Chronic toxicity of triazine-based and non-triazine ultraviolet filters toward Chlorella vulgaris: Low ecological risk of triazine-based compounds.

Low-dose chronic toxicity can induce sublethal biological effects, which is of great significance for assessing the ecological toxicity of UV filters. In this study, we investigated the chronic toxicity of three triazine-based UV filters including bis-ethylhexyloxyphenol methoxyphenyl triazine (BEMT), diethylhexyl butamido triazone (DBT), and ethylhexyl triazone (EHT) and three non-triazine UV filters: diethylamino hydroxybenzoyl hexyl benzoate (DHHB), avobenzone (AVB), and octocrylene (OCR) on Chlorella vulgaris. Results indicated that the triazine-based UV filters exerted no statistically significant effects (p > 0.05) on Chlorella vulgaris cell growth, photosynthetic pigment-contents, superoxide dismutase (SOD) and catalase (CAT) activities, or malondialdehyde (MDA) content throughout the entire exposure period (p > 0.05). Consequently, these compounds triggered no discernible antioxidant response in Chlorella vulgaris, implying that the exposure regimes were inadequate to induce measurable physiological alterations. By contrast, the three non-triazine UV filters exhibited markedly different chronic toxic effects (p < 0.05). The Chlorella vulgaris in the AVB treatment group exhibited a dynamic toxicity profile and induced reversible, adaptive oxidative stress. DHHB displayed sustained growth inhibition throughout the exposure period and primarily impairs Chlorella vulgaris growth via direct phototoxicity targeting the photosynthetic apparatus. While OCR manifested delayed toxicity, driven by irreversible, intense oxidative damage. Further investigations revealed that triazine-based UV filters could be efficiently biodegraded by Chlorella vulgaris, with removal efficiencies reaching 85 %. Collectively, these results demonstrate that triazine-based UV filters possess greater ecological safety than non-triazine counterparts. This study thus provides critical foundational data for the ecological risk assessment of emerging triazine-based UV filters.