Fish Remain High in Selenium Long after Mountaintop Coal Mines Close.

Mountaintop removal coal mining generates large volumes of waste rock. Weathering of this waste rock releases selenium, which can bioaccumulate to levels that can harm, and even extirpate, downstream fish communities. This is well demonstrated in ecosystems impacted by active mountaintop removal operations; however, less is known about the long-term impacts after coal mines close. Here, we show that mountaintop removal coal mines still present an acute threat to downstream fish populations, decades after mining ends. Crowsnest Lake (Alberta, Canada) receives runoff from the Tent Mountain Coal Mine, which closed in the 1980s and part of which was certified reclaimed. Fish in Crowsnest Lake contain tissue selenium concentrations (5-26 μg/g dry weight) that exceed guidelines and are among the highest documented in the literature. In contrast, tissue selenium concentrations in 840 fish from 29 reference lakes (without watershed coal mining) ranged from 0.2 to 2.5 μg/g. This study demonstrates that fish can remain high in selenium long after mountaintop removal coal mining ends, and it suggests that any further coal mine development may push the Crowsnest fishery beyond sustainability.