Toxicity evaluation of single and mixed antifouling biocides using the Strongylocentrotus intermedius sea urchin embryo test.

The present study evaluated the single and mixed toxicities of commonly used antifouling biocides (copper pyrithione, Sea nine 211, dichlofluanid, tolylfluanid, and Irgarol 1051) on the early embryogenesis of sea urchin Strongylocentrotus intermedius. Their toxicities were quantified in terms of the median effective concentration (EC50) reducing the embryogenesis success by 50%. For individual biocides to the embryos, the toxicity was in order of copper pyrithione>Sea nine 211> tolylfluanid>dichlofluanid>Irgarol 1051. The toxicities of mixture (binary, ternary, quaternary, and quinary) of compounds, evaluated by toxic unit, additivity index, and mixture toxicity index, showed that the copper pyrithione-Sea nine 211 combination was the most toxic with the EC50 value of 7.87 nM in all mixtures. Synergistic enhancements of toxicity were observed for all mixtures except the combination of tolylfluanid-Sea nine 211, revealing antagonistic effect. Both the concentration addition and independent action concepts failed to accurately predict the mixture toxicities of the antifouling combinations; thus, a new log K(OW)-based model was developed to predict the combined toxicities of these antifouling chemicals, which were capable of predicting the mixture toxicities of antifouling biocides (R(2)=0.33).