Date of this Version
Published in Environmental Contaminants in Biota: Interpreting Tissue Concentrations, 2nd edition, ed. W. Nelson Beyer & James P. Meador (Boca Raton: CRC, 2011).
Organotins are organometallic compounds that exhibit complex environmental chemistry and toxicity. The handbook of Chemistry and Physics (CRC 1975) lists more than 250 organotin compounds. Even though a number of these are specific compounds (e.g., triphenyltin [TPT]) that are listed as various salts (e.g., TPT chloride, sulfide, hydroxide, and bromide), there are dozens of unique compounds. Because a number of organotins will be considered here, Table 7.1 lists the compounds and their abbreviations.
The focus for this chapter is the occurrence of organotin compounds in aquatic organisms and the associated toxic responses. For aquatic organisms, we traditionally define the effective concentration for toxicity based on the ambient-exposure pathway (e.g., water, air, soil/sediment, prey); however, tissue residues reflect the bioavailable and effective target dose more accurately than the conventional "dose." The term "dose" is loosely applied; however, it most accurately defines that bioactive fraction occurring at the site of action. Differences in the inherent toxicity (potency) of compounds within and between mechanisms of toxic action (MeOAs) are more apparent in residuebased dose metrics than exposure-based dose metrics because the influence of many confounding factors can be taken into account and avoided. For example, a high percentage of the range for LC50 or EC50 values that are based on water or sediment concentrations are due to the variability in the bioavailable fraction and the uptake and elimination rate kinetics that determine bioaccumulation (Meador 2006). When tissue residues are used as the dose metric, differences in bioavailability and bioaccumulation are greatly reduced and we are left with just the potential variability in potency that may occur among species. In many cases, the range in values for a given toxicant among all species can be reduced by 4-5 orders of magnitude for ambient-exposure toxicity metrics to one order of magnitude when tissue-based toxicity metrics are considered (Meador 2006, Meador et al. 2008). The major advantage of this feature is in assessing concentrations of a given toxicant in feral organisms. Hence, we can more accurately determine the likelihood of potential toxic effects for some chemicals measured in field-collected organisms when a low variance is observed among species.