Induction of Imposex in Rock Shell, Thais clavigera, Exposed to Tributyltin and Other Antagonistic Chemicals

Abstract

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-female were found in control, sham (ethanol) and testosterone exposure groups, 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 + nonylphenol) 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 exposure groups compared to the control group. A negative correlation was obtained between TBT body residue and EROD activity, while a positive relationship was obtained between TBT body residue and the degree of imposex except for the TBT + DDT exposure group. Although TBT 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.