Health Effects of Commonly Occurring Disinfection Byproducts in Municipal Water Supplies

Abstract

Disinfectants such as chlorine, chloramine, chlorine dioxide, ozone, and ultraviolet radiation have been used to disinfect water containing disease‐causing waterborne pathogens at water treatment plants throughout the world. However, the chemical disinfectants can react with dissolved organic and inorganic constituents in treated water to form disinfection byproducts (DBPs). Although over 600 DBPs have been identified, despite recent improvements in analytical instrumentation, less than 50% of the total organic halides have been accounted for in drinking water. From the present knowledge of occurrence and health effects, the DBPs of concern are trihalomethanes, haloacetic acids, bromate, chlorate, and chlorite, although other DBPs, such as acetonitriles, acetaldehydes, ketones, nitromethanes, and other alkanes, have also been identified in drinking water. Epidemiological studies indicate an association between chronic ingestion of drinking water and increased risk of rectal, bladder, and colon cancer in humans, but these studies do not indicate whether the observed health effects are because of one or more of the hundreds of DBPs that are also present in drinking water. The disinfectants can also be hazardous at high concentrations, but toxicological studies show that their toxicity is likely not relevant at the low concentrations encountered in drinking water.