Chlorobenzenes other than hexachlorobenzene
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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 (CAS number)a identification formula
Monochlorobenzene MCB C6H5Cl 112.6 (108-90-7) 1,2-dichlorobenzene 1,2-DCB C6H4Cl2 147.0 (95-50-1) 1,3-dichlorobenzene 1,3-DCB C6H4Cl2 147.0 (541-73-1) 1,4-dichlorobenzene 1,4-DCB C6H4Cl2 147.0 (106-46-7) 1,2,3-trichlorobenzene 1,2,3-TCB C6H3Cl3 181.5 (87-61-6)
1,2,4-trichlorobenzene 1,2,4-TCB C6H3Cl3 181.5 (120-82-1)
1,3,5-trichlorobenzene 1,3,5-TCB C6H3Cl3 181.5 (108-70-3)
1,2,3,4-tetrachlorobenzene 1,2,3,4-TeCB C6H2Cl4 215.9 (634-66-2) 1,2,3,5-tetrachlorobenzene 1,2,3,5-TeCB C6H2Cl4 215.9 (634-90-2)
Table 1 (continued)
Compound Congener Molecular R.M.M (CAS number)a identification formula
1,2,4,5-tetrachlorobenzene 1,2,4,5-TeCB C6H2Cl4 215.9 (95-94-3)
Pentachlorobenzene PeCB C6HCl5 250.3 (608-93-5)
a Chemical Abstract Services registry number.
b R.M.M. - Relative molecular mass.
Table 2. Physical and chemical properties
Solubility Compound Melting Boiling Vapour Densityf in water at point point pressure 25 °C (mol/
(°C)a (°C)a at 25 °C litre) (Pa) (mg/litre)g
MCB -45.6 132.0 1665b 1.105820/4 2.6x10-3 (293) 1,2-DCB -17.0 180.5 197b 1.304820/4 6.2x10-4 (91.1) 1,3-DCB -24.7 173.0 269b 1.288420/4 8.4x10-4 (123) 1,4-DCB 53.1 174.0 90c 1,247520/4 2.1x10-4 (30.9) 1,2,3-TCB 53.5 218.5 17.3d NA 6.7x10-5 (12.2) 1,2,4-TCB 17.0 213.5 45.3d 1.454220/4 2.5x10-4 (45.3) 1,3,5-TCB 63.5 208761 24.0d NA 2.2x10-5 (3.99) 1,2,3,4-TeCB 47.5 254.0 5.2c NA 5.6x10-5 (12.1) 1,2,3,5-TeCB 54.5 246.0 9.8c NA 1.3x10-5 (2.81)
Table 2 (continued)
Solubility Compound Melting Boiling Vapour Densityf in water at point point pressure 25 °C (mol/
(°C)a (°C)a at 25 °C litre) (Pa) (mg/litre)g
1,2,4,5-TeCB 139.5 243.6 0.72c NA 1.0x10-5 (2.16)
PeCB 86.0 277.0 133 at 1.834216.5 3.3x10-6 98.6 °Ce (0.83)
a Melting points are rounded to the nearest 0.1 °C; Boiling points are at by a superscript (Weast, 1986).
b Vapour pressures obtained from the Antoine equation: log10p(kPa) = A-B/(
together with the values for the Antoiine constants (A,B,C).T = temperat
c From: MacKay et al. (1982). The value was derived from experimental data account the phase change from liquid to solid.
d Vapour pressures obtained from the equation: log10p(10-3torr) = -(A/T) + Sears & Hopke (1949).T = absolute temperature.
e From: Stull (1947).
f Density is relative to water, otherwise it has the dimensions g/ml. A s subscript indicates the temperature of water to which the density is ref
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
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
air continuous flow, aircraft trap purged in oven at sampling port; sorbent traps 220 °C with He; capillar with 4 changes column (30 m x 0.3 mm), gas chromatography-mass spectrometry (GC-MS) dat system
air 4-h samples collected on silanized glass column;
Amberlite XAD-Z resin at with photoionization det 100-200 ml/min; desorbed
water 500 ml with chromosorb 102, or GC analysis, glass capil 3.1 litres with 75 ml pentane columns; electron captur
water 40 ml with automated purge and GC analysis with trap; inert gas bubbled through simultaneous use of flam purged compounds directly on ionization detector (FID to column and Hall electrolytic conductivity detector (H
Table 3 (continued)
Matrix Sampling, extraction Analytical method
water liquid-liquid extraction of 120 ml GC analysis using 63Ni water with 38:1 water:hexane electron capture detecto (ECD), FID or HECD
water extraction of 4 litres water with compounds desorbed direc Tenax-GC 35/60 mesh; from glass column of centrifugation or vacuum Tenax-GC into GC by flas dessication of wet cartridge heating; flame ionizatio to remove water detector
water extraction of 1-litre sample with glass capillary column 20 ml cyclohexane-diethylether coupled to electron dete (1:1) on line with FID detecto water adsorption on 1 g of activated GC analysis, FID detecto charcoal in exposure chamber;
charcoal desorbed with 5 ml of carbon disulfide for >30 min
Table 3 (continued)
Matrix Sampling, extraction Analytical method
sediment Soxhlet extraction of 10-15 g GC analysis on glass with 41% hexane/59% acetone; capillary columns; elect back-extracted with water to capture detector remove acetone, through Na2SO4
and evaporated to 10 ml;
clean-up on Na2SO4 + deactivated Florisil column
sediment 10 g sediment treated by steam identification by relati distillation, soxhlet or retention-time matching ultrasonic extraction; clean-up ECD with mercury only needed when sulfur present
fish 15 g fish soxhlet extracted; GC analysis on glass clean-up with combination of capillary column, ECD alumina, silica gel, florisil and detector acidified florisil (fish), after removal of lipids blood hexane extraction on Synder borosilicate glass colum column using 3 g for GC and GC analysis; electron ca 710 g for GC/MS detector or GC/MS system
Table 3 (continued)
Matrix Sampling, extraction Analytical method
blood CCl4 extraction of 5 g of blood silanized glass column;
urine or 20 g urine, silica gel column analysis with photoioniz chromatography (CCl4 eluent) detector
blood 0.1-1 ml GC sample diluted to Tenax adsorbent heated a urine 5 ml with water and placed in a volatiles analysed by GC bubbler for purging on to Tenax for detection and
in liquid sample concentrator identification in a scre procedure
blood hexane/isopropanol extraction of GC analysis, electron ca approximately 25 g; H2SO4 detector digestion of hexane phase
adipose tissue extraction of tissue with GC analysis, capillary acetone-hexane, then fractionated column, ECD detection;
by gel permeation chromatography compounds (GPC); clean-up on Florisil column confirmed by gas chromatography-mass spec with selected ion monito
Table 3 (continued)
Matrix Sampling, extraction Analytical method
urine solutions stirred and heated to Analysis by GC/FID blood 50 °C, headspace above the adipose tissue solution purged on to Tenax GC cartridges; cartridges dessicated using anhydrous calcium sulfate
and thermally desorbed
urine 5 ml samples: GC equipped with an elec blood Urine: acidified with 0.5 ml capture (tritium) detect 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 elec benzene:acetone (1:19 v/v); capture detector;
repeated evaporation with hexane confirmation by GLC; mon 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 organochlor the clean-up procedures were quite complicated, because of the need to s to chromatographic analysis.
b Detection limits reported in µg/m3 for air and µg/litre or µg/kg for oth 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 benze
Chemical Major usesa
MCB Intermediate in the manufacture of chloronitrobenzenes, diph oxide, DDT, and silicones; as a process solvent for methylen diisocyanate, adhesives, polishes, waxes, pharmaceutical pro and natural rubber; as a degrading solvent
1,2-DCB In the manufacture of 3,4-dichloroaniline; as a solvent for range of organic materials and for oxides of non-ferrous met solvent carrier in the production of toluene diisocyanate; i manufacture of dyes; as a fumigant and insecticide; in degre hides and wool; in metal polishes; in industrial odour contr cleaners for drains
1,3-DCB As a fumigant and insecticide 1,4-DCB As a moth repellent, general insecticide, germicide, space d in the manufacture of 2,5-dichloroaniline and dyes; as a che intermediate; in pharmaceutical products; in agricultural fu 1,2,3-TCB Apart from use as a chemical intermediate, the uses are the those 1,2,4-trichlorobenzene
1,2,4-TCB As an intermediate in the manufacture of herbicides; dye car dielectric fluid; solvent; heat-transfer medium
1,3,5-TCB Solvent for products melting at high-temperatures; coolant i electrical insulators; heat-transfer medium, lubricant, and transformer oil; termite preparation and insecticide; in dye
Table 4 (continued)
Chemical Major usesa
1,2,3,4-TeCB Component in dielectric fluids; in the synthesis of fungicid 1,2,3,5-TeCB NA 1,2,4,5-TeCB Intermediate for herbicides and defoliants; insecticide;
moisture-resistant impregnant; in electric insulation; in pa protection
PeCB Formerly in a pesticide used to combat oyster drills; chemic intermediate
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 pro 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 1 1,2,4-TCB 3-10 x 103 3-9 x 102 1.2-3.7 x 1,3,5-TCB import import 1.1-2.1 x 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.
