Water Quality Criterion for the Protection of Human Health: Methylmercury

This document is the basis for a human health Ambient Water Quality Criterion (AWQC) for methylmercury. This AWQC replaces the AWQC for total mercury in published in 1980 and partially updated in 1997. Under Section 304(a) of the Clean Water Act, EPA must periodically revise criteria for water quality to accurately reflect the latest scientific knowledge on the kind and extent of all identifiable effects of pollutants on human health. This document uses new methods and information described in the Methodology for Deriving Ambient Water Quality Criteria for the Protection of Human Health (2000) (2000 Human Health Methodology) (US.E PA,2 000a,b). These new methods include updated approaches to determine toxicity dose-response relationships for both carcinogenic and noncarcinogenic effects, updated information for determining exposure factors, and new procedures to determine bioaccumulation factors.