A probabilistic risk assessment of the effects of methylmercury and PCBs on mink and kingfishers along East Fork Poplar Creek, Oak Ridge, Tennessee, USA

Abstract Over fifty years of operations, sorage, and disposal of wastes from the U.S. Department of Energy (U.S. DOE) Y-12 nuclear weapons facility at Oak Ridge, Tennessee, USA, has resulted in the contamination of water, sediment, biota, and floodplain soils of East Fork Poplar Creek. A preliminary assessment revealed that methylmercury and polychlorinated biphenyls (PCBs) were the contaminants of most concern. Because these contaminants are persistent, accumulate in tissues, and biomagnify up the food chain, piscivorous wildlife are the biota at greatest risk of exposure. The objective of this study was to estimate the risks posed by methylmercury and PCBs to two piscivorous species: mink and belted kingfishers. We conducted Monte Carlo simulations to estimate total daily intakes of each contaminant by each species and then integrated the resulting distributions with their respective dose–response curves to estimate risks. The results indicate that methylmercury poses a moderate risk to female mink (24% probability of at least 15% mortality) and kingfishers (50% probability of at least a 12–28% decline in fecundity depending on location). The PCBs pose a very serious risk to mink (52% probability of at least a 50% decline in reproductive fecundity), a species known to be especially sensitive to the effects of organochlorine substances, but little risk to kingfishers (<5% probability of a decline in reproductive fecundity greater than 10% at any location).