THE EFFECTS OF POLYCHLORINATED BIPHEYNLS (PCBs) ON AVIAN CARDIAC DEVELOPMENT

Abstract

Polychlorinated biphenyls (PCBs) are a class of synthetic organochlorines that are thermally stable, resistant to degradation, and persistent in the environment as a result of bioaccumulation and intermittent redistribution through trophic levels. These compounds were sold commercially as mixtures in the twentieth century and later banned due to their biological toxicity. There are 209 known PCB congeners, each with different toxicities and physical properties that cause a variety of adverse health effects. Moreover, the effects of PCB mixtures vary with exposure concentrations, PCB congener toxicity, and species sensitivity. However, limited information is available about the impact of PCBs on the development of the embryonic cardiovascular system. There is a major site of contamination along the upper Hudson River in New York; wildlife in that region have shown evidence of exposure to PCBs. The purpose of this research was to determine the impact of embryonic exposure to a PCB mixture and a single congener, both found in the upper Hudson River on the developing avian cardiovascular system. In study 1, tree swallow eggs (Tachycineta bicolor) were dosed with PCB 77 and incubated to hatch. Similarly, domestic chicken eggs (Gallus domesticus) were dosed with the PCB mixture at embryonic day zero and incubated to hatch in study 2. Eggs were monitored through incubation; other measures were taken at hatch along with tissue collection. Results showed that embryonic exposure to PCBs resulted in an absence of the ventricular wall compact layer and hypertrabeculation in tree swallow hatchlings in spite of no effect on survival. Embryonic exposure to a PCB mixture in domestic chickens resulted in compact layer absence as well as additional cardiomyopathies, including absence of the ventricular wall trabeculated layer, ventricular chamber dilation, abnormal heart wall and septal formations, and arrhythmias during embryonic development. In study 3, embryonic exposure to a PCB mixture was studied at Hamburger Hamilton stages 10, 16, and 20. Embryonic exposure to a PCB mixture resulted in abnormal proliferation of cardiomyocytes early in heart development. Dose-dependent mortality occurred in chicken embryos exposed to the PCB mixture. These results support other findings demonstrating PCB effects on the cardiovascular system. Further, these data showed dramatic adverse effects of the PCB mixture as well as a single congener found in the region of the upper Hudson River on the developing avian cardiac system.