Changes in concentrations of selenium and mercury in largemouth bass following elimination of fly ash discharge to a quarry.

Elimination of slurried fly ash discharges to a water-filled quarry was followed by a steady increase in concentrations of mercury in the axial muscle of resident largemouth bass (Micropterus salmoides). Average mercury concentrations in bass (adjusted for covariance with fish weight) increased from 0.02 micrograms/g to 0.17 micrograms/g in three years. Aqueous selenium concentrations in the quarry decreased from 25 micrograms/L to < 2 micrograms/L after elimination of fly ash discharges, but selenium concentrations in bass remained about three times background levels. Previous studies have shown selenium addition to be a viable means of ameliorating mercury contamination in fish in low alkalinity, low pH waters of northern Europe and Canada. These results suggest that selenium may also be effective at blocking the accumulation of methylmercury in harder, more alkaline waters.