Dichlorobenzenes
1,2-dichlorobenzene (1,2-DCB); 1,3-dichlorobenzene (1,3-DCB); 1,4-dichlorobenzene (1,4-DCB) (endorsed 1996)
Guideline
Based on aesthetic considerations, the concentrations of dichlorobenzenes in drinking water should not exceed the values shown below.
Dichlorobenzenes would not be a health concern unless concentrations exceeded the health-based guideline values shown below:
1,2-dichlorobenzene
1.5 mg/L
0.001 mg/L
1,3-dichlorobenzene
inadequate data
0.02 mg/L
1,4-dichlorobenzene
0.04 mg/L
0.0003 mg/L (300 ng/L)
General description
Dichlorobenzenes are widespread in the environment and may be present in drinking water though spills and discharges, from atmospheric deposition, or by contact with contaminated soils. Studies in Japan, England, Canada and the United States have reported concentrations in the range 0.0000005 mg/L (0.5 ng/L) to 0.013 mg/L. Most supplies tested are below 0.00001 mg/L (10 ng/L), with 1,2-DCB and 1,4-DCB the most widely detected isomers. Sources of human exposure to DCBs are mainly food and air.
The dichlorobenzenes impart an offensive taste and odour to water, with thresholds between 0.0003 mg/L and 0.02 mg/L.
1,4-DCB is used in toilet blocks to deodorise air, and as a moth repellent, and is widely diffused in the environment. 1,3-DCB is a minor fumigant and insecticide and can be formed from incomplete combustion of waste. 1,2-DCB is used primarily as a chemical intermediate for dyestuffs and pesticides.
Typical values in Australian drinking water
DCBs have not been found in Australian drinking waters. They are included here to provide guidance in the unlikely event of contamination, and because they have been detected occasionally in drinking water supplies overseas.
Treatment of drinking water
It is unlikely that DCB concentrations are reduced significantly during conventional water treatment processes. Removal using packed tower aeration or by the use of granular activated carbon is more than 90% effective and it is likely that concentrations below 0.001 mg/L can be achieved using these methods.
Measurement
A purge and trap gas chromatographic procedure can be used for analysis (USEPA Draft Method 502.1 1986). An inert gas is bubbled through the sample and the dichlorobenzenes trapped on an adsorbent. The adsorbent is then heated and the dichlorobenzenes analysed using gas chromatography with electron capture detection. The limit of determination is approximately 0.0002 mg/L.
Health considerations
DCBs are absorbed rapidly through the lungs and from the gastrointestinal tract, and then distributed to tissues, primarily to fat or fatty tissue, and the lungs and kidneys. They are metabolised by the liver to the respective chlorophenols and eliminated in urine.
An extensive review and summary of the human and animal toxicity data for chlorobenzenes is available (IPCS 1986).
In the various reported cases of human exposure to DCBs, inhalation is the primary route. Toxic effects include liver damage, blood disorders, and disturbances to the immune system, the central nervous system or the respiratory tract. Skin pigmentation and allergic dermatitis have followed skin contact.
In rodents, long-term gavage (measured force-feeding) studies showed high doses of 1,2-DCB (120 mg/kg body weight per day) to affect mainly the liver and kidney, but found no adverse effects at lower doses. On balance, the available evidence suggests that 1,2-DCB is neither mutagenic in tests with bacteria nor carcinogenic in rodents.
No data are available on chronic toxicity for 1,3-DCB. No mutagenic activity was seen in tests with bacteria.
Long-term gavage studies involving 1,4-DCB produced similar results to the 1,2-DCB studies. In addition, there is evidence that 1,4-DCB increases the incidence of kidney tumours in male rats and liver tumours in mice after long-term exposure. It did not exhibit mutagenic activity in tests with bacteria or mammalian cells.
The International Agency for Research on Cancer has concluded that 1,4-DCB is possibly carcinogenic to humans (Group 2B, inadequate evidence in humans but sufficient evidence in animals), but that 1,2-DCB is unclassifiable as to its carcinogenicity (Group 3, inadequate evidence in humans and animals) (IARC 1987).
Derivation of guideline
The guideline values for dichlorobenzenes in drinking water were determined as follows:
i) 1,2-dichlorobenzene:
The health-based guideline value of 1.5 mg/L was determined as follows:
where:
60 mg/kg body weight per day is the no-effect level from a 2-year gavage study using mice (NTP 1985).
70 kg is the average weight of an adult.
0.1 is the proportion of total daily intake attributable to the consumption of water.
2 L/day is the average amount of water consumed by an adult.
100 is the safety factor in using the results of an animal study as a basis for human exposure (10 for interspecies variations and 10 for intraspecies variations).
5/7 is used to convert data based on a 5 day per week gavage study to a 7-day week equivalent.
Other factors are as above.
This health-based guideline value exceeds the taste and odour threshold of 0.001 mg/L. The World Health Organization (WHO) guideline value of 1 mg/L was based on an adult body weight of 60 kg. The difference in the guideline values is not significant.
ii) 1,3-dichlorobenzene
There are insufficient long-term data to set a guideline value for 1,3-DCB in drinking water based on health considerations. The maximum concentration guideline of 0.02 mg/L is based on the aesthetic considerations of taste and odour.
iii) 1,4-dichlorobenzene
The health-based guideline value of 0.04 mg/L was determined as follows:
where:
150 mg/kg body weight per day is the lowest effect level based on the appearance of kidney tumours in a 2-year gavage study using rats (NTP 1987).
10,000 is the safety factor in using the results of an animal study as a basis for human exposure (10 for interspecies variations, 10 for intraspecies variations, 10 because a lowest effect level was used instead of a no-effect level, and 10 because carcinogenic effects were observed at the lowest doses used).
Other factors are as above.
5/7 is used to convert data based on a 5 day per week gavage study to a 7-day week equivalent.
This health-based value exceeds the taste and odour threshold of 0.0003 mg/L. The WHO guideline value of 0.3 mg/L did not include the additional factor of 10 for possible carcinogenic effects.
References
IARC (International Agency for Research on Cancer) (1987). IARC Monographs on the Evaluation of Carcinogenic Risks to Humans: Overall Evaluations of Carcinogenicity. An updating of IARC monographs volumes 1 to 42. World Health Organization, IARC, Supplement 7.
IPCS (International Programme on Chemical Safety) (1991). Chlorobenzenes other than hexachlorobenzene. Environmental Health Criteria, 128. World Health Organization, IPCS.
NTP (National Toxicology Program) (1985). Toxicology and carcinogenesis studies of 1,2-dichlorobenzene (o-dichlorobenzene) in F344/N rats and B6C3F1 mice (gavage studies). NTP Technical Report No. 255, Publication No. 86-2511. United States Department of Health and Human Services, National Institute of Health.
NTP (National Toxicology Program) (1987). Toxicology and carcinogenesis gavage studies of 1,4-dichlorobenzene in F344/N rats and B6C3F1 mice. NTP, Technical Report Series No. 319, Publication No. 87-2575, National Institute of Health, Bethesda, United States.
USEPA Draft Method 502.1 (1986). Volatile halogenated organic compounds in water by purge and trap gas chromatography. United States Environmental Protection Agency, Environmental Monitoring and Support Laboratory (ESML), Cincinnati, Ohio.
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