Dietary exposure of great blue heron (Ardea herodias) to PCDD/DFs in the Tittabawassee River floodplain, MI, USA

Concentrations of dioxin-like compounds, primarily polychlorinated dibenzofurans (PCDFs), in soils and sediments of the Tittabawassee River (TR) and associated floodplains downstream of Midland, Michigan (USA) were greater than upstream sites and prompted a site-specific risk assessment of great blue herons (GBH). Dietary exposure of GBH to PCDFs and polychlorinated dibenzo-p-dioxins (PCDDs) was evaluated based on site-specific concentrations of residues in prey items. Concentrations of σPCDD/DFs and 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents (TEQ_WHO-Avian) in prey items collected from the TR were consistently greater than those collected from associated reference areas (RAs) and further downstream in the Saginaw River (SR). The average daily dose (ADD_pot) of σPCDD/DFs to GBH was 45- to 54-fold greater along the TR and 12-fold greater along the SR when compared to the RA. σPCDD/DFs were normalized to TEQ_WHO-Avian, and fold differences in the ADD_pot increased, being 150- to 190-fold greater along the TR and 36-fold greater along the SR than they were in the RA. Greater fold changes in the ADD_pot based on TEQ_WHO-Avian between the RA and the TR and SR was due to prey items from the latter reaches having a greater relative toxic potency of σPCDD/DFs, primarily from greater amounts of 2,3,7,8-tetrachlorodibenzofuran but also 2,3,4,7,8-pentachlorodibenzofuran. Potential for adverse population-level effects from site-specific contaminant exposures were evaluated via comparison to selected toxicity reference values. The prediction of minimal to no risk of adverse population-level effects resultant from the assessment of site-specific dietary exposure of GBH to σPCDD/DFs along the TR and SR is consistent with site-specific assessments of tissue-based exposures as well as population condition. © 2010 Elsevier Inc.