BIOGEOCHEMISTRY OF ARCTIC GRAYLING (THYMALLUS ARCTICUS) IN THE FORTYMILE RIVER MINING DISTRICT, ALASKA

We report on the inorganic chemistry of Arctic grayling, an ecologically important resident freshwater sport and subsistence fish in the Fortymile River Mining District of the Interior Highlands Ecoregion in eastern Alaska. The study area has been mined for placer gold for over a century and is currently experiencing renewed mineral exploration activity. Historically Hg was used extensively to amalgamate fine gold from placer mining operations and, until now, the extent of the residual contamination on fish populations in this region has not been investigated. Functional biogeochemical baseline values and/or ranges are presented for the concentration of 38 elements in grayling muscle (fillet) tissue, liver tissue, and stomach contents. Geometric means for total Hg of 0.069 and 0.062 ppm in muscle and liver tissue, respectively, are reported. These levels are more than an order of magnitude below the FDA and EPA human consumption risk values for methylmercury in fish fillets. In addition, levels of As, Cd and Se were found to be well below risk-based EPA screening concentrations for human consumption. Fish tissue concentration data were normalized to fish weight and the relation of these normalized values to the geochemistry of regional lithologic units, bed sediments, and surface water were examined. In general, very little variability was noted in the normalized muscle tissue concentration data among samples at each of the eleven individual sites. Differences among sites (as determined by an unpaired t-test), however, were important for a few major nutrient elements (Ca, K, Mg, Na, and P), metals/metalloids (Cr, Hg, and Se), and an alkali metal (Cs). Close examination of the metal data showed no definitive link between non-systematic biogeochemical patterns and regional lithology. Stomach content material was examined for the occurrence and frequency of macroinvertebrate composition and chemistry and these data are reported along with the fish tissue chemistry data. Nitrogen isotope signatures of the muscle tissue indicate a restricted trophic position for the fish population, whereas the C and S isotope signatures indicate selectivity in feeding habits for individual fish in the sample set.