Recent impact of DDT contamination on Black Stork eggs

The contamination with DDT (1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane) and its breakdown products as a potential cause of population decline of Black Stork has been studied in Latvia since 2008. In order to test if contamination is local or widely distributed we collected failed eggs from nests also in Estonia, Belarus, Poland, Czech Republic, Germany and Belgium. DDT or its breakdown products were found in all analysed eggs. The ratio of p,p′-DDT as a proportion of all DDT products increased during the years of our research. Since the Black Stork has so far not been mentioned as a species affected by DDT we do not have information about its critical contamination effect levels. However, we also present data suggesting that DDT contamination might have affected Black Stork historically. Current data suggest that the reduction of eggshell thickness has not (yet) reached the levels described as critical for other affected species. However, we found a significant reduction of egg volumes, which in turn negatively affects hatching, as eggs below a threshold size fail to hatch. The ratio of small eggs versus normal eggs has increased by almost 10 % in recent years and is strikingly higher as compared to the pre-DDT period. There is also a significant correlation between eggs of reduced size and their respective DDE (1,1-bis(4-chlorophenyl)-2,2-dichloroethene) values.