Effects of TBT and 3-MC co-exposure on cytochrome P450 expression and activity in marine organisms

Tributyltin (TBT) is an organotin compound used as a chemical anti-fouling agent. This compound is most often found absorbed to the sediments in marinas and harbors where other contaminants such as polycyclic aromatic hydrocarbons are present. This study looked at the effects of TBT and 3-methylcholanthrene (3-MC) co-exposure on cytochrome P450 expression and enzymatic activity in the southern flounder (Paralichthys lethostigma) and the mud snail (Ilyanassa obsoleta). Fish and snails were treated with TBT, 3-MC or TBT plus 3-MC at various concentrations. Hepatic microsomes were analyzed for protein content, cytochrome P450 expression, ethoxyresorufin O-deethylase (EROD) activity, testosterone hydroxylase activity (flounder) or the development of imposex and reproductive effects (mud snail). The results indicate that co-exposure of 3-MC with TBT overcomes the effects of TBT exposure alone. No significant difference was observed in EROD activity between the 3-MC and the TBT plus 3-MC exposure groups. Interestingly, 3-MC co-exposure appeared to mediate the endocrine-disrupting effects of TBT exposure by reducing the penis size in imposex female snails and restoring their capacity to lay eggs.