Ecological risk assessment in a large river-reservoir. 4. Piscivorous wildlife

Over 50 years of operations of facilities on the Oak Ridge Reservation (ORR), Tennessee, has resulted in the release of contaminants into the water, sediment, and biota of the Clinch River and Poplar Creek, downstream of the ORR. An iterative, weight-of-evidence approach was employed to assess risks these contaminants present to four piscivorous wildlife species (osprey [Pandion haliaetus], great blue heron [Ardea herodias], mink [Mustela vison], and river otter [Lutra canadensis]) in the Clinch River/Poplar Creek (CR/PC) watershed. Available data consisted of literature-derived NOAELs and LOAELs, field surveys, and toxicity tests. Contaminants of potential ecological concern (COPECs) were identified by comparing point estimates of exposure to NOAELs and included mercury and PCBs. Exposure to COPECs was reestimated using Monte Carlo methods, first at individual locations, then over ecologically relevant spatial scales. These exposure distributions were compared to LOAELs. Estimated exposure for mink was not sufficient to present a risk from any COPEC. Mercury and PCBs presented a significant risk to river otter at one location each. Exposure of osprey and great blue herons to mercury represented a significant risk at one and two locations, respectively. Field surveys of heron rookeries and osprey nests indicated no adverse effects on reproduction. Mink fed fish from the Clinch River displayed reduced reproduction only in the most contaminated of five toxicity test diets; this reduction was not statistically significant, however. The maximum mercury and PCB exposures estimated for mink along the Clinch River were significantly lower than the toxicity test exposures associated with adverse effects. The weight of evidence indicates that contaminants from the ORR do not present a risk to mink, great blue heron, or osprey along the Clinch River; river otter, however, may be at risk from mercury and PCBs.