Application of a weight of evidence approach to evaluating risks associated with subsistence caribou consumption near a lead/zinc mine.

Overland transport of ore concentrate from the Red Dog lead/zinc mine in northwest Alaska to its seaport has historically raised concerns among local subsistence users regarding the potential impacts of fugitive dust from the operation, including the potential uptake of metals into caribou meat. Caribou are an integral part of life for northern Alaska Natives for both subsistence and cultural reasons. The Western Arctic caribou herd, whose range includes the Red Dog mine, transportation corridor, and port site, sometimes overwinter in the vicinity of mine operations. A weight of evidence approach using multiple lines of evidence was used to evaluate potential risks associated with subsistence consumption of caribou harvested near the road and mine. Data from a long-term caribou monitoring program indicate a lack of consistent trends for either increasing or decreasing metals concentrations in caribou muscle, liver, and kidney tissue. Lead, cadmium, and zinc from all tissues were within the range of reference concentrations reported for caribou elsewhere in Northern Alaska. In addition, a site use study based on data from satellite-collared caribou from the Western Arctic Herd showed that caribou utilize the area near the road, port, and mine approximately 1/20th to 1/90th of the time assumed in a human health risk assessment conducted for the site, implying that risks were significantly overestimated in the risk assessment. The results from multiple lines of evidence consistently indicate that fugitive dust emissions from Red Dog Operations are not a significant source of metals in caribou, and that caribou remain safe for human consumption.