AWWA JAW28436

A maximum contaminant level goal (MCLG) is established for a contaminant based on toxicology data on the contaminant's potential health effects associated with drinking water. This article explains toxicology reviews and discusses related issues. A contaminant's carcinogenicity determines how the US Environmental Protection Agency (USEPA) establishes an MCLG for that contaminant. Weight-of-evidence criteria for classifying carcinogens are given in a table, and the three classifications of contaminants (class 1--based on strong evidence, class 2--limited or equivocal evidence, or class 3--inadequate or no evidence) are described. Each of the three classifications is discussed in some detail, involving how risks are determined and what MCLG is set for each class of contaminant. The difference between MCLG and maximum contaminant level (MCL) is explained, as is the role of the best available technology (BAT) in setting an MCL. Some arguments against using animal-exposure studies for assessing human health effects are given. Includes tables.