Abstract

Given the apprehensions regarding the potential hazards posed by perfluorooctanoic acid (PFOA), industrial substitutes hexafluoropropylene oxide dimer acid (HFPO-DA) and trimer acid (HFPO-TA) have been increasingly used and frequently detected in the environment. However, a systematic comparative assessment of their toxicities, particularly in aquatic invertebrates, is still lacking. Therefore, acute and chronic toxic effects of HFPO-DA and HFPO-TA were assessed and compared in terms of survival, development, reproduction and antioxidant defense in Daphnia magna . The results indicated that HFPO-TA exhibited markedly higher acute toxicity compared to HFPO-DA. For individual development, HFPO-DA significantly increased heart rate, while both HFPOs elevated molting times. Regarding reproductive toxicity, HFPO-DA treatment initially promoted the reproductive process but subsequently turned to suppress it, while low-to-medium concentrations of HFPO-TA significantly inhibited reproduction, though high concentrations showed no significant differences in reproductive indices compared to controls. The alterations in hormone levels and gene expression profiles, combined with molecular docking predictions which suggested potential interactions with ecdysone receptor (EcR)/Ultraspiracle (USP) and vitellogenin (VTG) provides supportive evidence for their distinct toxicological profiles in D. magna . Both HFPOs were found to induce oxidative damage, with the IBRv2 index demonstrating that HFPO-TA caused more significant disturbances to the antioxidant defense system. Based on principal component analysis (PCA), it is speculated that HFPO-DA induced energy conservation for survival, whereas HFPO-TA may promote terminal reproductive investment under chronic stress. Collectively, these findings suggest that HFPO-DA and HFPO-TA may not be safe substitutes for PFOA, and HFPO-TA poses greater ecological risks to aquatic ecosystems.