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Despite the prevalence of mercury contamination in the Chesapeake Bay, large-scale patterns of mercury concentrations, and potential risks to fish, wildlife, and humans across the watershed, are poorly understood.

USGS researchers compiled data from state monitoring programs and recent research efforts to address this knowledge gap and assess fish mercury concentrations in the watershed’s freshwater habitats. Examining nearly 8,000 total mercury concentrations from 600 locations, researchers found that fish mercury concentrations spanned a 44-fold range. Although mean mercury concentrations tended to be moderate, 45%, 48%, and 36% of all samples exceeded benchmarks for human, avian piscivores, and fish risk, respectively. The percentage of fish exceeding these benchmarks was not uniform among species or locations. Variation in fish mercury concentrations highlights the roles of waterbody, landscape, and ecological processes in shaping mercury risk. Authors outline an integrated monitoring program that could identify key factors influencing mercury concentrations and strategies to mitigate risks across the watershed.

Willacker Jr., J.J., Eagles-Smith, C.A., Blazer, V.S., 2020, Mercury bioaccumulation in freshwater fishes of the Chesapeake Bay watershed: Ecotoxicology, p. online,

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