The present assay system using fresh cells of V. fischeri proves to be enough sensitive and reliable to evaluate the toxicities of antifouling chemicals, irrespective of whether they are present as single or mixed form. The results obtained by the present system show that the toxicities of these antifoulants markedly increase on combination when compared with their toxicity as single agents. On the whole, most of the EC50 values obtained for single chemicals were reduced to one-half to one-fifth on mixing with other chemicals, suggesting that toxicity enhancement has occurred. Remarkable synergetic effect was observed in the mixtures containing CuSO4 from the analyses ofboth EC50 and MTI values. The mechanism of toxicity enhancement by Cu2+ in the mixture might be attributed to the formation of lipophilic complex with organic molecules, which easily enter into the cell cytoplasm and function negatively for cellular activities.
According to the present data, the antifouling chemicals examined have a more serious impact on both environments and organisms than previously recognized. In particular, we have to keep in mind the marked stimulation of toxicity when organic chemicals or ions are mixed, as seen in natural environment. Thus, related studies of toxicity enhancement by various combinations of chemicals as well as their detailed mechanisms of actions are needed for a complete understanding of the environmental effects of these chemicals.
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