Antifouling biocide accumulation is a significant problem in aquatic environments. Most research focuses on biocides' individual toxicity; however, because biocides are mixed in water, toxic interactions may intensify their harmful effects. Therefore, this study investigated the cellular (EPC cell line) toxicity of three common anti-fouling biocides, individually and in combination. 24-hour and 96-hour IC50 levels of the biocides were 1.11-1.03 mg L-1 (DCOIT), 7.31-11.94 mg L-1 (dichlofluanid), and 54.98-78.06 mg L-1 (zineb). DCOIT + dichlofluanid combination was synergic, whereas other combinations were antagonists. Environmentally rele-vant levels of combinations were also tested, and only DCOIT + dichlofluanid combination affected cell pro-liferation rates at 96 h (p = 0.035) compared to the untreated control. We concluded that biocides might interact synergically, thus enhancing their adverse impacts, and constant exposure to the biocides at environmentally relevant concentrations may be deleterious to aquatic species.