Abstract
Common tern ( Sterna hirundo) eggs were collected from eight breeding colonies that differed in degree of polyhalogenated aromatic hydrocarbon (PHAH) pollution. The eggs were artificially incubated and the chicks sacrificed within 12 hours after hatching. Plasma thyroid hormones (total thyroxine (TT4), free thyroxine (FT4) and triiodothyronine (TT3)), hepatic T4-glucuronyltransferase (T4-UGT) activity, plasma retinol and yolksac retinoid levels were measured and compared with yolksac PHAH residues and hepatic ethoxyresorufin- and pentoxyresorufin- O-deethylase (EROD and PROD) activities. The yolksac PHAH residues measured were polychlorinated biphenyl (PCB), polychlorinated dibenzofuran (PCDF) and polychlorinated dibenzo- p-dioxin (PCDD). No significant differences were observed between colony average levels of plasma thyroid hormones (TT4, FT4 and TT3) nor plasma retinol levels and T4-UGT activities that could be related to colony average PHAH levels. However, average colony yolksac retinyl ester levels did show significant differences. When correlated for individual terns, significant correlations between all these parameters and PHAH levels or EROD or PROD activities were found. The correlation between hepatic T4-UGT and EROD and PROD activities was very strong, suggesting a concomitant induction of these drug metabolizing enzymes. The PHAH levels were expressed as dioxin equivalents (TEQs) based on toxic equivalence factors (TEFs) as proposed by Safe (1990, 1994). In addition to plasma retinol, another retinoid was found which resembles 3,4-didehydro-retinol (vitamin A2) in chromatographic and spectroscopic behaviour. This putative plasma vitamin A2 was significantly positive correlated with the yolksac TEQs and with the hepatic EROD activity. Esters of both retinol and putative vitamin A2 were detected in the yolksac. The average yolksac vitamin A2 levels of the cleanest Zeewolde colony were significantly higher than the average levels in the other colonies.
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