Risk assessment case study - Chloroform and related substances

Chlorine, used as an important disinfectant for drinking water, can react w ith naturally occurring organic matter to form chloroform, bromodichloromet hane, chlorodibromomethane and bromofonn. Chloroform and other trihalometha nes have been shown to increase tumours of the liver. kidney or large intes tine in rats or mice. The risk to man from these contaminants must be asses sed carefully since there is considerable benefit associated with the use o f chlorine. The weight of evidence suggests that chloroform is non-genotoxi c and there are data, for each site, to indicate that rumours only occur at high doses where there is also tissue damage. Bromodichloromethane has als o been shown to increase liver and kidney tumours but this and bromoform ha ve been shown to increase large intestinal rumours in rats. The weight of e vidence is that they are only weak genotoxins and they do not appear to be active in vivo. It is probable that the mechanism for the liver and kidney rumours is the same as for chloroform but the mechanism for the large intes tinal tumours is uncertain. However, the toxicity and carcinogenicity of th ese substances is profoundly affected by dosing in corn oil. New studies su ggest that dosing in drinking water would not result in increases in rumour s. The evidence suggests that the use of a threshold approach, based on a t olerable daily intake, would be the most appropriate way of determining saf e levels in drinking water. (C) 2000 Elsevier Science Ltd. All rights reser ved.