Induction of Imposex in Rock Shell, Thais clavigera, Exposed to Organotins and Other Endocrine Disrupting Chemicals

Interactions of both feminizing and masculinizing chemicals inducing imposex in gastropod were investigated with a long-term exposure experiment. Imposex-free rock shell(Thais-clavigera)was exposed to TBT and other antagonistic chemicals (nonylphenol and DDT), P450 inducer (phenobarbital) and natural sex hormone (estrogen) mixtures for 60 days. None of imposexed-females were found in control, sham (ethanol) and testosterone exposure group, on the other hand imposex was induced in the TBT and all the TBT+antagonist mixture groups. After 60-day exposure, frequency of imposexed-female ranged from 31-68%. Female mean penis length (FMPL) of imposexed-female ranged from 0.87-2.58 mm, and relative penis length indices were from 7.2 to 21.2%. However, the degrees of imposex were different among the exposure groups. The FMPLS of three exposure groups (TBT+estrogen, + DDT and +nonylphe- not) were less than that of the TBT exposure group. Ethoxyresorufin-O-deethylase (EROD) activities in gastropod decreased in the TBT and all the TBT+antagonist ekposure groups compared to the control group. A negative correlation was abtained between TBT body residue and EROD activity, while a positive relationship was obtained between 737 body residue and the degree of imposex except for the TBT +DDT exposure group. Although 737 concentration was relatively high in the TBT+DDT exposure group, the TBT +DDT exposure group demonstrated low EROD activity and low degree of imposex. These results indicate that a certain antagonistic effect of DDT occurred in induction of imposex by TBT.