A REVIEW OF MONOCHLOROBENZENE IN DRINKING WATER
Report No FR0120

J CRIDDLE

Jun 1990

SUMMARY

I OBJECTIVES

To review the information on the toxicity of monochlorobenzene (MCB) with reference to drinking water and to discuss the setting of a drinking water guide level for this compound.

II REASONS

MCB is commonly found in the environment, including drinking water supplies. There is a need to provide water suppliers with sound guidance on the maximum levels of toxic substances that should be permitted in drinking water. The WHO is undertaking a review of drinking water guidelines for a number of substances. This review is part of the UK water industry's contribution to that process of establishing new guidelines based on sound scientific assessment of the latest available data.

III CONCLUSIONS

MCB has a low odour threshold in water.

It is of relatively low acute and chronic toxicity. There is evidence that MCB increases the incidence of liver nodules in male rats when given orally but little indication that MCB is mutagenic although it may bind to DNA. It does not appear to be embryotoxic or teratogenic.

IV RECOMMENDATIONS

The proposed guideline values based on toxicity data are greatly in excess of the reported odour thresholds for MCB in drinking water. The guideline value for MCB should be set on the basis of odour.

V RESUME OF CONTENTS

MCB is a widely used industrial chemical and is a common environmental contaminant. The toxicology of MCB is reviewed and consideration is given as to how this relates to the safety of drinking water. MCB has been shown to be of low acute and chronic toxicity. MCB given to laboratory rodents in high doses induced an increase in liver neoplasms in male rats but not in female rats or male and female mice. MCB does not appear to be mutagenic although it does bind to DNA. The mechanism of action is probably non-genotoxic.

MCB does not appear to be teratogenic. A guideline for MCB in drinking water can be calculated using an uncertainty factor applied to a No Observed Adverse Effect Level (NOAEL) from animal studies but the guideline value would be greatly in excess of the odour threshold.

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