Emerging Contaminants and the MCL Development Process

Under the Safe Drinking Water Act, US EPA evaluates chemical contaminants in drinking water for regulation. Based on the chemical’s hazard and potential for exposure, EPA may enact a non-enforceable Maximum Contaminant Level Goal (MCLG) followed by a Maximum Contaminant Level (MCL). Regulation of contaminants in drinking water often lags behind occurrence and detection in ground and surface waters. With an increased emphasis on using the best available scientific methods, the process of MCL development requires more time and specific expertise. This presentation will briefly review past methods of MCL development and compare these with current methods using two chemicals recently evaluated by US EPA in the MCLG process. The current methods of chemical evaluation will also frame the discussion on the emerging issue of perfluorinated compounds (PFAS). PFAS present a difficulty in that they are a large class of chemicals in which most of the chemicals have very little toxicological information available to form the basis of an MCLG; however, the information on several members of the class have spurred concern among communities, regulatory agencies, and other stakeholders.