Toxicity of sediment-associated tributyltin to infaunal invertebrates: Species comparison and the role of organic carbon

Experiments with three species of infaunal invertebrates (a polychaete, Armandia brevis and amphipods, Rhepoxynius abronius and Eohaustorius washingtonianus) with different modes of feeding gave a wide range in toxic response to sediment associated tributyltin (TBT), while exhibiting consistent lethal tissue residues. These studies showed that bioaccumulation and toxicity of sediment-associated TBT were strongly controlled by the organic carbon content of the sediment, which we concluded was primarily due to its influence on interstitial water (IW) concentrations of TBT. Major differences in the response to sediment-associated TBT were found between species, which was attributed to differences in their rates of uptake and elimination of this compound. Predictions for bioaccumulation and toxicity for each species based on these toxicokinetic rates were matched closely by observed values. Based on comparisons of water-only and IW exposures (when water and sediment concentrations of TBT were in equilibrium) and predictions made with toxicokinetic rates, the major route of uptake for each of the species tested appeared to be from dissolved TBT. We determined the mean (sd) organic-carbon normalized sediment-water partition coefficient (Koc) to be approximately 25 100 (5500) for TOC values ranging from 0.3 to 1.0%, which was five times higher than the reported Kow. Additionally, we determined the dissolved organic carbon—water partition coefficient (Kdoc) to be 1652, which was three fold lower than the Kow. The results also showed that the Koc could be influenced by infaunal organisms, presumably by reducing IW concentrations below predicted values, which raises questions about the environmental relevance of sediment bioassays using these organisms and the expected IW concentrations present in field sediments.