Tributyltin(TBT)has been widely used as antifouling paint for vessels and,as a result,has been released into aquatic environment since the 1960s. Although the use of TBT paints has been banned recently,significant quantities of TBT and its metabolites are still detectable in many regions. They can exist for long periods in aquatic organisms and sediments. It is widely acknowledged that triorganotins,especially TBT compounds,are among the most toxic substances ever introduced deliberately into the marine environment. The toxic effects of TBT have been documented in several experimental systems,however, due to its adverse impacts on the ecosystems,the development of sensitive bioassay systems with multi-endpoints are essential for risk assessment and mechanism study.
Toxicity bioassay techniques,as a powerful approach for environmental assessment and toxicity testing,has become a fundamental tool to evaluate the early warnings of potential environmental pollutants that are hazardous to the health of humans and wild animals. However,the organism should meet several criteria before it is selected as a bioindicator. It should have endpoints sensitive to the tested pollutants,can operate rapidly and easily,can allow the testing of a large number of samples in a small volume, and is inexpensive. The free living nematode Caenorhabditis elegans has been proved to be a good model for the evaluation of toxicological effects of environmental chemicals or toxins,the results are comparable to that of mammalians. In the present study,the nematode C. elegans was employed to investigate the toxicity of TBT. To determine the acute toxic effects of TBT to C. elegans,a range of worm strains were exposed to graded doses of TBT for 48 h. The median lethal concentrations(LC₅₀)were estimated in these strains with different genes knocked out. To screen the sensitive sublethal endpoints for the risk assessment of TBT to the environment, the body size,fecundity and brood size were assayed in the wild type N2. The results presented here implicated that the nematode C. elegans could be used as substitutive model in evaluation the toxic effects of TBT in the environment. The 48 h LC₅₀ observed on the wild type and mutant strains for TBT were in the order of egl-1(n487)＜ced-4(n1162)＜cep-1(gk138)=cep-1(lg12501)＜ced-9(n1950)＜clk-2(mn159)＜ced-3(n717)＜N2＜opIs34(hus-1::GFP) ＜opIs56(egl-1::GFP)＜daf-16(mn86)＜hus-1(op241)＜daf-2(e1370). The results of LC₅₀ suggested that the strains carrying the mutant genes daf-2, hus-1 and daf-16 are less sensitive than that of N2,respectively. Conversely,egl-1,ced-4,cep-1,ced-9 and clk-2 loss-of-function strains exhibited more sensitive to TBT exposure than that of N2,implying that these genes may contribute to the protection effects from TBT toxicity in C. elegans. Therefore,egl-1(n487)is one of the most sensitive strains to TBT stress,while long-lived daf-2(e1370)is one of the most tolerant strains to TBT stress. In our study,the body length of C. elegans was inhibited as low as 10 nmol/L TBT. The fecundity decreased significantly at the dose exceeding 50 nmol/L,similar effects were observed for brood size. Our present results indicated that LC₅₀ of the mutated strain egl-1(n487),the body length,brood size and fecundity of C. elegans are the sensitive endpoints to indicate TBT contamination in aquatic environments.