Variations in polychlorinated biphenyl congener composition in eggs of Mediterranean water birds in relation to their position in the food chain.

The concentrations of the principal PCB congeners and the SigmaPCB were determined in eggs of eight species of water birds collected in two areas of the Mediterranean region. The results for SigmaPCB levels indicate statistically significant differences between the species; in the Po delta the higher values are for those species which feed mainly on fish. Differences exist between the congeners and their percentages when compared with the total residue. Tetrachlorobiphenyls constitute a larger proportion of the SigmaPCB in Avocet and Black-winged Stilt, two species whose diet consists mainly of invertebrates. The main component in all the species is 22'44'55' and its presence varies between 11.4% in Avocet and 21.2% in Audouin's Gull. It is suggested that there is a link between the uptake of PCBs and the position of the species in the food chain.