WATER CHLORINATION - ESSENTIAL PROCESS OR CANCER HAZARD

Chlorine has been successfully used for the control of waterborne infe ctious disease for nearly a century. In the 1970s it was found that ch lorine reacted with natural organic matter present in surface waters t o produce disinfection by-products (DBP). Concern focused initially on the trihalomethanes (THM), but a wide variety of DBPs are now known t o result from chlorination. Chlorination of drinking water has been on e of the most effective public health measures ever undertaken. There are a number of alternatives to chlorination that are in active use in many parts of the world, but the risks associated with their by-produ cts are even less well established than for chlorination. Moreover, th e use of these alternatives vary in their effectiveness and some requi re greater sophistication in their application. This can mean less pro tection to public health as a result of inappropriate application and control. Therefore, hazards associated with the use of such a clearly beneficial process as chlorination must be carefully considered not on ly in an absolute sense, but also in the context of alternative approa ches for producing a safe drinking water. The key question is whether the hazards associated with by-products have been sufficiently well es tablished to warrant regulations that will undoubtedly have both posit ive and negative impacts on the public health. This symposium examined the toxicological and epidemiological data on chemical hazards associ ated with chlorination and attempted to measure this hazard against co mpeting microbial risks, The first presentation discussed the availabl e analytical epidemiological studies, A second presentation dealt with the importance of chlorination to the prevention of waterborne infect ious disease, Pharmacokinetic, mechanistic, and modeling information o n the prototypical DBP, chloroform, were discussed and contrasted with data on brominated THMs to determine if it was scientifically appropr iate to regulate THMs as a single toxicological class. The fifth prese ntation dealt with the carcinogenic properties of a potent mutagen tha t is produced by chlorination. The final presentation discussed the ha loacetates, carcinogenic DBPs whose concentrations approach and occasi onally exceed those of the THMs. Clearly, there is a need to carefully weigh these different types and sometimes competing risks when consid ering the delivery of drinking water to ever-increasing populations fo r which there are finite sources of fresh water. (C) 1995 Society of T oxicology