Acute Toxicity of Seven Perfluoroalkyl Substances (PFAS) in Daphnia magna and Raphidocelis subcapitata

Among environmental pollutants of emerging concern, perfluoroalkyl substances (PFASs) are one of the classes of compounds most in the spotlight. Currently, there are few or as yet unknown effects that PFAS emissions may cause on aquatic ecosystems. Among the thousands of known PFASs, this research project evaluated the toxicity of several compounds that are normally found in the environment. Some of them are well-known compounds, such as PFOA and PFNA, while others are considered to be replacement compounds for new-generation PFASs, such as PFHpA, PFHxA, PFBA, PFBS, and GenX. As the Environmental Protection Agency is constantly seeking updated toxicological data to assess the toxicological framework of PFASs, this study provides toxicity data on two aquatic trophic levels. PFAS toxicity was evaluated on Daphnia magna according to the OECD 202 test and on Raphidocelis subcapitata according to the US-EPA OCSPP 850.4500: Algal Toxicity test. Among the two species, it was generally observed that algae are more sensitive to PFAS than daphnia. In fact, the EC50 value for the compound under analysis was lower for algae (EC50 mg/L: PFNA, 90.5; PFOA, 45.54; PFHpA, 385.98; PFHxA, 957.42; PFBA, 30.03; PFBS, 105.8; GenX, 738.0) than the Daphnids (EC50 mg/L: PFNA, 187.5; PFOA, 705.9; PFHpA, >1000; PFHxA, >1000; PFBA, >1000; PFBS, >1000; GenX, 785.7). These data suggest that the alga Raphidocelis subcapitata is more sensitive to these molecules than Daphnia magna. As noted by previous research, PFASs can impair the photosynthetic system, causing downstream alteration of cell duplication and inhibition of algal growth. Since it appears that Daphnia is not the most sensitive organism to these molecules in acute exposure, this does not mean that these compounds cannot cause reproductive and growth damage in chronic exposure. In fact, it has been observed that following the organisms for another ten days after acute exposure the toxicity is more severe than that observed at 48 h of exposure, confirming the delayed toxicity. These data will be crucial to better understand the real impact of these molecules on the environment. In addition, they will be useful in laying the groundwork for further research on the chronic toxicity of PFASs and their possible interaction in mixtures.