Antagonistic and Synergistic Effects of Antifouling Chemicals in Mixture

Abstract

Toxicity of mixed chemicals is not always equal to the sum of those by the individual chemicals. In this article, the authors have evaluated the toxicities of typical antifouling chemicals present as a single form or in combination and showed some examples to demonstrate the interaction effects between different toxicants. In terms of bioluminescent assay using fresh cells of Vibrio fischeri DSM 7151, the EC50 values of single antifoulants such as tributyltin chloride (TBT-Cl), zinc 2-pyridinethiol 1-oxide (Zn-pt), copper 2-pyridinethiol 1-oxide (Cu-pt), zinc bis(N,N′-dimethyl)dithiocarbamate (Ziram), copper sulfate (CuSO4), 4,5-dichloro-2-(n-octyl)-3(2H)-isothiazolone (SEA-NINE 211), triphenylborane pyridine (TPBP), 3-iodo-2-propynyl butylcarbamate (IPBC), 3-(3,4-dichlorophenyl)-1,1-dimethylurea (Diuron), N-dichlorofluoromethylthio-N′,N′-dimethyl-N-phenylsulfamide (DCF), and 2-methylthio-4-tert-butylamino-6-cyclopropylamino-s-triazine (Irgarol 1051) were determined to be 0.02, 0.08, 0.12, 0.22, 0.31, 0.35, 0.75, 8.49, 12.74, 39.02, and >40 mg l−1 at 30 min of incubations, respectively. Then, 45 different combinations composed of two antifoulants each were evaluated. From the analyses of EC50 values, typical patterns of interaction for the combinations were classified into three groups – antagonistic, synergistic, and additive effects – based on the inhibition difference between single chemicals and their mixtures. Mixture toxicity indices (MTIs) were also introduced to evaluate the interaction effect of each combination. The results showed that the partial additivity was observed for most of the combinations examined, and there was no antagonistic effect among the present combinations of chemicals. Additive effects were observed in the cases of Diuron, TPBP, and SEA-NINE 211 when they were mixed with IPBC. Marked synergistic effects were recognized for Irgarol 1051, Ziram, Zn-pt, and Cu-pt when CuSO4 coexisted, from which the authors concluded that Cu2+ makes these chemicals more toxic against various types of organisms in the aquatic environments.