Rivers downstream of mining activities contain high levels of metals

River sediments and fish tissue downstream of hard-rock mining activities in the northern Rockies contain elevated levels of metals, according to a new report by the US Geological Survey.

The report, Concentrations of Selected Trace Elements in Fish Tissue and Streambed Sediment in the Clark Fork-Pend Oreille and Spokane River Basins, Washington, Idaho, and Montana, 1998, states that arsenic, cadmium, copper, lead, mercury, and zinc levels were higher than national median levels, with some concentrations at levels that can adversely affect aquatic life.

Although the metal concentrations in bed sediments did not appear to be a good predictor of concentrations in fish tissue, production mine densities upstream from sampling sites were found to be strongly related to the bed sediment concentrations. According to the authors of the report, the new data can be used by government agencies and organisations to identify areas where environmental contamination may pose health concerns for humans and wildlife.

“Although trace-element concentrations in bed sediment exceeded various guidelines, no concentrations in sport fish fillets exceeded US Environmental Protection Agency screening values for the protection of human health,” said Terry Maret, a US Geological Survey scientist, and co-author to the report. “This is noteworthy because lead and mercury can bioaccumulate in aquatic biota and are pollutants of concern around mining sites in the study area.”

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