The Occurrence of Disinfection By-Products (DBPs) of Health Concern in Drinking Water

Results of a Nationwide DBP Occurrence Study

EPA/600/R-02/068 September 2002
Source:
http://www.epa.gov/athens/publications/EPA_600_R02_068.pdf

INTRODUCTION

More than 500 disinfection by-products (DBPs) have been reported in the literature for the major disinfectants currently used (chlorine, ozone, chlorine dioxide, chloramines), as well as their combinations (Richardson, 1998). Of these reported DBPs, only a small percentage have been quantified in drinking waters. Thus, there is significant uncertainty over the identity and levels of DBPs that people are actually exposed to in their drinking water. Moreover, only a limited number of DBPs have been studied for adverse health effects. To determine whether the other DBPs pose an adverse health risk, more comprehensive quantitative occurrence and toxicity data are needed. To address this issue, scientists at the U.S. Environmental Protection Agency’s (USEPA’s) National Exposure Research Laboratory (NERL) initiated a proposal for a Nationwide DBP Occurrence Study.

Due to the large number of DBPs identified in drinking waters in the United States and other countries, it is not feasible to quantify all of them, so a way of prioritizing them was needed. Prior to this occurrence study, a multidisciplinary group of experts from the USEPA Office of Water and the USEPA Office of Prevention, Pesticides, and Toxic Substances had initiated a prioritization effort for the >500 DBPs reported in the literature according to their predicted adverse health effects (Woo et al., 2002). An in-depth, mechanism-based, structural activity relationship (SAR) analysis, supplemented by an extensive literature search for genotoxicity and other data, was used to rank the carcinogenic potential of these DBPs. Approximately 50 DBPs that received the highest ranking for potential toxicity, and that were not already included in the USEPA’s Information Collection Rule (ICR), were selected for this occurrence study. Those ~50 DBPs are denoted ‘high priority’ DBPs in this report.

The ‘high priority’ DBPs include brominated, chlorinated, and iodinated species of halomethanes, brominated and chlorinated forms of haloacetonitriles, haloketones, haloacids, and halonitromethanes, as well as analogues of MX [3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone] (Table 1). Chemical Abstract Services (CAS) numbers are provided in Table 1 when they were available. Previously, MX had been determined to be the most mutagenic (to Salmonella bacteria) DBP ever identified in drinking water, accounting for as much as 20-50% of the total mutagenic activity measured in chlorinated drinking water samples (Kronberg and Vartiainen, 1988; Backlund et al., 1988; Meier et al., 1987). MX has also been shown to be carcinogenic in laboratory animals (Komulainen et al., 1997). Yet, very little drinking water occurrence data has been obtained for MX, so its potential hazard to humans has not been determined. There have also been recent reports of brominated DBP forms of MX (BMXs) (Suzuki and Nakanishi, 1995). These brominated DBP species are of concern because brominated species of DBPs have been shown to be significantly more carcinogenic than their chlorinated analogues. Brominated nitromethanes have also been recently shown to be extremely cytotoxic and genotoxic in mammalian cells (Plewa et al., 2002; Kargalioglu et al., in press). Specifically, they have been shown to be at least an order of magnitude more genotoxic to mammalian cells than MX and have genotoxicities greater than all of the regulated DBPs, except for monobromoacetic acid. It is interesting that dibromonitromethane and 11 bromonitromethane received the highest priority ranking of all DBPs in the SAR toxicity analysis effort.


It should be noted that Table 1 lists the identity of more than 50 high priority target species. During method development, additional species in the same analyte group were included for some of the drinking water plant surveys.

Because most of the high priority DBPs were from chlorine or chloramine disinfection, a few additional ozone and chlorine dioxide DBPs that were not ranked as a high priority were also included for completeness (i.e., to provide more information on those alternative disinfectants). In addition, methyl tert-butyl ether (MtBE) and methyl bromide, which are volatile organic compounds (VOCs) but not DBPs, were included in the list of target analytes because they are important source water pollutants, and their measurement would provide valuable occurrence information. Regulated and some ICR DBPs were also included in this study for comparison purposes (Table 2). In addition, routine water quality measurements, such as total organic carbon (TOC), total organic halide (TOX), assimilable organic carbon (AOC), and bromide were determined.