Evaluating macrophyte extracts as eco-friendly antifouling additives for freshwater made-man structures: a field...

Biofouling on artificial aquatic surfaces yields substantial economic losses and operational challenges. Traditional antifouling strategies often rely on synthetic chemical coatings, which have harmful environmental impacts, thus environmentally sustainable solutions, such as natural antifouling compounds are increasingly being sought. Extracts derived from the aquatic macrophytes Pontederia crassipes and Typha domingensis have demonstrated potential antifouling properties in preliminary studies; however, their efficacy under natural field conditions remains unverified. This study is the first to evaluate the antifouling potential of these macrophyte extracts when incorporated with epoxy coatings in a natural freshwater environment (Salto Grande Reservoir, Uruguay River). Stainless steel substrates were treated with 2.5, 5, and 10 g L^-1 of lyophilized macrophyte extracts combined with epoxy and compared to uncoated and epoxy-coated controls. Over a 165-h period, biofouling was assessed via chlorophyll levels, bacterial counts, macro-organism presence and attachment and taxonomic diversity. Analytical techniques, including gas and liquid chromatography, along with Fourier transform infrared spectroscopy, were employed to identify active compounds in extracts. The P. crassipes extract at 5 and 10 g L^-1 exhibited superior antifouling efficacy compared to T. domingensis. Coatings with P. crassipes significantly reduced bacterial colonization (37 %), algae growth (for different photosynthetic pigments), fungal presence, and macro-organism attachment (not found), while promoting the occurrence of opportunistic taxa less conducive to fouling. The observed antifouling activity may be attributed to specific chemical compounds, including long-chain hydrocarbons and phenolic derivatives, identified in the extracts. The study findings demonstrate the field antifouling efficacy of macrophyte extracts incorporated with epoxy coatings, highlighting P. crassipes as a particularly promising, sustainable antifouling candidate. Its high biomass availability and ease of cultivation enhance its potential for industrial-scale development as natural antifouling agents. This work provides critical insights into developing eco-friendly antifouling coatings that minimize environmental impact while maintaining efficacy in biofouling control being the first study to prove in a natural environment the antifouling potential of these macrophytes.