Biouptake, toxicity and biotransformation of triclosan in diatom Cymbella sp. and the influence of humic acid

Triclosan is one of the most frequently detected emerging contaminants in aquatic environment. In this study, we investigated the biouptake, toxicity and biotransformation of triclosan in freshwater algae Cymbella sp. The influence of humic acid , as a representative of dissolved organic matter , was also explored. Results from this study showed that triclosan was toxic to Cymbella sp. with 72 h EC 50 of 324.9 μg L −1 . Humic acid significantly reduced the toxicity and accumulation of triclosan in Cymbella sp. SEM analysis showed that Cymbella sp. were enormously damaged under 1 mg L −1 triclosan exposure and repaired after the addition of 20 mg L −1 humic acid. Triclosan can be significantly taken up by Cymbella sp. The toxicity of triclosan is related to bioaccumulated triclosan as the algal cell numbers decreased when intracellular triclosan increased. A total of 11 metabolites were identified in diatom cells and degradation pathways are proposed. Hydroxylation, methylation , dechlorination , amino acids conjunction and glucuronidation contributed to the transformative reactions of triclosan in Cymbella sp., producing biologically active products (e.g., methyl triclosan) and conjugation products (e.g., glucuronide or oxaloacetic acid conjugated triclosan), which may be included in the detoxification mechanism of triclosan.