Chlorobenzene

(endorsed 1996)

Guideline

Based on aesthetic considerations (taste), the concentration of chlorobenzene in drinking water should not exceed 0.01 mg/L.

Chlorobenzene would not be a health concern unless the concentration exceeded 0.3 mg/L.

General description

Chlorobenzene is used as a solvent and may be present in drinking water through contamination of water sources by spills or discharges. It has occasionally been detected in drinking water supplies in Canada and the United States at concentrations up to 0.005 mg/L. Inhalation from the atmosphere is believed to be the major route of environmental exposure.

Chlorobenzene has a low taste and odour threshold in water of about 0.01 mg/L.

It is used primarily as a solvent for pesticide formulations, in di-isocyanate manufacture, as a degreasing agent for mechanical parts, and in the production of nitrochlorobenzene. It is also used in the production of other halogenated organic compounds.

Typical values in Australian drinking water

Chlorobenzene has not been found in Australian drinking waters. It is included here to provide guidance in the unlikely event of contamination, and because it has been detected occasionally in drinking water supplies overseas.

Treatment of drinking water

Aeration or adsorption onto granular activated carbon will remove chlorobenzene from water.

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 chlorobenzene trapped on an adsorbent. The adsorbent is then heated and chlorobenzene analysed using gas chromatography with electron capture detection. The limit of determination is 0.0002 mg/L.

Health considerations

In humans, chlorobenzene is absorbed after ingestion or inhalation, and distributed primarily to adipose tissue and to the liver and kidney. It is metabolised into 4-chlorocatechol, which is excreted in urine.

An extensive review and summary of the human and animal toxicity data for chlorobenzenes is available (IPCS 1991).

There are few data on the effects of chlorobenzene on humans, and those that are available are of poor quality. They consist mainly of cases of poisoning and occupational exposure, with the principal effect being disturbances to the central nervous system.

Studies over 2 years using rats and mice reported adverse effects to the liver, kidneys, and blood-cell formation at high doses (250 mg/kg body weight per day). There is evidence of an increase of liver tumours in male rats fed doses of 120 mg/kg body weight per day of monchlorobenzene for 2 years. No increases were observed in female rats, or in male and female mice. Chlorobenzene was not mutagenic in tests with bacteria, but may bind to RNA and DNA.

Derivation of guideline

The health-based guideline value for chlorobenzene in drinking water was determined as follows:

$$\text{ 0.3 mg/L } = \dfrac{\text{ 60 mg/kg body weight per day x 70 kg x 0.1 }}{\text{ 2 L/day x 500 }} \times \dfrac{\text{ 5 }}{\text{ 7 }}$$

where:

• 60 mg/kg body weight per day is the no-effect level from a 2-year gavage study using rats (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.

• 500 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 and 5 for limited evidence of carcinogenicity).

• 5/7 is used to convert data based on a 5 day per week feeding study to a 7-day week equivalent.

This health-based guideline value is greater than the taste and odour threshold of 0.01 mg/L.

References

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 chlorobenzene in F344/N rats and B6C3F1 mice (gavage studies). NTP Report No. 261, Publication No. 86-2517. United States Department of Health and Human Services, National Institutes of Health.

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.