INTERNATIONAL PROGRAMME ON CHEMICAL SAFETY
ENVIRONMENTAL HEALTH CRITERIA 153
Carbaryl
This report contains the collective views of an international group of
experts and does not necessarily represent the decisions or the stated
policy of the United Nations Environment Programme, the International
Labour Organisation, or the World Health Organization.
First draft prepared by Professor F. Kaloyanova
(National Center of Hygiene and Medical Ecology
Sofia, Bulgaria) and Dr. P.P. Simeonova
(University of Sofia, Bulgaria)
Published under the joint sponsorship of
the United Nations Environment Programme,
the International Labour Organisation,
and the World Health Organization
World Health Orgnization
Geneva, 1994
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of the biological action of chemicals.
WHO Library Cataloguing in Publication Data
Hexachlorobutadiene.
(Environmental health criteria: 153)
1. Carbaryl - adverse effects 2. Carbaryl - toxicity
3. Environmental exposure I.Series
ISBN 92 4 157153 5 (NLM Classification QU 98)
ISSN 0250-863X
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CONTENTS
1. SUMMARY AND EVALUATION, CONCLUSIONS AND RECOMMENDATIONS
1.1. Summary and evaluation
1.1.1. Identity, properties, and analytical methods
1.1.2. Production and uses
1.1.3. Environmental transport, distribution, and
transformation
1.1.4. Environmental levels and human exposure
1.1.5. Kinetics and metabolism
1.1.6. Effects on organisms in the environment.
1.1.7. Effects on experimental animals and in vitro
test systems
1.1.7.1 Reproduction
1.1.7.2 Mutagenicity
1.1.7.3 Carcinogenicity
1.1.7.4 Effects on different organs and systems
1.1.7.5 Primary mechanism of toxicity
1.1.8. Effects on humans
1.2. Conclusions
1.2.1. General population exposure
1.2.2. Subpopulations at high risk
1.2.3. Occupational exposure
1.2.4. Environmental effects
1.3. Recommendations
2. IDENTITY, PHYSICAL AND CHEMICAL PROPERTIES, ANALYTICAL METHODS
2.1. Identity
2.2. Physical and chemical properties
2.3. Conversion factors
2.4. Analytical methods
3. SOURCES OF HUMAN AND ENVIRONMENTAL EXPOSURE
4. ENVIRONMENTAL TRANSPORT, DISTRIBUTION, AND TRANSFORMATION
4.1. Volatilization and air transportation
4.2. Water
4.2.1. Hydrolysis
4.2.2. Photolysis
4.2.3. Degradation by microorganisms
4.2.4. Persistence in surface water
4.2.5. Removal from water
4.2.6. Persistence in sea water
4.2.7. Bioaccumulation/biomagnification
4.3. Soil
4.3.1. Adsorption, desorption
4.3.2. Transformation
4.3.2.1 Photolysis in soil
4.3.3. Biotransformation in soil
4.3.4. Degradation by microorganisms
4.3.5. Persistence in soil
4.3.6. Interaction with other physical, chemical, or
biological factors
4.3.7. Vegetation
4.3.7.1 Uptake and transformation in plants
5. ENVIRONMENTAL LEVELS AND HUMAN EXPOSURE
5.1. Environmental levels
5.1.1. Air
5.1.2. Water
5.1.3. Soil
5.1.4. Food and animal feed
5.1.4.1 Fruit, vegetables, and grain
5.1.4.2 Animal products
5.1.4.3 Animal feed crops
5.1.5. Other products
5.1.6. Terrestrial organisms
5.2. General population exposure
5.2.1. Exposure through the food
5.2.2. Exposure during insect control
5.3. Occupational exposure during manufacture, formulation,
or use
6. KINETICS AND METABOLISM
6.1. Absorption
6.2. Distribution
6.3. Metabolism
6.3.1. In vitro studies on animal tissues
6.3.2. In vivo studies on animals
6.3.3. Metabolic transformation in plants
6.3.4. In vitro studies with human tissues
6.3.5. In vivo studies on humans
6.4. Elimination and excretion in expired air, faeces, urine,
milk, and eggs
7. EFFECTS ON ORGANISMS IN THE ENVIRONMENT
7.1. Microorganisms
7.1.1. Soil microorganisms
7.1.2. Aquatic microorganisms
7.2.1. Aquatic invertebrates
7.2.2. Fish
7.2.2.1 Acute toxicity
7.2.2.2 Short-term
and long-term toxicity
7.2.3. Amphibians
7.3. Terrestrial organisms
7.3.1. Worms
7.3.2. Insects
7.3.3. Birds
7.3.4. Mammals
7.4. Effects on the population and ecosystem
8. EFFECTS ON EXPERIMENTAL ANIMALS AND IN VITRO TEST SYSTEMS
8.1. Single exposures
8.1.1. Oral toxicity
8.1.2. Acute inhalation toxicity
8.1.3. Dermal toxicity
8.1.4. Other routes of exposure
8.2. Skin and eye irritation, sensitization
8.2.1. Skin and eye irritation
8.2.2. Sensitization
8.3. Short- and long-term oral exposure
8.4. Short- and long-term inhalation toxicity
8.5. Reproduction and developmental toxicity
8.5.1. Mammalian reproductive
toxicity studies
8.5.1.1 Mouse
8.5.1.2 Rat
8.5.1.3 Gerbil
8.5.2. Mammalian developmental
toxicity studies
8.5.2.1 Mouse
8.5.2.2 Rat
8.5.2.3 Guinea-pig
8.5.2.4 Rabbit
8.5.2.5 Dog
8.5.2.6 Pig
8.5.2.7 Monkey
8.5.3. Reproductive and developmental toxicity studies
in non-mammalian species
8.5.3.1 Fish
8.5.3.2 Amphibian
8.5.3.3 Birds
8.5.4. Appraisal
8.6. Mutagenicity of carbary
and N-nitrosocarbaryl
8.6.1. Genotoxicity assays in vitro
8.6.1.1 Primary DNA damage
8.6.1.2 Gene mutation assay
8.6.1.3 Chromosomal aberration
assays and sister
chromatid exchange
8.6.2. Genotoxicity in vivo
8.6.2.1 Host-mediated assay
8.6.2.2 Drosophila melanogaster and
other insects
8.6.2.3 Chromosomal aberrations
and sister chromatid
exchange
8.6.2.4 Dominant lethal assays
in rodents
8.6.3. Other end-points
8.6.3.1 Cell transformation
8.6.3.2 Aneuploidy induction
8.6.4. Appraisal
8.7. Carcinogenicity
8.7.1. Carcinogenicity studies
of carbaryl in rodents
8.7.1.1 Mouse
8.7.1.2 Rats
8.7.1.3 Overall appraisal of carbaryl
carcinogenicity
8.7.2. Carcinogenicity studies
of N-nitrosocarbaryl
8.7.2.1 Rats
8.7.2.2 Mice
8.7.2.3 Overall evaluation
of the carcinogenicity of
N-nitrosocarbaryl
8.7.3. Carcinogenicity of ß-carbaryl
8.8. Special studies
8.8.1. Neurotoxicity
8.8.2. Effects on the immune system
8.8.2.1 Appraisal on immunotoxicology
8.8.2.2 In vivo studies
8.8.2.3 In vitro studies
8.8.3. Effects in blood
8.8.4. Effects on the liver and other organs
8.8.5. Effects on serum glucose
8.8.6. Interactions with the
drug metabolizing enzyme system
8.8.7. Effects on the endocrine system
8.8.8. Other studies
8.9. Factors modifying toxicity, toxicity of metabolites
8.9.1. Factors modifying toxicity
8.9.2. Toxicity of metabolites
8.9.3. N-nitrosocarbaryl
8.10. Mechanism of toxicity - mode of action
8.10.1. Inhibition of cholineresterase activity
9. EFFECTS ON HUMAN BEINGS
9.1. General population exposure
9.1.1. Acute toxicity, poisoning incidents
9.1.2. Controlled human studies
9.1.3. Long-term exposure
9.2. Occupational exposure
9.2.1. Epidemiological studies
10. PREVIOUS EVALUATION BY INTERNATIONAL BODIES
REFERENCES
APPENDIX
RESUME ET EVALUATION, CONCLUSIONS ET RECOMMANDATIONS
RESUMEN Y EVALUACION, CONCLUSIONES Y RECOMENDACIONES
WHO TASK GROUP ON ENVIRONMENTAL HEALTH CRITERIA FOR CARBARYL
Members
Dr C.D. Carrington, Food and Drug Administration (FDA) Washington,
DC, USA (Chairman).
Dr N. Chernoff, US Environmental Protection Agency, Research
Triangle Park, North Carolina, USA
Dr T.S.S. Dikshith, VIMTA Labs Ltd, Hyderabad, India
Professor F. Kaloyanova, National Center of Hygiene and Medical
Ecology, Sofia, Bulgaria (Rapporteur)
Professor Yu.I. Kundiev, Institute for Occupational Health, Kiev,
Ukraine (Vice-Chairman)
Dr D. Osborn, Institute of Terrestrial Ecology, Monks Wood
Experimental Station, Huntingdon, United Kingdom
Professor C. Ramel, University of Stockholm, Stockholm, Sweden
Professor Shou-Zheng Xue, Shanghai Medical University, Shanghai, The
People's Republic of China
Observers
Dr S. Kozlen, Rhône-Poulenc, Lyon, France (Representative from
Rhône-Poulenc)
Dr P.G. Pontal, Rhône-Poulenc, Lyon, France (Representative from
ECETOC)
Mr D. Demozay, Rhône-Poulenc, Lyon, France (Representative from
GIFAP)
Secretariat
Dr K.W. Jager, International Programme on Chemical Safety, WHO,
Geneva, Switzerland (Secretary)
NOTE TO READERS OF THE CRITERIA MONOGRAPHS
Every effort has been made to present information in the
criteria monographs as accurately as possible without unduly
delaying their publication. In the interest of all users of the
environmental health criteria monographs, readers are kindly
requested to communicate any errors that may have occurred to the
Director of the International Programme on Chemical Safety, World
Health Organization, Geneva, Switzerland, in order that they may be
included in corrigenda, 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, Case
postale 356, 1219 Châtelaine, Geneva, Switzerland (Telephone No.
9799111).
* * *
This publication was made possible by grant number 5 U01
ES02617-14 from the National Institute of Environmental Health
Sciences, National Institutes of Health, USA.
* * *
NOTE: The proprietary information contained in this document
cannot replace documentation for registration purposes, because the
latter has to be closely linked to the source, the manufacturing
route, and the purity/impurities of the substance to be registered.
The data should be used in accordance with paragraphs 82-84 and
recommendations paragraph 90 of the Second FAO Government
Consultation (1982).
ENVIRONMENTAL HEALTH CRITERIA FOR CARBARYL
A WHO Task Group on Environmental Health Criteria for Carbaryl
met at the World Health Organization, Geneva, from 21 to 25
September 1992. Dr K.W. Jager, of the IPCS, welcomed the
participants on behalf of the Director IPCS and the three IPCS
cooperating organizations (UNEP/ILO/WHO). The Group reviewed and
revised the draft criteria monograph and made an evaluation of the
risks for human health and the environment from exposure to
carbaryl.
The first draft was prepared by Professor F. Kaloyanova of the
National Center of Hygiene and Medical Ecology and Dr P.P.
Simeonova, Medical Faculty, University of Sofia, Bulgaria, who also
prepared the second draft, incorporating comments received following
circulation of the first drafts to the IPCS contact points for
Environmental Health Criteria monographs.
Dr K.W. Jager of the IPCS Central Unit was responsible for the
scientific content of the document, and Mrs M.O. Head of Oxford,
England, for the editing.
The fact that Rhône-Poulenc Agro, Lyon, France, made available
to the IPCS and the Task Group its proprietary toxicological
information on the product under discussion 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 this publication are gratefully acknowledged.
1. SUMMARY AND EVALUATION, CONCLUSIONS AND RECOMMENDATIONS
1.1 Summary and evaluation
1.1.1 Identity, properties, and analytical methods
Carbaryl is the common name for the carbamic acid derivative
1-naphthyl N-methylcarbamate. The technical grade product is a white
crystalline solid, with a low volatility; it is poorly soluble in
water, which is stable to light and heat, but easily hydrolysed in
alkaline media. The FAO has established a minimum specification of
98% purity, with an impurity limit of 0.05% for ß-naphthyl
N-methylcarbamate.
Carbaryl and its metabolites are analysed using numerous
analytical procedures, such as thin-layer chromatography,
spectro-photometry, gas chromatography, high pressure liquid
chromatography, and chemical ionization mass spectrometry. Detection
limits of below one nanogram are achievable and recovery is usually
more than 80%.
1.1.2 Production and uses
Carbaryl has been used for about 30 years as a contact and
ingestion insecticide with some systemic properties and controls a
wide range of pests. The principal production plant is in the USA.
Carbaryl is processed by more than 290 formulators into over 1500
different products.
1.1.3 Environmental transport, distribution, and transformation
Under most conditions, carbaryl is not persistent in the
environment. In water, the hydrolysis half-life is dependent on the
temperature, pH, and the initial concentration, and varies from
several minutes to several weeks. The major degradation product is
1-naphthol.
Accumulation of carbaryl, expressed as a bioconcentration
factor in the aquatic environment, has been studied in freshwater
fish and found to be in the range of 14-75. Carbaryl is adsorbed
more readily on soils with a high organic content than on sandy
soils. At the usual application rates, under "good agricultural
practice", dissipation is rapid, with a half-life of 8 days to
1 month under normal conditions. Carbaryl may occasionally be
carried by rainfall and soil cultivation from the surface into the
subsoil (one metre from the surface).
Carbaryl contaminates vegetation, either during spraying, or by
migrating through contaminated soil into plants.
The degradation of carbaryl in the environment is determined by
the extent of the volatilization, photodecomposition, and chemical
and microbial degradation occurring in soil, water, and plants. The
rate of decomposition is more rapid under hot climatic conditions.
1.1.4 Environmental levels and human exposure
Food represents the major source of carbaryl intake for the
general population.
Residues in total dietary samples are relatively low, ranging
from trace amounts to 0.05 mg/kg. In the USA, the daily intake
during the first years of carbaryl application was 0.15 mg/day per
person (in 7.4% of the composites); this decreased to 0.003 mg/day
per person in 1969 (in only 0.8% of the composites). During the
period of application, carbaryl may be found, occasionally, in
surface water and reservoirs.
The general population can be exposed to carbaryl during pest
control operations in both the home and recreation areas.
Workers can be exposed to carbaryl during its manufacture,
formulation, packing, transportation, storage, and during and after
application. Concentrations in the working-air environment during
production varied from <1 mg/m3 to 30 mg/m3. Significant dermal
exposure may occur in industrial and agricultural workers if
protective measures are inadequate.
1.1.5 Kinetics and metabolism
Carbaryl is rapidly absorbed in the lungs and digestive tract.
In human volunteers, dermal absorption of 45% of an applied dose in
acetone occurred in 8 h. However, in vitro dermal penetration data
and toxicity data indicate that dermal absorption usually occurs at
a much lower rate.
The principal metabolic pathways of carbaryl are ring
hydroxylation and hydrolysis. As a result, numerous metabolites are
formed and subjected to conjugation with the formation of
water-soluble sulfates, glucuronides, and mercapturates, excreted in
the urine. Hydrolysis results in the formation of 1-naphthol, carbon
dioxide, and methylamine. Hydroxylation produces 4-hydroxycarbaryl,
5-hydroxycarbaryl, N-hydroxymethylcarbaryl, 5-6-dihydro-5-6-
dihydroxycarbaryl, and 1,4-naphthalendiol. The principal metabolite
in humans is 1-naphthol.
Under normal exposure conditions, the accumulation of carbaryl
in animals is unlikely. Carbaryl is excreted primarily via the
urine, since the product of its hydrolysis, 1-naphthol, is mainly
detoxified to water-soluble conjugates. Enterohepatic cycling of
carbaryl metabolites is also considerable, especially after oral
administration.
The hydrolysis product, N-naphthol carbamic acid, is
spontaneously decomposed to methylamine and carbon dioxide. The
methylamine moiety is later demethylated to carbon dioxide and
formate, the latter being excreted mainly in the urine.
Carbaryl metabolites are also present in a small percentage of
the absorbed doses in saliva and milk.
1.1.6 Effects on organisms in the environment
LC50 values for crustacea vary from 5 to 9 µg/litre (water
fleas, mysid shrimps), 8 to 25 µg/litre (scud), and 500 to
2500 µg/litre (crayfish). Aquatic insects have a similar range of
sensitivity. Plecoptera and Ephemeroptera (stoneflies and mayflies)
are the most sensitive groups. Molluscs are less susceptible with
EC50s in the range of a few mg/litre. For fish, most LC50 values
are between 1 and 30 mg/litre. Salmonids are the most sensitive
group.
The acute toxicity for birds is low. The LD50 for waterfowl
and game birds is >1000 mg/kg. The most susceptible bird tested is
the red-winged blackbird (LD50= 56 mg/kg). There was no evidence
of field effects on birds in forest areas sprayed with 1.1 kg
carbaryl/ha.
Carbaryl is very toxic for honey-bees and earthworms. The oral
LD50 for the former is 0.18 µg/bee (about 1-2 mg/kg).
There are indications that carbaryl may temporarily influence
the species composition of both terrestrial and aquatic ecosystems.
For instance, one study showed that effects on certain terrestrial
invertebrate communities may persist for at least 10 months
following a single application.
1.1.7 Effects on experimental animals and in vitro test systems
The acute toxicity, expressed as the LD50, varies
considerably according to species, formulation, and vehicle.
Estimates of the oral LD50 for the rat range from 200 to
850 mg/kg. Cats are more sensitive with an LD50 of 150 mg/kg. Pigs
and monkeys are less sensitive with an LD50 of >1000 mg/kg.
The maximum achievable aerosol concentration of carbaryl of
792 mg a.i./m3 during a 4-h exposure resulted in the mortality of
one out of five female rats. Carbaryl aerosols, at concentrations of
20 mg/m3, decreased cholinesterase activity (ChEA) in cats during
single 4-h exposures, but this concentration did not have any
observable effects in rats.
Carbaryl is a mild eye irritant and has little or no
sensitizing potential. During long-term studies, the NOEL was
10 mg/kg body weight (200 mg/kg diet) for rats, and 1.8 mg/kg body
weight (100 mg/kg diet) for dogs. The long-term inhalation NOEL for
cats is 0.16 mg/m3. Carbaryl has a low cumulative potential.
1.1.7.1 Reproduction
Carbaryl has been shown to affect mammalian reproduction and
perinatal development adversely in a number of species. Effects on
reproduction include impairment of fertility, decreased litter size,
and reduced postnatal viability. Developmental toxicity is seen as
increased in utero death, reduced fetal weight, and the occurrence
of malformation. With the exception of a small number of studies,
all adverse reproductive and developmental effects were noted only
at doses that caused overt maternal toxicity, and, in a number of
cases, the maternal animal was more sensitive to carbaryl than the
conceptus. The maternal toxic effects included lethality, decreased
growth, and dystocia. Data indicate that the reproductive and
developmental processes of mammals are not especially sensitive to
carbaryl compared with the susceptibility of the adult organism.
1.1.7.2 Mutagenicity
Carbaryl has been evaluated for its potential mutagenicity in a
number of in vitro and in vivo tests, in bacterial, yeast,
plant, insect, and mammalian systems, testing a variety of
end-points.
The available evidence indicates that carbaryl does not have
any DNA-damaging properties. There have been no reports of confirmed
induction of mitotic recombination, gene conversion, and UDS in
prokaryotes ( H. influenzae, B. subtilis) and eukaryotes
( S. cerevisiae, A. nidulans, cultured human lymphocytes, and rat
hepatocytes) in vitro.
Negative results were obtained in tests for gene mutations in a
large number of bacterial assays, with the exception of two cases.
In several studies of gene mutations in mammalian cells in vitro,
carbaryl produced only one equivocal positive result in a cell
culture study. However, the study had several shortcomings and the
result has not been confirmed in any other comparable studies.
Chromosomal damage with high dosages of carbaryl has been
reported in vitro in human, rat, and hamster cells, and in plants.
No such effects have been observed in mammalian tests in vivo,
even at doses as high as 1000 mg/kg.
Carbaryl has been shown to induce disturbances in the spindle
fibre mechanism in plant and mammalian cells in vitro. The
relevance of plant assays for extrapolation to humans is unclear.
It can be concluded that the available data-base does not
support the presumption that carbaryl poses a risk of inducing
genetic changes in either the somatic or the germinal tissue of
humans.
The nitrosated product of carbaryl, N-nitrosocarbaryl, is
capable of inducing mitotic recombination and gene conversion in
prokaryotes ( H. influenzae, B. subtilis) and eukaryotes
( S. cerevisiae) in vitro, and gives positive results in
E. coli spot tests.
Furthermore, experimental results indicate that
N-nitrosocarbaryl binds to DNA, causing alkali-sensitive bonds and
single-strand breakage.
Nitrosocarbaryl has not been established as a clastogen
in vivo (bone marrow and germ cells), even at high toxic doses.
1.1.7.3 Carcinogenicity
Carbaryl has been studied for its carcinogenic potential in
numerous studies on rats and mice. The results of most of these
studies were negative, but the studies were old and did not meet
contemporary standards. However, new studies on mice and rats, which
meet modern standards, are in progress.a
The latest IARC evaluation (IARC, 1987) concluded that there
were no data on cancer in humans and that the evidence of
carcinogenicity in experimental animals was inadequate. Carbaryl
could not be classified as to its carcinogenicity for humans
(Group 3).
N-nitrosocarbaryl has been shown to induce tumours locally in
rats (either sarcoma at the site of injection or forestomach
squamous cell carcinoma, when given by the oral route). Given the
human chemistry of carbaryl, the risk of N-nitrosocarbaryl
carcinogenicity in humans from carbaryl exposure can be judged as
negligible.
aThese studies have not yet been reviewed by the IPCS. The
company performing these studies has indicated that there is a
significant increase in tumors at the highest dose in both species.
1.1.7.4 Effects on different organs and systems
(a) Nervous system
The effects of carbaryl on the nervous system are primarily
related to cholinesterase inhibition and are usually transitory. The
effects on the central nervous system were studied in rats and
monkeys. Oral doses of 10-20 mg carbaryl/kg for 50 days were
reported to disrupt learning and performance in rats.
In a small study on pigs, carbaryl (150 mg/kg body weight in
the diet for 72-82 days) was reported to produce a number of
neuromuscular effects. Reversible leg weakness was noticed in
chickens given high doses of carbaryl. No evidence of demyelination
was observed in the brain, sciatic nerve, or in spinal cord sections
examined microscopically. Similar effects were not observed in
long-term rodent studies.
(b) Immune system
Carbaryl, when administered in vivo, at doses causing overt
clinical signs, has been reported to produce a variety of effects on
the immune system. Many of the effects described were detected at
doses close to the LD50. Most studies on rabbits and mice at doses
permitting survival have not produced significant effects on the
immune system. Shortcomings of several of these studies were a lack
of consistency and, sometimes, overt contradiction between results,
which prevents the description of a defined immunotoxic mechanism.
(c) Blood
Carbaryl has been reported to affect coagulation, but there are
conflicts about the direction of the effect. In glucose-6-phosphate
dehydrogenase-deficient sheep erythrocytes, carbaryl produced a
dose-dependent increase in methaemoglobin (Met-Hb) formation. Human
serum albumin reacted in vitro with the ester group of carbaryl.
Carbaryl binds free blood amino acids.
(d) Liver
Disturbances have been reported in the carbohydrate metabolism
and protein synthesis and detoxification function of the liver in
mammals. Carbaryl is a weak inducer of hepatic microsomal
drug-metabolizing activity. Phenobarbital sleeping time is
shortened. The hepatic levels of cytochrome P-450 and b5 are
increased. Changes in liver metabolism may account in part for the
three-fold increase of the carbaryl LD50 in carbaryl-pretreated
rats.
(e) Gonadotropic function
Carbaryl has been reported to increase the gonadotropic
function of the hypophysis of rats.
1.1.7.5 Primary mechanism of toxicity
Carbaryl is an inhibitor of cholinesterase activity. This
effect is dose-related and quickly reversible. There was no aging of
the carbamylated cholinesterase. All identified metabolites of
carbaryl are appreciably less active cholinesterase inhibitors than
carbaryl itself.
1.1.8 Effects on humans
Carbaryl is easily absorbed through inhalation and via the oral
route and less readily by the dermal route. Since the inhibition of
cholinesterase (ChE) is the principal mechanism of carbaryl action,
the clinical picture of intoxication is dominated by ChE inhibition
symptoms, such as: increased bronchial secretion, excessive
sweating, salivation, and lacrimation; pinpoint pupils,
bronchoconstriction, abdominal cramps (vomiting and diarrhoea);
bradycardia; fasciculation of fine muscles (in severe cases,
diaphragm and respiratory muscles also involved); tachycardia;
headache, dizziness, anxiety, mental confusion, convulsions, and
coma; and depression of the respiratory centre. Signs of
intoxication develop quickly after absorption and disappear rapidly
after exposure ends.
In controlled studies on human volunteers, single doses of less
than 2 mg/kg were well tolerated. A single dose of 250 mg
(2.8 mg/kg) produced moderate ChE inhibition symptoms (epigastric
pain and sweating) within 20 min. Complete recovery occurred within
2 h of treatment with atropine sulfate.
In cases of occupational overexposure to carbaryl, mild
symptoms are observed long before a dangerous dose is absorbed,
which is why severe cases of occupational intoxication with carbaryl
are rare. During agricultural application, dermal exposure may play
an important role. No local irritative effect is usually observed,
however, the appearance of a skin rash after accidental splashing
with carbaryl formulations has been described.
There are conflicting data about the effects of carbaryl on
sperm count and changes in sperm morphology in plant workers. No
adverse effects on reproduction have been reported.
The most sensitive biological indicator of carbaryl exposure is
the appearance of 1-naphthol in the urine and a decrease in ChE
activity in the blood. Levels of 1- naphthol in the urine can be
used as a biological indicator, if there is no 1-naphthol in the
working environment. During occupational exposure, 40% of the urine
samples contained more than 10 mg total 1-naphthol/litre. In one
case of acute intoxication, 31 mg/litre was found in the urine. The
hazard level is >10 mg/litre and the symptomatic level 30 mg
1-naphthol/litre urine ( Data sheet on carbaryl, WHO, 1973,
VBC/DS/75.3).
Measurement of the ChE activity can be a very sensitive test
for monitoring, provided that measurement is carried out soon after
exposure.
1.2 Conclusions
The hazards of carbaryl for human beings are judged to be low,
because of its low vapour pressure, rapid degradation, rapid
spontaneous recovery of inhibited cholinesterase, and the fact that
symptoms usually appear well before a dangerous dose has accumulated
in the body. Good carcinogenicity studies, which meet modern
standards, are not yet available.
1.2.1 General population exposure
Residue levels of carbaryl in food and drinking-water, which
remain after its normal use in agriculture, are far below the
acceptable daily intake (ADI) (0.01 mg/kg body weight per day) and
are not likely to produce health hazards in the general population.
1.2.2 Subpopulations at high risk
Use of carbaryl for public health purposes in the home or in
recreation areas may create overexposure, if the rules for its
application are neglected.
1.2.3 Occupational exposure
By enforcing reasonable work practices, including safety
precautions, personnel protection, and proper supervision,
occupational exposure during the manufacture, formulation, and
application of carbaryl will not create hazards. Undiluted
concentrations must be handled with great care, because improper
work practices may cause skin contamination. Air concentrations in
the workplace should not exceed 5 mg/m3.
1.2.4 Environmental effects
Carbaryl is toxic for honey-bees and earthworms. It should not
be applied to crops during flowering.
With normal use, carbaryl should not cause environmental
concern. Carbaryl is adsorbed on soil to a great extent and does not
readily leach into ground water. It is rapidly degraded in the
environment and therefore is not persistent. Use of carbaryl should
not result in harmful short-term effects on the ecosystem.
1.3 Recommendations
* The handling and application of carbaryl should be
accomplished with the care given to all pesticides.
Instructions for proper usage, provided on the package
containing the chemical, should be carefully followed.
* The manufacture, formulation, use, and disposal of
carbaryl should be carefully managed to minimize
contamination of the environment.
* Regularly exposed worker populations should receive
periodic health evaluations.
* The application of carbaryl should be timed to avoid
effects on non-target species.
* Carcinogenicity studies that meet modern standards should
be conducted.
2. IDENTITY, PHYSICAL AND CHEMICAL PROPERTIES, ANALYTICAL METHODS
2.1 Identity
Structural formula
Molecular formula: C12H11N02
Common name: Carbaryl (BSI)
CAS chemical name: 1-naphthalenylmethylcarbamate (9CI)
CAS registry number: 63-25-2
RTECS registry number: FC5950000
Common synonyms:
alpha-naftyl- N-methylkarbamat, alpha-naphthalenyl
methylcarbamate, alpha-naphthyl methylcarbamate, alpha-naphthyl
N-methylcarbamate, carbamic acid, methyl-, 1-naphthyl ester,
N-methyl-alpha-naphthyl-urethan, N-methyl-1-naftyl-
carbamaat, N-methyl-1-naphthyl-naphthyl carbamate,
N-methyl-1-naphthyl-carbamat, N-methylcarbamate de
1-naphtyle, N-metil-1-naftil-carbammato, 1-naphthol
N-methyl-carbamate, 1-naphthyl methylcarbamate, 1
naphthyl- N-methyl-karbamat
The most commonly used chemical name is 1-naphthyl- N-
methyl-carbamate.
Common trade names:
Arilat, Arilate, Arylam, Atoxan, Bercema, Caprolin, Carbacine,
Carbatox, Carbavur, Carbomate, Carpolin, Denapon, Dicarbam,
Dyna-carbyl, Karbaryl, Karbatox, Karbosep, Menaphtam, Monsur,
Mugan, Murvin, Oltitox, Panam, Pomex, Prosevor, Ravyon,
Seffein, Sevimol, Sevin, Vioxan
The most commonly used trade name is Sevin.
Previous codes:
Compound 7744, ENT 23,969, ENT 23969, Experimental insecticide
7744, Germain's HSDB 952, NAC, NMC 50, Union Carbide 7744
Purity:
The technical product is principally manufactured in the USA;
however, there are other minor sources in other parts of the
world.
The technical product manufactured in the USA is produced to a
minimum purity of 99% w/w carbaryl with a <0.05% w/w content
of the 2-naphthyl carbamate isomer (sometimes known as
"beta-carbaryl").
FAO specifies a minimum purity of 98% w/w carbaryl with <0.05%
w/w content of the 2-naphthyl carbamate isomer.
2.2 Physical and chemical properties
Some of the physical properties of carbaryl are listed in
Table 1.
Pure carbaryl is a white crystalline solid without odour.
The explosion limit for dust (finely divided particles) in air
is 20.3 g/m3 (approximately 2500 ppm). It is non-corrosive
(Weston, 1982).
The volatility may increase 4-fold when the relative humidity
is increased from 8 to 80%.
Table 1.Physical properties
Melting point (°C) 142
Boiling point (°C) decomposing
Solubility in water (30 °C) 40 mg/litre
Specific density (20 °C) 1.23
Relative vapour density -
Vapour pressure 1.17 x 10-6-3.1 x 10-7
mmHg at 24-25 °C
Flash point 193 °C
Octanol/water partition 1.59-2.3
coefficient (log Kow)
Flammability (explosive) limits -
Relative molecular mass 201
The solubility of carbaryl increases with temperature (Bowman &
Sans, 1985). In sea water at 18 °C, the solubility is 31 mg/litre
(Karinen et al., 1967). Carbaryl is soluble to some extent in most
organic solvents, and it is soluble in corn oil. It is lipophilic
(Kanazawa, 1981).
It is stable to light and heat (up to 70 °C) and acids, but
easily hydrolysed by alkaline materials (Dittert & Higuchi, 1963).
It is a strong oxidizer.
The quality of carbaryl depends upon the purity of the
precursor, 1-naphthol. The amount of the 2-naphthylcarbamate isomer
found as a contaminant in the final product is directly related to
the purity of this precursor. 1-Naphthol, free of 2-naphthol
(undetectable), is produced in the USA today through the catalytic
conversion of naphthalene. However, 1-naphthol produced by other
manufacturing processes may contain 2-naphthol as a byproduct.
High pressure liquid chromatography (HPLC) has been used to
determine 1- and 2-naphthol in their mixtures in ratios 500:1, in
order to check for traces of contamination in samples of a
commercially important insecticide. The results have been summarized
in Table 2 (Argauer & Warthen, 1975).
Table 2.2-Naphthol recovered from carbaryl samplesa
Sample and size Amount of 2-naphthyl Amount of
methylcarbamate added 2-naphthol
for recovery check found
USA produced
250 mg Union Carbide
99.66% active None Undetectable
500 mg Ortho Sevin
50% wettable powder None Undetectable
570 mg Union Carbide
44% aqueous slurry None Undetectable
310 mg Union Carbide
80% wettable powder None Undetectable
310 mg Union Carbide
80% wettable powder 2.5 mg 1.7 mg
310 mg Union Carbide
80% wettable powder 0.50 mg 0.33 mg
Foreign origin
250 mg Sample A-
technical None 2.3 mg
250 mg Sample B-
technical None 14 mg
500 mg Sample C-
50% wettable powder None 12.4 mg
500 mg Sample D-
50% wettable powder None 1.3 mg
aFrom: Argauer & Warthen (1975).
2.3 Conversion factors
1 ppm = 8.22 mg/m3 of air;
1 mg/m3 = 0.12 ppm.
2.4 Analytical methods
The methods used to determine carbaryl are summarized in
Table 3. They vary considerably in relation to the equipment used.
As an alternative to chemical analysis, Bowman et al. (1982) used
a simple bioassay system procedure to determine foliar residues for
a safe re-entry period and to screen food for residues. Daphnia
and Hyalella were used as highly sensitive test organisms.
The Joint FAO/WHO Codex Alimentarius Commission has given
recommendations for the methods of analysis to be used for the
determination of carbaryl residues (FAO/WHO 1986a).
Table 3. Methods of analysis
Medium Sampling preparation Analytical Detection limit Comments Reference
methods
Meat extraction by paper test based 0.5 mg/kg Filatov & Brytskov
acetone on ChE determination; (1972)
butyryl choline
as a substrate and
phenol red as an
indicator
Air thin-layer 0.2 ng qualitative Wagner (1973)
chromatography 0.5-50 ng
quantitative
Air (carbaryl absorption in UV spectro- 1 mg/kg carbaryl lambda max. Klisenko (1965)
and methanol photometry 281 nm 1-naphthol
1-naphthol) lambda max. 296 nm
Soil plant extraction by thin-layer 0.1 µg recovery 80-95% Kovaleva &
hexane, acetone, chromatography sensitivity 0.02 mg/kg Talanov (1978a)
chloroform
Cow's milk and spectrophotometry 0.002 mg/litre - milk recovery 79-81% Hurwood (1967)
tissues p-nitro-benzene
diazonium fluoborate 0.02 mg/kg - tissues fortification 9.5-5 µg
coupling method
Urine 1-naphthol extraction with gas chromatography 0.02 mg/litre recovery 89-95% Shafik et al. (1971)
benzene tritium detector
Table 3 (continued)
Medium Sampling preparation Analytical Detection limit Comments Reference
methods
Air of working absorption in sodium gas chromatography, Krechniak & Foss
environment hydroxide solution electron capture (1981)
with simultaneous detector
hydrolysis to
1-naphthol;
derivatization by
1-fluoro-2-4
dinitro-benzene
Spinach Chicory sulfuric acid for electron capture 0.2 mg/kg in fortified Tilden & van
hydrolysis to for chromatography crop extract; 20 pg for Middelem (1970)
methylamine salt; pure standards
4-bromobenzoyl
chloride used to
produce derivative
4-bromo-N-methyl
benzamide
Water carbaryl extraction with gas chromatography 0.2 µg/litre recovery for carbaryl, Deuel et al. (1985)
and 1-naphthol dichloromethane H-3 source electron 100%; for naphthol, 90%
capture detector or
63Ni detector
Soil carbaryl extraction with 0.01 mg/kg for recovery for carbaryl,
and 1-naphthol 20% diethylester fortified soil 89.8%; for 1-naphthol,
in dichloromethane samples 79.4%
Table 3 (continued)
Medium Sampling preparation Analytical Detection limit Comments Reference
methods
Air ambient series of gas HPLC with ultraviolet Currier et al. (1982)
scrubbers charged detection at 220 nm
with methanol;
particulate deposit
on Teflon discs
Pads methanol ethanol HPLC 50 ng/pad (103.2 cm2) sensitive, inexpensive Bogus et al. (1985)
extraction; selective procedure
absorption and
elution of reversed
phase solid support
Post-mortem extraction procedure HPLC ultraviolet recovery: blood and Duck & Woolias (1985)
specimens on Extrelut column; detection reversed urine 99%; liver and
protein precipitation phase stomach tissue 95%
with acetonitrile
Foliage surface extraction HPLC recovery: at 5 ng/kg Pieper (1979)
by trichloromethane fortification level
Grass, etc. extraction by CH3CN grass 89.5%;
geranium 86.5%
Water extraction by CH2Cl2 aspen 75%;
Douglas fir 49.8%;
at 0.1 mg/litre level
Table 3 (continued)
Medium Sampling preparation Analytical Detection limit Comments Reference
methods
Soil extraction by soil 103%;
acetonitrile + water stream water 99.7%;
sediment 101%
Water, soil, extraction by thin-layer 0.5 mg/kg qualitative carbaryl and 1-naphthol Klisenko et al. (1972)
cow's milk, benzene ( n-hexane, chromatography
tissue (liver, diethyl ether)
kidney, heart,
lungs, etc.)
Vegetables and extraction by HPLC Recovery 83-97% at Ting et al. (1984)
fruits methanol (10% in 0.5 mg/kg fortification
petroleum ether) or level. Detailed
acetonitrile clean-up description of the
on a florasil column method is given
Water and Serum single extraction by HPLC 0.5 ng/ml Analysis time is Strait et al. (1991)
methanol after 1 ml 10 min Recovery in
of C18 solid-phase water > 99%
extraction columns
Plants methanol and liquid chromatography 0.01 mg/kg Recovery varies from Krause (1985a,b)
mechanical reverse phase; LC 86 to 121%
ultrasonic column using
homogenizer used acetonitrile - water
for extraction mobile phase
Table 3 (continued)
Medium Sampling preparation Analytical Detection limit Comments Reference
methods
Marion-berries extracted by Luke chemical ionization Recommended when GC Cairns et al. (1983);
procedure (Luke et mass spectrometry retention data are
al., 1975, 1981) with both methane inconclusive
cited by Cairns and ammonia as
(1983); eluted reagent gases
through florisil
using 50% mixed
petroleum ethers
Honey-bees extraction by gas chromatography, 0.03-0.10 mg/kg Recovery 95-100% Kendrick et al. (1991)
diethyl ether nitrogen-phosphorous
clean-up using ionization detector
silica cartridge
3. SOURCES OF HUMAN AND ENVIRONMENTAL EXPOSURE
Carbaryl was first synthesized in 1953 and, in 1958, the Union
Carbide Corporation began its commercial production. Carbaryl is now
processed by more than 290 formulators into 1537 different
registered products (Harry, 1977, unpublished report). Carbaryl is
formulated as a 50 and 85% wettable powder, 1.75-50% dust, oil-and
water-based 4% liquid suspension, and 5 and 10% granules and baits.
Annual production is of the order of 10 000 tonnes. It is produced
by the reaction of 1-naphthol with methylisocyanate.
Carbaryl is widely used, in many countries, as a broad spectrum
contact and ingestion insecticide with some systemic properties, and
is recommended for use at 0.25-2.7 kg active ingredient per hectare
to control various insect pests. Up to 10 kg/ha per season can be
used on tree fruits. In the USA, carbaryl is registered for the
control of about 560 different pests. It is used on more than 115
food and fibre crops, trees, and ornamentals. About 40% of the
quantity used is applied to cotton (Kuhr & Dorough, 1976; Mastro &
Cameron, 1976; Payne et al., 1985). In combination with other
substances, or alone, carbaryl is used as a plant regulator for
apple thinning (Looney & McKellar, 1984; Looney & Knight, 1985).
In veterinary practice, carbaryl is used on cattle, poultry,
and pets, especially to control flies, mosquitos, ticks, and lice,
some of which are vectors of disease.
Carbaryl (5% formulation Carbacide) is used to treat human body
louse infestation (Sussman et al., 1969).
4. ENVIRONMENTAL TRANSPORT, DISTRIBUTION, AND TRANSFORMATION
4.1 Volatilization and air transportation
Carbaryl has a low volatility and a low air-water partition
coefficient. Thus, only limited evaporation can be anticipated after
treatment. Some traces of carbaryl in the air and in fog, resulting
from spray drift, may be detected at a certain distance from the
treated areas. A maximum level of 0.09 mg/m3 in the air has been
reported.
The dimensionless air-water partitioning constant (Henry's Law
Constant) for carbaryl has been evaluated to be 5.3x10-6
(Schomburg et al., 1991).
Deuel et al. (1985) studied the persistence of carbaryl in
paddy water. Results indicated that no measurable dissipation could
occur as a result of volatilization. In contrast to the results from
Deuel, using the BAM model, Lee et al. (1990) calculated that 50
days after treatment, 0.63% of the carbaryl applied to soil could
have been volatilized and 78.84% degraded.
4.2 Water
4.2.1 Hydrolysis
In pure, sterilized water, kept in the dark, the persistence of
carbaryl is pH-dependent. Carbaryl is rather stable in acidic
conditions. Its half-life at pH 7 is 10-16 days, and at pH 8 it is
1.3-1.9 days only. At pH levels higher than 8, its half-life is in
the range of a few hours, or even less (Aly & El Dib, 1971a).
Carbaryl is an example of an N-substituted carbamate that
hydrolyses readily in water. In this mechanism, an acid-base
equilibrium is established and the conjugate carbamate undergoes an
elimination type reaction to give an unstable carbamic acid that
decomposes to the primary amine and CO2. Initially, the principal
non-biological degradation pathway of carbaryl in water, however,
involves base-catalysed hydrolysis to 1-naphthol (Khasawinah, 1977).
Aly & El Dib (1971a,b, 1972) conducted studies to determine the
physical factors that may influence the degradation of carbamates,
including carbaryl, in aquatic systems. Hydrolysis of carbaryl in
alkaline medium was a function of hydroxyl ions in solution and was
first order with respect to these ions. Carbaryl was so sensitive to
hydroxide ions that, at high base concentrations, the liberation of
1-naphthol was too fast (few minutes) to be measured by conventional
methods. Carbaryl was stable to hydrolysis at the acid pH range of
3-6. At pH 7, a rise in the hydrolysis rate was observed, which
increased with increase in pH. Carbaryl was very susceptible towards
hydrolysis in aqueous solutions at neutral and alkaline pH values. A
series of kinetic studies was carried out at different temperatures
(3-33 °C) to study the temperature dependence of the rate of
hydrolysis. Results showed that an increase in temperature resulted
in an increase in the reaction velocity.
Wauchope & Haque (1973) reported that, in weak acidic
solutions, carbaryl and 1-naphthol were stable for several weeks, in
the dark or under laboratory light. In basic solutions, the basic
form of 1-naphthol (1-naphthoxide) was light sensitive.
1-Naphthoxide ion was transformed into 2-hydroxy-1,4-naphthoquinone;
this was confirmed by mass spectrometry.
Khasawinah (1977) carried out the hydrolysis of carbaryl in the
dark, in aqueous buffer solutions at temperatures of 25 and 35 °C.
Increasing the pH and temperature of the buffer accelerated the
disappearance of carbaryl and the formation of 1-naphthol.
Rate constants (at 20 °C) were determined for the purely
chemical hydrolysis of carbaryl in water containing solvents at pH
values ranging from 4 to 8 (Chapman & Cole, 1982). The solvent
composition (water/ethanol = 99/1) was close to pure water and the
solutions were sterilized to ensure that only chemical reactions
were taking place. The half-lives for carbaryl were calculated from
pseudo-first order disappearance rate constants (Table 4).
Fisher & Lohner (1986) conducted tests on the environmental
fate of carbaryl as a function of pH. In both a microcosm and
abiotic studies, greater amounts of carbaryl were detected in water
at pH 4, than at pH 6 or 8.
Hydrolysis of labelled carbaryl in aqueous solution was
conducted by Carpenter (1990) under dark conditions. When
degradation occurred, the major degradation product of significance
was 1-naphthol. No other degradation product accounted for more than
2% of the radioactivity and no volatile products were generated
during the hydrolysis reaction. The test systems were sterile and
the transformation/degradation mechanism was purely chemical
hydrolysis.
Carbaryl half-lives in aqueous solution observed by different
authors are summarized in Table 4.
Table 4. Half-life of carbaryl at different pH values and temperatures in aqueous solution (days)
pH Temperature References
3 4 5 6 7 8 9 10 (°C)
10.5 1.3 0.1 0.01 Aly & El Dib (1971a, 1972)
0.12 0.01 25° Wauchope & Haque (1973)
stable stable 0.14 25° Khasawinah (1977)
stable 29 0.02 35°
1500 15 0.15 27° Wolfe et al. (1978)
2100a 406 14 1.9 20° Chapman & Cole (1982)
104 71.6 1.4 Fisher & Lohner (1986)
171.4 16.5 25° Larkin & Day (1986)
stable 11.6 0.13 Carpenter (1990)
12.5
a pH 4.5
4.2.2 Photolysis
There is sufficient evidence to suggest that photodecomposition
will account for some loss of carbaryl in clear surface waters
exposed to sunlight for long periods. In turbid waters, light
penetration is greatly reduced, thus photolysis will play only a
minor role in the decomposition of carbaryl.
The primary effect of ultraviolet light radiation (UVR) seems
to be cleavage of the ester bond, however, other modifications in
the carbaryl molecule occur. Crosby et al. (1965) studied the
photodecomposition of carbaryl and found several other
cholinesterase inhibitory substances, in addition to 1-naphthol,
indicating that these substances retained the intact carbamate ester
group, and that irradiation resulted in changes at other positions
in the molecule. Both UVR and natural sunlight caused decomposition
of carbaryl, however, the extent of photodecomposition was not the
same under the different conditions of irradiation. Intense UV
irradiation generally resulted in the formation of a greater number
of degradation products. It is expected that the effects of natural
sunlight UVR (292-400 nm) on the photodegradation rate and the
nature of the degradation products would differ from those of the
shorter wavelength irradiations used above.
The effect of UVR on the photodegradation of carbaryl was
studied by Aly & El Dib (1971b, 1972). Generally, the concentration
of carbaryl decreased with time, however, the photolysis rate
gradually decreased. Photodecomposition proceeded at increasing
rates as the pH values of solutions increased. After an exposure
time of 60 min, the decomposition rates of carbaryl at pH 5, 7, and
8 were 50, 57, and 78%, respectively. The half-life at pH 8 was
<20 min while, at pH 5, it was approximately 80 min. The main
decomposition product after 5 min of exposure in all irradiated
solutions was 1-naphthol. However, its concentration also decreased
as the irradiation time was increased, indicating that 1-naphthol
also underwent photolysis, as soon as it appeared in solution. The
photodecomposition of 1-naphthol was also affected by the pH of the
medium. The half-lives of carbaryl and 1-naphthol were 39 and
60 min, respectively, at pH 7 and 8, and 43 min at pH 8.
The photochemistry of carbaryl was studied by Addison et al.
(1975) in aerated and pure ethanol, cyclohexane, isopropyl alcohol,
and tert-butanol. Irradiation of carbaryl produced 1-naphthol and
small amounts of naphthamides, naphthalene, and
ß-napthyl-1-naphthol. In cyclohexane, 1-naphthol was the only
decomposition product.
Khasawinah (1977) conducted a photolysis study on labelled
carbaryl in an aqueous solution buffered at pH 6. The study
terminated before the actual half-life was reached. The half-life
was calculated to be 40-50 days. The author stated that under field
conditions it is expected that carbaryl will photodegrade slowly and
that photodegradation does not play a major role in the
environmental degradation of carbaryl.
The direct photolysis half-life of carbaryl in sunlight was 6.6
days in distilled water (Wolfe et al., 1978). On the basis of the
results of the methods of Zepp et al. (1976) and Zepp & Cline
(1977), the calculated half-life for direct photolysis was about
50 h in a clear water body, near the surface. The annual variation
of the photolysis half-life of carbaryl according to season of the
year was calculated. As the intensity of the sunlight increases, so
do photolysis rates. Carbaryl absorbs UV-B radiation most strongly,
and, thus, can also be photolysed under overcast conditions (cloudy
days). UVR is absorbed by water, and the photolysis rate decreases
as the water deepens. In spring and summer, when carbaryl is
applied, the rate of photolysis is about four times that in winter
months. In distilled water under the June midday sunlight at pH 5.5,
the half-life of carbaryl was 45 h.
Deuel et al. (1985) studied the photodecomposition of
carbaryl in deionized water. They confirmed that carbaryl could be
photodecomposed in an aquatic environment.
The influence of different aqueous systems (rivers, lakes, and
seawater) on the photochemical degradation of some carbamate
insecticides in Greece was studied by Samanidou et al. (1988). In
lake and sea water, carbaryl was almost completely degraded by
sunlight within 4 and 2 days, respectively, in the presence of
oxygen. One day of UV irradiation in river, lake, and sea water,
respectively, resulted in 98%, 87%, and 99% degradation. The high
concentration of suspended matter in river and lake water influences
the absorption of sunlight and consequently the degradation of
carbaryl.
Das (1990a) exposed sterile water, buffered at pH 5, with
labelled carbaryl to artificial sunlight (548.8 watts/m2) for
360 h; 65% of the carbaryl had disappeared by the end of the 360-h
period. The major degradation product was 1-naphthol. In control
test solutions, incubated in the dark, changes in carbaryl
concentrations were insignificant.
4.2.3 Degradation by microorganisms
A review of the chemical and microbial degradation of carbaryl
in aquatic systems has been published by Paris & Lewis (1973).
The rate of hydrolysis of carbaryl in neutral and slightly
basic conditions was so rapid that differences reported between
sterilized and non-sterile water were usually were minor. Thus, it
is generally considered that the microbial degradation of carbaryl
in natural water plays only a secondary role in comparison with
chemical hydrolysis.
The bacterial decomposition of 1-naphthol by ring cleavage was
reported in farm pond water (Hughes & Reuszer, 1970). They studied
bacterial populations in pond water containing drainage water from
carbaryl-treated fields. Their data were the earliest to show that
bacteria can adapt to live on carbaryl and that when this occurs one
strain dominates. They also showed that there may be a minimum
period of time before bacteria can degrade carbaryl and a minimum
concentration below which bacteria will not multiply rapidly enough
to cause degradation.
Ahlrichs et al. (1970) found bacteria that could break the
ring structure of carbaryl, however data concerning the role of
microorganisms in the elimination of insecticides from surface water
were variable.
In a study by Hughes (1971) a bacterium ( Flavobacterium sp.)
was isolated from pond water, which degraded 1-naphthol to
o-hydroxycinnamic acid, salicylic acid, and an unidentified
product. In this study, the bacteria cleaved the naphthalene ring,
since both hydroxycinnamic acid and salicylic acid each have only a
single phenol ring.
Aly & El Dib (1972) studied the biodegradation of carbaryl in
Nile River water in 5-gallon containers, which was buffered to
maintain a pH of 7.2 and held at 25±2 °C under aerobic conditions.
The concentration of carbaryl in water decreased progressively with
time and 89% of the added amount of carbaryl (4.75 mg/litre)
degraded in 6 days. 1-Napthol, which appeared as a degradation
product, did not result only from the chemical hydrolysis of
carbaryl, since a sterile buffered solution showed negligible
hydrolysis. 1-Naphthol was produced mainly as a result of the
biological activity of microorganisms in river water. Subsequent
additions of increasing concentrations of carbaryl disappeared in
shorter periods of time, and there was no build-up of 1-naphthol.
Carbaryl disappeared more rapidly in Nile River water containing
sewage. Thus, the authors considered that natural waters and sewage
contain microorganisms capable of degrading carbaryl and 1-naphthol.
A number of marine microorganisms, including algae, bacteria,
fungi, and yeasts, were tested by Sikka et al. (1973, 1975) for
their ability to metabolize carbaryl or 1-naphthol. None of them was
able to degrade carbaryl to a significant extent. Only a very small
amount of carbaryl was metabolized to form water-soluble metabolites
by the algae Cyclotella nana and Dunaliella tertiolecta.
1-Naphthol was degraded to water- and ether-soluble metabolites by
Culcitalna achraspora, Halosphaeria mediosetigera, Humicola
alopallonella, Aspergillus fumigatus, Serratia marina, Spirillum
sp., and Flavobacterium sp. The organisms differed greatly in
their ability to convert carbaryl to water-soluble products, and
also in their ability to degrade 1-naphthol. Overall, 1-naphthol
appeared more susceptible to degradation than carbaryl, and
filamentous fungi appeared to possess a greater ability to degrade
1-naphthol than bacteria or yeast.
Bacteria isolated from river water were also capable of
degrading 1-naphthol (Bollag et al., 1975; Czaplicki & Bollag,
1975). After 60 h of incubation with 14C-labelled 1-naphthol, it
was possible to trap 44% as CO2 and 22% was recovered. The release
of labelled CO2 clearly indicated that complete biodegradation of
carbaryl had taken place via rupture of the naphthyl ring. However,
15-20% of radioactivity remained in the growth medium. This suggests
that at least 2 different pathways may be involved in the
degradation of 1-naphthol by these bacteria. The radioactivity in
the growth medium was partitioned and the dominant product was
identified as 4-hydroxy-1-tetralone, which suggests an alternative
pathway that involves hydroxylation of the naphthyl ring in the
4-position and conversion of an aromatic ring to an aliphatic cyclic
compound. Walker et al. (1975a) confirmed this pathway with a soil
pseudomonad.
Paris et al. (1975) found that, in heterogeneous bacterial
cultures in water, bacteria did not significantly degrade carbaryl
but did utilize 1-naphthol, produced from hydrolysis, as a carbon
source. Products of the bacterial degradation of the 1-naphthol were
1,4-naphthoquinone and 2 unidentified compounds. Hydrolysis and
photolysis contributed significantly to the degradation of carbaryl,
since half-lives were short compared with those of biolysis.
Within 7 days of incubation in river water, 92% of carbaryl or
1-naphthol disappeared (Prima et al., 1976); 68% was removed by
biochemical degradation, and 24% by a physico-chemical process.
Liu et al. (1981) measured the rate of carbaryl degradation
at pH 6.8 both with, and without, bacteria obtained from lake
sediment. Without the lake sediment inoculum, the half-life of
carbaryl was 8.3 days under aerobic conditions and 15.3 days under
anaerobic conditions. With bacterial metabolism, half-lives of 6.8
and 5.8 days, respectively, were measured. After the addition of
cometabolites (glucose and peptone), the half-lives were further
reduced to 3.8 and 4.2 days, respectively. Thus, bacterial
degradation played a much greater role in the degradation of
carbaryl under anaerobic conditions.
Microbial activity was an important factor in the breakdown of
carbaryl in water from a pond and creek (Szeto et al., 1979).
Autoclaving prior to the addition of carbaryl and incubating for 50
days increased the recovery from 39 to 57% (creek water) and from 28
to 58% (pond samples containing sediment).
Boethling & Alexander (1979) studied the degradation of
carbaryl in stream water (pH 7.5-8.6) at extremely low
concentrations. They reported that, at initial concentrations of 30
and 300 mg/litre, more than 60% of the carbaryl was degraded to
CO2 within 4 days, but 10% or less was converted to CO2 at
0.3 mg/litre and 0.0003 mg/litre. At these two latter
concentrations, CO2 was generated at rates not exceeding 3% of the
starting material per day. The authors concluded that laboratory
tests on bio-degradation are usually conducted with concentrations
of chemicals higher than those found in rivers, lakes, and marine
waters and, therefore, will not accurately predict the environmental
behaviour of microorganisms.
Sharom et al. (1980) compared the persistence of carbaryl in
natural water, distilled water, sterilized natural water, and
sterilized distilled water. Carbaryl disappeared from all four types
of water, which was considered to show that chemical processes
played a major role, and biological processes, a secondary role, in
the degradation of carbaryl in water.
Chaudhry & Wheeler (1988) maintained a Pseudomonas sp.
isolated from a pesticide waste disposal site on a medium containing
normal and radiolabelled carbaryl. Pseudomonas sp. degraded
carbaryl and the authors concluded that Pseudomonas sp. may have
potential as biological treatments for waste and groundwater.
4.2.4 Persistence in surface water
The agricultural use of carbaryl may indirectly produce
residues in surface water and in sediment, following application, as
result of drift or from soil-bound particles. In general, carbaryl
is not expected to persist in the aquatic environment. Although it
is stable to hydrolysis in acidic water, at the pH of most surface
fresh waters (7-8.2), it is highly susceptible to hydrolysis.
Biologically-mediated degradation and photolysis are secondary
mechanisms; sediment and humic substances also influence the
persistence of carbaryl in aquatic systems.
Half-lives of carbaryl in natural water, calculated from
experimental results, are summarized in Table 5. In one case, with
exceptionally cold and acidic conditions, the half-life was in the
range of 70 days. In most cases, half of the carbaryl degraded in a
few days, or even in less than one day.
Table 5. Percentage of carbaryl degraded in water, a certain number of days after treatment,
and the corresponding approximate half-lives
Origin of water Days % Half-life References
after (days)
treatment
laboratory 7 95 1 Eichelberger & Lichtenberg (1971)
pond < 0.5 Romine & Bussian (1971)
containers 6 89 2 Aly & El-Dib (1972)
microcosm < 5 Kanazawa (1975)
river 7 92 2 Prima et al. (1976)
lab. pond water 42 80-82 18 Szeto et al. (1979)
lab. + sediment < 2
lab. creek water 42 60-63 30
lab. + sediment < 7
lab. drainage 28 100 4 Sharom et al. (1980)
field, drainage 6 100 1 Osman & Belal (1980)
brooks, rivers, 1 Stanley & Trial (1980)
streams
stream 17 100 3 Ott et al. (1981)
Table 5. Contd
Origin of water Days % Half-life References
after (days)
treatment
lab. sewage 42 100 11 Odeyemi (1982)
lab. fresh water 60 100 < 15
rice irrigation 10 80 4 Thomas et al. (1982)
pond 1 60 100 8 Gibbs et al. (1981, 1984)
pond 2 138 77 2-3 rice fieldDeuel et al. (1985)
microcosm (pH 4-8) 7 31-73 13-4 Fisher & Lohner (1986)
stream < 0.1 Sundaram & Szeto (1987)
stream 1-3 100 < 1 Springborn (1988b)
rice irrigation < 1 Springborn (1988a)
ponds (18 °C) 4 100 1 Hanazato & Yasuno (1989)
ponds (4 °C) 10 30 20
45 95 10
ponds (4-20 °C) 0.4-0.9 Hanazato & Yasuno
(1990a,b)
aRounded.
The behaviour and persistence of carbaryl in water from a pond
and creek, with and without sediment, were studied under simulated
conditions in the laboratory by Szeto et al. (1979). At 9 °C,
carbaryl was less persistent in pond water (pH 7.5-7.8) than in
creek water (pH 7-7.1). Carbaryl degraded to 18-20% of the initial
amount after 42 days in pond water samples and to 37-40% of the
initial amount in creek water samples after 50 days. The higher pH
of pond water compared with creek water may have contributed to this
effect. The presence of sediment did not affect the rate of loss of
carbaryl, but approximately 50% of the remaining carbaryl was found
in the sediment. Microbial activity was a major factor in the
degradation of carbaryl in this study.
Eichelberger & Lichtenberg (1971) measured the persistence of
carbaryl in river water at room temperature and pH 7.3-8. From an
initial concentration of 10 µg/litre, only 5% could be detected
after 1 week and none was detected at 2 weeks. At the time of
disappearance of carbaryl, 1-naphthol could not be detected.
In Egypt, Osman & Belal (1980) mentioned that residues present
in irrigation and drainage canals following application of carbaryl
disappeared from the water 6 days after spraying.
The persistence of carbaryl was tested by Odeyemi (1982) who
incubated water samples treated wtih 45 mg/kg under tropical
greenhouse conditions (Nigeria). According to colorimetric
measurements, carbaryl disappeared after 42 days of incubation in
sewage water, and after 60 days in fresh water samples.
The impact of an experimental aerial application of carbaryl
(Sevin-4-oil) on woodland ponds in Northern Maine (USA) was studied
by Gibbs et al. (1981, 1984). Carbaryl was applied at the rate of
840 g/ha. Maximum residues levels of 734 µg/litre were detected in
the water, and about 4860 µg/kg (dry weight) in the sediment. In one
pond, carbaryl was not found after 62 days. Data from another pond
showed residues equivalent to 23% of the initial residue after 138
days, and 13% of the initial residues persisting after 375 days.
Investigators noted a rapid movement of carbaryl into bottom
sediments with persistence up to 16 months in this compartment,
compared with 14 months in the water. The anaerobic state of the
organic substrate and acidic conditions in one pond may have
contributed to greater persistence. The lower residue levels in the
other pond were attributed to a greater flow of water.
Hanazato & Yasuno (1990a,b) conducted studies in experimental
outdoor concrete ponds in Japan. Water received three treatments
with carbaryl in order to produce a minimal concentration of
0.5 mg/litre on 12, 19, and 20 October. The water temperature, which
was 20 °C at the start of the experiment, declined steadily to 4 °C
in early December and then did not change. The pH increased from 7.3
on the third day after the start of the experiment to about 9 on the
13th day. It remained between 8-9 until the end of the experiment.
The concentration of carbaryl in water decreased exponentially and
it was no longer detected 4 days after the first and second
treatments and 11 days after the third treatment. The half-lives for
the three treatments were respectively 0.36, 0.40, and 0.86 days.
The corresponding times for 90% degradation were, respectively,
1.18, 1.32, and 2.84 days.
Carbaryl was added to 60 litres of water and 15 kg of soil held
in 110-litre, plastic, garbage containers, buried partially in open
ground (Junk et al., 1984). Carbaryl was studied at the high and
low concentrations of 4 g/litre and 0.2 g/litre, respectively.
Additional variables studied included aeration (1 litre/min) and
peptone nutrients (0.1% by weight). Data obtained from this
experiment demonstrated that soil and water in an inexpensive
container provide satisfactory conditions for the containment of
pesticides so that chemical and biological degradation can occur.
Hydrolysis of carbaryl was rapid.
Deuel et al. (1985) studied the persistence of carbaryl and
the 1-naphthol metabolite in paddy water under flooded rice
cultivation conditions. Persistence was evaluated with respect to
time, application rates (1.1 and 5.6 kg/ha), and irrigation scheme
(intermittent or continuous). Results showed that application rate
and time of sample collection had a significant influence on the
carbaryl residues recovered in paddy water during the 3-year study.
They were found to be greater in plots under intermittent
irrigation, but only in 2 of the 3 years. Carbaryl residues in water
were greatest in years when rainfall occurred within 24 h of foliar
application. Using intermittent treatment data, carbaryl was
determined to dissipate to half the initial residue level within
48-59 h.
4.2.5 Removal from water
As already mentioned, Chaudhry & Wheeler (1988) proposed that
Pseudomonas sp. may have potential as a biological treatment for
waste and groundwater.
According to Miles et al. (1988a,b), the degradation rates of
N-methylcarbamate insecticides, including carbaryl and its
metabolite 1-naphthol, were more rapid in chlorinated water than in
pure water. Half-lives of carbaryl were as follows:
carbaryl control pH 7:10.3 days
carbaryl control pH 8: 1.2 days
carbaryl chlorinated pH 7: 3.5 days
carbaryl chlorinated pH 8: 0.05 days.
A separate experiment with 1-naphthol in chlorinated water
showed that this product is highly unstable with a half-life of the
order of minutes. A water source contaminated with carbaryl and
treated by chlorination will have lower concentrations of the
insecticide in the effluent.
Mason et al. (1990) studied the removal of carbaryl from
drinking-water by the disinfectants, Cl2, ClO2, and O3.
Carbaryl did not react with chlorine or with ClO2, but reacted very
rapidly with O3. Therefore removal/degradation of carbaryl can be
achieved using ozonization.
4.2.6 Persistence in sea water
Under laboratory conditions, the persistence of carbaryl in sea
water is slightly higher than that in freshwater and, according to
temperature, lighting, and microbial presence, its half-life varies
from a few days to about one month. The salt content of natural
waters (ionic strength) may affect the rate of hydrolysis of
carbamates (Christenson, 1964). Thus, carbaryl is expected to be
more stable to hydrolysis in waters with a high salt content than in
freshwater.
Carbaryl may enter marine systems when it is used to control
oyster pests and predators, such as oyster drills, mud shrimp, ghost
shrimp, and star fish (Loosanoff et al., 1960a,b; Lindsay, 1961;
Loosanoff, 1961; Snow & Stewart, 1963; Haydock, 1964; Haven et al.,
1966). However, Hurlburt et al. (1989) stated that tidal action
diluted the insecticide rapidly and that larvae are unlikely to be
subjected to high concentrations of carbaryl for more than several
hours.
The persistence of carbaryl in estuarine water was studied in
the laboratory by Karinen et al. (1967). Samples of water
containing 5, 10, or 25 mg carbaryl/litre and 3% NaCl were buffered
at pH 8 and kept in aquaria at 8 °C. In the absence of mud, the
concentration of carbaryl decreased 50% in 38 days, with most of the
decrease accounted for by the production of 1-naphthol. In another
experiment, naphthyl-14C and carbonyl-14C carbaryl (6.8-8.7 mC)
were used with cold carbaryl at total concentrations of 15 and
25 mg/litre, respectively, and maintained at 20 °C. About 50% of the
carbaryl was hydrolysed in 4 days and, after 17 days, the carbaryl
had almost disappeared with 43% converting to 1-naphthol.
Fluorescent light slightly accelerated the hydrolysis of carbaryl to
1-naphthol. When mud was added to the aquarium system, both carbaryl
and 1-naphthol in sea water declined to less than 10% of the initial
concentration in 10 days. Both compounds were adsorbed by the mud,
where decomposition continued at a slower rate than in sea water.
1-Naphthol persisted in mud for a short period of time, but carbaryl
could be detected for approximately 3 weeks. The naphthol moiety of
the carbaryl molecule was converted to more persistent products. The
experiment with labelled carbaryl demonstrated degradation by
hydrolysis of carbamate and oxidation of the naphthyl ring to
produce 14CO2 and 14CH4. In a preliminary field study,
estuarine mud flats were treated with carbaryl at 11.2 kg/ha (dose
used to control pests in oysters beds); carbaryl could be detected
in the mud for up to 42 days. 1-Naphthol concentrations were found
only after the first day, which may indicate that hydrolysis
proceeds slowly in mud.
The fate of 1-naphthol was studied in simulated marine systems
by Lamberton & Claeys (1970). 1-Naphthol was unstable in the
alkaline environment of sea water, since light and microorganisms
enhanced its degradation to CO2 and other products. 1-Naphthol was
relatively stable in an oxygen-free aqueous solution.
Odeyemi (1982) incubated water samples treated with 45 mg
carbaryl/litre under tropical greenhouse conditions (Nigeria).
According to colorimetric measurements, about 77% of the insecticide
had disappeared after 63 days of incubation in seawater, whereas it
had completely disappeared after 42 days of incubation in sewage
water, and after 60 days in freshwater samples.
4.2.7 Bioaccumulation/biomagnification
Because of its low persistence in water, and its even faster
degradation by living organisms, carbaryl has very low
bio-accumulation properties and presents no risk of biomagnification
under practical conditions.
Kanazawa (1975) studied the uptake and excretion of carbaryl by
Pseudorasbora parva. Fish were reared for 30 days in an aquarium
containing carbaryl at about 1 mg/litre. In water, 95% of the
carbaryl was degraded in 6 days. One day after treatment, residues
of carbaryl in P. parva reached 7.5 mg/kg, which was the maximum
uptake.
Kanazawa et al. (1975) studied the distribution and
metabolism of 14C-1-naphthyl-labelled methylcarbamate (carbaryl)
in an aquatic model ecosystem containing 10 kg soil, 80 litre water,
and catfish ( Ictalurus punctatus), crayfish ( Procambarus sp.),
daphnids ( Daphnia magna), snails (Physa sp.), algae ( Oedogonium
cardiacum) and duckweed ( Lemna minor). After 20 days, 31% of the
radioactivity was lost, 67.85% remained in the soil (about 45%
unextractable residues), 1.1% was present in water, and only 0.1%
was recovered in organisms. Bioaccumulation ratios were calculated
from radioactivity recovery and were likely to be low in the case of
animals. In the case of plants, they were apparently higher, but as
they are based only on radioactivity, including normal synthesis
reutilizing 14CO2 and not on real carbaryl measurement, they
should be considered as an overestimation of the true
bioconcentration factor for carbaryl (Table 6).
A flow-through bioconcentration study was conducted with
bluegill sunfish ( Lepomis macrochirus) exposed to 0.093 mg
carbaryl/litre for 28 days followed by a depuration phase in which
bluegill were held for 14 days in untreated water (Chib, 1986a; Chib
et al., 1986). Analysis of fillet, whole fish, and visceral
portions indicated a rapid uptake of carbaryl. Bioconcentration
factors ranged from 14x to 75x, for fillet and viscera,
respectively. Data suggest that fish stopped accumulating carbaryl
after day 7 of uptake, indicating that a steady state had been
reached.
Table 6. Accumulation of 14C radioactivity expressed as carbaryl
equivalenta by various aquatic organismsb
Carbaryl
Concentration in water 1.66 (1 day)
µg/litre 9.45 (22 days)
Concentration in soil 2.43 (start)
mg/kg 2.55 (22 days)
Organisms mg/kg BARc
Algae 37.9 4000
Duckweed 34.2 3600
Snail 2.81 300
Catfish 1.33 140
Crayfish 2.48 260
aCarbaryl not actually measured.
bFrom: Kanazawa et al. (1975).
cBioaccumulation ratio calculated by dividing mg/kg of dried
tissues by mg/litre in water at harvest.
By the end of the 14-day depuration period, over 90% of the
accumulated carbaryl was eliminated.
The persistence and accumulation of radiolabelled carbaryl
(technical, 99%), administered in either food or water
(flow-through), was studied in catfish ( Ictalurus punctatus) over
a 56-day period (Korn, 1973). Fish were removed periodically for
whole-body residue analysis. Intact carbaryl was not distinguished
from 1-naphthol. Accumulation from dietary carbaryl (2.8 mg/kg per
week) was 11 and 9 mg/kg tissue at 3 and 56 days, respectively. Fish
accumulated 1% or less of the available pesticide via dietary
exposure. The mean total accumulation of carbaryl (and/or metabolite
residues) after 56 days of exposure to water containing 0.25 mg
carbaryl/litre was 11 mg/kg. Fish exposed via the water retained
0.0001% carbaryl. Fish exposed to 2.8 mg/kg per week via diet
eliminated residues rapidly after they were placed on a
carbaryl-free diet for 28 days. However, residues remained constant
for 28 days in fish previously exposed to 0.25 mg carbaryl/litre
water for 56 days. The authors speculated that the greater
persistence of carbaryl residues from the water might be due to the
persistence in fish of 1-naphthol.
The low accumulation and rapid elimination of carbaryl in fish
were confirmed in other laboratory work (Kanazawa, 1975, 1981).
The biodegradation of carbaryl, was studied by Bogacka & Groba
(1980) in a model system simulating the river-water and aqueous
ecosystem conditions. The rate of pesticide decay in water depended
on the initial concentration, temperature, and the kind of model.
Lowering the temperature inhibited this process. The accumulation of
carbaryl in bottom sediments or in aquatic organisms (algae, snails,
and fish) was not observed at concentrations of 10 or 50 µg/litre.
Trace quantities of 1-naphthol could be detected occasionally.
4.3 Soil
4.3.1 Adsorption, desorption
Carbaryl is adsorbed on soil. Most Koc values were in the
range of 100-600, which corresponds to medium to strong adsorption.
Only in some soils from Eastern Australia was carbaryl apparently
less tightly bound (Koc 90-220). Taking into account both the
adsorption/desorption properties and the short persistence of
carbaryl in soil, it can be calculated that the compound has low to
moderate mobility in soil and will remain in the top layers, when
applied under actual agricultural conditions (normal dose rates).
Leenheer & Ahlrichs (1971) stated that fast adsorption rates for
carbaryl on soil particles were related to organic matter (OM) and
were of the order expected for physical adsorption.
Carbaryl desorption and movement in the soil was studied in 1-m
soil columns in glass tubes, which had a drain (LaFleur, 1976a).
Desorption by added water was rectilinear for carbaryl (soil range
1-200 µmol/kg). The movement of carbaryl in the column was a
function of the percentage of the organic matter. In soil containing
5.16% organic matter, carbaryl reached the 40-cm section of the
column only. When the organic matter content of the soil was low
(0.22-0.57%), about one-half of the added carbaryl moved through the
column and was found in the effluent, after addition of a volume of
water that was equal to six months' rainfall. Briggs (1981) also
reported that increasing levels of organic matter in soils resulted
in an increase in the adsorption of carbaryl.
On the basis of the comparative mobility of carbaryl on soil
thin-layer chromatography (TLC) plates using 4 US soils (silt loam,
loam, Norfolk sandy loam, and silty clay loam), Chib & Andrawes
(1985) concluded that the mobility of carbaryl is low to moderate.
With water elution equivalent to about 580 mm of rainfall, the major
portion of carbaryl was in the top 10 cm of soil, thus exhibiting
low mobility. Only 0.6% of the applied 14C was eluted with the
water. Approximately 70% of the applied carbaryl was degraded to
volatile gases during the 30-day incubation.
Aly et al. (1980) studied the adsorption of carbaryl at
different temperatures on Ca-bentonite and on two Egyptian soils
(Nile alluvial and a highly calcareous soil). Carbaryl adsorption
increased as the temperature decreased. Ca-bentonite exhibited the
highest degree of adsorption followed by the Nile alluvial soil and
the calcareous soil. The factors that contributed most to the total
adsorption of carbaryl were the soil contents of clay, calcium
carbonate, and organic matter.
The adsorption-desorption and mobility of carbaryl in 3 soils,
and in a stream sediment were studied by Sharom et al. (1980). The
order of adsorptive capacity was organic soil (75.3% OM, pH 6.1) >
sediment (2.8% OM, pH 6.6) > sandy loam (2.5% OM, pH 6.8) > sand
(0.7% OM, pH 7). Desorption occurred in greatest amounts from sand
> sandy loam > sediment. Leachability studies were consistent with
the adsorption/desorption results and a water solubility of
40 mg/litre. Carbaryl leached more from the sand than from the
organic soil.
In another adsorption/desorption study on carbaryl on sand,
sandy loam, silt loam, silty clay loam, and on aquatic sediment
using batch equilibrium techniques, Chib (1985a) concluded that
carbaryl binds strongly to soil/sediment matrices. This depends on
the carbaryl concentration in solution (the more in solution, the
more on soil) and on the organic content of soil. Desorption
isotherms for carbaryl at low concentrations were nearly flat with
all soils, indicating that carbaryl was tightly bound to the
substrates and difficult to move.
The transport of carbaryl in the soil was also studied under
natural conditions. High-volume rainfall occurring shortly after
carbaryl has been applied to a field can generate the low-level
transport of the pesticide to non-target areas (Caro et al.,
1974). Carbaryl is adsorbed on soil surfaces to a great extent.
Laboratory measurements of absorption isotherms gave a Freundlich k
value of 2.2. Of the 4 kg of carbaryl applied in a watershed, only
5.77 g (0.16%) were found in run-off water and sediment during the
season; (75 and 25% of the seasonal loss, respectively). The
distribution coefficient between sediment and water was 0.33.
Carbaryl had completely disappeared from the sediment by day 70, but
still remained in the water at low concentrations.
Carbaryl could still be found in the soil, 1-2 years after
application at 2 kg 85% WP/ha. It is carried by rainfall and
cultivation from the surface layers of the soil into the deeper
layers. During the first few days after application, it was found in
the root zone. After 3 months, 90% of the carbaryl was present in
the surface layers, and, after 300 days, it was found in the soil at
a depth of 60-70 cm. Rainfall was not specified (Molozhanova, 1968).
Carbaryl was applied to a sandy loam field plot at a dose of
25.4 kg/ha. A shallow water table was present at 1.1 m depth
(LaFleur, 1976b). Rainfall during the following 16 months was
182 cm. After this length of time, the upper 1 m contained 6% of the
applied carbaryl. No carbaryl was found in the 0-20 cm layer after
the fourth month. The half-life of carbaryl in the upper 1 m was >1
month. Carbaryl appeared in the underlying groundwater within 2
months following treatment and could be detected through the eighth
month. The maximum groundwater concentration occurred at the end of
the second month (about 60 µg/litre). The dose rate was more than 10
times the usual one and the persistence was overestimated, as well
as the residues that might be present in shallow groundwater.
Norris (1991) reported a terrestrial field soil dissipation
study conducted with carbaryl under actual use conditions. Carbaryl
was applied to broccoli in California at 2.24 kg/ha, five times, on
a weekly schedule. It was also applied once to sweet corn in North
Carolina at a rate of 7.12 kg a.i./ha. The half-life in soil was
estimated to be 6-12 days at the California site and about 4.8 days
at the North Carolina site. Carbaryl residues were found mainly at a
depth of 0-15 cm, which indicates that carbaryl has a low potential
for leaching through the soil profile under typical agronomic
practices.
4.3.2 Transformation
Degradation of carbaryl in soil occurs as a result of the
activity of microorganisms, and through physical and chemical
effects. It undergoes hydrolysis, oxidation, and other chemical
processes and, on the surface of the soil, is subjected to
photolysis. When applied at the usual doses, carbaryl has a short
persistence in soil. In the field, under temperate and warm climatic
conditions, the half-life of carbaryl in the soil does not exceed
one month (Table 7).
4.3.2.1 Photolysis in soil
Studies have been conducted on the photolysis of carbaryl in
soil. In one study, volatile substances were first identified and
quantified and then soil TLC plates were used over a 30-day period
to quantify degradation products (Chib, 1986b). The calculated
half-life of carbaryl in sandy loam soil on TLC plates irradiated
with a high-pressure mercury vapour lamp (200 watt, Hanovia) at
25 °C was 2.5 days. In controls kept in the dark, labelled carbaryl
degraded with a half-life of >30 days. CO2 was the only major
volatile degradation product from all treatments. The other soil
degradation products identified were 5-hydroxy carbaryl,
N-hydroxymethyl carbaryl and 1-naphthol. Only carbaryl and
1-naphthol were present in control soil extracts. The degradation
products in the irradiated soil extracts suggest that hydrolysis and
oxidation are the main mechanisms in the degradation of carbaryl
under soil photolysis conditions.
Das (1990b) also studied the photolysis of carbaryl in soil.
Labelled carbaryl was applied to a sandy loam on plates
(9.8±0.3 mg/kg) and maintained in artificial sunlight,
intermittently (12 h irradiation + 12 h darkness) for 30 days. The
measured irradiance of the artificial sunlight (502.6 watts/m2)
was comparable to the natural sunlight (545.8 watts/m2). The
evolution of volatile substances was also monitored. Controls were
incubated in the dark. The calculated half-life of irradiated
samples was 41 days (each day 12 h irradiation + 12 h darkness). No
major metabolites were formed under irradiated conditions.
4.3.3 Biotransformation in soil
The persistence and metabolism of 14C-carbaryl (200 mg/kg)
was studied in 5 different soil types by Kazano et al. (1972).
Persistence was influenced by soil type, and the production of
14CO2 varied from 2.2% (loamy sand) to 37.4% (clay loam) of the
initial radioactivity during 32 days of incubation at 25 °C. The
amount of radioactivity left in the soil after extraction was
proportional to the soil organic matter content. A significant
amount (17-57%) of the remaining radiolabel could not be extracted
with organic solvents. Analysis of the extractable residues
indicated the presence of 1-naphthyl N-hydroxymethylcarbamate,
4-hydroxy-1-naphthyl methylcarbamate and 5-hydroxy-1-naphthyl
methylcarbamate, but these were not confirmed. The main pathway of
degradation in soil was probably hydrolysis of the carbamate
linkage, producing CO2 and the corresponding phenol, though it is
possible that hydroxylation of the ring or the methyl carbon
precedes hydrolysis. 1-Naphthol decomposed more rapidly in clay than
in sandy loam. Most of the radioactivity (83-92%) was recovered in
the soils after 60 days of incubation. 1-Naphthol was immobilized on
humic substances in the soil, not by mechanical adsorption, but by
chemical bonding. Four metabolites (coumarin, the others not
identified) were also produced by a soil Pseudomonas.
Gill & Yeoh (1980) studied the degradation of carbaryl in an
extract of flooded paddy field soil (pH 3.7-4.8, organic matter
content 0.5-3%, very high clay content) extract and in the paddy
fish ( Trichogaster pectoralis). Under flooded conditions, the soil
half-life of carbaryl was about 7 weeks. The major significant
metabolite was 1-naphthol. Soil moisture plays an important role in
the extent of degradation since, under flooded conditions and 100%
field capacity, the degradation of carbaryl was more extensive than
under 0 and 50% field capacity, providing more evidence that
microorganisms play an important role in carbaryl degradation in
paddy-field soil. Where sufficient moisture is available, oxidative
mechanisms become important giving rise to ring and N-methyl
hydroxylation in addition to cleavage of the carbonyl moiety, a
common pathway of carbaryl metabolism. Carbaryl was also found to be
more persistent in acidic soil than in alluvial soil.
Rajagopal et al. (1983) measured the residues of carbaryl and
of the 1-naphthol metabolite in 3 flooded soils (organic matter
0.54-1.61%, pH 6.2-9.5) following three applications of the test
substance. Samples received either 1, 2, or 3 applications of
carbaryl in aqueous solution. The concentration of carbaryl
decreased with incubation time in all soils. The disappearance of
the first 50% of the substance in all soils ranged from 10 to 15
days. Subsequent samplings provided evidence for the enrichment of
carbaryl-degrading microorganisms in retreated soils. Thus, the
disappearance time for 75% of the compound was 20-26 days for 3
applications, 28-30 days for 2 applications, and >30 days for 1
application. It appears that carbaryl degradation under flooded
conditions does not follow a clear kinetic pattern (e.g., first
order). However, the first order degradation rates were similar for
the first, second, and third applications for 0-10 days. Degradation
proceeded by hydrolysis with 1-naphthol as the major product, the
amounts formed decreasing with incubation time in 2 out of the 3
soils. The disappearance of 1-naphthol was faster in retreated soils
and may not be attributed only to degradation, because significant
amounts of 1-naphthol may be bound to humic substances, especially
in soils with a high organic matter content.
The persistence of carbaryl was studied in 4 soils under
flooded conditions by Venkateswarlu et al. (1980). They recovered
a substantial portion of carbaryl from all soils 15 days after
application. The recovery ranged from 37% in an alluvial soil to 73%
in an acid sulfate soil. They concluded that flooded conditions
enhance carbaryl degradation.
The metabolism of 14C-carbaryl and 14C-1-naphthol in moist
and flooded soils was studied by Murthy & Raghu (1989) in a
continuous flow-through system, over a period of 28 days, permitting
a 14C-mass balance. The percentage distribution of radiocarbon in
organic volatile compounds, CO2, and extractable and
non-extractable (bound) fractions of soils was determined. Organic
volatile compounds could not be detected in either carbaryl- or
1-naphthol-treated soils. More 14CO2 (25.6%) was evolved from
moist than from flooded soil (15.1%), treated with carbaryl. The
mineralization of14C-1-naphthol was negligible. The level of
extractable radiocarbon was higher (5.5%) in flooded soil treated
with carbaryl. Less than 1% was the parent compound, and carbaryl
was mainly metabolized to 5-hydroxycarbaryl in moist soil and to
4- and 5-hydroxycarbaryl in flooded soil. The extractable
radiocarbon amounted to 18.2% and 24.3% in moist and flooded soils,
respectively, and there was less than 1% of the parent compound with
1-naphthol treatment. Most of the 14C was found as soil-bound
residues, levels being higher with 1-naphthol treatment than with
carbaryl. The humus fraction of the soil organic matter contributed
most to soil-bound residues of both carbaryl and 1-naphthol.
Aerobic and anaerobic soil metabolism studies were conducted
with carbaryl applied to sandy and clay loam soils in the dark
(Wilkes et al., 1977; Khasawinah, 1978). Under aerobic conditions
at room temperatures (23-25 °C), the half-life of carbaryl was
approximately 9-17 days in sandy loam soil (Texas) and 21-27 days in
clay loam (California). Lower temperature (15 °C) nearly doubled its
half-life. The only solvent-extractable apolar material was parent
carbaryl. A major proportion of the radioactivity initially applied
to the soil was lost as CO2. It appears that, under aerobic
conditions, carbaryl was degraded so that 1-naphthol carbon was lost
as CO2, or it was incorporated into the organic matter of the soil
(1-naphthol was not detected). After 112 days, carbaryl levels
declined to 3.6% (average in Texas soil) and 15% (average in
California soil) of the initial application.
In an aerobic, soil study conducted by Miller (1990) with a
sandy loam soil from North Carolina, soil was incubated with
labelled carbaryl in the dark and maintained at 25±1 °C. The
concentration of the parent compound rapidly decreased to a mean
value of 11.9% of the applied dose by day 14. A significant amount
of radioactivity was recovered as CO2. The average maximum value
of CO2 was 59.8% by day 14. The only other major degradation
product was 1-naphthol (maximum concentration of 34.9% of applied
dose by day 1). Base hydrolysis released 41% of the unextractable
residue. Carbaryl rapidly degraded under aerobic conditions with a
half-life of 5.5 days.
Murthy & Raghu (1991) studied the fate of carbaryl in the soil
environment as a function of pH, with respect to the formation of
extractable and non-extractable (soil-bound) residues. Soil samples
(sandy clay, sandy loam, and clay) containing C14-carbaryl
(10 mg/kg) were incubated at 28-30 °C for periods ranging from 7 to
56 days. More 14C-residues could be extracted from sandy clay and
sandy loam than from clay soil, under both moist and flooded
conditions. In general, flooding had no influence on the extractable
14C-residues. Thin-layer chromatography of chloroform extracts
revealed the presence of carbaryl and 1-naphthol. At the end of 56
days, the percentage of carbaryl recovered was 32.1, 6.4, and 1% in
sandy clay (pH 4.2), sandy loam (pH 6.8), and clay soils (pH 8.3),
respectively. The authors considered that there appeared to be a
correlation between soil pH and soil-bound residue formation as an
increase in soil pH was reflected in increased bound residues. The
humin portion of soil organic matter accounted for most of the
14C-residues. Low recoveries in sandy clay and in sandy loam soils
may stem from the possible mineralization of carbaryl.
Carbaryl persistence in the soil was studied under normal
conditions of application (Caro et al., 1974) of 5.03 kg/ha in
granules applied in corn seed furrows. About 135 days were required
for 95% of the carbaryl to disappear (Fig. 1). The pesticide
remained stable in the soil for 25 days (in some cases, more than
116 days) and then decayed rapidly. This decay is an indirect
indication of microbiological degradation.
This hypothesis is sustained by the finding that the stability
of carbaryl in the soil is affected by the nature of the treatments
applied during the period preceding its application. In soil that
had been treated with carbaryl 6 months before sampling, more than
70% of the added radiolabelled carbaryl was degraded after 4 days,
measured by the disappearance of radioactivity. Only 10% was lost in
orchard soil that had been treated for 15 years with various
pesticides, and only 3% was lost in soil that had never been treated
with pesticides. It appeared that soil that was treated with
carbaryl for 6 months increased the ability of the microorganisms to
degrade carbaryl (Rodriguez & Dorough, 1977).
Carbaryl was applied in soil at an agricultural rate and
incorporated to a depth of 6 inches (15 cm) (Heywood, 1975). At 28
days after treatment, 63% of the applied dose appeared as CO2 and
the identifiable residual carbaryl was about 6% of that applied.
In India, degradation of carbaryl was studied in a greenhouse
by Brahmaprakash & Sethunathan (1984, 1985). Since a soil planted
with crops may be more dynamic and complex than unplanted soil,
because of increased microbial activity, they studied carbaryl
persistence in soil (pH 6.2, organic matter 1.6%) planted with rice
in a greenhouse, under flooded and non-flooded conditions. Carbaryl
disappeared more rapidly from soils planted with rice than from
those without rice, under both flooded and non-flooded conditions.
The amount of carbaryl decreased to between 30.2 and 32.1% of the
original level within 30 days in unplanted soil under both flooded
and non-flooded conditions. During this same period, the carbaryl
concentration decreased to 17-18% of the original level in planted
soil under both water regimes. Degradation occurred by hydrolysis,
but there was no appreciable difference in the rates of degradation
between flooded and non-flooded soils. The rate of degradation of
carbaryl was little affected by moisture. Further degradation of
1-naphthol was slow in both planted and unplanted systems. A
significant portion of the ring-14C accumulated in the soil as
1-naphthol and soil-bound residues. Evolution of 14CO2 from the
labelled