Imposex induction in Nucella lima (Gmelin) via mode of exposure to tributyltin

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Exposure of Nucella lima (Gmelin) to seawater or Mytilus trossulus (Gould) flesh containing tributyltin (TBT) for 4 months resulted in the development of imposex, the superimposition of male reproductive tract characteristics in female snails, in a time-dependent manner. Specific imposex characteristics measured in female snails included growth of a penis and vas deferens, and an increase in the magnitude of two imposex indices, relative penis size (RPS) and the vas deferens sequence (YDS) index. Imposex characteristics developed to a similar degree in snails fed TBT-contaminated mussels (0.362 μg TBT/g wet weight) or exposed to 0.064 μg TBT/1 in seawater by the 2nd month of exposure. After exposure to TBT for 4 months, intensification of imposex characteristics continued during a subsequent 10-month recovery period when snails were held in TBT-free laboratory seawater and fed TBT-free mussels. No significant differences in mortality and feeding rates occurred between control snails and those exposed to 0.064 μg TBT/1 seawater or those exposed to TBT-laden mussels; significant mortality and a decreased feeding rate occurred in snails exposed to 0.914 μg TBT/1 seawater, indicating that this concentration is close to the long-term LC 50. TBT was bioaccumulated from both food and seawater in direct relationship to concentration and length of exposure. Debutylization of TBT occurred at a slow rate in all experimental groups, but a higher proportion of TBT was metabolized to DBT and MET in snails exposed to 0.914μg TBT/1 seawater. For N. lima, TBT bioaccumulation from food and resulting imposex responses are equivalent to low level exposures to TBT in seawater.