Assessment of Heavy Metals in Red King Crabs Following Offshore Placer Gold Mining

Abstract

Red king crabs, Paralithodes camtschaticus, with commercial and subsistence importance, seasonally occur nearshore in Norton Sound, north-eastern Bering Sea, Arctic Alaska. Since the end of the nineteenth century, the coastal area in the northern Sound has been intensively mined for placer gold. Mining was extended offshore in 1986–1990. Heavy metal concentrations in the crabs were monitored during 1987–1990 to assess the impact of offshore mining. Crabs were only present in the study area during ice-covered months when mining was seasonally suspended. Arsenic, Cd, Cr, Cu, Pb, Ni, Zn and Hg concentrations in muscle and hepatopancreas tissues were generally not different between mined and unmined reference (control) areas. Furthermore, concentrations of these metals were not different in similar surficial sediments upcurrent and downcurrent of mining. The concentrations of most metals in both tissues fluctuated over the study period, with no temporal trend. Exceptions were for Hg in muscle tissue and As in hepatopancreas tissue which showed progressive significant increases each year. Also, there was a fractionation of selected metals between the two tissues; Cr, Pb and Zn were greater in muscles, whereas Cd, Cu and Ni were greater in hepatopancreas. Arsenic and Hg had similar concentrations in both tissues. All elemental concentrations in the crab muscles from Norton Sound were below or within the range of concentrations observed in red king crabs from five other locations in the North Pacific, including a mined area. In Norton Sound, all metals, except Cd, were at least an order of magnitude below the US Food and Drug Administration guidance levels for contamination or human consumption. This investigation demonstrated that mining activities did not affect the concentrations of the heavy metals measured in red king crabs.