Tributyltin (TBT) effects on Hexaplex trunculus and Bolinus brandaris (Gastropoda: Muricidae): Imposex induction and sex hormone levels insights

Tributyltin (TBT)-induced imposex in gastropods is often cited as a prime example of environmental endocrine disruption. Several endocrine-related hypotheses have been proposed to define possible mechanisms by which TBT causes imposex. Recently, it has been demonstrated that mollusks have the ability to control endogenous steroid levels (i.e., testosterone and estradiol) by esterification with fatty acid and TBT may impact this metabolic pathway. Hence, this study was designed to investigate the presence and levels of sexual steroids (testosterone and estradiol) in the two TBT sensitive Muricids species Hexaplex trunculus and Bolinus brandaris, and to clarify the sex related impact of TBT in free and esterified steroid levels. Two months exposure to TBT (5 and 50 ng TBT L−1) induced imposex and led to a significant increase in the severity of the phenomenon in the high TBT exposure group but statistical tests failed to detect an effect in 5 ng TBT L−1 treatment. The steroid levels found in both sexes revealed that testosterone and estradiol were present in the free and esterified forms in the digestive gland-gonad complex. Both hormones were predominantly found in the esterified form, although clear sex differences were not observed. In females of B. brandaris, 2 months exposure to TBT at 50 ng TBT L−1 induced a significant elevation of free testosterone and a decrease in the esterified fraction. In females of H. trunculus, TBT led to a significant elevation of both free and esterified testosterone. In contrast, TBT had no effect in male's testosterone levels, although it led to an increased trend in penis lengths. Free and esterified estradiol levels were not affected by TBT in both sexes of B. brandaris but free estradiol was increased in females of H. trunculus. Overall, the present study demonstrates that TBT exposure leads to steroid imbalance in both species, with a boost of free testosterone levels in females. Although TBT increases male penis length, no effects in male steroid levels were recorded in both species. Hence, TBT impacts in testosterone and estradiol metabolism is sex dependent, and does not seem to be associated with the increase of male penis length observed in TBT exposed animals.