Effects of polychlorinated biphenyls (PCBs) on reproduction, physiological processes, and biomarkers in tree swallows (Tachycineta bicolor)

Abstract

Tree swallow (Tachycineta bicolor) nestlings were studied at ten sites exhibiting a range of polychlorinated biphenyl (PCB) contamination. Nesting success, offspring survival, and growth and developmental parameters were recorded. In addition to determining PCB concentrations in eggs, twelve-day-old nestlings, and food items, hepatic cytochromes P450-associated monooxygenase activities (BROD and EROD) were quantified as a biomarker of exposure. Eggs and nestlings from one site were dosed with model cytochromes P450 inducers, beta-naphthoflavone (BNF), 3-methylcholanthrene, PCB 126, and various Aroclors. A subset of microsomal samples was examined by protein immunoblotting. Heart and skin samples from nestlings were examined immunohistochemically to determine relative amounts and cellular location of CYPIA. Effects on gender and gonadal development of nestling offspring were assessed. A range of PCB contamination was seen in composite sediment (0.02-16ppm) and egg (0.7-9.7ppm) samples from the field sites. While there were only subtle differences between reproductive and growth parameters from nestlings at various sites, body burdens of PCBs were significantly different and correlated strongly with PCB levels in sediment, eggs, and food sources. PCBs were deposited in Tree swallow eggs and accumulated in nestlings. There was no evidence of abnormal gonadal development or anatomical gender alteration due to PCB exposure in nestling Tree swallows. Although BNF induced cytochromes P450 as assessed by enzyme activity and protein immunoblotting, PCBs were ineffective inducers except in the case of pipped embryos which were treated in ovo with PCB 126 and exhibited dose-related enzyme induction. BROD and EROD activities correlated significantly with each other (r > 0.8). Differences between sites and treatments show that there is a cytochrome P450 biomarker response in Tree swallows which is indicative of contaminant exposure and effects. Tree swallows appear to be resistant to the reproductive and physiological effects of PCBs and cytochrome P450 induction at field sites may be due to parallel contaminants. Due to their resilience to PCB contamination, Tree swallows did not prove to be a good sentinel species. However, Tree swallows are good indicators of PCB exposure through chemical analyses of tissues.