An ecological risk assessment for great horned owls and bald eagles exposed to polychlorinated biphenyls and total DDT at the Kalamazoo River Superfund site, Michigan

Selection of receptors is a key element of effective risk and natural resource damage assessments. This is especially critical when site-specific field studies are employed. The great horned owl (Bubo virginianus; GHO) has advantages over other species as a key tertiary terrestrial receptor that can be used as an integrated measure of exposure to residues in a multiple-lines-of-evidence approach. The methods described herein exploit attributes of the GHO including its propensity to nest in artificial nesting platforms, which allows for better control of experimental conditions than normally experienced in studies of wildlife. The GHO was used in a multiple-lines-of-evidence study of polychlorinated biphenyls (PCBs) and p,p'-dichlorodiphenyltrichloroethane (DDT) exposures at the Kalamazoo River Superfund Site (KRSS) in Kalamazoo and Allegan Counties, Michigan. Over the course of five yrs, 48 artificial and six natural GHO nests, covering approximately 14 active territories along approximately 38 km of river floodplain, were monitored for activity at the KRSS. The study examined risks from total PCBs, including 2,3,7,8-tetrachlorodibenzo- p-dioxin equivalents (TEQWHO-Avian), and total DDTs (sum of DDT/DDE/DDD; SigmaDDT) by measuring concentrations in eggs and nestling blood plasma. Dietary modeling was also completed to estimated potential ingested dose for the contaminants of concern (COCs) from site foraging activities. An ecological risk assessment compared concentrations of the (COCs) in eggs, plasma, or diet to toxicity reference values to generate hazard quotient values descriptive of potential risk to resident raptor populations. Productivity/relative abundance measures for KRSS GHOs were compared with other GHO populations. Egg shell thickness was measured to assess effects of p,p'-dichlorodiphenyldichloroethylene (p,p'-DDE) on egg viability. Tissues data, dietary exposure estimates, and productivity/relative abundance measures indicated no population level effects were present at the Upper reach of the Kalamazoo River Superfund Site, closest to the sources of PCB contamination to the River. Bald eagles (Haliaeetus leucocephalus) residing at the Kalamazoo River Site were also studied using the multiple-lines-of-evidence approach. Observations of reduced productivity and elevated contaminant concentrations in eagle eggs and nestling plasma collected from the site indicated that contaminant exposures were likely at the threshold for adverse population effects for resident bald eagle populations. Additionally, data bases describing the concentrations of total PCBs in eggs and nestling plasma of great horned owls and total PCBs and p,p'-DDE in eggs and nestling plasma of bald eagles from the Great Lakes region were used to develop a relationship to predict concentrations of PCBs and DDE in eggs from measure concentration in nestling plasma. An accurate conversion factor to translate nondestructive plasma-based contaminant concentrations to comparable egg-based concentrations will prove valuable to risk assessors investigating the potential effects of chemical exposures to raptors.