Toxicity of Tributyltin to Four Species of Freshwater Benthic Invertebrates Using Spiked Sediment Bioassays

Abstract

Abstract The toxicity of tributyltin (TBT) in sediment in fresh water was determined using spiked sediment bioassays for four benthic invertebrates, (the oligochaete worm Tubifex tubifex, the chironomid Chironomus riparius, the amphipod Hyalella azteca, and the mayfly Hexagenia). Although there was some degradation of spiked TBT into dibutyltin (DBT) and monobutyltin (MBT) in the sediment-water mixtures during the equilibration phase before toxicity testing, the contribution of these degradation products to the observed toxicity was assumed to be minimal based on evidence that TBT is up to orders of magnitude more toxic to many aquatic organisms than its degradation products. The results of this work indicated that Hexagenia was the most sensitive benthic organism to TBT of the four organisms tested (by factors up to about 7), with an IC50 (growth) value for TBT of 0.6 µg Sn/g dry weight. This value is about six times greater than mean concentrations of TBT observed in sediment in fresh water in surveys conducted across Canada before and after the regulation of antifouling uses of TBT in 1989. However, maximum TBT concentrations in sediment before and after regulation exceeded the IC50 (growth) value for Hexagenia, and were close to the lower limits of toxicity ranges for H. azteca and T. tubifex (cocoons/adult and young/adult). Consequently, at the time of surveys before and after the TBT regulation there was potential for adverse effects of TBT in some sediments to some freshwater benthic species.