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Hidden Gems - Mercury in Fish Tissue Across the Western United States and Implications of Selenium Interactions with Mercury

S.A. Peterson 1 & N.V.C. Ralston 2

1 United States Environmental Protection Agency, National Health and Environmental Effects Research Laboratory, Western Ecology Division, Corvallis, OR 97333.
2 University of North Dakota, Energy and Environmental Research Center, 15 North 23 rd Street, Stop 9018 Grand Forks, ND 58202-9018.

We collected 2,707 fish from 626 stream/river sites in 12 western USA states using a probability design to assess the spatial extent of whole fish mercury (Hg) concentrations. In all large (> 120 mm) fish, total Hg concentrations (mean µg·g -1; SD; n) in both piscivores (0.260; 0.241; 332)and non-piscivores (0.090; 0.101; 1,895) exceeded the wet weight detection limit of 0.0024 µg·g -1 (Peterson, et al., 2007). Hg concentrations were most strongly related to fish length and trophic guild rather than environmental factors tested. Salmonidae, the most commonly occurring family, exceeded 0.1 µg Hg·g -1 (deemed protective for fish-eating mammals) in 11.1% of assessed stream length and exceeded the filet equivalent of 0.3 µg Hg·g -1 (USEPA water quality based Hg criterion) in 2.3% of assessed stream length. Piscivores were found at fewer sites, but their Hg concentrations exceeded 0.1 µg·g -1 in 93% of assessed stream length, and the 0.3 µg Hg·g -1 filet equivalent concentration in 56.8% of assessed stream length. Recent publications (Raymond and Ralston, 2004) suggest that a molar ratio of selenium (Se) in excess of Hg in fish tissue nullifies the potential Hg toxicity. Hg is found in fish everywhere across the western United States. Se concentrations across the same area vary from very high to low. We are developing the Se : Hg molar ratios for all fish collected in the above survey, thereby assessing areas at greatest risk for fish tissue Hg toxicity across the western United States relative to Se/Hg interactions.


Peterson, S.A., J. Van Sickle, A.T.Herlihy, and R. M. Hughes. 2007. Mercury concentration in Fish from Streams and Rivers Throughout the Western United States. Environ. Sci. Tech. 41(1):58-65.

Raymond, L.J. and N.V.C. Ralston. 2004. Mercury:selenium interactions and health implications. Seychelles Medical and Dental Journal, Special Edition 7(1):72-77.

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