Mercury in soils at the abandoned Red Devil mine in southwest Alaska

Elizabeth A. Bailey*, U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508, USA, eabailey@usgs.gov, Mark E. Hines, Dept. of Biological Sciences, University of Alaska Anchorage, AK 99508, John. E. Gray, Peter. M. Theodorakos, U.S. Geological Survey, P.O. Box 25046, MS 973, Denver, CO 80225

The behavior of mercury in soils is important in understanding the overall biogeochemical cycle of mercury. Much of the mercury in aquatic systems can originate from terrestrial sources. We have been measuring total Hg (THg), methylmercury (MeHg) and Hg(II) for four years in soil samples collected from the Red Devil mercury mine in southwest Alaska. The mine was once Alaska’s largest mercury producer and is currently a high priority site for waste removal and remediation activities by the BLM. For selected samples we have also conducted radiotracer experiments to measure the formation and degradation of MeHg. Consistently high levels of THg (up to 3,200 mg/kg), MeHg (up to 8.4 (g/kg, and Hg(II) (up to 16.0 mg/kg) were measured at various locations around the mine site. Whereas upstream and background concentration values for all three Hg species are significantly lower, the proportion of MeHg to THg at the upstream and background sites is much higher (up to 0.225%) than at the mine sites (less than 0.001%). We observed both methylating and demethylating activities in soils from the mine site and from upstream and background sites. Methylmercury production, as measured by the amount of added 203Hg that was methylated during sample incubation, was consistently higher at the upstream and background sites than at the mine sites. Methylmercury degradation, as measured by the amount of added 14CH3Hg that was demethylated during sample incubation, was more active in the mine sites than in the upstream and background sites. We speculate that mercury resistant bacteria that produce enzymes required for MeHg degradation processes are more likely to be active in sites highly contaminated with mercury such as near the mine than at the relatively uncontaminated upstream or background sites.