Drinking Water Disinfection Byproducts: Review and Approach to Toxicity Evaluation

Abstract

There is widespread potential for human exposure to disinfection byproducts (DBPs) in drinking water because everyone drinks, bathes, cooks, and cleans with water. The need for clean and safe water led the U.S. Congress to pass the Safe Drinking Water Act more than 20 years ago in 1974. In 1976, chloroform, a trihalomethane (THM) and a principal DBP, was shown to be carcinogenic in rodents. This prompted the U.S. Environmental Protection Agency (U.S. EPA) in 1979 to develop a drinking water rule that would provide guidance on the levels of THMs allowed in drinking water. Further concern was raised by epidemiology studies suggesting a weak association between the consumption of chlorinated drinking water and the occurrence of bladder, colon, and rectal cancer. In 1992 the U.S. EPA initiated a negotiated rulemaking to evaluate the need for additional controls for microbial pathogens and DBPs. The goal was to develop an approach that would reduce the level of exposure from disinfectants and DBPs without undermining the control of microbial pathogens. The product of these deliberations was a proposed stage 1 DBP rule. It was agreed that additional information was necessary on how to optimize the use of disinfectants while maintaining control of pathogens before further controls to reduce exposure beyond stage 1 were warranted. In response to this need, the U.S. EPA developed a 5-year research plan to support the development of the longer term rules to control microbial pathogens and DBPs. A considerable body of toxicologic data has been developed on DBPs that occur in the drinking water, but the main emphasis has been on THMs. Given the complexity of the problem and the need for additional data to support the drinking water DBP rules, the U.S. EPA, the National Institute of Environmental Health Sciences, and the U.S. Army are working together to develop a comprehensive biologic and mechanistic DBP database. Selected DBPs will be tested using 2-year toxicity and carcinogenicity studies in standard rodent models; transgenic mouse models and small fish models; in vitro mechanistic and toxicokinetic studies; and reproductive, immunotoxicity, and developmental studies. The goal is to create a toxicity database that reflects a wide range of DBPs resulting from different disinfection practices. This paper describes the approach developed by these agencies to provide the information needed to make scientifically based regulatory decisions.

Risk assessment of trihalomethanes from tap water in Fortaleza, Brazil

“…Chlorination, the most commonly used method to disinfect tap water, has led to a sharp decrease in both mortality and morbidity from many diseases known to be waterborne (Boorman et al 1999). However, the presence of chlorinated disinfection by-products (DBP) in tap water is of concern from a public health aspect because they are suspected to be carcinogenic (Attias et al 1995;Moudgal et al 2000;Tokmak et al 2004;Komulainen 2004).…”

Trihalomethane formation in ozonated and chlorinated surface water

“…It also ensures the microbiological stability within the distribution systems. However, nowadays it is well known that chlorine reacts with natural organic matter to form several organic halides termed as disinfection by-products (Boorman et al 1999;Richardson et al 2000). Examples include trihalomethanes (THMs), haloacetic acids (HAAs), haloacetonitriles (HCNs), haloketones (HKNs), and chloropicrin.…”

Chloroform in runoff water—a two-year study in a small catchment in Southeast Sweden

“…There is strong evidence that chloroform is naturally formed in soil and subsequently transported to air and groundwater (Hoekstra et al 1998;Khalil and Rasmussen 2000;Haselmann et al 2000a, b;Dimmer et al 2001). The finding that chloroform is produced naturally has raised concern, since it is toxic and natural sources seem to be as significant as anthropogenic sources (Boorman et al 1999;Bove et al 2002;Laturnus et al 2002).…”