Toxicity of vessel antifouling coating lixiviates in target and non-target marine microalgal species: multi-taxa and biological multi-level approach testing

The development of a microfilm is one of the very first steps in the succession process, taking place on bare surfaces exposed to aquatic environments, where microalgae, especially diatoms, are among the early colonizers. To prevent or minimize this undesired growth in artificial structures antifouling (AF) measures are applied, coatings being the most common ones. This work studied the effects of two commercially available coatings, a traditional biocide-based one (BC) and an alternative foul-release (FR) one, from a multi-taxa and biological multilevel approach. Three microalgae species were selected, including pelagic non-target species and a benthic target diatom, and exposed for 72 h to AF lixiviates to measure various biological endpoints. Toxicity screening assays revealed that exposure to BC lixiviates inhibited growth in all test species and affected photosynthetic efficiency differently, the diatom being the most sensitive one, while FR lixiviate primarily induced subcellular responses, rather than major physiological impairments. Additionally, exposure altered total pigment content in the three tested algae, particularly under BC treatments. Subcellular responses demonstrated differences in biomarkers of oxidative stress (catalase and glutathione S-transferase activities and lipid peroxidation levels) in the microalgae between BC and FR treatments. Cellular metal sorption levels did not show clear differences across treatments nor species. Overall, exposure to BC and FR antifouling lixiviates directly affected both target and non-target microalgae species, although the type and magnitude of the responses varied according to species and treatments. Multi-taxa and multi-level approaches with microalgae provide a broad overview of the biological responses and serve as a valuable tool in aquatic toxicology.