Comparative Toxicity of Perfluorooctanoic Acid (PFOA) and Perfluorobutanoic Acid (PFBA) Exposure in Two Microalgae Species

Widespread environmental contamination by per- and poly-fluoroalkyl substances (PFAS) has driven the phaseout of traditional long-chain compounds; however, the toxicity of their highly mobile, short-chain replacements to aquatic microorganisms remains less well characterized. This study compared the toxicity of perfluoroalkyl carboxylic acid (PFCA): long-chain perfluorooctanoic acid (PFOA, C8) and the short-chain perfluorobutanoic acid (PFBA, C4) in two structurally distinct microalgae, Prymnesium parvum and Chlorella sorokiniana. P. parvum was more sensitive to PFAS exposure than C. sorokiniana, with significant growth inhibition occurring at 25–50 mg/L and complete mortality at 100 mg/L, whereas C. sorokiniana exhibited significant effects at concentrations ≥200 mg/L. PFBA exhibited greater toxicity than PFOA in both species, with IC50 values of 25.81 and 64.30 mg/L, respectively, in P. parvum and 101.4 and 277.1 mg/L, respectively, in C. sorokiniana. PFBA induced reactive oxygen species (ROS) generation, lipid peroxidation, and significantly increased in cell volume and chlorophyll content in P. parvum, whereas C. sorokiniana exhibited oxidative responses primarily at higher concentrations and no significant changes in cell dimensions or chlorophyll content. The responses indicate that oxidative stress is an important component of PFCA toxicity and sensitivity differs substantially between microalgal species. The contrasting responses may be associated with differences in cellular structure and physiology, although the underlying mechanisms require further investigation. Overall, PFCA toxicity was both compound- and species-dependent, and the greater toxicity of PFBA under the tested conditions demonstrates that short-chain replacement PFCAs should not be assumed to have lower biological toxicity than their long-chain counterparts.