A REVIEW OF THE DICHLOROBENZENES IN DRINKING WATER
Report No FR0075
A P WHITEHEAD
To review the information on the toxicity of DCB's with reference to drinking water and to discuss the setting of a drinking water guide level for these compounds.
DCB's are ubiquitous in the aquatic environment and are frequently detected in surface and drinking water. 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 a sound scientific assessment of the latest available data.
The DCB's have very low taste and odour thresholds in water. 1,2- and 1,4-DCB have been well studied but there is only very limited data available on the toxicity of 1,3-DCB.
The DCB's are of relatively low acute and chronic toxicity. There is evidence that 1,4-DCB increases the incidence of some tumours, when given orally to rats or mice but little indication that the DCB's are mutagenic in any of the test assays used, either in vivo or in vitro. Neither 1,2- or 1,4-DCB were found to be embryo-toxic or teratogenic.
The guideline values, based on toxicity data, are greatly in excess of the reported taste and odour thresholds for the DCB's in drinking water. No guideline value based on health considerations could be recommended for 1,3-DCB. The maximum permissible concentrations for DCB's in water should be set on the basis of odour, which is detectable at the lowest concentration.
V RESUME OF CONTENTS
The DCB's are widely used industrial chemicals and are common environmental contaminants. The toxicology of the three isomers of DCB is reviewed and consideration is given as to how this relates to the safety of drinking water. The DCB's have been shown to be of low acute and chronic toxicity but there is only very limited data on 1,3-DCB, 1,2-DCB did not induce tumours in laboratory animals but 1,4-DCB given to rats and mice at high doses over their lifetime induced renal tumours in male rats, and liver tumours in mice. The DCB's do not appear to be mutagenic and the mechanism of action is probably non-genotoxic. The DCB's do not appear to be teratogenic. Guidelines for drinking water can be calculated for 1,2- and 1,4-DCB using an uncertainty factor applied to a no observed adverse effect level from animal studies but the guideline values would be greatly in excess of the taste and odour thresholds.
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