Chemical Measures of Similarity Among Disinfection By-Product Mixtures

Abstract

There are few measures that can be used to distinguish among mixtures of disinfection by-products (DBPs) produced in the chlorination or chloramination of drinking water. Objective measures of similarities among DBP mixtures would greatly simplify judgments about the risk that may be associated with exposure to DBPs in a given water supply. Major by-products of chlorination/chloramination include the trihalomethanes (THMs) and haloacetic acids (HAAs), which are routinely measured for compliance to regulations. A key question is whether measurement of similar amounts of these DBPs is indicative of the myriad other DBPs that are known to be produced. This article utilized data from a survey of 35 utilities in the United States that included several additional parameters, including members of the haloacetonitrile, trihaloacetaldehyde, and halopropanone classes. Based upon the distribution of bromine in the THM class, the concentrations of unmeasured brominated and bromochlorinated compounds could be determined. This allowed determination of whether measures of the THM and/or HAA classes reflected the amounts of these less abundant classes. Variations in relative yields among DBP classes were observed with water source type and with whether chlorine or chloramine was used as the disinfectant. However, most of the variability was attributable to geographic location. The relative abundance of brominated by-products also varied among water sources. Recent documentation that potent by-products, such as nitrosamines, are selectively produced in particular water systems and preferentially with chloramination indicates that more measures of individual DBP are needed to evaluate similarity among DBPs mixtures.

The views expressed in this article are those of the individual authors and do not necessarily reflect the views and policies of the U.S. EPA. Those sections prepared by U.S. EPA scientists have been reviewed in accordance with the U.S. EPA peer and administrative review policies and approved for presentation and publication. Mention of trade names or commercial products does not constitute endorsement or recommendations for use.

The authors acknowledge the support that Richard Bull received during this project through a contract with the U.S. Environmental Protection Agency (U.S. EPA). The authors appreciate the many helpful comments and suggestions of Richard C. Hertzberg, PhD (Emory University), Susan D. Richardson, PhD (U.S. EPA/ORD/NERL-Athens), and Belinda Hawkins, PhD (U.S. EPA/ORD/NCEA). These comments greatly improved this article.