SS4.06 Speciation, Bioavailability, and Impacts of Atmospheric Trace Metals in Aquatic Systems
Date: Wednesday, June 12, 2002
Location: Poster Session - VCC
 
Bloom, N, S, Frontier Geosciences, Seattle, USA, NicolasB@FrontierGeosciences.com
PreusEM, Frontier Geosciences, Seattle, USA, EveP@FrontierGeosciences.com
 
A ONE-YEAR MICROCOSM EXPERIMENT: CHANGES IN SPECIATION OF FRESHWATER SEDIMENTS SPIKED WITH 5 MERCURY COMPOUNDS
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As part of a study of historic mining-related mercury pollution in the Cache Creek (CA) watershed, we performed a lab-scale experiment monitoring changes in speciation of Hgo, HgS, m-HgS, HgCl2, and gold mine tailings. These were added at ~10 ppm to separate beakers of organic-rich sediment, previously shown to have a high methylation potential. Loosely covered beakers containing the sediment, under a water layer, were allowed to incubate at ambient outdoor temperature and lighting. Samples from each were taken at seven intervals during one year, immediately analyzed for CH3Hg, and processed by a five-step selective sequential extraction to determine inorganic Hg speciation. Overall, the synthetic mercuric sulfides remained unavailable for methylation. All other compounds as well as the mine tailings were readily methylated. Ultimately, microcosms spiked with these compounds had a majority of mercury in the organo-complexed fraction, and resulted in similar CH3Hg percentages. This experiment shows that for a given sediment type, the form of Hg added has a big effect on both the kinetics of methylation, and on the equilibrium concentration of methyl mercury in the sediment