Efficacy, microbial disruption, and algal toxicity of commercial antifouling coatings: A multi-level assessment

To mitigate marine biofouling, copper- and zinc-based antifouling (AF) paints are widely used, although their severe environmental toxicity is well established. Silicone-based fouling-release coatings (FRCs) have emerged as alternatives that prevent adhesion through surface properties rather than biocidal activity. However, their effectiveness and ecological impact across marine environments remain insufficiently assessed. This study compared the performance and environmental effects of five commercial coatings: two biocidal, two FRCs, and one inert coating. Panels were statically exposed for seven months at five European sites spanning salinity and temperature gradients. Fouling development was monitored monthly, and coating leachates were tested on red macroalgae and bacteria. Ecotoxicological assays included growth inhibition of Ceramium tenuicorne, Aliivibrio fischeri bioluminescence, Escherichia coli stress biosensors, quorum-sensing (QS) assays, and biofilm formation of marine bacteria. Field experiments showed that FRCs consistently outperformed copper-based coatings in efficacy toward biofouling, even under static conditions. Copper-based leachates were highly toxic to C. tenuicorne (EC₅₀ ≈ 0.46%), whereas FRC leachates showed minimal effects and were about 100 times less toxic. Microbial assays revealed that all coatings-including the biocide-free formulations-altered microbial physiology and behavior: leachates induced protein-damage responses, and both QS signaling and biofilm formation were species-specific, confirming that biocide-free does not mean biologically neutral. These results demonstrate that antifouling leachates act not only as toxicants but also as chemical cues shaping microbial communication and early colonization. Integrating microbial-level responses into antifouling evaluations is therefore essential. Overall, FRCs remain the most environmentally acceptable option, combining strong antifouling performance with minimal toxicity.