Trace-elements (Hg, Se, Cd, and Pb) and chlorinated hydrocarbons (HCB, α-HCH, γ-HCH, DDTs, and PCB) were analysed in eggs of seven species of birds (White Pelican, Common Cormorant, Pygmy Cormorant, Glossy Ibis, Grey Heron, Night Heron, and Mallard) collected in the Danube Delta. The species are at various levels of the food-chain.
Trace elements:—cadmium and lead occurred in very low concentrations (Cd<0.025 μg/g dw; Pb<0.250 μg/g dw) as is usually the case; mercury reached high levels in predatory birds (4.9 ppm in the Common Cormorant); selenium concentrations were quite high but homogeneous in the different species. No correlation between selenium and mercury concentrations was found, suggesting that the possible protective action of selenium enters into effect only when a certain threshold of mercury concentration has been reached.
Chlorinated hydrocarbons:—DDTs (particularly pp'DDE) occured at very high levels in the first three species; PCB levels are lower than those of DDTs; the PCB/DDE ratio is about 0.3–0.8 (such values are described as typical of agricultural zones and quite different from those found in the Mediterranean and in the East Atlantic); Lindane is present in amounts greater than those found in the two above-mentioned areas; α-HCH and HCB levels are similar to those of other areas. The possible pathway of these toxicants within the body and their impact on reproductive success is discussed, albeit somewhat conjecturally.