Fly Ash and Mercury: Does Selenium in Ash Inhibit Methylmercury Bioaccumulation?

(Oak Ridge National Laboratory 2010) Selenium is known to have an antagonistic effect on the mammalian toxicity of inorganic mercury, and appears to play a role in reducing the accumulation of methylmercury in fish in some aquatic ecosystems. The Biological Monitoring and Abatement Program (BMAP) at Oak Ridge National Laboratory (ORNL) has measured mercury and selenium concentrations in largemouth bass over a 20 year span in a quarry that once received direct discharges of slurried fly ash.
When monitoring started in 1990, a year after ash disposal in the quarry was discontinued, mercury concentrations in fish averaged less than 0.02 ppm, and selenium exceeded concentrations in fish from regional reference sites by five-fold. Over the next 10 years, mercury concentrations in bass steadily increased to over 1 ppm before reaching an apparent steady-state, and selenium concentrations decreased but never returned to background levels. During this time, streamflow into the quarry drained a large basin that had been filled with fly ash prior to its direct discharge to the quarry.
In the mid 2000’s, the trends reversed relative to historical patterns: selenium concentrations in bass increased while mean mercury concentrations in fish decreased over the same period. ORNL and TVA staff sampled fish from the ash stilling pond at the Kingston steam plant in 2009, with results similar to those observed in Rogers Quarry in the mid 1990’s. Average mercury concentration in bluegill from the stilling pond was 0.01 ppm and selenium was 2.4 ppm. An experimental re-circulating indoor stream mesocosm system has been established at ORNL to investigate the production and bioaccumulation of methylmercury in mercury-contaminated stream ecosytems.
Results to date indicate that waterborne inorganic and methylmercury concentrations to closely simulate levels typical of mercury-contaminated East Fork Poplar Creek in Oak Ridge. We have proposed to use this system to investigate whether trace additions of selenite can inhibit the production and/or bioaccumulation of methylmercury without elevating selenium concentrations in aquatic biota to unacceptable levels.
To view the full article please go to: