Persistent organochlorine residues in livers of six species of Ciconiiformes (aves) from Spain

Liver samples of 42 birds belonging to 6 species of Ciconiiformes (grey heron (n = 17), little egret (n = 12), cattle egret (n = 1), glossy ibis (n = 1), little bittern (n = 1), and white stork (n = 10)), collected from two different zones of Spain (Ebro Delta and Madrid) in 1992-1997, were analyzed for organochlorine pesticides and PCBs. SigmaPCBs (sum of concentrations of individual congeners), p,p'-DDE, HCB, gamma-HCH, and heptachlor epoxide were the most prevalent residues detected in all samples (occurrence > 95%). There were no statistically significant differences in organochlorine levels between grey herons and little egrets, while levels of SigmaPCBs, p,p'-DDE, HCB, gamma-HCH, and heptachlor were significantly lower for white storks. These results could be explained by the different habitat of these species, aquatic in the Ebro Delta (grey herons, little egrets) and dry in Madrid (white stork), and their diverse feeding habits.