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() Speciation and Bioavailability of Hg in Contaminated Sediments, Pinchi Lake Mine BC.

Veiga, M.1, Veiga, S.M.B.1, Baker, R.F.2, Turner, R.R.3, 1 University of British Columbia, Vancouver, BC, Canada2 Azimuth Consulting Group, Vancouver, BC, Canada3 RT Geosciences, Squamish, BC, Canada

ABSTRACT- Pinchi Lake Mercury Mine produced metallic mercury (Hg) from 1940 to 1944 (wartime operation) and again from 1968 to 1975 (modern operation). Hg contaminated tailings (calcines) were deposited along the lake foreshore during the wartime operation and dispersed throughout the lake by wind-driven currents. As part of a 2001 ecological risk assessment, bioavailability and biomagnification of Hg and methyl mercury (MeHg) in sediment and lower trophic level biota was investigated. Mineralogical studies of sediments deposited during wartime revealed that Hg exists in sediments (up to 857 ppm dw) primarily as non-exchangeable, non-labile forms, such as cinnabar or mercury oxide, however the predominant Hg-bearing phase differed among sites. We found a positive correlation between weakly-extractable humic substances (extracted by 1M ammonium hydroxide) and higher Hg bioavailability, measured as methyl mercury (MeHg) in chironomid larvae tissue. MeHg in chironomids (>0.3 ppm dw) was much higher than MeHg concentration in the corresponding sediment. Despite elevated inorganic mercury and MeHg concentrations in calcines surrounding the mine, there was no relationship between benthic community richness and abundance and Hg concentration. Spatial differences in Hg speciation and bioavailability at Pinchi Mine has implications for management and remedial options for the former mine site.

Key words: Sediment, Mercury, Speciation, Bioavailability

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