Single-species tests fall short: broadening toxicity assessments of organic UV filters on marine microalgae

Sunscreen products, essential for photoprotection, introduce organic UV filters into aquatic environments, raising concerns about their ecotoxicological impacts. This study evaluates the sensitivity of seven marine microalgae species spanning diverse taxonomic groups to six organic UV filters (benzophenone-3, butyl methoxydibenzoylmethane, ethylhexyl triazone, homosalate, 2-ethylhexyl salicylate, and octocrylene). Growth rate and chlorophyll a fluorescence were analyzed after 72 hr exposures at concentrations of 10, 100, and 1,000 µg/L. Growth rate was revealed to be the most sensitive indicator, with significant interspecies variability in response to UV filters. Results revealed that Tisochrysis lutea exhibited better sensitivity than the commonly used Phaeodactylum tricornutum, which demonstrated low sensitivity across endpoints. Among UV filters, 2-ethylhexyl salicylate and homosalate were the most toxic, significantly affecting growth and fluorescence in multiple species. Interestingly, growth inhibition often coincided with increased fluorescence, suggesting species-specific compensatory mechanisms. These findings underscore the limitations of relying solely on P. tricornutum in standardized toxicity tests and advocate for the inclusion of sensitive species to improve ecological relevance. Integrating growth and fluorescence metrics in high-throughput assays could advance risk assessment methodologies for emerging contaminants like UV filters.