Contaminants in eggs of some waterbird species from the Scheldt estuary, SW Netherlands

Abstract

The contaminated Scheldt estuary is a wetland of international importance for waterbirds. In eggs of Common Terns ( Sterna hirundo) from the brackish zone, concentrations of Hg, Cr, Cu, Cd, Zn, and PAHs did not exceed no-observed effect levels reported in the literature. Eggshell thickness did not differ from the pre-DDT period. However, concentrations of PCB-118 (0.1–0.7 μg g −1 WW) may indicate adverse effects on reproductive success. In terns' eggs from the marine zone, PCB-118 did not exceed the no-observed effect concentration. In eggs of Black-headed Gulls ( Larus ridibundus) concentrations of HCB, lindane, DDT and dieldrin are low and showed no spatial gradient. PCB levels, on the other hand, are high in the brackish zone where adults forage on intertidal flats and eight times lower in eggs from the North Sea coast where adults feed mainly inland. No adverse effect on breeding success of Black-headed Gulls was observed in the field. The estimated biomagnification factor for PCB-153 for Oystercatcher ( Haematopus ostralegus) is higher than for terns and gulls.