Biological effects of polychlorinated dibenzo-p-dioxins, dibenzofurans, and biphenyls in bald eagle (Haliaeetus leucocephalus) chicks

During the 1992 breeding season, eggs of bald eagles (Haliaeetus leucocephalus) were collected within a gradient of exposure to chlorinated hydrocarbon pollutants, particularly from pulp mill point sources, on the southern coast of British Columbia, Canada. Twenty-five eggs were placed in a laboratory incubator, of which 18 hatched; chicks were sacrificed within 24 h. Hatching success was not significantly different between eggs taken from pulp mill sites and reference sites. A hepatic cytochrome P4501A (CYP1A) cross-reactive protein was induced nearly sixfold in chicks from near a pulp mill at Powell River compared to those from a reference site (p < 0.05). Hepatic ethoxyresorufin-O-deethylase (EROD) and benzyloxyresorufin O-dealkylase (BROD) activities were also significantly elevated in chicks from nests located near pulp mills compared to reference sites (p < 0.0005 and p < 0.02, respectively). A hepatic CYP2B cross-reactive protein was threefold higher in chicks from pulp mill versus reference sites, but the difference was not significant. Residual yolk sacs of eggs collected near pulp mill sites contained greater concentrations of 2,3,7,8-substituted polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) compared to reference areas. No significant differences in concentrations of polychlorinated biphenyls (PCBs), non-ortho congeners, and organochlorine pesticides occurred among sites. Regressions showed that the hepatic CYP1A cross-reactive protein and EROD and BROD activities were positively correlated with 2,3,7,8-TCDD, 2,3,7,8-TCDE and toxic equivalents (TEQs(WHO)-World Health Organization toxic equivalence factors) in yolk sacs. No significant concentration-related effects were found for morphological, physiological, or histological parameters, such as chick growth, edema, or density of thymic lymphocytes. Using hepatic CYP1A induction as a biomarker, a no-observed-effect-level (NOEL) of 100 ng/kg and a lowest-observed-effect-level (LOEL) of 210 ng/kg TEQs(WHO) on a whole egg (wet weight basis) are suggested for bald eagle chicks.