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Harvard Invites Exponent Scientist to Lecture on Treating Mercury-Contaminated Lake


March 28, 2012

Dr. Elizabeth (Betsy) Henry, a Senior Managing Scientist in Exponent’s Environmental and Earth Sciences practice, will be speaking April 13, 2012 at the Environmental Science and Engineering Seminar Series at Harvard’s School for Engineering and Applied Sciences. The title of her talk is “Assessment of Nitrate Addition for Control of Methylmercury Production in Onondaga Lake.”

Onondaga Lake in Syracuse, NY, has been impacted by a long history of municipal and industrial activity, including two former mercury cell chlor-alkali plants. In addition to nearshore sediment dredging and capping to address sediment toxicity concerns, the Consent Decree for the Onondaga Lake Superfund Site includes performance of a pilot study to evaluate the potential effectiveness of nitrate at reducing the formation of methylmercury in bottom waters of the lake where oxygen becomes depleted during summer stratification. Prior to implementing the pilot study in 2011, redox species (including oxygen, nitrate, and sulfide), total mercury, and methylmercury were monitored in 2006-2010 to evaluate the roles of oxygen and nitrate in controlling methylmercury concentrations in lake water. Due to the doubling of nitrate concentrations in lake water resulting from installation of a denitrification system at the sewage treatment plant, there is now an approximate two week delay relative to 2006 in the depletion of oxygen and nitrate at the deepest depths in the lake. The maximum mass of methylmercury in the hypolimnion in 2007-2010 was 3-10 times lower than that observed in 2006 and 5-17 times lower than in 1992. Improvements in water quality have resulted in a significant decrease in methylmercury concentrations throughout the lake. Fish tissue concentrations are also responding to the decreased methylmercury. To assess benefits of supplemental nitrate addition, a 3-year pilot test with extensive monitoring began in 2011. The 2011 results indicated the lowest methylmercury concentrations yet observed in Onondaga Lake water.

For more information, please see the seminar website.