Exposure and Multiple Lines of Evidence Assessment of Risk for PCBs Found in the Diets of Passerine Birds at the Kalamazoo River Superfund Site, Michigan

ABSTRACT

Dietary exposures of passerine birds at the Kalamazoo River, Michigan, were examined due to the presence of polychlorinated biphenyls (PCBs) in the terrestrial and aquatic food webs. Average potential daily doses in diets were 6- to 29-fold and 16- to 35-fold greater at a contaminated location than at a reference location for PCB exposures quantified as total PCBs and 2,3,7,8–tetrachlorodibenzo-p-dioxin equivalents (TEQs), respectively. Birds with diets comprised of primarily aquatic insects had greater dietary exposure than birds with diets of primarily terrestrial insects. Risk associated with dietary exposure varied with the selection of the threshold for effects including hazard quotients, which exceeded 1 in instances where the most conservative toxicity reference values were utilized. Risk based on concentrations of PCBs in the tissues indicated little risk to avian species, and co-located studies evaluating reproductive health did not suggest that observed incidences of diminished reproductive success were related to PCB exposure. Measures of risk based on comparison to toxicity reference values (TRVs) were consistent with direct measures of ecologically relevant endpoints of reproductive fitness, but uncertainty exists in the selection of threshold values for effects in these species especially based on TEQs. This is largely due to the absence of species-specific, dose-response relationships. Therefore, the best estimate of risk is through the application of multiple lines of evidence.

Key Words:

• insects
• birds
• bioaccumulation
• dietary exposure
• risk assessment
• trophic level

ACKNOWLEDGEMENTS

The authors extend a special thanks to the students and employees at the Michigan State Aquatic Toxicology Laboratory, Michigan State University Kellog Biological Station, Entrix, Inc., and the Kalamazoo Nature Center. We also thank the Kalamazoo River Study Group for funding this study.

Notes

^a Calculated from TRV selected from Custer et al. (2003).

^b Calculated from TRV selected from Henning et al. (2003).

^c Calculated from TRV selected from USEPA (2000).