A national statistical survey assessment of mercury concentrations in fillets of fish collected in the U.S. EPA national rivers and streams assessment of the continental USA

• Hg fish tissue results from 541 U.S. sites on =>5th order streams in 2008–2009.
• Site selection was probabilistic and nationally-representative.
• 25.4% (137 sites, 13 071 river miles, (21 036 km)) > 300 ug kg−1 HH and WV thresholds.
• No difference observed between results from urban vs. non-urban sites or among three eco-regions.
• Most exceedances in top predator species.

The U.S. EPA conducted a national statistical survey of fish fillet tissue with a sample size of 541 sites on boatable rivers =>5th order in 2008–2009. This is the first such study of mercury (Hg) in fish tissue from river sites focused on potential impacts to human health from fish consumption to also address wildlife impacts. Sample sites were identified as being urban or non-urban. All sample mercury concentrations were above the 3.33 ug kg−1 (ppb) quantitation limit, and an estimated 25.4% (±4.4%) of the 51 663 river miles assessed exceeded the U.S. EPA 300 ug kg−1 fish-tissue based water quality criterion for mercury, representing 13 144 ± 181.8 river miles. Estimates of river miles exceeding comparable aquatic life thresholds (translated from fillet concentrations to whole fish equivalents) in avian species were similar to the number of river miles exceeding the human health threshold, whereas some mammalian species were more at risk than human from lower mercury concentrations. A comparison of means from the non-urban and urban data and among three ecoregions did not indicate a statistically significant difference in fish tissue Hg concentrations at p < 0.05.