotes to
extraction and clean-up procedures. With samples of food and
feeds, for example, a limit of determination of 0.01 mg/kg is
normally regarded as acceptable, but in water and air far lower
levels are achievable, depending on the care and effort taken.

It should be recognized that there is considerable variation in
the results that can be obtained on the same sample by different
analysts and in different laboratories and variations of 100% are
by no means uncommon at the lower end of the scale. A valuable
account of the variation found among 120 laboratories for a sample
of butterfat containing known amounts of 11 different chlorinated
hydrocarbon insecticides was given by Elgar (1979).

3. SOURCES OF HUMAN AND ENVIRONMENTAL EXPOSURE

3.1. Natural Occurrence

Aldrin and dieldrin are not known to occur as natural products.

3.2. Man-Made Sources

3.2.1. Production levels and processes; uses

3.2.1.1 World production figures

The first laboratory synthesis of aldrin and dieldrin was in
1948 by J. Hyman & Co. (Thompson, 1976). The method was licensed
to Shell and manufacture began in 1950, first in the USA and later
on in the Netherlands (IARC, 1974).

Production has decreased since the early 1960s. The production
capacity was 20 000 tonnes in 1971, and the estimated 1972
production was 13 000 tonnes. In 1984, less than 2500 tonnes of
aldrin and dieldrin were manufactured, approximately one third of
which was used in Australia, the United Kingdom, and the USA (Van
Duursen, 1985).

Up to the late 1960s and early 1970s, aldrin and dieldrin were
used throughout the world. Since then, many countries have
severely restricted or banned their use, especially in agriculture,
because of their persistent character in the environment (IARC,
1974). The main remaining uses are in the control of disease
vectors and termites and industrial applications.

3.2.1.2 Manufacturing processes

Aldrin is synthesized by the Diels-Alder reaction of
hexachlorocyclopentadiene with an excess of bicycloheptadiene at
100 °C. The yield is more than 80%, calculated on the
hexachlorocyclopentadiene (Melnikov, 1971).

Commercial production of dieldrin is believed to be through
epoxidation of aldrin with a peracid (e.g., peracetic or perbenzoic
acid), but an alternate synthetic route involves the condensation
of hexachlorocyclopentadiene with the epoxide of bicycloheptadiene
(Galley, 1970).

3.2.1.3 Release into the environment during normal production

Loss of aldrin and dieldrin, together with isobenzan, in waste
water from a manufacturing plant in the Botlek area of the
Netherlands caused deaths among sandwich terns (Sterna
sandvicentis), eider ducks (Somateria mollissima), and, to a lesser
extent, some other bird species, feeding on marine organisms
containing high levels of these insecticides in the Wadden Sea
during 1962 - 65. Following improvement of the waste-water
purification of the plant, the residue levels in the marine
organisms decreased during subsequent years (Koeman, 1971).

3.2.2. Uses

3.2.2.1 Aldrin

Aldrin is a highly effective broad-spectrum soil insecticide.
It kills insects by contact and ingestion, and possesses slight
fumigant action within the soil, which ensures distribution in the
top soil where the pests are found.

It is used to control soil insects, including termites, corn
rootworms, seed corn beetle, seed corn maggot, wireworms, rice
water weevil, grasshoppers, and Japanese beetles, etc. Crops
protected by aldrin soil treatment include corn and potatoes; it is
used as a seed dressing on rice. Aldrin is also used for the
protection of wooden structures against termite attack. It is
supplied mainly as an emulsifiable concentrate or wettable powder.

3.2.2.2 Dieldrin

Dieldrin is used mainly for the protection of wood and
structures against attack by insects and termites and in industry
against termites, wood borers, and textile pests (moth-proofing).
It acts as a contact and stomach poison.

Dieldrin is no longer used in agriculture. It has been used as
a residual spray and as a larvacide for the control of several
insect vectors of disease. Such uses are no longer permitted in a
number of countries.

It is available as an emulsifiable concentrate or wettable
powder.

4. ENVIRONMENTAL TRANSPORT, DISTRIBUTION, AND TRANSFORMATION

4.1. Transport and Distribution Between Media

4.1.1. Leaching of aldrin and dieldrin

As would be expected from their very low water solubility,
hydrophobic character, and strong adsorption by soil, aldrin and
dieldrin are very resistant to downward leaching through the soil
profile.

Since one of the major uses of aldrin is as a soil insecticide,
aldrin-treated soil is an important source of aldrin in the
environment.

Bowman et al. (1965) studied the leaching of aldrin through six
different types of soil, by passing water through them. In five
out of six soil types, only traces were recovered in the leachates.
However, 16% of applied aldrin was found in the leachate from a
sandy soil type. Other studies indicate that leaching of aldrin
through soil is minimal (Harris, 1969; Herzel, 1971; El Beit et
al., 1981a,b).

A study was carried out to determine the possible involvement
of aldrin applied for the control of termites around house
foundations. Seven types of soil collected from different
geographical areas in the USA were investigated by placing the
soils (adjusted to 0, 5, 10, or 15% water content) in glass
columns. The soil columns were separated into five layers of 5 cm
by filter paper support cloth. An emulsion of aldrin was placed on
the top of the column, equivalent to 0.365 kg aldrin/m². The
layers of soil were removed approximately 24 h after application of
the emulsion and the concentration of aldrin determined.
Penetration below 20 cm did not occur in any soil at any of the
water contents. In certain soils, penetration only took place in
the first 5 cm and, in others, in the third layer (10 - 15 cm).
Water content also plays a role in the penetration. In another
study, layers of 4 cm were used, with comparable results (Carter &
Stringer, 1970).

Several field studies on the leaching of aldrin through
different types of soil have been carried out. In these studies,
aldrin was applied to the surface or tilled to a depth of about 15
cm at dose levels of 1.8 - 20.7 kg/ha. From the results, it is
clear that, even up to 5 years after application, aldrin and
dieldrin were still present in the treated layer, with little
penetration to layers immediately below the treated layer. From
these studies, it appears that there is little movement
(Lichtenstein et al., 1962; Daniels, 1966; Park & McKone, 1966).
However, Wiese & Basson (1966) found some movement, even in clay
soil.

In studies by Powell et al. (1979), sandy soil in which tomato
plants were growing was sprayed with an aldrin emulsion (2.2 kg/ha)
on six occasions at intervals of 1 - 2 weeks. Approximately one

year after the final treatment, soil core samples were taken and
the concentrations of aldrin and dieldrin in the 0 - 5, 5 - 10,
10 - 15, 15 - 22.5 cm layers were determined. About 73% of the
total residue in the 0 - 22.5 cm layer was in the 0 - 15 cm layer.
The ratio of aldrin to dieldrin in the four strata was similar.
The remark should be made that in this study there were a number of
confounding factors (e.g., the field was ploughed).

Stewart & Fox (1971) applied aldrin as a spray to four turf
plots at doses of 3.3, 4.4, or 6.6 kg/ha. Loam and silt soil core
samples were taken to a depth of 30 cm 9 - 13 years after
treatment. Aldrin was not detected; 93 - 100% of the total
dieldrin in the 30 cm core was in the top 15 cm layer of soil.

In studies by Lichtenstein et al. (1971), aldrin was applied to
a silt loam at a rate of 4.4 kg/ha and rototilled to a depth of
10 - 12.5 cm. After 10 years, the percentage of the applied aldrin
in the 0 - 22.5 cm layer was 0.18% as aldrin and 5.2% as dieldrin.
The ratios of concentrations in the 0 - 15 cm layer relative to the
15 - 22.5 cm layer were: aldrin, 2.5; dieldrin, 4.9.

¹⁴C-Aldrin was incorporated to a depth of 15 cm in experimental
plots in which potatoes were grown in the Federal Republic of
Germany (sandy loam; equivalent to 2.9 kg/ha) and England (sandy
clay loam; equivalent to 3.2 kg/ha). After 6 months, the
concentrations of aldrin in both cases were as follows: at 0 - 10
cm, 0.58 and 0.59 mg/kg; at 10 - 20 cm, 0.23 mg/kg and < 0.01
mg/kg; at 20 - 40 cm 0.02 and < 0.01 mg/kg and at 40 - 60 cm, < 0.01
mg/kg (in both locations) (Klein et al., 1973). In a parallel
study, the ¹⁴C activity in leach water collected at a depth of 60
cm was determined over a 3-year period; the cumulative rainfall
during this period was 160 cm. About 10% of the ¹⁴C activity,
applied initially to a depth of 15 cm, was found in the leachate
over a period of 3 years. Almost all the ¹⁴C activity was present
as dihydrochlordene dicarboxylic acid (Moza et al., 1972).

In studies by Stewart & Gaul (1977), aldrin (5.6 and 11.2
kg/ha) was incorporated to a depth of 15 cm into a sandy loam soil
for three successive years. Various crops were grown and soil
samples were collected for 14 years. Residues of aldrin and
dieldrin below 15 cm were negligible in the tenth year after the
initial application, whereas the residues of aldrin plus dieldrin
in the 0 - 15 cm layer were 0.2 and 1.7 mg/kg, respectively, at the
two different treatments levels.

The results of these leaching studies indicate the almost
quantitative adsorption of aldrin by organic matter and clay
minerals. Water molecules compete with aldrin for the adsorption
sites in clay minerals, and it has been found that aldrin is bound
to a greater extent in dry soil (Baluja et al., 1975; Kushwaha et
al., 1978b). The adsorption and desorption of aldrin has been
studied by Tejedor et al. (1974) in whole soil and in the clay and
organic (humic) fractions. It was concluded that the organic
fraction was mainly involved in the adsorptive uptake of aldrin and
that the clay fraction was the major factor affecting the retention

of aldrin. There does not appear to be a simple relationship
between water solubility and leaching, presumably because of the
variations in the adsorptive capacity of clay minerals in various
types of soil (Yaron et al., 1967). A chromatographic model of the
movement of pesticides through soils has been proposed (King &
McCarty, 1968; Oddson et al., 1970).

In the laboratory, the investigations by Eye (1968) and Harris
(1969) of the transport of dieldrin by water through soil are
particularly relevant and are consistent with the chromatographic
model for chemicals in soil of King & McCarty (1968). The elution
of dieldrin from soil by 1600 ml water was investigated in a study
of six types of soil placed in chromatographic columns. The
dieldrin content of the total eluate, as a proportion of the
applied dieldrin, varied from 1% (loam soil) to 65% (soil
containing 93% sand) (Bowman et al., 1965).

The leaching of dieldrin through soil columns (30 cm diameter)
was studied by Thompson et al. (1970). A dieldrin emulsion was
applied to the surface (equivalent to 31 kg dieldrin/ha) of soil
columns 35 cm deep, and water was added to the surface until about
30 litres (equivalent to about 6 months rainfall) had passed down
the columns in 120 h. It was concluded that dieldrin did not
readily leach from the three types of soil investigated into
drainage water, and that cracks and crevices caused by drying or by
earthworms and other animals favour the leaching of dieldrin. The
results of an investigation using sloping troughs gave results
consistent with the soil column study.

4.1.2. Surface run-off

Run-off from treated land caused by soil erosion is a potential
source of dieldrin residues in surface waters in areas where
erosion is not controlled by good farming practice. Sediments
bearing aldrin and dieldrin can result in low concentrations in
aqueous solution, although these are limited due to adsorption onto
the sediments. Thus, rain-water run-off (without sediment) does
not appear to be a major contributor.

Richard et al. (1975) and Sparr et al. (1966) sampled various
surface waters in the USA and reported levels of dieldrin ranging
from < 1 to 42 ng/litre and of aldrin in the region of 0.05
µg/litre.

To gain data on the erosion of treated land, Caro & Taylor
(1971) and Caro et al. (1976) incorporated dieldrin into the soils
of two small watersheds in Ohio, USA, and studied run-off losses
over a three-year period. In the first case, there was practically
no surface soil erosion and the total loss of dieldrin was confined
to run-off water. The area was 1.07 ha and the loss over the
period was less than 0.5 g dieldrin, the highest level in the water
being 4 µg/litre. In the second study, there was a substantial
loss of soil by erosion and the amount of dieldrin lost in the
solid sediment was 77 g in only 8 months. The loss in the water
itself was just under 2.5 g and the highest water concentration was

20 µg/litre. It should, however, be borne in mind that in this
case the soil had been mechanically compacted to aggravate the
effects of erosion, so that it is questionable whether the results
bear much relation to normal agricultural practice. The authors
commented that there was only a poor correlation between rainfall
events and the amounts of dieldrin lost.

Sediment-bearing residues of aldrin or dieldrin will yield some
of their burden to true solution in the water which they enters.
Sharom et al. (1980) showed that the ratio of dieldrin
concentration in soil to that in water (in equilibrium with the
soil) was between 100 and 500 for mineral soils, whilst that same
ratio for aldrin was likely to be around 5 - 6 times higher. Thus,
with 1 mg dieldrin/kg sediment, one could expect a water
concentration of about 10 µg/litre.

The movement of aldrin and dieldrin by run-off and soil erosion
was studied by Haan (1971). Each pesticide was applied at 1.65
kg/ha to the surface of small plots, mainly consisting of silt loam
(slope, 1 - 2%), in a greenhouse. Water was applied and the run-
off water, sediment, and surface soil (0.6 cm deep) were analysed.
It was estimated that 94.8% and 95.4%, respectively, of the applied
aldrin and dieldrin remained in the surface soil (0.6 cm depth).
It was concluded that there was no difference in the potential for
loss from soil by rainfall, whether the rainfall occurred shortly
after aldrin application or several days later.

4.1.3. Loss of aldrin and dieldrin from soils - volatilization

Most authors consider that the principal loss of aldrin and
dieldrin from soils is by volatilization. There is widespread
evidence for this, although other mechanisms (sections 4.4.1 and
4.4.2) may also play an important role.

Volatilization from soils was first demonstrated when it was
shown that mosquitoes were killed by vapour emanating from treated
soil blocks (Barlow & Hadaway, 1955, 1956; Gerolt, 1961).

When aldrin is incorporated into the soil, it is most readily
lost from the surface layer. Subsequently, material from deeper
layers has to rise to the surface to replenish what was lost. The
position is somewhat complicated by its gradual conversion to the
less volatile dieldrin, although this, too, behaves in a
qualitatively similar manner.

There are two routes to the surface: transport in ascending
capillary water - analogous to the process of salinization - and
vapour diffusion through the soil pores. Both of these processes
are strongly affected by hydrophobic adsorption, a phenomenon
common to many hydrophobic pesticides of low water solubility.
Adsorption by the soil has the effect, at practical rates of
application, of reducing the vapour pressure and hence the
saturation vapour density in the soil atmosphere. It also reduces
the maximum concentration in the soil solution.

There is a very extensive literature on soil adsorption,
especially of dieldrin and the following general situation is now
well established.

Adsorption, as measured by reduced vapour density, takes place
in all soils but is greatest at low moisture levels; that is to say
soils in equilibrium with air of relative humidity below around
95%. (Barlow & Hadaway, 1955, 1956; Gerolt, 1961; Harris, 1964,
1972; Igue et al., 1972).

In dry soils, mineral components play the most important part,
whereas in moist soils it is organic matter that dominates (Harris
& Lichtenstein, 1961; Harris et al., 1966; Harris & Sans, 1967;
Harris, 1972). In fact, Harris demonstrated a linear relation
between organic matter and adsorption in moist soils. On the other
hand, in a dry mineral soil with predominantly montmorillonitic
clay and very low organic matter, practically no dieldrin
volatilized until the relative humidity of the air in equilibrium
with soil reached saturation. At this point volatilization readily
resumed.

In moist soils, Spencer et al. (1969) found that adsorption,
expressed as a reduction in vapour density, became less marked as
the dieldrin level increased. At 20 °C, 10% moisture in the soil,
and 1 mg dieldrin/kg soil, the dieldrin vapour density was only 2
ng/litre, compared with 52 ng/litre when the dieldrin level in the
soil was increased to 25 mg/kg. This level is close to the figure
for free dieldrin. Similar results were reported at 30 °C and
40 °C by Spencer & Cliath (1973).

In dry soils, however, adsorption is far stronger. At 100 mg
dieldrin/kg moist soil (Spencer et al., 1969), the depression in
vapour pressure was negligible. However, as the moisture content
of the soil fell to a critical level of 2.1%, there was a dramatic
decrease in vapour density, so that below 2% moisture the vapour
density was practically zero. The same authors showed that the
level of water in their soil needed to provide a monomolecular
layer was 2.8%. They concluded that the critical point at which
adsorption increased was when the monomolecular layer started to be
lost, leaving adsorption sites available for occupation by
dieldrin. Restoration of the moisture status of the soil, however,
restored the vapour density to its original level.

Whilst most of these studies were carried out on one soil, Gila
silt loam, and whilst the figures would be different for other
soils, the qualitative conclusions are largely valid for all soils.
Adsorption is expected to be least on sandy soils of low organic
matter content.

Adsorption by soils can also be determined by measuring the
reduction in the saturation concentration of the soil solution
(Eye, 1968; Tejedor et al., 1974; Baluja et al., 1975). As in the
case of reduced vapour pressure caused by adsorption by moist
soils, the organic matter content of the soil was the principal
soil characteristic affecting adsorption from solution. Eye (1968)

also demonstrated the dominating influence of organic matter,
whereas clay content, surface area, and cationic exchange capacity
showed very little correlation. These findings are compatible with
those of Yaron et al. (1967).

In studies involving the percolation of dieldrin, dissolved in
water, through columns of soils with differing contents of organic
matter, Sharom et al. (1980) also showed that the soil capacity for
adsorption was largely determined by its content of organic matter.
Moreover, adsorption followed the Freundlich adsorption equation.
They reported Freundlich adsorption constants for a range of soils
and pesticides, including dieldrin, and showed that, for a given
pesticide, adsorption was strongly dependent on the organic matter
content of the soil. Moreover, the strength of adsorption by a
given soil depended mainly on the water solubility of the
pesticide, so that dieldrin, with its low water solubility, was
more strongly adsorbed than, for instance, the much more water-
soluble lindane. Although aldrin was not studied, it may be
inferred from these data that aldrin would be adsorbed
correspondingly more strongly, owing to a much lower water
solubility than that of dieldrin.

4.1.3.1 Movement within the soil profile - mass flow

Spencer & Cliath (1973) concluded from laboratory studies that
dieldrin could ascend the soil profile by mass flow in capillary
water moving up to the surface through a moisture gradient, and
that this mechanism could account for 3 - 30% of the total upward
movement. However, with low solubility products such as dieldrin,
Jury et al. (1983) pointed out that volatilization decreases with
time, because ascent to the surface is rate limiting. With high
solubility compounds, however, the reverse is true as more material
reaches the surface, dissolved in capillary water, to become
available for evaporation. However, it is not only water
solubility that determines the behaviour, but the value of Henry's
constant for the partition of the compound between air and water.
These authors considered the critical value to be 2.7 x 10^-5; above
this value mass flow is progressively less important. The value of
Henry's constant for dieldrin (6.7 x 10^-4) is substantially higher
(Jury et al., 1983) and that for aldrin higher still, so that on
this basis it is doubtful whether mass flow ever does play a
significant role in the transport of aldrin or dieldrin up the soil
profile.

In support of the view that transport by mass flow is not
appreciable, the mathematical models that have been proposed to
describe the loss of aldrin and dieldrin from soils (Farmer &
Letey, 1974; Mayer et al., 1974; Jury et al., 1983) tend to
demonstrate, in comparisons with laboratory data, that ascent to
the surface is predominantly by vapour diffusion rather than mass
flow.

4.1.3.2 Movement within the soil profile - diffusion

Diffusion is regarded as the main route by which aldrin and
dieldrin ascend the soil profile to reach the surface. Diffusion
increases with soil temperature, concentration, decreasing
adsorption capacity (usually the same as decreasing organic
matter), maintenance of moisture content above the wilting point,
and the "tortuosity" of the soil pore system (a measure of the
openness of the soil). With regard to moisture content, Farmer &
Jensen (1970) found that diffusion coefficients of dieldrin in
three soils in equilibrium with air of 94% relative humidity were
9.7, 4.4, and 3.8, but at 75% relative humidity the values were
0.6, 0.4, and 0.4, respectively. According to Farmer & Letey
(1974), the critical moisture level is probably the "fifteen
atmosphere percentage", usually considered to be a reasonable
measure of the water content at the wilting point.

Tortuosity increases as soils are compacted. Working with
moist soils of differing bulk densities, Farmer et al. (1973),
showed that diffusion of dieldrin was about twice as fast in a soil
with a density of 0.75 g/cm³as when it was compressed to a bulk
density of 1.5 g/cm³.

4.1.3.3 Actual volatilization losses - laboratory studies

Lichtenstein & Schulz (1970) reported that aldrin was lost by
volatilization from a silt loam soil about 20 times faster than
dieldrin. Helene et al. (1981) reported a 31% loss of aldrin from
a highly humic soil after 120 days but 62% from a soil of low
organic matter content.

In studies of moist soils in volatilization chambers, Farmer et
al. (1972) and Igue et al. (1972) found that the rate of loss by
volatilization gradually decreased with time. However, if
translated into terms of the open field, this could still represent
a loss of between 0.2 and 1.4 kg/ha per year, depending on the
depth of incorporation.

With a surface application of dieldrin in a microagroecosystem
chamber, Nash (1983) reported loss of dieldrin at the rate of 1 - 4
g/day, but this rate fell to about a half of its initial value
within 6 - 7 h. Incorporation of the dieldrin had the effect of
greatly slowing this loss rate (Nash, 1983).

4.1.3.4 Actual volatilization losses - field studies

The data on volatilization losses in the field are limited and
refer only to dieldrin. Caro & Taylor (1971) reported loss by
volatilization from an incorporated dieldrin application (5.6
kg/ha) of 2.8% of that applied (after 18 weeks). Spencer et al.
(1973) cited unpublished studies by Caro & Taylor (1971) where a
surface application was lost at the rate of 3% per hour. In a
later study, Caro & Taylor (1976) found that 4.5% of a dieldrin
application was lost by volatilization in the first year after
treatment. By the autumn, the loss rate was only 0.2 g/ha per day,

although this increased to 0.9 g/ha per day immediately after the
land was cultivated, due, presumably, to the exposure of fresh
soil.

Taylor et al. (1972, 1976) estimated a loss of dieldrin of 0.2
kg/ha from an incorporated application of dieldrin. However, only
6% remained from a surface application after 16 weeks, although in
this case a small amount was recovered as photodieldrin (Turner et
al., 1977).

Willis et al. (1972) demonstrated an 18% loss from a very high
application (22 kg/ha) of dieldrin after 5 months where the soil
was kept moist by irrigation. However, losses were substantially
less when the soil was not irrigated or when maintained under flood
conditions. The maximum rate of loss by volatilization was 0.2
kg/ha per day.

4.1.4 Losses of residues following treatment of soil with aldrin

One of the earliest systematic studies of the decline of aldrin
and dieldrin residues in soils, arising from the application of
aldrin to the soil, was by Decker et al. (1965), who sampled a wide
range of soils of known treatment history from Illinois, USA. They
demonstrated the transformation of aldrin to dieldrin and
considered that the loss of residues was a two-stage process.
There was a comparatively rapid loss in the first year after
treatment, a typical loss being 75% of the applied dose.
Thereafter, residues declined with a half-life of 2 - 4 years, the
reduced rate being apparently due to the greater proportion of
dieldrin in the residues. Elgar (1966) incorporated 2.2 kg
aldrin/ha into soils in the United Kingdom and reported somewhat
similar results for the decline of residues, although there were
indications that the rate of decline slowed in later years as the
level in the soil fell to around 0.3 mg/kg. Further studies of
this kind have been reported by Lichtenstein et al. (1970), Onsager
et al. (1970), and Korschgen (1971). Although the rates of decline
were very variable, they were not inconsistent with the data of
Decker et al. (1965), bearing in mind the inherent variability of
soil data.

There are indications that loss rates are higher in tropical
soils than in temperate climates. Whilst Agnihotri et al. (1977)
found that epoxidation was faster in tropical than temperate soils,
leading to the possibility of slower decline because of higher
dieldrin levels, Gupta & Kavadia (1979) found in India that
declines were often much faster. In one case, half of the aldrin
applied had been lost in only 38 days. Wiese & Basson (1966) also
reported comparatively high loss rates in South Africa. Using
three rates of treatment and three soils, they found that half of
the original application was lost between 1 and 2 months.

Elgar (1975) conducted a series of studies in temperate, warm
temperate, and tropical soils and reported rates of decline that
were compatible with those of Decker et al. (1965). Again, losses
from the tropical sites occurred more rapidly than from the

temperate sites. He deduced the following empirical expression to
describe loss rates, expressed as the sum of aldrin and dieldrin
residues surviving n years after a single application.

C(n) = fC(o)(1-p)^n-1

In this expression, C(o) is the initial residue level, C(n) is the
level after n years, f is the proportion remaining after the first
year, and p is the proportion lost in each of the succeeding years.
In Elgar's studies, the mean estimate of these latter two
parameters was f = 0.25 and p = 0.44, but in the Decker work, the
value of p was somewhat less. It is also possible to derive an
equation that describes the accumulation of residues in a soil
subject to a regular routine of annual applications. The
implications of this equation are that residue levels do not
continue to increase indefinitely, but reach a plateau. In the
case of Elgar's data, the plateau level, one year after the last of
n applications, would be around 60% of the level observed
immediately after the first application. This prediction is well
borne out by the soil monitoring data presented in Table 1.

Studies of the decline of residues arising from aldrin applied
for the control of termites (Bess & Hylin 1970; Carter & Stringer,
1970) reveal slower rates of decline than would be expected,
considering the deep application.

Separate studies have been carried out on dieldrin residue
losses. These show considerably slower rates of decline than in
the case of aldrin, but there is a very wide range in the data
reported. Thus, Edwards (1966) reported that the average time for
the disappearance of 95% of the residues was 8 years, but Wiese &
Basson (1966) found much faster rates. Intermediate rates were
reported by Stewart & Fox (1971) and Beyer & Gish (1980). It seems
probable that the rate of decline of dieldrin in the soil is
reasonably well reflected by Elgar's equation for the years that
succeed the first year of aldrin application.

4.1.5. Losses of residues from water

The partition of dieldrin between the vapour phase and water
was determined by a dynamic gas-flow method using ¹⁴C-dieldrin
(Atkins & Eggleton, 1970). The partition coefficient at 20 °C
(expressed on a weight/volume basis for air and water) was constant
at 540, up to a concentration of 0.033 mg dieldrin/litre water. At
higher concentrations, there was a rapid increase in the partition
coefficient, which was attributed to the aqueous solution becoming
saturated at 0.033 mg/litre. Using the values for vapour pressure
(3.47 x 10^-4Pa) and water solubility found in this study, the
wash-out ratio for the removal of dieldrin vapour from atmospheric
air by rain was 0.65. It was suggested that the concentration of
dieldrin in the rainfall in London (Abbott et al., 1965) (Table 6)
may indicate the presence of dieldrin in particulate matter in the
atmosphere rather than in the vapour phase.

Table 1. Concentrations of aldrin and dieldrin in soil^a
------------------------------------------------------------------------------------------------------------------------------
Location Year Use Number Mean concentration Comments Reference
of in mg/kg (maximum
sites value in brackets)
aldrin dieldrin
------------------------------------------------------------------------------------------------------------------------------
United aldrin: potatoes 21 0.02 0.09 LD < 0.03 mg/kg Wheatley et
Kingdom (0.12) (0.41) al. (1962)

1965 aldrin: potatoes; 10 0.15 0.48 LD not reported; apparently Davis (1968)
dieldrin: seed-dressing, (0.7) (0.7) < 0.02 mg/kg; various soil
carrots, and wheat; types; residues in soil
cumulative applications microfauna also determined
during 5 years prior to
sampling (0.14-3.4
kg/ha)

Canada

S.W. Ontario 1964-65 aldrin: various crops; 13 0.19 0.57 LD < 0.1 mg/kg; soil of Harris et al.
known usage (0.8) (1.3) various types (sandmuck); (1966)
aldrin used to a
considerable extent
(1954-60) on 27 sites

no reported use 1961-64 14 0.18 0.25
(2.1) (1.6)

none used 1954-64 5 LD LD

Atlantic 1965 aldrin: 1-5 applications LD 0.01 mg/kg; no detectable Duffy & Wong
provinces during 15 years prior to residues of aldrin or (1967)
sampling; cumulative dieldrin in orchard soils to
application 0.5-45 kg/ha; which aldrin/dieldrin had
not been applied

root crops 18 0.46 0.41
(1.5) (1.45)

vegetables 17 0.66 0.36
(2.5) (1.35)
------------------------------------------------------------------------------------------------------------------------------

Table 1. (contd.)
------------------------------------------------------------------------------------------------------------------------------
Location Year Use Number Mean concentration Comments Reference
of in mg/kg (maximum
sites value in brackets)
aldrin dieldrin
------------------------------------------------------------------------------------------------------------------------------
Southern 1971 aldrin: tobacco 4 (50 ND 0.16 LD 0.001 mg/kg; woodlots Frank et al.
Ontario samples) (0.19) were adjacent to treated (1974)
areas, but not directly
sprayed

cereals 4 (60 ND 0.16
samples) (0.19)

woodlots 12 ND trace
samples

Saskatchewan 1970 soil from 21 vegetable 41 0.03 0.06 LD 0.005 mg/kg; aldrin found Saha & Sumner
farms samples (0.28) (0.77) in 25% of samples; dieldrin (1971)
found in 55% of samples

Southern 1972-75 soil samples from LD < 0.0004 mg/kg; dieldrin Frank et al.
Ontario orchards had been used (1955-65) (1976)
at recommended rates of
0.8-1.3 kg/ha

apple: 0-15 cm 31 ND 0.03
(0.38)
15-30 cm ND 0.001
(0.03)

Southern 1972-75 sweet cherry: 16 Frank et al.
Ontario 0-15 cm ND 0.001 (1976)
(0.01)
15-30 cm ND LD

sour cherry: 12
0-15 cm ND 0.005
(0.04)
15-30 cm ND 0.003
(0.02)
------------------------------------------------------------------------------------------------------------------------------

Table 1. (contd.)
------------------------------------------------------------------------------------------------------------------------------
Location Year Use Number Mean concentration Comments Reference
of in mg/kg (maximum
sites value in brackets)
aldrin dieldrin
------------------------------------------------------------------------------------------------------------------------------
Southern peach: 11
Ontario 0-15 cm ND 0.04
(contd.) (0.11)
15-30 cm ND 0.02
(0.07)
vineyards: 16
0-15 cm ND 0.009
(0.035)
15-30 cm ND 0.004
(0.023)

USA

Seven eastern 1965 aldrin and dieldrin in 3 LD 0.05 mg/kg; proportions Seal et al.
states crops: of soil samples with (1967)
measurable residues:

peanuts: 5 ND 0.15 potatoes, 76%; carrots,
(0.20) 21%; peanuts, 100%
carrots: 19 ND 0.19
(0.26)
potatoes: 25 ND 0.10
(0.20)

1965-67 aldrin and dieldrin used 17 (278 0.02 0.21 LD 0.01 mg/kg; aldrin Stevens et al.
regularly samples) (0.47) (2.84) detected in 15% of samples (1970)
and dieldrin in 67% of
samples from areas of
regular use

limited use 16 LD 0.001
(0.001)

no known use 18 LD LD
------------------------------------------------------------------------------------------------------------------------------

Colorado 1967 aldrin: various soil 11 0.16 0.19 LD < 0.02 mg/kg; some Mullins et al.
types (1-4.3% organic (0.61) (0.44) fields had been treated (1971)
matter); nominal annually for 9 years; time
concentrations in soil at of last treatment prior to
time of application: sampling varied from 0-9
0.06-6.75 mg/kg years

dieldrin: nominal 9 ND 0.05
concentrations in soil at (0.30)
time of application:
0.13-0.63 mg/kg

Arizona 1968 3 types of soil (organic 13 LD 0.0003 LD not defined; appears to Laubscher et
matter 0.5-6.6%) from (0.0013) be about 0.0001 mg/kg; no al. (1971)
area downwind of relationship between
an area of insecticide concentration of dieldrin
use and distance from area of
application

10 major 1969 samples of soil 71 0.02 0.79 LD 0.01 mg/kg; aldrin in Wiersma et al.
areas of (0.96) (16.72) 4.2% of samples and (1972)
onion growing dieldrin in 73% of samples

9 areas 1969 samples of soil 92 0.01 0.17 LD 0.01 mg/kg; aldrin in Sand et al.
growing sweet (0.11) (2.18) 3.3% and dieldrin in 60.9% (1972)
potatoes of samples

Rice-growing 1972 samples of soil 99 0.01 0.04 LD 0.01 mg/kg; aldrin in Carey et al.
areas (0.25) (0.27) 39% and dieldrin in 85% of (1980)
samples

USA National 1970 samples of soil 1506 0.02 0.04 LD 0.01 mg/kg; aldrin in Crockett et al.
Monitoring (4.25) (1.85) 13% and dieldrin in 31% of (1974)
Program samples
(35 states)
------------------------------------------------------------------------------------------------------------------------------

12 states in 1970 average application of 12 (389 0.05 0.07 LD <0.01 mg/kg; dieldrin Carey et al.
the cornbelt dieldrin was 1.3 kg/ha samples) (2.98) (2.04) residues attributed (1973)
region primarily to the use of
aldrin; aldrin had been
used in one or more years
from 1954

14 cities 1970 soil from urban areas 356 LD 0.1 LD < 0.03 mg/kg; aldrin Carey et al.
sampled to a depth of (12.8) not detected in any (1976)
7.6 cm samples; dieldrin in
samples from 22 sites
(6.5%) in 6 cities

Japan, S.W.

Kyushu 99 0.07 0.29 LD 0.001 mg/kg Suzuki et al.
district samples (1.01) (1.73) (1973)
------------------------------------------------------------------------------------------------------------------------------
^aLD = limit of detection; ND = not determined.
The rate of dry deposition of dieldrin (vapour phase) on grass,
calculated from the results of wind tunnel studies, was 4 x 10^-2
cm/second. The average lifetime of dieldrin in the atmosphere,
assuming loss by wash-out and dry deposition only, was estimated to
be 28 weeks (Atkins & Eggleton, 1970).

The rate of transfer of dieldrin from water to air and vice
versa has been determined (Slater & Spedding, 1981). The transfer
velocity from water, measured in a wind tunnel, increased as the
air speed (measured at 6 cm above the water surface) increased.
When there was no air movement, the transfer velocity was 2.6 x
10^-5cm/second compared to 15 x 10^-5cm/second at an air velocity
of 31.1 km/h. The transfer velocity from air to water was measured
by passing air through a column of downward-flowing water, and was
found to increase as the interfacial velocity increased from 0.9 x
10^-2cm/second (at 10 km/h) to 5.2 x 10^-2cm/second (at 34.2 km/h).
It was suggested that the exchange of dieldrin between water and
air was controlled by diffusive processes either in the air
boundary or water boundary layers. The Henry's law constant (ratio
of the concentrations in air and aqueous phases at equilibrium) for
dieldrin was 1.3 x 10^-3at 20 °C. It was concluded that the
resistances to transfer of dieldrin from water to air and vice
versa were similar.

The physical and thermodynamic principles of exchanges of
chemicals between water and air have been discussed (Mackay &
Wolkoff, 1973; Liss & Slater, 1974; Mackay & Leinonen, 1975; Mackay
et al., 1979; Smith et al., 1981). An estimate of the half-life of
the evaporation of dieldrin at 25 °C from a column of water of 1 m
depth was derived by Mackay & Leinonen (1975). Although this
estimate (539 days) is not based on the most recent and reliable
values for the vapour pressure and water solubility of dieldrin, it
is probably of the right order.

4.1.6. Aldrin and dieldrin in the atmosphere

Small amounts of dieldrin have been detected in the atmosphere
(Table 6). Baldwin et al. (1977) conducted a study at Bantry Bay
on the west coast of Ireland, well away from point sources of
emission. They found concentrations of dieldrin between 0.06 and
1.6 ng/kg, with an average of 0.36 ng/kg, but no aldrin,
photodieldrin, or photoaldrin. No dieldrin was detected on solid
matter trapped on filter pads; the limit of determination ranged
from 1.1 to 7.2 pg/kg (parts per thousand trillion of air).

The reason for the very low level of occurrence of dieldrin in
the global atmosphere, if, as seems probable, a major part of the
aldrin used in agriculture escapes from the soil by evaporation,
has been the subject of considerable speculation. It appears
unlikely that direct photochemical reactions are involved, since
there have been no reports of photodieldrin being detected.
Washout by rain may be an important factor. Indeed, Baldwin et al.
(1977) cited literature figures for Hawaii of 1 - 97 ng/litre, and
Abbott et al. (1965) reported 1 - 95 ng/litre in rainfall in London
and other locations in the United Kingdom. MacCuaig (1975), on the

other hand, working in the vicinity of a dieldrin application in
Ethiopia, reported 100 µg/litre in rainwater. These results
support the suggestion of Atkins & Eggleton (1970) that, though
washout of the atmosphere by rain would be inefficient in the case
of dieldrin, it could lead to substantial losses. If this were so,
dieldrin deposits would be expected on soil adjacent to treated
areas, but the fact that large areas of soil in the cornbelt of the
USA (Carey et al., 1973) have no detectable levels of aldrin or
dieldrin seems to cast doubt on the extent to which rain acts to
disperse aldrin and dieldrin onto untreated land near to treated
areas.

It would appear possible, therefore, that there are losses of
aldrin and dieldrin in the atmosphere. Glotfelty (1978) mentioned
the high reactivity of free radical species in the atmosphere, in
particular hydroxyl radicals. These could presumably play an
important role in the degradation of molecules occurring as vapour.

4.1.7. Aldrin and dieldrin in water

The data regarding the occurrence of aldrin and dieldrin in
both ground and surface waters are summarized in Table 7 (section
5.1.3). As would be expected from the extreme resistance of
dieldrin and, especially, aldrin to leaching from soil, the
occurrence of either compound in groundwater is rare. Spalding et
al. (1980) took a series of groundwater samples in Nebraska, USA,
where aldrin had been used extensively for the control of corn
rootworm and could not detect it in any of the samples. Their
limit of determination was between 5 and 10 ng/litre. Junk et al.
(1980) reported somewhat similar results from Nebraska. Richard et
al. (1975), in a wide-ranging study, examined the water supplied to
a series of cities in Iowa, USA, from boreholes. Again, no aldrin
or dieldrin was reported; their limit of determination appears to
have been 0.5 ng/litre.

Surface waters, by contrast, have often been reported to
contain small amounts of dieldrin. In a programme of sampling
various surface waters in Iowa, Richard et al. (1975) reported
levels of dieldrin ranging from 3 to 75 ng/litre in rivers and
streams and levels in reservoirs from 3 to 18 ng/litre. In rivers
in Iowa and Louisiana, levels ranged from < 1 to 42 ng/litre.
During the period 1976 - 80, dieldrin was found in 2.4% of samples
from national surface waters in the USA, (maximum concentration of
0.61 µg/litre) and in 21.7% of national surface water sediments
(maximum concentration of 5300 µg/kg) (Carey & Kutz, 1985).

The dieldrin in surface water probably comes from run-off from
treated land. Sparr et al. (1966) sampled drainage ditches and a
river in a maize growing area in northwest Indiana, USA. Levels
reached 0.6 µg/litre in the river but, in the ditches from fields
treated with aldrin at up to 5.6 kg/ha, levels seldom exceeded the
limit of determination (0.05 µg/litre). Water draining from rice
paddies that had been planted with aldrin-treated seed also
contained small amounts of dieldrin (1 µg/litre after seeding and

falling by the 14th week to 0.07 µg/litre). The authors calculated
that about 1 g of aldrin had been lost from the rice paddy surface
water during the whole 14-week period.

Hindin et al. (1964) reported aldrin in irrigation water up to
2.3 µg/litre, but no dieldrin. However, in view of the readiness
with which aldrin is epoxidized to dieldrin in surface waters,
there must be some doubt as to the identity of the residue they
actually measured.

It does appear that dieldrin can occur in surface waters
draining from agricultural areas, but the amounts are usually so
small that they could not be expected to represent a major
proportion of the product applied to the soil. The ultimate fate
of these small levels of dieldrin in water is not known. It is
probably that adsorption onto particulate matter, volatilization,
and various degradation mechanisms all play a role.

4.2 Translocation From Soil Into Plants

The uptake of aldrin and dieldrin by plants is much higher in
root crops than in grain crops. It is influenced by the levels in
soils, the strength of adsorption, and the depth of application.

In grain crops, it is rare for residues to reach detectable
levels in the grain (FAO/WHO, 1970a; Gupta & Kavadia, 1979). Root
crops are much more prone to take up residues from treated soils,
as observed by Harris & Sans (1967) who found that carrots,
radishes, and turnips had the highest residues. Onions, lettuce,
and celery were intermediate and cole crops showed no detectable
uptake at all (Lichtenstein, 1959).

The level of aldrin and dieldrin in the soil influences the
degree of uptake as shown by Lichtenstein et al. (1970) and Edwards
(1973a,b), who both reported on ratios of the concentrations in
plants to those in the soil. Further work by Onsager et al.
(1970), Voerman & Besemer (1975), Bruce & Decker (1966), and Saha
et al. (1971) provided compatible results.

The availability of aldrin and dieldrin for uptake by plants
depends on the strength of adsorption by the soil and especially
the organic matter fraction. Harris & Sans (1967), Beall & Nash
(1969), Beestman et al. (1969), and Nash et al. (1970) demonstrated
that crops tend to take up more residues from soil of low than of
high organic matter. Adding activated charcoal to soil reduced
dieldrin uptake by 70% or more in carrots and potatoes
(Lichtenstein et al., 1971).

Deep application of dieldrin greatly reduces the uptake (Beall
& Nash, 1972). Residues in the plants from a deep (31 - 32 cm)
application were only 1% of those from superficial application.
The authors commented that a possible treatment for reducing the
uptake of old soil residues by crops would be simply to plough them
under.

The mechanism of uptake by crops is not entirely clear and
appears to vary considerably from species to species. Beall & Nash
(1971), in work with soyabeans grown on soil treated with ¹⁴C-
labelled dieldrin, found that residues were taken up both by
absorption through the roots and by absorption of vapour through
the leaves. In the case of cereals, it seems unlikely that root
uptake occurs to any great extent (Powell et al., 1970; Gutenmann
et al., 1972; Gupta et al., 1979). This probably accounts for the
very low levels found in cereal grains from treated crops. On the
other hand, it would seem almost certain that it is root uptake
which accounts for the residues found in root crops.

4.3. Models of the Behaviour of Water and Chemicals in Soil

Various models for the movement of water and chemicals in
porous media have been developed, based on physical variables such
as vapour pressure, diffusibility, and adsorption, etc. (Keller &
Alfaro, 1966; Bresler & Hanks, 1969; Lindstrom et al., 1971;
Davidson & McDougal, 1973; Pionke & Chester, 1973; Van Genuchten et
al., 1974). Models for run-off from soil have also been proposed
(Crawford & Donigian, 1973; Bailey et al., 1974; Bruce et al.,
1975). These models may be useful as a means of defining more
precisely the behaviour of aldrin and dieldrin in soil.

4.4. Biodegradation of Aldrin and Dieldrin

When used to protect crops from soil insects, aldrin is usually
incorporated into the soil in which the plants are grown. For this
reason, most of the work on the biodegradation of aldrin in
agriculture has been concerned with the soil system.

4.4.1. Epoxidation of aldrin

The most important transformation of aldrin in the soil is its
conversion by epoxidation to dieldrin (Fig. 2, section 6.3.1.1).
Epoxi