Prioritizing pathogens for potential future regulation in drinking water.

A method alternative to the EPA’s determination of microorganisms of regulatory concern for drinking water quality is proposed. Drinking water in the U.S. is among the safest in the world but outbreaks of disease linked to drinking water still occur. For example, from 1991 to 2002 there were 183 reported waterborne disease outbreaks caused by chemical contaminants (16%), viruses (8%), bacteria (17%), protozoa (21%), and unidentified agents of acute gastrointestinal illness (38%) (1). The majority of these outbreaks were linked to groundwater (76%) with surface water accounting for 18%. Water in these outbreaks was provided by community systems (36%), noncommunity systems (39%), and individual wells (25%), and outbreaks were associated with untreated groundwater (32%), treatment failures or deficiencies (32%), and problems in the distribution system (23%). It has been estimated that annually in the U.S., up to 19.5 million cases of all types of illnesses may be associated with contaminated drinking water (1), 4.3-11 million cases of which are acute gastrointestinal illness (2). Consequently, water suppliers and regulators expend considerable effort and resources to ensure the safety of and improve the quality of drinking water through enhanced treatment strategies and technologies, and stricter regulations. The Contaminant Candidate List. Under the Safe Drinking Water Act Amendments of 1996 the U.S. Environmental Protection Agency (EPA) must develop and publish a contaminant candidate list (CCL) identifying contaminants (and groups of related contaminants) that are currently unregulated in drinking water and that may pose risks to public health. The amendments specifically require EPA to consider the following criteria to determine whether a contaminant may require listing on the CCL: (1) the contaminant may have an adverse effect on the health of persons; (2) the contaminant is known to occur or there is a substantial likelihood that the contaminant will occur in public water systems with a frequency and at levels of public health concern; and (3) in the sole judgment of the EPA Administrator, regulation of such a contaminant presents a meaningful opportunity for health risk reduction for persons served by public water systems. The CCL is not a regulation itself. Rather, it is a determinative process; EPA must decide whether or not to regulate at least five CCL contaminants with a National Primary Drinking Water Regulation. The 1996 Safe Drinking Water Act amendments require that the CCL is reviewed and revised every 5 years. The first CCL (CCL1) was published in March 1998 (3), CCL2 was published in February 2005 (4), and the draft CCL3 was published for public comment in the Federal Register on February 21, 2008 (5). Table 1 lists all microbial contaminants included on the previous two CCLs, the current draft CCL3, and those selected by an alternative approach, which is described in this paper. It is noteworthy that all of the required regulatory determinations to date have been decisions to not regulate CCL contaminants, including the microbe Acanthamoeba from CCL1 (6) and 11 contaminants from CCL2 (7). The recurring determination that none of the CCL pathogens listed during the last 11 years should be regulated, or lack sufficient information to make a regulatory determination, raises questions regarding the effectiveness of the CCL process SH UT TE RS TO CK Environ. Sci. Technol. 2009, 43, 5165–5170