Mercury Subsurface Maxima in Sediments: a Diagnostic for Anthropogenic Origins

Multimedia environmental surveys and monitoring studies have shown the major sources of mercury contamination in the Lake Superior watershed to be from former industrial and municipal direct discharges and present airborne sources. Walleye from the St. Louis River, the largest US tributary to Lake Superior, and siscowet trout from the lake continue to show elevated mercury tissue levels, limiting safe human and wildlife consumption. The main routes of mercury bioaccumulation in fish appear to be from airborne deposition and recent contaminated sediment sources and through the benthic and planktonic food chains. No evidence for significant background from geologic sources is indicated in upstream river sediments or from Lake Superior sediment core samples dating from about 2000 to 8000 years. B. P.