Toxicity assessment of exposure to four short- and ultra-short PFAS using <i>Daphnia magna</i> and <i>Hydra vulgaris</i> as models

Short- and ultra-short per- and polyfluoroalkyl substances (PFAS) such as perfluorobutanoic acid (PFBA, 4C), perfluorobutane sulfonic acid (PFBS, 4C), trifluoroacetic acid (TFA, 2C) and trifluoromethane sulfonic acid (TFMS, 1C) were detected in various environmental matrices, but studies addressing the effects attributed to exposure are still scarce. This study aimed to (1) investigate acute toxicity of these emerging PFAS using <i>Daphnia magna</i> (immobility, mortality, reproduction, and body size) and <i>Hydra vulgaris</i> (morphological changes and reproduction) and (2) assess the sub-chronic/chronic toxicity of TFA in both species. Glutathione S-transferase (GST) activity was also assessed in both species after long-term exposure to TFA. Chemical analysis confirmed presence and stability of the 4 PFAS in exposure media. For all tested PFAS, endpoints examined after acute tests were not markedly affected by exposure and LC₅₀ values were > 1000 mg/L. However, this toxicity was significantly affected by media acidification induced by the tested chemicals (LC₅₀ = 316 and 31,6 mg/L for <i>D. magna</i> and <i>H. vulgaris</i>, respectively). Long-term exposure to TFA did not significantly induce any effect on both species and GST levels were not altered. Overall, results suggest lower toxicity of ultra/short-chain PFAS to these species under selected exposure conditions. However, additional studies investigating multigenerational effects of these PFAS using realistic environmental concentrations are needed to overcome the significant gaps in our understanding of short/ultra-short PFAS-induced toxicity.