Epa's Assessment of Mercury in Fish From U.S. Rivers

Elevated mercury concentrations in fish are the leading cause of fish consumption advisories. In a continuing effort to characterize the extent of mercury contamination in U.S. waters, EPA’s Office of Water and Office of Research and Development collaborated to conduct the first statistically-based survey of mercury in fish from U.S. rivers (under the framework of the National Rivers and Streams Assessment). Fish were collected at 542 randomly selected river sites (≥ 5th order) in the lower 48 states during 2008 and 2009. One composite sample of five similarly sized adult fish of the same species was collected at each site, focusing on fishes commonly consumed by humans. Largemouth bass Micropterus salmoides and smallmouth bass M. dolomieu accounted for 34% and 24% of all composites, respectively. Fillets were analyzed for total mercury using a Direct Mercury Analyzer. Mercury was detected at quantifiable levels in all samples. Based on this probabilistic study, the mean and maximum concentrations of mercury in fish fillets from U.S. rivers were 229 ppb and 1,419 ppb, respectively. Probability-based results showed that 25.3% (or 13,071 river miles) of the total 51,663 river miles included in this survey had mercury fish tissue concentrations that exceeded EPA’s 300 ppb human health screening value.