Evaluation of the impact of in-ovo exposure to dicofol on avian reproduction

To assess the possible impact of the currently used organochlorine insecticide, dicofol, on the development and reproduction of avian species, in ovo exposure experiments to its p,p' and o,p' isomers were performed using Japanese quail (Coturnix japonica) eggs. o,p'-Dicofol (0.3-100 µg/g of egg) and p,p'-dicofol (3-100 µg/g) were injected into the yolk prior to incubation and hatched chicks were raised to adulthood. In ovo treatment with o,p'-dicofol impaired the eggshell-forming ability of female quails after sexual maturity; eggshell strength, mass, and thickness were significantly reduced at minimum dosages of 3, 1, and 0.3 µg/g, respectively. o,p'-Dicofol also caused abnormal development of the right oviduct independently of the dose; even a female exposed at the lowest dose tested (0.3 µg/g) possessed a large right oviduct. Minor but significant mass reductions of both the left oviduct and the testis were observed only at 10 µg/g. In addition, the transcript of a gene encoding cytochrome P450 cholesterol side-chain cleavage in the gonads of male hatchlings was markedly reduced by o,p'-dicofol treatment. p,p'-Dicofol did not have any marked effects on the reproductive systems, although some significant changes in eggshell formation and oviduct morphology were observed. The results indicate that transovarian exposure, especially to o,p'-dicofol, could damage avian reproduction mainly through eggshell thinning.