Temporal changes of fish mercury concentrations in mining-affected Pinchi Lake, BC

The Pinchi Mine produced metallic mercury from 1940 to 1944 (historical) and from 1968 to 1975 (modern operation). From 2010 – 2012, the mine underwent decommissioning and reclamation to ensure that terrestrial areas affected by the mine do not pose unacceptable risks to ecological resources. Historical operations included placement of roasted ores (calcines) in the lake opposite the old mill. This resulted in highly elevated mercury concentrations in nearshore sediments. This source, as well as broad aerial deposition of elemental mercury during the roasting process in both operations, increased the mercury load to sediments throughout the lake. Prior to 2000, there were limited data on mercury in fish from Pinchi Lake. Detailed fish mercury studies were conducted in 2000, 2006 and 2011, focusing on mercury-size relationships of lake trout (Salvelinus namaycush), whitefish (Coregonus sp.) and rainbow trout (Oncorhynchus mykiss). While fish mercury concentrations have declined by nearly an order of magnitude from their peak in 1974, the rate of decrease in mercury concentrations has slowed since 2000. The focus of temporal comparisons is based on length-standardized fish size, because of the positive correlation between mercury concentration and size. Overall, mercury concentration in fish have declined from their peaks in the late 1970s (>5 ppm), but remain elevated in Pinchi relative to nearby Stuart and Tezzeron lakes in lake trout (0.53 ppm), whitefish (0.25 ppm) and rainbow trout (0.18 ppm). Given the longevity and size of lake trout and slow burial rate of historically contaminated sediments, the timeframe for recovery of the lake to ‘regional’ fish mercury concentrations is unknown. Risk assessments have evaluated potential implications of fish consumption on local wildlife species (eagle, grebe, otter), as well as on human health. Continued monitoring of fish mercury concentrations is part of the risk management plan for the site.Non UBCUnreviewedOthe