Biochemical and developmental effects of dietary exposure to polychlorinated biphenyls 126 and 153 in common tern chicks (Sterna hirundo)

Effects of PCBs were studied in common terns (Sterna hirundo). Hatchlings from eggs collected from Dutch breeding colonies and incubated artificially were raised to an age of 21 d. The birds were fed fish spiked with PCB 126 alone or in combination with PCB 153 (1:1,000), resulting in concentrations in the food ranging from 0.01 to 1.2 ng toxic equivalents (TEQs)/g wet weight. The most sensitive effect parameter was induction of hepatic CYP1A-associated ethoxyresorufin-O-deethylation (EROD) activity, and a nonlinear concentration-effect relationship could be determined with the TEQ concentration (r = 0.967, p < 0.001). Induction of pentoxyresorufin-O-depenthylation and methoxyresorufin-O-demethylation activities was observed at dose levels similar to those that induced EROD activity. The estimated lowest-observed-effect level for induction of CYP1A in the common tern was approx. 25 ng TEQ/g liver lipid, which was caused by concentrations in the food of approx. 0.6 ng TEQ/g fish wet weight. At these concentrations, a 50% reduction in plasma total thyroxine compared with controls also was observed. Concentrations of plasma total thyroxine were negatively correlated with hepatic TEQ concentrations (r = 0.523, p < 0.01), but the shape of the nonlinear concentration-effect relationship did not allow determination of a lowest-observed-effect level. No changes were found for hepatic hydroxylation of testosterone. Bursa weight decreased proportionally to hepatic concentrations of TEQs (r = 0.433, p < 0.05) and showed a similar sensitivity as that observed for EROD activity. Concentrations of TEQs in The Netherlands are approx. 0.1 ng TEQ/g wet weight fish, which is approximately six times lower than the lowest-observed-effect level for CYP1A induction in terns as estimated in this study. It is concluded that no overt effects on growth and development in the common tern are expected with this background exposure during the posthatch period.