Research in Action
Disinfection Byproducts: What’s In Our Drinking Water?
Chemical disinfection by-products (DBPs) are compounds that can be found in drinking water when the chemicals used to disinfect source water, before it is distributed into public drinking water supplies, reacts with organic matter and/or bromide/iodide that naturally occurs in the source water. Source water used to provide drinking water can be rivers, lakes, streams, groundwater, even seawater. Disinfectants used to treat source water include chlorine, ozone, chlorine dioxide, and chloramine.
We have only known about DBPs since 1974, when chloroform was identified in tap water as a DBP that was formed during chlorination of source water. Since then, hundreds of DBPs have been identified in drinking water and millions of people in the U.S. are potentially exposed to them every day.
Knowing that thousands of people died from waterborne illnesses before disinfection of drinking water started in the early 1900s, it is vitally important to disinfect drinking water, however it is also important to minimize the chemical DBPs formed during drinking water treatment because several DBPs have been linked to cancer in laboratory animals. EPA regulates some DBPs, but many more have still not been identified and tested for toxicity or cancer effects — only about 50 percent of the total organic halide (chlorine, iodine, bromide) measured in chlorinated drinking water has been accounted for.
Additionally, much less is known about DBPs formed during newer disinfection treatment using chemicals such as ozone, chlorine dioxide, and chloramine, which are gaining popularity in the U.S. Are these alternatives safer than chlorine? What kinds of by-products form? What about unidentified chlorine DBPs that people are exposed to both from drinking and from showering or bathing?
EPA research is aimed at finding out what these disinfection by-products are and thoroughly characterizing the chemicals formed in drinking water treatment, with the goal of minimizing any harmful DBPs that are formed.
An iodine occurrence study that measured iodo-acid DBPs and iodo-THMs in drinking waters from 23 cities in the U.S. and Canada studied their genotoxicity and cytotoxicity. The iodo-acids are important because iodoacetic acid has been found to be more genotoxic to mammalian cells than the currently regulated DBPs. This study underscored the increased formation of iodo-DBPs with chloramination, an increasingly popular disinfectant in the U.S.
In another study, EPA scientists combined chemical and toxicological characterization (emphasizing newer reproductive and developmental effects) of complex DBP mixtures. This research is known as the Four Lab Study because it involved collaboration of scientists from four EPA Laboratories (Health and Environmental Effects, Exposure, Risk Management, and Environmental Assessment). The research covered potential health concerns that cannot be addressed directly by toxicological study of individual DBPs or defined DBP mixtures. In essence, it provided toxicological information for the complete drinking water mixture — both known DBPs and the unidentified fraction of DBPs. The next phase of this work includes a larger battery of toxicological endpoints and focuses on chlorinated drinking water.
- A recent iodo-DBP occurrence study provided the first quantitative occurrence data for genotoxic iodo-acid DBPs and information on their formation in chloraminated drinking water.
- The first phase of the Four Lab Study reports results from an integrated chemical/toxicological research study to investigate the toxicological effects of complex DBP mixtures.
- A Nationwide DBP Occurrence Study provided important quantitative information on unregulated DBPs that have the potential to cause adverse health effects. Several of these DBPs have concentrations similar to some that are already regulated.
- The use of alternative disinfectants can produce higher levels of these DBPs, compared to chlorine.
Technical Contact: Susan Richardson