Metabolism and subtle toxic effects of butyltin compounds in starfish

Abstract

The sea star Leptasterias polaris, an important predator in the benthic community of the St. Lawrence Estuary (eastern Canada), was used in assessing the degradation potential and toxicological implications of tributyltin (TBT) ingested with food. TBT was chosen as a representative of the organotins, a group of wide-spread chemicals used as biocides and plastic stabilizers. Male and female individuals were fed daily with TBT-contaminated mussels for a 53-day period. Their digestive system showed a relatively constant TBT concentration (0.26 ± 0.10 μg/ g wet mass) throughout the experiment. Sequential debutylation occurred within 2 weeks, first yielding dibutyltin (DBT) which seemed to accumulate more readily in the caeca (up to 1.10 μg/g), and then monobutyltin (MBT) which appeared only in few individuals at low concentrations (below 0.35 μg/g). Although the total amount of TBT ingested from food continuously increased throughout the experiment (mean of 657 μg for a starfish fed over 53 d), the total amount of tin traced in the analyzed starfish tissues remained below 80 μg, suggesting an excretion system and/or a storage of tin in an undetectable form. All species of the contaminant remained barely detectable in the gonads. Nevertheless, a histological study revealed smaller mature oocytes and thinner epithelium in the gonads of the contaminated individuals compared to control organisms. These results show that sea stars and possibly other echinoderms, avoid immediate accumulation of TBT by dealkylating the toxicant to less harmful metabolites. However, this natural defense process was only partly effective and subtle effects on reproductive organs were induced by disturbing reserve acquisition in growing gametes.