Comparison of p‐ṕ‐DDE and o‐ṕ‐DDE on Eggshell Thickness and Ca Binding Activity of Shell Gland in Ducks

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Abstract
One of the main ectoxicological effects of DDT and its stable metabolite DDE is to reduce the reproductive success in several species of birds by decreasing the thickness of the eggshell. In 2 different strains of ducks (A. platyrhynchos) addition of 40 mg/kg dry wt of p,p-DDE to the diet for 45 days produced a significant and long-lasting reduction of the shell thickness, measured as eggshell index. The reduction was more marked in Indian Runner Ducks (IRD; 30 .+-. 3%) than in a Swedish .times. Rouen breed (SR; 10 .+-. 2%). The p,p-DDE residues in the egg yolk + egg white were almost similar in the 2 strains; 38 .+-. 2 and 51 .+-. 6 ppm (wet wt), respectively. In the IRD 40 mg/kg of o,p-DDE in the diet for 45 days was much less potent in reducing the eggshell index (8 .+-. 3%) than the p,p isomer; the amount of residue of the o,p isomer in the eggs (2.2 .+-. 0.1 ppm) was also smaller. A homogenate of the shell gland from the SR breed accumulated 45Ca2+ in the presence of ATP. The accumulation was inhibited .apprx. 50% by 5 mM sodium azide and 100% by 3 mM mersalyl. p,p- and o,p-DDE in the incubation medium both reduced the Ca2+ binding, in a similar and dose-dependent manner. The threshold concentration was .apprx. 20 ppm: 40 ppm reduced the accumulation by .apprx. 40%. DDE may reduce eggshell thickness by inhibiting the Ca binding to the membranes of the cells of the eggshell gland.