INTERNATIONAL PROGRAMME ON CHEMICAL SAFETY
ENVIRONMENTAL HEALTH CRITERIA 128
CHLOROBENZENES OTHER THAN HEXACHLOROBENZENE
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 Ms M.E. Meek and Ms M.J. Giddings,
Health and Welfare Canada
Published under the joint sponsorship of
the United Nations Environment Programme,
the International Labour Organisation,
and the World Health Organization
World Health Orgnization
Geneva, 1991
The International Programme on Chemical Safety (IPCS) is a joint
venture of the United Nations Environment Programme, the International
Labour Organisation, and the World Health Organization. The main
objective of the IPCS is to carry out and disseminate evaluations of
the effects of chemicals on human health and the quality of the
environment. Supporting activities include the development of
epidemiological, experimental laboratory, and risk-assessment methods
that could produce internationally comparable results, and the
development of manpower in the field of toxicology. Other activities
carried out by the IPCS include the development of know-how for coping
with chemical accidents, coordination of laboratory testing and
epidemiological studies, and promotion of research on the mechanisms
of the biological action of chemicals.
WHO Library Cataloguing in Publication Data
Chlorobenzenes other than hexachlorobenzene
(Environmental health criteria: 128)
1. Chlorobenzenes - adverse effects
2. Chlorobenzenes - toxicity
3. Environmental exposure
4. Environmental pollutants I. Series
ISBN 92 4 157128 4 (NLM Classification QV 633)
ISSN 0250-863X
(c) World Health Organization 1991
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CONTENTS
1. SUMMARY
1.1. Identity, physical and chemical properties, analytical
methods
1.2. Sources of human and environmental exposure
1.2.1. Production figures
1.2.2. Uses
1.2.3. Release of chlorobenzenes into the environment
1.3. Environmental transport, distribution, and transformation
1.3.1. Degradation
1.3.2. Fate
1.4. Environmental levels and human exposure
1.4.1. Chlorobenzenes in the environment
1.4.2. Human exposure
1.4.2.1 General population
1.4.2.2 Occupational
1.5. Kinetics and metabolism
1.6. Effects on aquatic organisms in the environment
1.7. Effects on experimental animals and in vitro systems
1.8. Effects on humans
1.8.1. General population
1.8.2. Occupational exposure
1.9. Conclusions
2. IDENTITY, PHYSICAL AND CHEMICAL PROPERTIES, ANALYTICAL METHODS
2.1. Identity
2.1.1. Primary constituent
2.1.2. Technical product
2.2. Physical and chemical properties
2.3. Organoleptic properties
2.4. Conversion factors
2.5. Analytical methods
3. SOURCES OF HUMAN AND ENVIRONMENTAL EXPOSURE
3.1. Natural occurrence
3.2. Man-made sources
3.2.1. Production
3.2.2. Uses
3.2.3. Sources in the environment
4. ENVIRONMENTAL TRANSPORT, DISTRIBUTION, AND TRANSFORMATION
4.1. Transport and distribution
4.2. Persistence and fate
4.2.1. Persistence
4.2.2. Abiotic degradation
4.2.2.1 Photolysis
4.2.2.2 Hydrolytic and oxidative reactions
4.2.3. Biodegradation and biotransformation
4.2.4. Bioaccumulation
4.2.5. Biomagnification
4.2.6. Ultimate fate following use
5. ENVIRONMENTAL LEVELS AND HUMAN EXPOSURE
5.1. Environmental levels
5.1.1. Air
5.1.2. Water
5.1.3. Soil
5.1.4. Food
5.1.5. Human milk
5.1.6. Consumer products
5.2. Human exposure from all sources
5.2.1. General population
5.2.2. Occupational exposure
5.3. Human monitoring data
6. KINETICS AND METABOLISM
6.1. Absorption
6.2. Distribution
6.3. Metabolic transformation
6.4. Elimination and excretion
6.5. Binding to protein
6.6. Effects on metabolizing enzymes
7. EFFECTS ON ORGANISMS IN THE ENVIRONMENT
7.1. Microorganisms
7.1.1. Bacteria and protozoa
7.1.2. Unicellular algae
7.2. Aquatic organisms
7.2.1. Plants
7.2.2. Invertebrates
7.2.3. Fish
7.3. Terrestrial biota
7.4. Model ecosystems
8. EFFECTS ON EXPERIMENTAL ANIMALS AND IN VITRO TEST SYSTEMS
8.1. Single exposure
8.2. Skin and eye irritation, skin sensitization
8.3. Short-term exposures
8.4. Long-term exposures
8.5. Chronic toxicity and carcinogenicity
8.6. Mutagenicity and related endpoints
8.6.1. In vitro systems
8.6.2. In vivo tests on experimental animals
8.6.3. Human in vivo studies
8.7. Developmental and reproductive effects
9. EFFECTS ON HUMANS
9.1. Case reports
9.1.1. General population exposure
9.1.2. Occupational exposure
9.2. Epidemiological Studies
10. EVALUATION OF HUMAN HEALTH RISKS AND EFFECTS ON THE ENVIRONMENT
10.1. Evaluation of human health risks
10.1.1. Exposure of the general population
10.1.2. Occupational exposure
10.1.3. Toxic effects
10.1.4. Risk evaluation
10.1.4.1 General population
10.1.4.2 Occupationally exposed population
10.2. Evaluation of effects on the environment
10.2.1. Levels of exposure
10.2.2. Fate
10.2.3. Bioavailability and bioaccumulation
10.2.4. Degradation
10.2.5. Persistence
10.2.6. Toxic effects on organisms
10.2.7. Risk evaluation
11. CONCLUSIONS AND RECOMMENDATIONS FOR PROTECTION OF HUMAN HEALTH
AND THE ENVIRONMENT
11.1. Conclusions
11.2. Recommendations
11.2.1. Public health measures
11.2.2. Human health risk evaluation
11.2.3. Environmental risk evaluation
12. PREVIOUS EVALUATIONS BY INTERNATIONAL BODIES
REFERENCES
RESUME
RESUMEN
WHO TASK GROUP ON ENVIRONMENTAL HEALTH CRITERIA FOR CHLOROBENZENES
OTHER THAN HEXACHLOROBENZENE
Members
Dr U. G. Ahlborg, Karolinska Institute, Institute of Environmental
Medicine, General Toxicology, Stockholm, Sweden
Dr S. Dobson, Institute of Terrestrial Ecology, Monks Wood
Experimental Station, Huntingdon, Cambridgeshire, England
(Vice-Chairman)
Dr P. E. T. Douben, Research Institute for Nature Management, Arnhem,
Netherlands
Dr R. J. Fielder, Department of Health, MED TEH Division, Hannibal
House, London, England
Dr R. A. Jedrychowski, Institute of Occupational Medicine, Lodz,
Poland
Dr S. K. Kashyap, National Institute of Occupational Health,
Ahmedabad, India (Chairman)
Dr T. Lakhanisky, Institut d'Hygiène et d'Epidémiologie, Brussels,
Belgium
Dr D. C. Villeneuve, Health Protection Branch, Environmental Health
Centre, Tunneys Pasture, Ottawa, Ontario, Canada
Dr R. S. H. Yang, National Institute of Environmental Health Sciences,
Research Triangle Park, North Carolina, USA (present address: College
of Veterinary Medicine and Biomedical Sciences, Colorado State
University, Fort Collins, Colorado, USA)
Observers
Dr L. Caillard, Rhone-Poulenc, Service Toxicologie, Les Miroirs,
Paris, France
Secretariat
Dr G.C. Becking, International Programme on Chemical Safety,
Interregional Research Unit, World Health Organization, Research
Triangle Park, North Carolina, USA (Secretary)
Ms M.J. Giddings, Environmental Health Directorate, Health Protection
Branch, Environmental Health Centre, Tunneys Pasture, Ottawa, Ontario,
Canada (Temporary Adviser, Co-Rapporteur)
Ms M.E. Meek, Environmental Health Directorate, Health Protection
Branch, Environmental Health Centre, Tunneys Pasture, Ottawa, Ontario,
Canada (Temporary Adviser, Co-Rapporteur)
WHO TASK GROUP ON ENVIRONMENTAL HEALTH CRITERIA FOR CHLOROBENZENES
OTHER THAN HEXACHLOROBENZENE
A WHO Task Group on Environmental Health Criteria for Chlorobenzenes
other than Hexachlorobenzene met at the Institut d'Hygiène et
d'Epidémiologie, Brussels, Belgium, from 25 to 29 June 1990. Dr T.
Lakhanisky opened the meeting and welcomed the Members on behalf of
the host institute, and on behalf of the Ministère de la Santé
Publique et de l'Environnement, who sponsored the meeting. Dr G.C.
Becking addressed the meeting on behalf of the three cooperating
organizations of the IPCS (UNEP, ILO, WHO). The Task Group reviewed
and revised the draft criteria document, and made an evaluation of the
risks for human health and the environment from exposure to
chlorobenzenes other than hexachlorobenzene.
The drafts of this document were prepared by Ms M.E. Meek and Ms M.J.
Giddings, Health and Welfare Canada, Health Protection Branch, Ottawa,
Canada. Dr G.C. Becking, IPCS Interregional Research Unit, WHO,
Research Triangle Park, North Carolina, was responsible for the
overall scientific content of the document, and Mrs M.O. Head, Oxford,
England, for the editing.
The Secretariat wishes to acknowledge the extensive comments from: Dr
U. Schlottmann, Federal Ministry of the Environment, Germany
(chemistry and environmental effects), and Dr R. Fielder, Department
of Health, United Kingdom (effects on experimental animals), during
the initial review of the document.
Dr S. Dobson, Co-Chairman of the Task Group, and Dr P.E.T. Douben
deserve special thanks for their significant contributions and
revisions of the draft document during the meeting, particularly the
sections dealing with environmental effects.
The efforts of all who helped in the preparation and finalization of
this publication are gratefully acknowledged.
NOTE TO READERS OF THE CRITERIA DOCUMENTS
Every effort has been made to present information in the criteria
documents as accurately as possible without unduly delaying their
publication. In the interest of all users of the environmental health
criteria documents, readers are kindly requested to communicate any
errors that may have occurred to the Manager of the International
Programme on Chemical Safety, World Health Organization, Geneva,
Switzerland, in order that they may be included in corrigenda, which
will appear in subsequent volumes.
* * *
A detailed data profile and a legal file can be obtained from the
International Register of Potentially Toxic Chemicals, Palais des
Nations, 1211 Geneva 10, Switzerland (Telephone no. 7988400/7985850).
1. SUMMARY
This publication focuses on the risks for human health and the
environment from exposures to: monochlorobenzene (MCB);
dichlorobenzenes (DCB); trichlorobenzenes (TCB); tetrachloro-benzenes
(TeCB); and pentachlorobenzene (PeCB). Chlorine substitution is
indicated as follows: 1,2-dichlorobenzene (1,2-DCB);
1,2,3-trichlorobenzene (1,2,3-TCB), etc.
1.1 Identity, Physical and Chemical Properties, Analytical Methods
Chlorobenzenes are cyclic aromatic compounds formed by the addition of
1-6 atoms of chlorine to the benzene ring. This yields 12 compounds:
monochlorobenzene, three isomeric forms each of di-, tri-, and
tetrachlorobenzenes, as well as penta- and hexachlorobenzenes.
Chlorobenzenes are white crystalline solids at room temperature,
except for MCB, 1,2-DCB, 1,3-DCB, and 1,2,4-TCB, which are colourless
liquids. In general, the water solubility of chlorobenzene compounds
is low, decreasing with increased chlorination. Flammability is low,
the octanol/water partition coefficients are moderate to high,
increasing with increasing chlorination, and the vapour pressures are
low to moderate, decreasing with increasing chlorination. The taste
and odour thresholds are low, particularly for the lower chlorinated
compounds.
Commercial chlorobenzenes, even when purified, contain various amounts
of closely related isomers. For example, pure MCB may contain as much
as 0.05 % benzene and 0.1 % DCBs, while technical 1,2-DCB may contain
up to 19 % of the other DCBs, 1 % TCBs, and up to 0.05 % MCB. No
evidence of contamination by polychlorinated dibenzo- p-dioxins
(PCDDs) and dibenzofurans (PCDFs) has been reported.
A large number of sampling techniques have been developed for
chlorobenzenes, depending on the medium. These range from solvent
extraction procedures for aqueous media, to the use of absorbents for
airborne compounds. The analytical technique of choice for the
determination of chlorobenzenes in environmental samples is gas-liquid
chromatography (GLC).
1.2 Sources of Human and Environmental Exposure
1.2.1 Production figures
Available data on chlorobenzene production levels are from the period
1980-83, when global production was estimated to be 568 x 106 kg,
though the use of chlorobenzenes has declined in some countries since
then. About 50 % of this amount was manufactured within the USA and
the remainder primarily in Western Europe and Japan. MCB accounted for
70 % of the global production, 1,2-DCB, 1,4-DCB, and 1,2,4-TCB being
produced at 22 x 106, 24 x 106, and 1.2-3.7 x 106 kg,
respectively.
MCB and DCBs are produced by the direct chlorination of benzene in the
liquid phase, using a catalyst, while TCBs and TeCBs are produced by
the direct chlorination of appropriate chlorobenzene isomers, in the
presence of a metal catalyst.
1.2.2 Uses
Chlorobenzenes are used mainly as intermediates in the synthesis of
pesticides and other chemicals; 1,4-DCB is used in space deodorants
and as a moth repellent. The higher chlorinated benzenes (TCBs and
1,2,3,4-TeCB) have been used as components of dielectric fluids.
1.2.3 Release of chlorobenzenes into the environment
The release of chlorobenzenes into the environment occurs primarily
during manufacture, and through the dispersive nature of their uses.
For example, in the USA, between 0.1 and 0.2 % of the 1983 production
of 130 x 106 kg of MCB was estimated to have been lost to the
environment. Releases of chlorobenzenes from waste disposal, including
incineration of municipal waste, are much lower. However, the
incineration of chlorobenzenes may lead to the emission of PCDDs and
PCDFs.
1.3 Environmental Transport, Distribution, and Transformation
1.3.1 Degradation
Chlorobenzenes are removed from the environment principally by
biological, and, to a lesser extent, by non-biological mechanisms;
however, they are considered moderately persistent in water, air, and
sediments. Residence times in water of 1 day in rivers and over 100
days in ground water have been reported. In air, chemical and
photolytic reactions are presumed to be the predominant pathways for
chlorobenzene degradation, with residence times in the range of 13-116
days reported for MCB, DCBs, and an unspecified TCB isomer.
Many microorganisms from sediments and sewage sludge have been shown
to degrade chlorobenzenes. It would appear that the higher chlorinated
compounds are less readily degraded, and such degradation occurs only
under aerobic conditions. Under anaerobic conditions in soil and
ground water, DCB, TCBs, and PeCBs are usually resistant to microbial
degradation.
1.3.2 Fate
Chlorobenzenes released into the aquatic environment will be
redistributed preferentially to the air and to sediment (particularly
organically rich sediments). Limited information has shown that levels
1000 times those found in water have been detected in sediments,
particularly in highly industrialized regions. Retention of
chlorobenzenes in soil increases with the organic content of the soil;
there is a positive correlation between the degree of chlorination of
the compound and its adsorption on organic matter. Limited evidence is
available showing that sediment-bound residues are bioavailable to
organisms; i.e., aquatic invertebrates can take up residues from
sediment, and plants, from soil.
1.4 Environmental Levels and Human Exposure
1.4.1 Chlorobenzenes in the environment
Mean levels of chlorobenzenes (mono- to tri-) in ambient air are of
the order of 0.1 µg/m3, with maximum levels of up to 100 µg/m3. No
data are available on levels of TeCB and PeCB in ambient air, though
these chemicals have been detected in fly ash from municipal
incinerators. Levels of chlorobenzenes in indoor air are similar to
those in ambient air; however, levels much higher than those in the
ambient air have been reported in heavily polluted areas, and in
enclosed spaces where chlorobenzene-containing products have been
used.
Chlorobenzenes (mono- to penta-) have been detected in surface waters
in the ng/litre-µg/litre range, with occasional levels of up to tenths
of one mg/litre reported near industrial sources. Levels of
chlorobenzenes in industrial waste waters may be higher and vary
according to the nature of the processes used.
All chlorobenzene congeners have been detected in the drinking-water
samples analysed. The lower chlorinated compounds were found most
frequently and in the highest concentrations, with the 1,4-DCB isomer
predominating; however, the mean concentrations of any chlorobenzene
detected have generally been less than 1 µg/litre and have rarely
exceeded 50 µg/litre.
Data from well-designed monitoring programmes on chlorobenzene levels
in food have not been found; available information has mainly been
confined to concentrations in fish in the vicinity of industrial
sources and to isolated incidents of contamination of meat products.
All chlorobenzene isomers (mono- to penta-) were detected in
freshwater trout, with levels ranging from 0.1 to 16 µg/kg. In another
study, levels of total chlorobenzenes in freshwater fish varied from
a mean of 0.2 mg/kg fat in lightly polluted areas to 1.8 mg/kg fat in
an industrialized area. There is some indication that concentrations
of chlorobenzenes in freshwater fish increase with increasing degree
of chlorination of the compound. The few studies available indicate
levels of 1,4-DCB in some marine fish of 0.05 mg/kg (wet weight).
In the available studies on chlorobenzene levels in meat and milk,
limited primarily to samples from contaminated areas, concentrations
of 0.02-5 µg/kg have been reported.
In 2 surveys of human milk, the levels of all chlorobenzene congeners,
except MCB, were quantified. In one study, the levels of DCBs averaged
25 µg/kg milk, whereas the TCB and TeCB isomers and PeCB were found at
mean levels of less than 5 µg/kg milk. Levels in the second survey
were much lower, mean concentrations ranging from 1 µg/kg (1,2,3-TCB
and PeCB) to a maximum of 6 µg/kg (1,3- and 1,4-dichlorobenzene).
1.4.2 Human exposure
1.4.2.1 General population
On the basis of limited data, the daily intake of chlorobenzenes
within the general population appears to be greatest from air,
particularly for the lower, more volatile compounds (0.2-0.9 µ/kg body
weight). Intake from food compared with that from other sources
increases with increasing degree of chlorination; food contributes a
greater percentage of the total daily intake of TeCBs and PeCB than
air. However, exposure levels for such congeners are likely to be less
than 0.05 µg/kg body weight. A limited number of studies have shown
that, on a body weight basis, breast-fed infants may receive a higher
dose of chlorobenzenes than members of the adult population.
1.4.2.2 Occupational
It is not possible to make an accurate quantification of occupational
exposure to chlorobenzenes on the basis of available data. However,
levels of 1,4-DCB ranged between 42 and 288 mg/m3 in one plant, and
levels of MCB of up to 18.7 mg/m3 were found in other chemical
plants.
1.5 Kinetics and Metabolism
All chlorobenzenes appear to be absorbed readily from the
gastrointestinal and respiratory tracts in humans and experimental
animals, with absorption influenced by the position of the chlorine in
different isomers of the same congener. The chlorobenzenes are less
readily absorbed through the skin.
After rapid distribution to highly perfused organs in experimental
animals, absorbed chlorobenzenes accumulate primarily in the fatty
tissue, with smaller amounts in the liver and other organs.
Chlorobenzenes have been shown to cross the placenta, and have been
found in the fetal brain. In general, accumulation is greater for the
more highly chlorinated congeners. There is considerable variation,
however, in the accumulation of different isomers of the same
congener.
In both humans and experimental animals, the metabolism of
chlorobenzenes proceeds via microsomal oxidation to the corresponding
chlorophenol. These chlorophenols can be excreted in the urine as
mercapturic acids, or as glucuronic acid or sulfate conjugates. TeCB
and PeCB are metabolized at a slower rate and remain in the tissues
for longer periods than the monochloro- to trichloro- congeners. Some
of the chlorobenzenes induce a wide range of enzyme systems including
those involved in oxidative, reductive, conjugation, and hydrolytic
pathways.
In general, elimination of the higher chlorinated benzenes is slower
than that of the MCB and DCB congeners, and a greater proportion of
the tri- to penta- congeners are eliminated unchanged in the faeces.
For example, 17% of a dose of 1,2,4-TCB was eliminated in the faeces
after 7 days, whereas 91-97% of 1,4-DCB was eliminated as metabolites
in the urine after 5 days. The position of the chlorine atoms on the
benzene ring is also an important determinant of the rate of
metabolism and elimination, the isomers with two adjacent
unsubstituted carbon atoms being more rapidly metabolized and
eliminated.
1.6 Effects on Aquatic Organisms in the Environment
Available information on the effects of chlorobenzenes on the
environment is mainly focused on acute effects on aquatic organisms.
In general, toxicity increases with the degree of chlorination of the
benzene ring. While MCB, 1,2-DCB, 1,3-DCB, 1,2,4-TCB, 1,3,5-TCB, and
1,2,4,5-TeCB all exhibit a low toxicity for microorganisms, the
toxicity of the TCBs and TeCBs is, with the exception of 1,2,4,5-TeCB,
slightly higher than that of the other compounds; in unicellular
aquatic algae, EC50 values for 96-h cell growth or chlorophyll a
production ranged from over 300 mg/litre for MCB to approximately 1
mg/litre for 1,2,3,5-TeCB. Some aquatic invertebrates appear more
sensitive to chlorobenzenes, but levels required for 48- or 96-h
lethality are still near, or well above, 1 mg/litre (e.g., Daphnia
magna at 2.4 mg/litre for 1,2-DCB, and up to 530 mg/litre for
1,2,4,5-TeCB).
The 96-h LC50 for bluegill sunfish ranged between 0.3 mg/litre for
PeCB and 24 mg/litre for MCB. In embryo-larval assays, the chronic
toxicity limits for DCBs varied between 0.76 and 2.0 mg/litre for the
fathead minnow; in the estuarine sheepshead minnow, the chronic
toxicity limits for 1,2,4-TCB and 1,2,4,5-TeCB were 0.22 and
0.13 mg/litre, respectively. Newly-hatched goldfish and large-mouth
bass were the most susceptible life-stage with LC50s (96-h) of 1 and
0.05 mg/litre, respectively, for MCB.
No data are available on the effects of chlorobenzenes on terrestrial
systems.
1.7 Effects on Experimental Animals and In Vitro Systems
With few exceptions, the chlorobenzenes are only moderately toxic for
experimental animals, on an acute basis, and, generally, have oral
LD50s greater than 1000 mg/kg body weight; from the limited data
available, dermal LD50s are higher. The ingestion of a lethal dose
leads to respiratory paralysis, while the inhalation of high doses
causes local irritation and depression of the central nervous system.
Acute exposures to non-lethal doses of chlorobenzenes induce toxic
effects on the liver, kidneys, adrenal glands, mucous membranes, and
brain, and effects on metabolizing enzymes.
Studies on skin and eye irritation caused by chlorobenzenes have been
restricted to 1,2,4-TCB and 1,2-DCB. Both produce severe discomfort,
but no permanent damage was noted after direct application to the
rabbit eye. 1,2,4-TCB is mildly irritating to the skin and may lead to
dermatitis after repeated or prolonged contact. No evidence of
sensitization was found.
Short-term exposures (5-21 days) of rats and mice to MCB and DCBs at
hundreds of mg/kg body weight resulted in liver damage and
haematological changes indicative of bone marrow damage. Liver damage
was also the major adverse effect noted after the short-term exposure
of rats or rabbits to other chlorobenzenes (TCB-PeCB), at doses
slightly lower than those for MCB and DCBs. Several of the
chlorobenzene isomers studied induced porphyria, the isomers with
para chlorine atoms being the most active (i.e., 1,4-DCB, 1,2,4-TCB,
1,2,3,,4-TeCB, and PeCB). The general order of toxicity noted for
TeCBs and PeCB after short-term exposure was: 1,2,4,5-TeCB
>PeCB>1,2,3,4- and 1,2,3,5-TeCB, which correlated well with the
levels found in fat and liver.
Long-term exposure studies (up to 6 months) on several species of
experimental animals indicated a trend for the toxicity of
chlorobenzenes to increase with increased ring chlorination. However,
there was considerable variation in the long-term toxicities of
different isomers of the same congener. For example, 1,4-DCB appeared
to be much less toxic than 1,2-DCB. There was a good correlation
between toxicity and the degree of accumulation of the compound in the
body tissues, female animals being less sensitive than males. Major
target organs were the liver and kidney; at higher doses, effects on
the haematopoietic system were reported and thyroid toxicity was noted
in studies on 1,2,4,5-TeCB and PeCB.
In a bioassay for the carcinogenicity of MCB, there was an increased
incidence of hepatic neoplastic nodules in the high-dose group
(120 mg/kg body weight) of male F344 rats, but no treatment-related
increases in tumour incidence in female F344 rats or male or female
B6C3F1 mice. There was no evidence for the carcino-genicity of
1,2-DCB in male or female F344 rats or B6C3F1 mice (60 or 120 mg/kg
body weight).
In a bioassay for the carcinogenicity of 1,4-DCB, there was a
dose-related increase in renal tubular cell adenocarcinomas in male
F344 rats and an increase in hepatocellular carcinomas and adenomas in
both sexes of B6C3F1 mice. No evidence of carcinogenicity was
reported in male and female Wistar rats, or female Swiss mice,
following inhalation of slightly higher doses of 1,4-DCB (estimated to
be 400 mg/kg per day for rats and 790 mg/kg per day for mice) for
shorter periods. However, available data indicate that the induction
of renal tumours by 1,4-DCB in male F344 rats and the associated
severe nephropathy and hyaline droplet formation are species- and
sex-specific responses associated with the reabsorption of
alpha-2-microglobulin.
Available data are inadequate for the assessment of the
carcinogenicity of the higher chlorinated benzenes (tri- to penta-).
Although available data from in vitro and in vivo assays for
isomers other than 1,4-DCB are limited, chlorobenzenes do not appear
to be mutagenic. On the basis of a more extensive database for
1,4-DCB, it can be concluded that this compound has no mutagenic
potential, either in vivo or in vitro.
There has been no evidence that chlorobenzenes are teratogenic in rats
and rabbits. The administration of MCB and DCBs to rats or rabbits via
inhalation at concentrations >2000 mg/m3 (approximately 550 mg/kg
body weight per day) and, orally, at concentrations >500 mg/kg body
weight, resulted in minor embryotoxic and fetotoxic effects. However,
such doses were clearly toxic to the mother. Although there is some
evidence that TCBs, TeCBs, and PeCB are embryotoxic and fetotoxic at
doses that are not toxic for the mother, available data are
inconsistent.
1.8 Effects on Humans
1.8.1 General population
Reports on the effects of CBs on the general population are restricted
to case reports from accidents and/or the misuse of products
containing the lower chlorinated benzenes (MCB, 1,2-DCB, 1,4-DCB, and
an unspecified isomer of TCB). Little or no information is available
on dose, chemical purity, or dose:time relationships and observed
effects, such as myeloblastic leukaemia, rhinitis, glomerulonephritis,
pulmonary granulomatosis, dizziness, tremor, ataxia, polyneuritis, and
jaundice, cannot be quantified.
No epidemiological studies on the health effects of chlorobenzenes in
the general population have been reported.
1.8.2 Occupational exposure
During the manufacture and use of chlorobenzenes, clinical symptoms
and signs of excessive exposure include: central nervous system
effects and irritation of the eyes and upper respiratory tract (MCB);
haematological disorders (1,2-DCB); and central nervous system
effects, hardening of the skin, and haematological disorders including
anaemia (1,4-DCB). However, such symptoms come only from case reports,
and are difficult to quantify, since little information on actual
levels, chemical purity, or dose:time relationships is available.
The few epidemiological studies on workers exposed to chlorobenzenes
that have been reported concern only MCB, 1,2-DCB, 1,4-DCB, and
1,2,4,5-TeCB. Although effects on the nervous system, on neonatal
development, and on the skin have been reported after MCB exposures,
the 3 studies were not adequate for assessing risk, because of
methodological problems, such as exposure assessment, mixed exposures,
and lack of control groups. Similar criticism can be made of the study
on 1,4-DCB, in which eye and nose irritation was reported, as well as
the study in which chromosomal aberrations resulting from exposure to
unspecified levels of 1,2-DCB and 1,2,4,5-TeCB were reported.
1.9 Conclusions
If good industrial practices are followed, the risks associated with
occupational exposure to chlorobenzenes are considered to be minimal.
The present risk assessment also indicates that current concentrations
of chlorobenzenes in the environment pose a minimal risk for the
general population, except in the case of the misuse of
chlorobenzene-based products or their uncontrolled discharge into the
environment. However, this assessment is based on limited monitoring
data and additional information is needed to substantiate this
conclusion. Reduction of the widespread use and disposal of
chlorobenzenes should, however, be considered because:
(a) Chlorobenzenes may act as precursors for the formation of
polychlorinated dibenzodioxins/polychlorinated dibenzofurans
(PCDDs/PCDFs), e.g., in incineration processes.
(b) These chemicals can lead to taste and odour problems in
drinking-water and fish.
(c) Residues persist in organically-rich anaerobic sediments and
soils, and ground water.
For most chlorobenzenes, the assessment of risk has been based on
non-neoplastic effects. However, neoplastic effects were taken into
consideration in the risk assessment for MCB and 1,4-DCB. Available
data indicate that the observed increase in renal tumours in rats
caused by 1,4-DCB is a species- and sex-specific response that is
unlikely to be relevant for humans. On the basis of evidence of
increased DNA replication in the mouse liver and the increased
incidence of hepatocellular adenomas and carcinomas in mice, 1,4-DCB
may act as a non-genotoxic carcinogen in the rodent liver. The
increased incidence of hepatic neoplastic nodules observed in the
high-dose group of male rats in a bioassay for carcinogenicity
indicates that MCB may also be a non-genotoxic carcinogen.
2. IDENTITY, PHYSICAL AND CHEMICAL PROPERTIES, ANALYTICAL METHODS
2.1 Identity
2.1.1 Primary constituent
The chlorinated benzenes are cyclic aromatic compounds in which the
hydrogen atoms of the benzene ring have been replaced by 1-6 chlorine
substituents (Fig. 1). This substitution yields 12 compounds,
including: monochlorobenzene, 3 isomeric forms of dichlorobenzene, 3
isomers of trichlorobenzene, 3 isomers of tetrachlorobenzene,
pentachlorobenzene, and hexachlorobenzene. The identification features
for the congeners ranging from mono to pentachlorobenzene are
summarized in Table 1.
Hexachlorobenzene is the subject of a separate Environmental Health
Criteria publication and will not be evaluated here.
2.1.2 Technical product
There are no widely established trade specifications for commercial
chlorobenzenes. Pure commercial monochlorobenzene may contain 0.05 %
or less of benzene and up to 0.1 % of dichlorobenzenes. Technical
grade 1,2-dichlorobenzene contains up to 19 % of the other 2
dichlorobenzene isomers, 1 % of trichlorobenzenes, and up to 0.05 % of
monochlorobenzene, while purified 1,2-dichlorobenzene contains up to
0.05 % of monochlorobenzene and 0.2 % of 1,2,4-trichlorobenzene.
Technical grade 1,4-dichlorobenzene contains up to a total of 0.1 % of
mono- and trichlorobenzenes and 0.5 % of each of the other
dichlorobenzene isomers. Commercial 1,2,4-trichlorobenzene may contain
up to 0.1 % of mono-chlorobenzene, 0.5 % of dichlorobenzenes, and
0.5 % of tetrachlorobenzenes (Kao & Poffenberger, 1979).
Polychlorinated dibenzodioxins or dibenzofurans were not detected in
trichlorobenzenes, tetrachlorobenzenes, or penta-chlorobenzene (Buser,
1979).
2.2 Physical and Chemical Properties
The physical and chemical properties of the chlorobenzenes (mono- to
penta-) are presented in Table 2.
MCB, 1,2-DCB, 1,3-DCB, and 1,2,4-TCB are colourless liquids, while all
other congeners are white crystalline solids at room temperature. In
general, the solubility of chlorobenzenes in water is poor (decreasing
with increasing chlorination), flammability is low, the octanol/water
partition coefficients are moderate to high (increasing with
increasing chlorination), and vapour pressures are low to moderate
(decreasing with increasing chlorination).
2.3 Organoleptic Properties
The odour and taste thresholds for different isomers of the same
chlorobenzene appear to be similar: 0.01-0.02 mg/litre for MCB and
0.001-0.002 mg/litre for both 1,2-DCB and 1,4-DCB (Varshavskaya,
1968). Piet et al. (1980) reported that the odour thresholds for 1,2-
and 1,4-dichlorobenzenes in Rhine tap water were 10 and 0.3 µg/litre
respectively, while 1,2,4-TCB was detected at a level of 5 µg/litre.
Using available experimental data, Amoore & Hautala (1983) determined
water-dilution odour thresholds for MCB, 1,2-DCB, 1,4-DCB, and
1,2,4-TCB to be 0.050, 0.024, 0.011, and 0.064 mg/litre (ppm),
respectively. Odour thresholds in air for these compounds are 0.68,
0.30, 0.18, and 1.4 µlitre/litre (ppm), respectively. Fomenko (1965)
reported that the thresholds for smell and taste for 1,2,4,5-TeCB were
0.006 mg/litre and 0.0064 mg/litre, respectively.
2.4 Conversion Factors
At 25 °C and 101.3 kPa, the conversion factors for chlorobenzenes in
air are as follows:
monochlorobenzene: 1 ppm=4.55 mg/m3: 1 mg/m3=0.22 ppm
dichlorobenzenes: 1 ppm=6.00 mg/m3: 1 mg/m3=0.17 ppm
trichlorobenzenes: 1 ppm=7.42 mg/m3: 1 mg/m3=0.13 ppm
tetrachlorobenzenes: 1 ppm=8.83 mg/m3: 1 mg/m3=0.11 ppm
pentachlorobenzene: 1 ppm=10.24 mg/m3: 1 mg/m3=0.10 ppm
Table 1. Information on the identity of chlorobenzenes
Compound Congener Molecular R.M.M.b Synonyms
(CAS number)a identification formula
Monochlorobenzene MCB C6H5Cl 112.6 chlorobenzene
(108-90-7) phenyl chloride
1,2-dichlorobenzene 1,2-DCB C6H4Cl2 147.0 ortho-dichlorobenzene
(95-50-1) o-dichlorobenzene
1,3-dichlorobenzene 1,3-DCB C6H4Cl2 147.0 meta-dichlorobenzene
(541-73-1) m-dichlorobenzene
1,4-dichlorobenzene 1,4-DCB C6H4Cl2 147.0 para-dichlorobenzene
(106-46-7) p-dichlorobenzene
1,2,3-trichlorobenzene 1,2,3-TCB C6H3Cl3 181.5 vic-trichlorobenzene
(87-61-6) v-trichlorobenzene
1,2,6-trichlorobenzene
1,2,4-trichlorobenzene 1,2,4-TCB C6H3Cl3 181.5 1,2,4-trichlorobenzol
(120-82-1)
1,3,5-trichlorobenzene 1,3,5-TCB C6H3Cl3 181.5 s-trichlorobenzene
(108-70-3) TCBA
sym-trichlorobenzene
1,2,3,4-tetrachlorobenzene 1,2,3,4-TeCB C6H2Cl4 215.9 benzene, 1,2,3,4-
(634-66-2) tetrachloro-
1,2,3,5-tetrachlorobenzene 1,2,3,5-TeCB C6H2Cl4 215.9 benzene, 1,2,3,5-
(634-90-2) tetrachloro-
Table 1 (continued)
Compound Congener Molecular R.M.M.b Synonyms
(CAS number)a identification formula
1,2,4,5-tetrachlorobenzene 1,2,4,5-TeCB C6H2Cl4 215.9 benzene, tetrachloride
(95-94-3) benzene, 1,2,4,5-
tetrachloro-
s-tetrachlorobenzene
Pentachlorobenzene PeCB C6HCl5 250.3 1,2,3,4,5-
(608-93-5) pentachloro-benzene
QCB
a Chemical Abstract Services registry number.
b R.M.M. - Relative molecular mass.
Table 2. Physical and chemical properties
Solubility Log Henry's Soil Blood/air
Compound Melting Boiling Vapour Densityf in water at octanol/water Law sorption partition
point point pressure 25 °C (mol/ partition constant coefficient coefficientj
(°C)a (°C)a at 25 °C litre) coefficientg (kPa m3/ (KOC)i
(Pa) (mg/litre)g mol)h
MCB -45.6 132.0 1665b 1.105820/4 2.6x10-3 2.98 0.377 466 30.8
(293)
1,2-DCB -17.0 180.5 197b 1.304820/4 6.2x10-4 3.38 0.198 987 423
(91.1)
1,3-DCB -24.7 173.0 269b 1.288420/4 8.4x10-4 3.48 0.366 1070 201.4
(123)
1,4-DCB 53.1 174.0 90c 1,247520/4 2.1x10-4 3.38 0.160 1470 NA
(30.9)
1,2,3-TCB 53.5 218.5 17.3d NA 6.7x10-5 4.04 0.306 3680 NA
(12.2)
1,2,4-TCB 17.0 213.5 45.3d 1.454220/4 2.5x10-4 3.98 0.439 2670 NA
(45.3)
1,3,5-TCB 63.5 208761 24.0d NA 2.2x10-5 4.02 0.233 NA NA
(3.99)
1,2,3,4-TeCB 47.5 254.0 5.2c NA 5.6x10-5 4.55 0.261 NA NA
(12.1)
1,2,3,5-TeCB 54.5 246.0 9.8c NA 1.3x10-5 4.65 0.593 8560 NA
(2.81)
Table 2 (continued)
Solubility Log Henry's Soil Blood/air
Compound Melting Boiling Vapour Densityf in water at octanol/water Law sorption partition
point point pressure 25 °C (mol/ partition constant coefficient coefficientj
(°C)a (°C)a at 25 °C litre) coefficientg (kPa m3/ (KOC)i
(Pa) (mg/litre)g mol)h
1,2,4,5-TeCB 139.5 243.6 0.72c NA 1.0x10-5 4.51 0.261 6990 NA
(2.16)
PeCB 86.0 277.0 133 at 1.834216.5 3.3x10-6 5.03 0.977 58 700 NA
98.6 °Ce (0.83)
a Melting points are rounded to the nearest 0.1 °C; Boiling points are at atmospheric pressure (760 mm), unless otherwise indicated
by a superscript (Weast, 1986).
b Vapour pressures obtained from the Antoine equation: log10p(kPa) = A-B/(T+C) - 0.8751 presented by Kao & Poffenberger (1979),
together with the values for the Antoiine constants (A,B,C).T = temperature in °C.
c From: MacKay et al. (1982). The value was derived from experimental data obtained above 25 °C and extrapolated to 25 °C, taking into
account the phase change from liquid to solid.
d Vapour pressures obtained from the equation: log10p(10-3torr) = -(A/T) + B and values for the constants (A and B) are presented by
Sears & Hopke (1949).T = absolute temperature.
e From: Stull (1947).
f Density is relative to water, otherwise it has the dimensions g/ml. A superscript indicates the temperature of the liquid and a
subscript indicates the temperature of water to which the density is referred (Weast, 1986).
g From: Miller et al. (1984).
h From: MacKay & Shiu (1981).
i Derived from: Karlokoff et al. (1979).
j From: Sato & Nakajima (1979).
NA - values either not given in the reference indicated or not found in the literature.
2.5 Analytical Methods
Some methods for the sampling and determination of chlorobenzenes in
various environmental media and human tissues and fluids are
presented in Table 3.
The analytical technique of choice for the determination of
chlorobenzenes in environmental samples is gas-liquid chromatography
(GLC). However, the methods of collection and preparation of samples
for GLC analysis vary considerably, depending on the medium and the
laboratory. Columns with silicone-based stationary phases or Tenax
resins, and electron capture detectors, appear to be the most widely
used.
Tenax-GC resins appear to be the most commonly used absorbent for
the air sampling of chlorobenzenes (Sievers et al., 1980; Krost et
al., 1982; Pellizzari, 1982), though XAD resins have also been used
(Langhorst & Nestrick, 1979). Air pollutants collected on Tenax-GC
resins can be desorbed directly on to the GLC column by heating the
absorber. XAD resins can be extracted with carbon tetrachloride, an
aliquot of which can then be injected into a gas chromatograph
(Langhorst & Nestrick, 1979).
Solvent extraction is a simple and effective technique for
recovering chlorobenzenes from water samples. Hexane, pentane, and a
1:1 mixture of cyclohexane and diethyl ether have been identified as
suitable extraction solvents for these compounds (Oliver & Bothen,
1980; Piet et al., 1980; Otson & Williams, 1981). Alternatively,
preconcentration of the chlorobenzenes on organic resins, such as
Chromosorb 102 and Tenax-GC, is also effective (Oliver & Bothen,
1980; Pankow & Isabelle, 1982). The purge-trap method is also often
used to concentrate the volatile halogenated benzenes before
analysis using GC (Jungclaus et al., 1978; Pereira & Hughes, 1980;
Otson & Williams, 1982).
The extraction of chlorobenzenes from aquatic sediments or soil can
be achieved by solvent or Soxhlet extraction (Oliver & Bothen, 1982;
Lopez-Avila et al., 1983; Onuska & Terry, 1985). Solvents commonly
used are acetone and/or hexane. The extract is generally dried using
sodium sulfate, followed by clean-up on a Florisil column before GLC
analysis.
For the detection of chlorobenzenes in fish samples, solvent or
Soxhlet extraction with subsequent clean-up on Florisil and GC
analysis with electron capture detection have commonly been used
(Lunde & Ofstad, 1976; Kuehl et al., 1980; Oliver & Bothen, 1982).
Vacuum extraction and the direct purge and trap method have also
been used to quantify levels of MCB in fish tissue (Hiatt, 1981).
Table 3. Analytical methods for chlorobenzenesa
Matrix Sampling, extraction Analytical method Detection limitsb Reference
air continuous flow, aircraft trap purged in oven at NA Sievers et al. (1980)
sampling port; sorbent traps 220 °C with He; capillary
with 4 changes column (30 m x 0.3 mm),
gas chromatography-mass
spectrometry (GC-MS) data
system
air 4-h samples collected on silanized glass column; GC MCB 3.2 Langhorst & Nestrick
Amberlite XAD-Z resin at with photoionization detector DCBs 4.2 (1979)
100-200 ml/min; desorbed TCBs 5.9
TeCB 7.1
PeCB 9.2
water 500 ml with chromosorb 102, or GC analysis, glass capillary MCB 0.5 Oliver & Bothen
3.1 litres with 75 ml pentane columns; electron capture DCBs 0.001 (1980)
TCBs 0.0001
TeCB 0.00005
PeCB 0.00001
water 40 ml with automated purge and GC analysis with FID Otson & Williams
trap; inert gas bubbled through simultaneous use of flame MCB < 0.1 (1982)
purged compounds directly on ionization detector (FID) 1,2-DCB 0.2
to column and Hall electrolytic 1,3-DCB 0.1
conductivity detector (HECD) 1,4-DCB 0.1
HECD
MCB 0.1
1,2-DCB 0.1
1,3-DCB 0.1
1,4-DCB 0.1
Table 3 (continued)
Matrix Sampling, extraction Analytical method Detection limitsb Reference
water liquid-liquid extraction of 120 ml GC analysis using 63Ni FID Otson & Williams
water with 38:1 water:hexane electron capture detector MCB 5 (1981)
(ECD), FID or HECD 1,2-DCB 2
1,4-DCB 2
1,2,4-TCB 2
ECD
MCB ND
1,2-DCB 5
1,4-DCB 5
1,2,4-TCB < 1
HECD
MCB 1
1,2-DCB < 1
1,4-DCB < 1
1,2,4-TCB < 1
water extraction of 4 litres water with compounds desorbed directly NA Pankow & Isabelle
Tenax-GC 35/60 mesh; from glass column of (1982)
centrifugation or vacuum Tenax-GC into GC by flash
dessication of wet cartridge heating; flame ionization
to remove water detector
water extraction of 1-litre sample with glass capillary column NA Piet et al. (1980)
20 ml cyclohexane-diethylether coupled to electron detector
(1:1) on line with FID detector
water adsorption on 1 g of activated GC analysis, FID detector MCB concentration range: Blanchard & Hardy
charcoal in exposure chamber; 0.058-19.4 mg/litre (1985)
charcoal desorbed with 5 ml of
carbon disulfide for >30 min
Table 3 (continued)
Matrix Sampling, extraction Analytical method Detection limitsb Reference
sediment Soxhlet extraction of 10-15 g GC analysis on glass MCB 1500 Oliver & Bothen
with 41% hexane/59% acetone; capillary columns; electron DCBs 5 (1982)
back-extracted with water to capture detector TCBs 0.4
remove acetone, through Na2SO4 TeCBs 0.2
and evaporated to 10 ml; PeCB 0.05
clean-up on Na2SO4 + deactivated
Florisil column
sediment 10 g sediment treated by steam identification by relative 1,3-DCB 1.5 Onuska & Terry
distillation, soxhlet or retention-time matching after 1,3,5-TCB 1.0 (1985)
ultrasonic extraction; clean-up ECD 1,2,4-TCB 0.8
with mercury only needed when 1,2,3-TCB 0.8
sulfur present 1,2,3,5-TeCB 0.5
1,2,4,5-TeCB 0.5
1,2,3,4-TeCB 0.5
PeCB 0.4
fish 15 g fish soxhlet extracted; GC analysis on glass MCB 1500 Oliver & Bothen
clean-up with combination of capillary column, ECD DCBs 5 (1982)
alumina, silica gel, florisil and detector TCBs 0.4
acidified florisil (fish), after TeCBS 0.2
removal of lipids PeCB 0.05
blood hexane extraction on Synder borosilicate glass column, DCBs approx. 2 Bristol et al.
column using 3 g for GC and GC analysis; electron capture TCBs approx. 1.5 (1982)
710 g for GC/MS detector or GC/MS system TeCBs approx. 1
PeCB approx. 1
Table 3 (continued)
Matrix Sampling, extraction Analytical method Detection limitsb Reference
blood CCl4 extraction of 5 g of blood silanized glass column; GC Blood Langhorst & Nestrick
urine or 20 g urine, silica gel column analysis with photoionization MCB approx.23 (1979)
chromatography (CCl4 eluent) detector DCBs approx. 4
TCBs approx. 5
TeCBs approx. 6
PeCB approx. 9
Urine
MCB approx. 6
DCBs approx. 6
TCBs approx. 1
TeCBs approx. 2
PeCB approx. 2
blood 0.1-1 ml GC sample diluted to Tenax adsorbent heated and NA Balkon & Leary (1979)
urine 5 ml with water and placed in a volatiles analysed by GC/MS
bubbler for purging on to Tenax for detection and
in liquid sample concentrator identification in a screening
procedure
blood hexane/isopropanol extraction of GC analysis, electron capture NA Lunde & Bjorseth
approximately 25 g; H2SO4 detector (1977)
digestion of hexane phase
adipose tissue extraction of tissue with GC analysis, capillary DCBs ND LeBel & Williams
acetone-hexane, then fractionated column, ECD detection; 1,3,5-TCB 11.0 µg/kg (1986)
by gel permeation chromatography compounds 5.9 µg/kg
(GPC); clean-up on Florisil column confirmed by gas 1,2,3,5-TeCB 13.1 µg/kg
chromatography-mass spectrometry 1,2,3,4-TeCB 4.8 µg/kg
with selected ion monitoring PeCB 1.9 µg/kg
Table 3 (continued)
Matrix Sampling, extraction Analytical method Detection limitsb Reference
urine solutions stirred and heated to Analysis by GC/FID MCB Michael et al.
blood 50 °C, headspace above the blood 98c (1980)
adipose tissue solution purged on to Tenax GC urine 86c
cartridges; cartridges dessicated adipose 13c
using anhydrous calcium sulfate
and thermally desorbed DCB
blood 86c
urine 79c
adipose 57c
urine 5 ml samples: GC equipped with an electron urine 94c McKinney et al.
blood Urine: acidified with 0.5 ml capture (tritium) detector blood 78c (1970)
concentrated HCl, then extracted
with benzene Extracts dried over
anhydrous sodium sulfate
Blood: plasma extracted with
benzene, then dried with
anhydrous sodium sulfate
adipose tissue 2-g samples extracted with analysis by GC with electron NA Mes et al. (1982)
benzene:acetone (1:19 v/v); capture detector;
repeated evaporation with hexane confirmation by GLC; monitored
to remove traces of benzene; by mass spectrometry
fat-free extract chromatographed
on Florisil-silicic acid column
Table 3 (continued)
a Often, the primary aim of the analyses was quantification of organochlorine compounds, other than chlorobenzenes. In these cases,
the clean-up procedures were quite complicated, because of the need to separate different organochlorine pesticide residues, prior
to chromatographic analysis.
b Detection limits reported in µg/m3 for air and µg/litre or µg/kg for other media, unless noted otherwise.
NA - information not available in the paper.
ND - not detected during analysis.
c Indicates recovery percentages from spiked samples.
Solvent extraction is also used in the determination of
chlorobenzenes in biological matrices, such as blood and urine. For
less volatile compounds (tri-, tetra-, and pentachlorobenzenes),
solvent extraction is followed by column chromatographic clean up
and quantification (Lamparski et al., 1980; Mes et al., 1982). For
the more volatile compounds (mono-, dichlorobenzenes), a modified
purge-trap method with a capillary GC can be used (Michael et al.,
1980). The chlorobenzenes are then quantified using a GC with
detection by electron capture (McKinney et al., 1970; Morita et al.,
1975; Lunde & Bjorseth, 1977), photoionization (Langhorst &
Nestrick, 1979), or mass spectrometry (Balkon & Leary, 1979; Bristol
et al., 1982; LeBel & Williams, 1986).
3. SOURCES OF HUMAN AND ENVIRONMENTAL EXPOSURE
3.1 Natural Occurrence
Natural sources of chlorobenzenes in the general environment have
not been identified; however, 1,2,3,4-TeCB has been identified in
the oil of a marsh grass (Miles et al., 1973).
3.2 Man-made Sources
3.2.1 Production
Monochlorobenzene and the dichlorobenzenes are produced commercially
by the direct chlorination of benzene in the liquid phase, in the
presence of a Lewis acid catalyst, such as ferric chloride. In the
liquid-phase chlorination of monochlorobenzene, 1,2-, and
1,4-dichlorobenzenes are the predominant products. Trichlorobenzenes
result from the chlorination of dichlorobenzenes with ferric
chloride, while tetrachlorobenzenes are produced by the addition of
chlorine to trichlorobenzenes in the presence of an aluminium
catalyst. Tetrachlorobenzenes can be used as the precursor in
pentachlorobenzene production (US EPA, 1985). Pentachloro-benzene is
also produced by the denitrification of penta-chloronitrobenzene and
the reductive dechlorination of hexa-chlorobenzene (Renner & Mücke,
1986).
About 50% of the world production of all chlorobenzenes
(estimated from data in US EPA (1985) to be 568 x 106 kg in 1983)
is manufactured in the USA. The remainder is produced mainly in
Western Europe and Japan. Monochlorobenzene makes up approximately
70 % of total world production of all chlorobenzenes.
Data on current, global chlorobenzene production volumes are not
available in readily retrievable references. Summaries of production
levels in 1980 and 1983 have been published and are presented in
Table 4 (IARC, 1982; US EPA, 1985). Although these may provide some
indication of present production levels, it appears that PeCB
production has ceased within the USA, and that the use of
chlorobenzenes as chemical intermediates has decreased. Therefore,
the actual level of production is probably less than that shown in
Table 4.
No information was found on the production of TCB, TeCB, and PeCB
congeners outside the USA. However, in 1979, the estimated
production of 1,4-DCB in Japan was 27.5 x 106 kg and that of
1,2-DCB was 13 x 106 kg (IARC, 1982).
Table 4. Production levels in the USA and possible uses of chlorinated benzenes
Chemical Major usesa Estimated annual
production in the USA
MCB Intermediate in the manufacture of chloronitrobenzenes, diphenyl 130 x 106 kg in 1980
oxide, DDT, and silicones; as a process solvent for methylene
diisocyanate, adhesives, polishes, waxes, pharmaceutical products,
and natural rubber; as a degrading solvent
1,2-DCB In the manufacture of 3,4-dichloroaniline; as a solvent for a wide 22 x 106 kg in 1980
range of organic materials and for oxides of non-ferrous metals; as a
solvent carrier in the production of toluene diisocyanate; in the
manufacture of dyes; as a fumigant and insecticide; in degreasing
hides and wool; in metal polishes; in industrial odour control; in
cleaners for drains
1,3-DCB As a fumigant and insecticide NA
1,4-DCB As a moth repellent, general insecticide, germicide, space deodorant; 24 x 106 kg in 1980
in the manufacture of 2,5-dichloroaniline and dyes; as a chemical
intermediate; in pharmaceutical products; in agricultural fumigants
1,2,3-TCB Apart from use as a chemical intermediate, the uses are the same as 23-74 x 103 kg
those 1,2,4-trichlorobenzene
1,2,4-TCB As an intermediate in the manufacture of herbicides; dye carrier, 1.2-3.7 x 106 kg
dielectric fluid; solvent; heat-transfer medium
1,3,5-TCB Solvent for products melting at high-temperatures; coolant in 1.1-2.1 x 105 kg
electrical insulators; heat-transfer medium, lubricant, and synthetic
transformer oil; termite preparation and insecticide; in dyes
Table 4 (continued)
Chemical Major usesa Estimated annual
production in the USA
1,2,3,4-TeCB Component in dielectric fluids; in the synthesis of fungicides NA
1,2,3,5-TeCB NA NA
1,2,4,5-TeCB Intermediate for herbicides and defoliants; insecticide; NA
moisture-resistant impregnant; in electric insulation; in packing
protection
PeCB Formerly in a pesticide used to combat oyster drills; chemical Not manufactured in
intermediate the USAa
a From: US EPA (1985).
NA - not available.
The total production capacity for all chlorobenzenes in Western
Europe during 1980 was estimated to be greater than 208 x 106 kg
(IARC, 1982).
Although data on production levels are scarce, it is apparent from
available information that chlorobenzenes (in particular MCB and
DCBs) are produced in high volumes. Use patterns shown in Table 4,
and estimated losses to the environment shown in Table 5, indicate a
high potential for human exposure and environmental contamination.
Table 5. Estimated quantities (kg) of chlorobenzenes lost to the environment
during manufacture in relation to total 1983 productiona
Chlorobenzene Losses during Losses to Total production
manufacture environment
MCB 1.9-3.0 x 105 1.5-2.6 x 105 130 x 106
1,2-DCB 1.1-2.1 x 105 30 x 103 22 x 106
1,3-DCB 2-6 x 102 NA NA
1,4-DCB 1.8-2.8 x 105 1.7-2.7 x 105 24 x 106
1,2,3-TCB 0.6-2 x 103 <1 x 102 23-74 x 103
1,2,4-TCB 3-10 x 103 3-9 x 102 1.2-3.7 x 106
1,3,5-TCB import import 1.1-2.1 x 105
TeCB NA NA NA
PeCB not manufactured NA NA
a Values calculated from US EPA (1985).
NA - data not available.
3.2.2 Uses
Use patterns may vary considerably among countries. A summary of the
uses of chlorinated benzenes in the USA is presented in Table 4.
Chlorobenzenes are used mainly as intermediates in the synthesis of
other chemicals, and as pesticides. The 1,4-DCB isomer is commonly
used in space deodorants and moth repellents, and several of the
higher chlorinated benzenes (TCBs, 1,2,3,4-TeCB) have been used in
dielectric fluids.
MCB also has potential as a functional fluid in external combustion
Rankine engines (Curran, 1981) and as a component in heat transfer
fluids in solar energy collectors (Boy-Marcotte, 1980).
The 1,4-DCB isomer is also being used in the USA as an intermediate
in the production of polyphenylene sulfide resin, an engineering
plastic with electrical and automotive applications.
3.2.3 Sources in the environment
Incineration of organochlorine and hydrocarbon polymers in the
presence of chlorine may result in the atmospheric release of
chlorobenzenes, though quantities are small in relation to the total
mass of carbon compounds incinerated (Ahling et al., 1978;
Lahaniatis et al., 1981a). Incineration of chlorobenzenes most
probably leads to the formation of polychlorinated dibenzodioxins
and dibenzofurans, as indicated by experimental studies on the
pyrolysis of various TCBs, TeCBs, and PeCB (Buser, 1979). Although,
in experimental studies, chlorobenzenes have been formed in
reactions between benzene and sodium hypochlorite (Hofler et al.,
1983), evidence that they are generated during public water
treatment is slight (Otson et al., 1982a).
On the basis of measurements of concentrations in flue gases from
all municipal waste incinerators in Sweden (N=24), the maximum
contribution of chlorobenzenes (di- to hexa-) to ambient air was
calculated, in 1985, to be 590 kg (Ahlborg & Victorin, 1987).
Average emissions of total chlorobenzenes from small-scale wood
burners for dry wood, in closed fireplace ovens, during 2-h sampling
periods, ranged from 24 to 80 µg/kg dry fuel (Rudling et al., 1980).
Several of the chlorinated benzenes have been identified as
microbial metabolites of lindane degradation (Macholz & Kujawa,
1985).
4. ENVIRONMENTAL TRANSPORT, DISTRIBUTION, AND TRANSFORMATION
The transport and fate of chlorobenzenes in the environment has not
been well characterized. However, it is possible to draw some
conclusions based on the physical and chemical properties of the
compounds and the results of a limited number of laboratory and
field studies.
4.1 Transport and Distribution
The water solubility, saturated vapour pressure, and partition
coefficients (Henry's Law constant, KH; soil sorption, Koc;
octanol/ water, Kow; blood/air), useful for the prediction of the
transport and distribution of the chlorobenzenes in the environment,
are presented in Table 2.
As shown by Henry's Law constant (KH - the equilibrium
distribution coefficient of a compound between air and water), all
chlorobenzenes released into the aquatic environment will evaporate
preferentially from water to the atmosphere, despite their high
relative molecular masses and comparatively low vapour pressures
(MacKay & Wolkoff, 1973). From these data, it can also be predicted
that the preferential distribution from water to air will decrease
with increasing chlorination. In a study on the volatility of MCB in
a model aquatic ecosystem, 96% of the compound was released to the
atmosphere (Lu & Metcalf, 1975). In experimental studies by Garrison
& Hill (1972), 99% of the test compounds MCB, 1,2-DCB, 1,4-DCB, and
1,2,4-TCB had evaporated from aerated distilled solutions within 4
h. In non-aerated solutions, evaporation was complete within 72 h.
The results of a 1-year field study on Lake Zurich, Switzerland,
confirmed that most of the 1,4-DCB present in the water was
transferred to the atmosphere. The half-life of the compound was
estimated to be approximately 100 days, 67% being lost to the
atmosphere; 2% entering lake sediments and 31% being present in the
lake outflow (Schwarzenbach et al., 1979). Wilson et al. (1981)
studied the transport of a mixture in water of more than 10 organic
chemicals, including MCB, 1,4-DCB, and 1,2,4-TCB, through a column
of sandy soil having a low organic matter content, over a 21-day
period. They reported that up to 50% of the MCB evaporated and
approximately 50% of all 3 chlorobenzenes was degraded or was
unaccounted for, indicating that the compounds are likely to leach
into ground water.
4.2 Persistence and Fate
The chlorobenzenes are environmentally persistent compounds, the
most likely degradation mechanisms being photochemical reactions and
microbial action. While bioconcentration has been demonstrated, the
potential for biomagnification in food chains has not been
investigated. Soils that are rich in organic matter and aquatic
sediments are probably the major environmental sinks for these
compounds.
4.2.1 Persistence
In water, 1,2-DCB and 1,2,4-TCB are considered moderately persistent
compounds with half-lives ranging from 1 day in rivers to 10 days in
lakes and 100 days in ground waters (Zoeteman et al., 1980).
Concentrations may be rapidly reduced with aerobic biological
degradation or volatilization, but chlorobenzenes are extremely
persistent under anaerobic conditions, or where volatilization
cannot occur, i.e., in ground water.
Turbulence is a major factor in the elimination of these compounds
from surface waters. Turbulence increases volatilization and
bio-degradation. It may also lead to more rapid photochemical
degradation through the propagation of sensitized photolysis and the
increased frequency of exposure of water particles to surface
sunlight (Zoeteman et al., 1980).
Wakeham et al. (1983) studied the fate and persistence of MCB,
1,4-DCB, and 1,2,4-TCB in tanks containing seawater and associated
planktonic and microbial communities, with simulated tidal
turbulence and seasonal temperature regimes (spring, summer,
winter). It was suggested that removal processes other than
volatilization, such as biodegradation and sorption on to particles,
are probably not very important for 1,4-DCB and 1,2,4-TCB, but that
MCB is subject to rapid biodegradation under the relatively warm
spring and summer water temperatures, when microbial activity is
greater than in winter.
Chlorobenzenes in the air are degraded by chemical or sunlight-
catalysed reactions, or they may be adsorbed onto particles that
settle or are removed with rain. In a 2-week study on air samples
from California and Arizona, Singh et al. (1981) estimated the
residence times of MCB, DCBs, and an unspecified TCB isomer to be
13, 18.6, and 116.0 days, respectively.
In soils, the DCBs, TCBs, and PeCB are usually resistant to
micro-bial degradation; primary degradation products are the
chloro-phenols (Ballschmiter & Scholz, 1980). In experiments using
radiolabelled 1,2,3- and 1,2,4-TCBs on fresh field soil, the
observed degradation rates were very slow, 0.35 and 1.00 nmol/day
per 20 g soil, respectively (Marinucci & Bartha, 1979). These
investigators also observed that evaporation of the chlorobenzenes
was reduced by increasing the amounts of organic material in the
soil. In another experiment using 14C-labelled MCB, 1,2- and
1,4-DCBs, and 1,2,3- and 1,2,4-TCBs in soil, Haider et al. (1974)
found that 18.3%, 1.1% and 20.3% of MCB, DCBs, and TCBs,
respectively, were released as carbon dioxide.
4.2.2 Abiotic degradation
The higher chlorinated chlorobenzenes are not particularly reactive
compounds and would, therefore, be expected to disappear only slowly
in the environment through chemical degradation. Photolysis and
oxidative and hydrolytic reactions are pathways by which the
compounds may be abiotically degraded.
4.2.2.1 Photolysis
Although chlorobenzenes absorb light only weakly above 290 nm, some
photodegradation can occur when they are irradiated with sunlight,
or light containing an equivalent broad spectrum of wavelengths.
Uyeta et al. (1976) demonstrated that chlorobenzenes (other than
1,2,3,5-TeCB and PeCB, which were not examined) form polychlorinated
biphenyls when irradiated with sunlight. However, the yields of
polychlorinated biphenyls were less than 1% of the initial amount of
chlorobenzene. Of the compounds tested, 1,2,3-TCB and 1,2,4,5-TeCB
were the most resistant to photodegradation, while 1,2,4-TCB and
1,2,3,4-TeCB were the most easily degraded. The number of chlorine
atoms in the polychlorinated biphenyl photoproducts was 1 less than
the number contained in 2 molecules of the parent chlorobenzene,
i.e., monochlorobenzene yielded a monochlorobiphenyl,
dichlorobenzenes yielded tri-chlorobiphenyls and so on. Hydrochloric
acid was also a reaction product. On the basis of these results, it
was suggested that the photoformation of polychlorinated biphenyls
from chlorobenzenes involves free radical reactions based on the
dehydrochlorination of 1 molecule from 2 molecules of the parent
chlorobenzene.
Studies on direct photodegradation, either with direct sunlight or
artificial light simulating natural conditions, suggest that the
chlorobenzenes can be photodegraded, though the reactions may be
slow (Crosby & Hamadmad, 1971; Akermark et al., 1976; Uyeta et al.,
1976; Choudhry et al., 1979; Choudhry & Webster, 1985). For example,
the half-life of 1,4-DCB, under artificial sunlight irradiation, was
estimated to be 115.5 h (Hanai et al., 1985). This value was
considerably greater than the half-lives of other air pollutants
(i.e., tetrachloroethylene, trichloroethylene, benzene, toluene,
ethylbenzene, 1,2,4-trimethylbenzene, n-octane, and n-nonane)
under similar conditions.
Reductive dechlorination is the main photochemical reaction that
occurs in proton-donating solvents and there is evidence that the
solvent is involved with the electronically excited reactant
molecule in the transition state complex. Photodegradation of the
tri- and tetrachlorobenzenes, using acetonitrile as the solvent in a
1:1 ratio with water, has been reported; however, it should be noted
that acetonitrile would not be present in this ratio under normal
environmental conditions (Choudhry et al., 1979; Choudhry & Webster,
1985). Some form of hydrogen-donating entity, such as a solvent
molecule or another chlorobenzene molecule, appears necessary for
the photochemical dechlorination of chlorobenzenes at wave-lengths
above 290 nm. It has been speculated (Akermark et al., 1976) that
such hydrogen-donating "photosensitizers" may be found in
naturally occurring organic substances and that
photodecomposition may be important as a degradative pathway, given
the general physical and chemical stability of the chlorobenzenes.
In addition to direct photolysis, chlorobenzenes may also be removed
from the environment by reaction with molecular species that are
photochemically produced from other atmospheric pollutants. Such a
possibility has been suggested, on the basis of studies involving
simulated atmospheric environments, for interactions between
monochlorobenzene or 1,4-dichlorobenzene and oxides of nitrogen
(Dilling et al., 1976; Kanno & Nojima, 1979; Nojima & Kanno, 1980).
Reaction mechanisms and rates of disappearance of the compounds were
poorly defined in these studies.
4.2.2.2 Hydrolytic and oxidative reactions
It is unlikely that simple hydrolysis is an important degradation
pathway for the chlorobenzenes in the environment.
Cupitt (1980) suggested that MCB and the DCBs may be removed from
the troposphere by reaction with hydroxyl radicals (considered to
be the most potentially reactive species in the troposphere),
and possibly also by reaction with ozone. This investigator used
estimated rate constants for the reaction with hydroxyl radicals
(assumed to have a tropospheric concentration of 1 x 106
molecules/cm3) and ozone (tropospheric concentration, 1 x 1012
molecules/cm3) to predict atmospheric residence times of 28 days
and 39 days for MCB and the DCBs, respectively.
Calculations by Cupitt (1980) suggest that ozonolysis contributes
very little to the removal of the compounds, because the rate
constants for the reaction of hydroxyl radicals with the
chlorobenzenes are some 9 or 10 orders of magnitude greater than
those for the corresponding reactions with ozone.
4.2.3 Biodegradation and biotransformation
The degradation of chlorobenzenes by microorganisms has been
reported in several studies using various substrates, such as soil,
sediment, and sewage sludge (Table 6). It can be speculated, from a
perusal of these data, that the more highly chlorinated benzenes are
not degraded microbiologically as readily as the less chlorinated
congeners; however, the data are insufficient to draw definitive
conclusions. Garrison & Hill, (1972) found that MCB, 1,2-DCB, and
1,4-DCB were completely volatized in less than one day from
solutions containing mixed cultures of aerobic organisms, but that
2% of 1,2,4-TCB remained after 80 h.
The major degradation mechanism is oxidative dechlorination leading
to the formation of hydroxylated aromatic compounds (mainly
phenols), followed by ring fission and, eventually, mineralization
to carbon dioxide and water. It has been suggested that, like
polychlorinated biphenyls, chlorobenzenes appear to be attacked by
microorganisms only under aerobic conditions (Kobayashi & Rittman,
1982; Bouwer & McCarty, 1984).
Schwarzenbach et al. (1983) studied the movement of 1,4-DCB from a
polluted river in Switzerland through a ground water aquifer to a
series of wells. Correlation between the indicators of
microbiological metabolic activity and the observed decrease in
concentrations of 1,4-DCB with increasing distance of the wells from
the river was taken as evidence of the biotransformation of 1,4-DCB
in the aquifer system. On certain occasions, the persistence of
1,4-DCB was well correlated with anoxic conditions that prevailed in
parts of the aquifer, suggesting that the biotransformation of the
compound is minimal under anaerobic conditions. These findings were
confirmed in laboratory experiments using sediments from this
aquifer. Results showed that the DCBs were transformed only under
aerobic conditions and that the rates of transformation were
different with each isomer, 1,4-DCB degrading at the faster rate
(Kuhn et al., 1985).
4.2.4 Bioaccumulation
The bioaccumulation of chlorobenzenes by aquatic organisms is
determined by their relative water and lipid solubility (thus
reflecting the octanol/water partition coefficients) and the number
of chlorine substitutions. Uptake from water increases with
increasing chlorination. The coefficient of adsorption on sediment
influences the uptake into terrestrial plants and sediment-living
aquatic invertebrates; the degree of chlorination is also correlated
with uptake.
Table 6. Degradation of chlorobenzenes by miroorganisms
Chlorobenzene; Organism Substrate Rate Remarks
Reference
MCB, DCBs, Pseudomonas sp. synthetic NAa DCBs metabolized to dichlorophenols and
TCBs and TeCBs medium dichloropyrocatechols; MCB, TCBs, and
Ballschmiter & TeCBs metabolized to their respective
Scholz (1980) chlorophenols
MCB, DCBs, and NA synthetic no significant degradation medium seeded with sewage effluent and
1,2,4-TCB medium observed after 11 weeks strictly maintained under denitrifying
Bouwer & conditions
McCarty(1983)
MCB NA estuarine half-life = 75 days radiolabelled compound used,
Lee & Ryan sediments; half-life = 150 days degradation rate measured by
(1979) estuarine waters evolution of radiolabelled CO2;
considerable reduction in rate observed
when temperature reduced to 9-13 °C
MCB Pseudomonas synthetic not measured P. putida grown with toluene as the
Gibson et al. putida medium sole carbon source, oxidized MCB to
(1968) 3-chlorocatechol
MCB planktonic and sea water spring half-life = 21 days tanks contained 13 m3 sea water
Wakeham et al. microbial summer half-life = 4.6 days with simulated turbulence and
(1983) winter half-life = 13 days seasonal patterns
Table 6 (continued)
Chlorobenzene; Organism Substrate Rate Remarks
Reference
MCB microbial strain synthetic NAa culture isolated from soil and sewage
Reineke & WR 1306 medium and was sensitive to sudden increases
Knackmuss in MCB concentrations, resulting
(1984) in prolonged lag phase or disturbed
exponential phase; 3-chlorocatechol
isolated from culture fluid;
organisms did not oxidize isomeric DCBs
1,2-DCB Acinetobacter activated >90% disappearance in mixture of 4 bacterial genera and 1 yeast,
Davis et al. + sewage sludge 7 days glucose as sole carbon source, incubation
(1981) Alcaligenes temperature 28 °C; some DCB may have been
+ lost by evaporation
Flavobacterium
+
Pseudomonas
+
Rhodotorula
1,4-DCB planktonic and sea water spring half-life = 18 days tanks contained 13 m3 sea water with
Wakeham et al. microbial summer half-life = 10 days simulated turbulence and seasonal patterns
(1983) winter half-life = 13 days
1,4-DCB microbial flora ground water NAa under aerobic conditions, concentrations
Schwarzenbach present aquifer of 1,4-DCB decreased with increasing
et al. (1983) distance of wells from the polluted
1,2,4-TCB NA activated after 5 days, 56% converted to radiolabelled compound used, degradation
Simmons et al. sludge CO2; 23% converted to polar measured by evolution of radiolabelled CO2
(1977) metabolites; 7% evaporated
Table 6 (continued)
Chlorobenzene; Organism Substrate Rate Remarks
Reference
1,2,3-TCB and NA soil mineralization rates nmol/day radiolabelled compounds applied at
1,2,4-TCB per 20 g soil: 1,2,3-: 0.33, 50 mg/kg soil, mineralization measured by
Marinucci & 0.38; 1,2,4-: 1.09, 0.93, evolution of radiolabelled CO2; both TCBs
Bartha 1.37 poisoned metabolic action of soil
(1979) bacteria; 1,2,3-TCB yielded 2,3- and
2,6-dichlorophenol; 1,2,4-TCB yielded
2,4-, 2,5- and 3,4-dichlorophenol
1,2,4-TCB planktonic and sea water spring half-life = 22 days tanks contained 13 m3 sea water with
Wakeham et al. microbial summer half-life = 11 days simulated turbulence and seasonal patterns
(1983) winter half-life = 12 days
PeCB NA soil half-life = 194, 345 days compounds applied to soil samples at
Beck & Hansen concentrations equivalent to 10 kg/ha,
(1974) concentrations measured using gas
chromatography; duplicate experiments, no
explanation given for differences in
half-lives measured
a NA - not available.
Topp et al. (1986) compared the uptake in plants of chlorobenzenes
from the soil and via the air in closed, aerated laboratory systems.
A negative correlation was demonstrated between the bioconcentration
factor (BCF) and the soil adsorption coefficient (based on soil
organic matter content) for the uptake into the roots of barley. The
adsorption of chlorobenzenes on soil organic matter increased with
increasing chlorination. However, expression of uptake in barley
roots in relation to the soil interstitial water concentration of
the chlorobenzenes produced a positive correlation between the BCF
and the octanol/water partition coefficients. Higher chlorinated
chlorobenzenes, therefore, are most readily taken up by the plant
roots, when they are available in soil interstitial water. This will
occur particularly in sandy soils with a low organic matter content.
Uptake of volatilized chlorobenzenes in leaves was extremely low
compared with root uptake. The correlation between uptake and
physical properties demonstrated in barley did not hold for corn;
the authors stated that the uptake of lipophilic compounds by
lipid-rich plants, or plants with oil channels, was unpredictable .
In a later study, Topp et al. (1989) studied the uptake and
distribution of 14C-labelled 1,2,4-TCB and PeCB in barley. The BCF
concentration decreased with time of exposure; this was a dilution
effect as the plant grew. The total load of chlorobenzene increased
over the whole growing period of the plant, but the rate of uptake
was greater in the early growth period. Uptake increased with
increasing chlorination but decreased in relation to the soil
concentration (BCF fell with increasing chlorination). There was
evidence of metabolism of the chlorobenzenes in the plant, with the
level of the parent compound falling over the course of the
experiment in relation to the rate of metabolism, and the levels of
uncharacterized"bound" residues. After growth in soil containing 2
µg each of 1,2,4-TCB and PeCB/kg (dry weight), harvested barley
grain contained 73 and 82 µg/plant, respectively. The concentrations
in the dry grain were 0.05 and
0.06 mg/kg for 1,2,4-TCB and PeCB, respectively.
Khezovich & Harrison (1988) used closed, flow-through bioassay
systems to investigate the bioavailability to chiromonid midge
larvae of sediment-bound MCB, 1,2-DCB, and 1,2,4-TCB. A sediment
with a high organic matter content (14.5%) was compared with a
sediment with a low organic content (3.6%). The bioconcentration of
the chlorobenzenes increased with increasing chlorination. The
experiment was run without equilibrium between the sediment and the
overlying water (flow-through of uncontaminated water) and after
equilibration of recirculated water. Most of the uptake of
chlorobenzenes occurred from the interstitial water between sediment
particles and the results of bioconcentration were best correlated
with the concentrations of the chlorobenzenes in the interstitial
water. Under non-equilibrium conditions, bioconcentration factors
were 5, 29, and 225 for MCB, 1,2-DCB, and 1,2,4-TCB, respectively.
Köneman & Van Leeuwan (1980) exposed guppies to 116 µg
1,4-DCB/litre, 48 µg 1,2,3-TCB/litre, 43 µg 1,3,5-TCB/litre, 12 µg
1,2,3,5-TeCB/litre, or 1.2 µg PeCB/litre for 19 days. The fish were
fed daily on commercial fish food. Concentrations in fish were
expressed in mg/kg. The results showed an increase in the rate of
uptake with increasing level of chlorination of the benzene ring.
After exposure, the fish were kept for 9 weeks in clear water to
study the rate of elimination. The rate constant of loss of 1,4-DCB
was described by a one-compartment model and was relatively high
(1.00/day). For the other CBs, the losses showed a clear biphasic
pattern with a decrease in the first, rapid rate of loss with
increasing level of chlorination. Consequently, the level of
bioaccumulation went up with increasing chlorination.
In a study performed by Opperhuizen & Stokkel (1988), 1-year-old
guppies were exposed for 42 days to 1,2,3,4-TeCB or PeCB at µg/litre
levels. There were 3 groups of fish: one with contaminated
Chromosorb (artificial sediment) added, one with uncontaminated
Chromosorb, and one without Chromosorb. The concentration of PeCB in
the water was reduced by the presence of contaminated sediment,
while neither type of particle affected the TeCB concentration in
the water. Addition of uncontaminated particles did not affect the
increase in chlorobenzene residues in the fish. However, the
presence of contaminated particles resulted in higher concentrations
of PeCB in exposed fish than in control fish. No effects were seen
with TeCB. The authors attributed this to the low levels of TeCB on
the particles compared with levels in the water. They concluded that
the influence of contaminated particles on the bioconcentration of
hydrophobic chemicals by fish depends on the hydrophobicity of the
chemicals. The particles may act as a source of the compounds.
Van Hoogen & Opperhuizen (1988) exposed guppies in acute toxicity
tests to 1,2,3-TCB, 1,2,3,4-TeCB, or PeCB in a continuous-flow
system. Fish died having reached the lethal dose of chlorobenzene
for fish, which was between 2.0 and 2.5 mmol/kg and was independent
of the exposure concentration. The authors suggested that this value
was not affected by the route of administration. In addition, the
level of chlorination did not influence the lethal dose expressed in
mmol/kg. When uptake and elimination rate constants were calculated,
any combination of exposure time and concentration required to reach
the lethal dose could be calculated.
4.2.5 Biomagnification
No studies were found concerning the possibility that concentrations
of chlorobenzenes may increase as they move up the food chain.
4.2.6 Ultimate fate following use
As discussed in section 4.1, there is a preferential exchange of
chlorobenzenes from water to the atmosphere. However, in natural
waters containing appreciable amounts of suspended organic matter,
chlorobenzenes may be retained and transported within the aquatic
environment. The accumulation of chlorobenzenes in aquatic sediments
is striking, concentrations being at least 1000 times higher than
those found in the water. Available data suggest, therefore, that
soils rich in organic matter may be a major environmental sink for
these compounds (Elder et al., 1981; Oliver & Nicol, 1982).
Historical evidence for the persistence of chlorobenzenes and for
sediments acting as an environmental sink for these compounds has
been reported by Durham & Oliver (1983). Radionuclide measurements
were used to construct age profiles for Lake Ontario sediments. The
age of lake bottom sediments near the mouth of the Niagara River was
correlated with the concentrations of chlorobenzenes found in the
sediment samples. Over an 80-year period, the concentrations of all
chlorobenzene isomers increased from 0.4 to 15 µg/litre in 1898-1904
to a peak of 18 to 1100 µg/litre in 1959-67, and then declined to 6
to 110 µg/litre in 1980-81. The rise and fall of chlorobenzene
levels closely followed the rise and fall of the total USA
production figures for all chlorobenzenes for a similar period. The
Niagara River is considered to be a major source of chlorobenzene
pollution in Lake Ontario (Oliver & Nicol, 1982).
In Canada, recent data indicate that levels of chlorobenzenes in
sediments are highest in the industrialized Central Region (Ontario
and Quebec). Mean concentrations of the dichlorobenzenes (the
congeners that are present at the highest levels) were 130 µg/kg for
the 1,2-isomer and 46 µg/kg for both the 1,3- and 1,4-isomers. Mean
levels of other congeners, which were also present at elevated
concentrations (above individual detection limits), were 43 µg/kg,
39 µg/kg, and 29 µg/kg for 1,2,3,4-TeCB, PeCB, and 1,2,4-TCB,
respectively (NAQUADAT, 1987).
When the proportion of each congener (di- to penta-) to the total
chlorobenzene content of the water of the Niagara River (a major
source) was compared with that found in the sediment of Lake
Ontario, Oliver et al. (1989) concluded that "increasing the
chlorine content on the benzene ring leads to higher relative
accumulation of the chemicals in sediments". DCBs, TCBs, TeCBs, and
PeCB constituted 68%, 21%, 8%, and 2% of the total chlorobenzenes
(di- to penta-) measured in the water samples from the Niagara
River; comparable values for sediment in Lake Ontario were 12%, 31%,
21%, and 9%, respectively.
5. ENVIRONMENTAL LEVELS AND HUMAN EXPOSURE
5.1 Environmental Levels
5.1.1 Air
Levels of chlorobenzenes in ambient outdoor air are presented in
Table 7. Although the available data are insufficient to make a
reliable estimate of human exposure from the atmosphere, it can be
concluded that mean levels of chlorobenzenes (mono- to tri-) in
ambient air are in the tenths of µg/m3 range; however, maximum
values can range up to 100 µg/m3. Seasonal variations in the
concentrations of 1,4-DCB in ambient air have also been reported,
with concentrations increasing with increasing temperature (Hanai et
al., 1985). No data are available concerning levels of
tetrachloro-benzene and pentachlorobenzene in the ambient air,
though these congeners have been detected (but not quantified) in
the fly ash from municipal incinerators (Eiceman et al., 1979,
1981).
Chlorobenzenes have also been detected in rainwater, presumably
through transfer from the ambient air; Pankow et al. (1983) found
all 3 DCB isomers and 1,2,4-TCB, at levels of less than 10 ng/litre
at selected sites in Oregon and California. In the United Kingdom,
1,4-DCB was detected in rainwater at a level of 0.01 ± 0.005
µg/litre (Fielding et al., 1981).
In general, the levels of the chlorobenzenes in indoor air (Table 8)
are similar to those in ambient air. However, in several cases,
levels have been much higher. For example, concentrations found in
basements in the Love Canal area (up to 190 µg/m3 for total
dichlorobenzenes) and in the wardrobe of a Tokyo residence (up to
1700 µg 1,4-DCB/m3 detected in 1 sample) may be explained by the
proximity of a chemical dump and the use of 1,4-DCB as a moth
repellent, respectively.
5.1.2 Water
Chlorinated benzenes have been detected in sewage sludge, municipal
waste water, surface and ground waters, and in drinking-water.
However, in 12 sewage sludges in the United Kingdom, the
concentrations of chlorobenzenes ranged from <0.01 mg/kg dry weight
for PeCB to 40.2 mg/kg dry weight for 1,3-DCB, with a general
reduction in concentration with increased chlorine substitution
(Rogers et al., 1989).
Table 7. Chlorobenzenes in outdoor air
Compound; Number of Location Concentrationb
Reference Samplesa (µg/m3)
MCB
Singh et al. (1981) * USA; cities:
Los Angeles, California 0.9 (2.3)
Phoenix, Arizona 0.9 (2.3)
Oakland, California 0.45 (1.4)
Harkov et al. (1983) 38 (35) USA; cities:
Newark, New Jersey 0.5
Elizabeth, New Jersey 0.4
Camden, New Jersey 0.3
Levine et al. (1985) 9 USA
Hamilton, Ohio ND - 43
Harkov et al. (1985) 7 (7) USA
Hazardous waste sites 0.2 - 3.6
and landfills in New (20.4)
Jersey
Lebret (1985) NA Netherlands
Ede and Rotterdam median <0.4 (0.4)
Pellizzari et al. (1986) USA; cities:
20 Greenboro, North Carolina median 0.029 (0.57)
11 Houston, Texas median 0.045 (1.3)
71 Elizabeth/Bayonnne, New Jersey median 0.43 (6.3)
Table 7 (continued)