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MERCURY IN STAMP SAND DISCHARGES: IMPLICATIONS FOR LAKE SUPERIOR MERCURY CYCLING
Citation:
Harting, S. L., W. C. Kerfoot, AND R. Rossmann. MERCURY IN STAMP SAND DISCHARGES: IMPLICATIONS FOR LAKE SUPERIOR MERCURY CYCLING. Presented at 42nd International Association for Great Lakes Research Conference, Case Western Reserve University, Cleveland, OH, May 14-28, 1999.
Description:
Approximately a half billion tons of waste rock from the extraction of native copper and silver ores was discharged into the Lake Superior basin. Stamping was the method of choice to recover these metals from the surrounding poor rock. This process created large amounts of extremely fine material that was transported to area waterways and, following strong offshore water movements such as the Keweenaw Current, is now widely dispersed through the Lake Superior Basin. The contribution of stamp sand discharges to copper concentrations in Lake Superior sediments has been recognized. However, the mercury content of this type of discharge has been heretofore unknown. Samples of native copper and silver ore, stamp sands, and poor rock from Michigan's Upper Pennisula were all found to contain mercury. Scanning electron microscope analysis has shown that the mercury is associated with copper or silver in the ore as a naturally occurring amalgam. There are two routes by which this source of mercury may be available for eventual uptake by aquatic organisms. One, offgassing of mercury vapor into the atmosphere from terrestrially-located stamp sands, and two, dispersal of mercury-enriched particles into environments favorable for mercury methylation.