Organochlorine residues and eggshell thinning in wood storks and anhingas

All 10 Wood Stork eggs collected at Merritt Island National Wildlife Refuge in 1973 contained residues of DDE (geometric mean 4.0 ppm wet weight) and PCBs (1.2 ppm). Nine other organochlorines were found at lower frequencies in the eggs. Eggshells from the recent period were 8.9% thinner (P < 0.001) than pre-1947 samples; decrease in eggshell thickness was more closely correlated with DDE than other organochlorines and correlation of DDE and eggshell thickness approached significance (P = 0.115).....Anhinga eggs were collected at 7 localities; 45 of the 46 eggs analyzed contained DDE residues and 24 contained PCBs. Residues of other organochlorines were found less frequently. Shell thickness of recent eggs from Louisiana and Mississippi was significantly less (-7.5%; P < 0.05) than the mean for pre-1947 eggs, but there was no significant change in shell thickness of eggs from Florida. The change in clutch mean eggshell thickness was significantly negatively correlated (P < 0.05) with the concentration of DDE in the eggs.