Toxicological impact assessment of the marine diatoms Skeletonema costatum and Navicula sp., using the anti-fouling agents CuSO4, DCOIT, and ECONEA.

Antifouling paints containing various chemical antifoulants are applied to prevent the attachment of marine organisms on submerged structures. However, these compounds can be released into the marine environment and adversely affect non-target marine species. This study compared the toxic effects of copper sulfate (CuSO₄), 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT), and ECONEA alone and in combination on the periphytic diatom Navicula sp. and the planktonic diatom Skeletonema costatum. The 72 h EC50 values revealed a toxicity order of DCOIT>ECONEA>CuSO4. For Navicula sp., EC50 values were 31.23 μg L-1 (DCOIT), 91.29 μg L-1 (ECONEA), and 793.80 μg L-1 (CuSO4), while S. costatum exhibited values of 15.50 μg L-1 (DCOIT), 49.01 μg L-1 (ECONEA), and 1524.01 μg L-1 (CuSO4), respectively, indicating that Navicula sp. generally showed lower sensitivity than S. costatum. Combined exposure to CuSO₄ and the two booster biocides at effective concentration (EC) levels of EC₁₀, EC₂₀, and EC₅₀ produced mixture effects that exceeded the additive toxicity predicted by both the concentration addition (CA) and independent action (IA) models, demonstrating non-additive interactions with stronger inhibitory effects than those observed under individual exposures. Analysis of oxidative stress revealed that reactive oxygen species' levels increased proportionally with antifoulant concentration. Although numerous studies have investigated antifoulant toxicity, research focusing on the toxicity of mixtures and in periphytic diatoms remains limited. The findings highlight the necessity of incorporating periphytic diatoms and complex exposure conditions into future ecotoxicological assessments to improve the accuracy of environmental risk evaluations for antifouling agents.