Ecological risk assessment in a large river‐reservoir: 7. Environmental contaminant accumulation and effects in great blue heron

Past plant operations and waste disposal on the Oak Ridge Reservation (ORR) have introduced an assortment of potentially harmful contaminants into the surrounding environment. Elevated concentrations of mercury (Hg) and PCBs have been found in fish collected from aquatic systems on the ORR, and a screening level risk assessment has identified piscivorous wildlife downstream from the ORR as being at risk. As a component of an ecological risk assessment of a large river‐reservoir system, the great blue heron ( Ardea herodias ) was chosen as an endpoint species to evaluate potential adverse effects of contaminants on piscivorous wildlife using aquatic systems on or downstream of the ORR. Eggs and chick liver, muscle, and fat samples were collected from two heron colonies located on and two colonies located off the ORR. Samples were analyzed for PCBs, mercury, chromium, and arsenic to determine if differences existed among colonies. Mean mercury and PCB concentrations were greater in eggs and chick tissues collected from colonies located on the ORR. However, no biologically significant differences were observed in fecundity or in egg physical measurements or chick physiological measurements between study locations. The results of this study do not indicate that the contaminant burdens in great blue heron chicks and eggs have a detrimental effect on heron populations utilizing aquatic habitats on the ORR.