Differential Metabolic, Behavioural, and Endocrine Effects of Bisphenol A and Emerging Bisphenol Substitutes in Daphnia magna

Bisphenol A (BPA) is one of the most extensively studied endocrine-disrupting chemicals, but its increasing replacement by alternative bisphenols has raised concerns about the safety of these substitutes. In the present study, we compared the effects of BPA, bisphenol F (BPF), bisphenol S (BPS), bisphenol Z (BPZ), bisphenol AP (BPAP), and bisphenol A diglycidyl ether (BADGE) in Daphnia magna, focusing on lipid storage, feeding activity, photomotor behaviour, and molecular biomarkers related to lipid metabolism and endocrine regulation. Feeding, behavioural, and gene transcription effects were assessed fo-llowing short term exposures of adolescent females for 1 day and lipid storage effects after exposures during an entire instar (3–4 days). The tested compounds produced distinct biological responses. BPA increased lipid storage accumulation, whereas exposure to BPF, BPS, BPZ, BPAP, and BADGE generally resulted in reduced lipid storage reserves. Several compounds also decreased feeding activity, suggesting that altered energy intake may contribute to the observed changes in lipid storage. Behavioural analyses revealed signi-ficant effects on photomotor responses, particularly after exposure to BPA, BPF, BPS, and BADGE. At the molecular level, bisphenol exposure modified the expression of genes involved in lipid metabolism, lipid transport, and endocrine-related pathways. BPA induced the expression of genes associated with lipid synthesis and storage, while compounds causing lipid storage depletion more frequently affected genes involved in lipid mobilisation and fatty acid metabolism. Marked effects were also observed for endocrine biomarkers. BADGE increased the expression of Neverland, a key gene in ecdysteroid biosynthesis, while reducing the expression of the juvenoid-responsive gene hb2 and vitellogenin. In contrast, BPF significantly increased hb2 transcription. Correlation analyses further supported links between metabolic, behavioural, and endocrine responses. Overall, the results show that bisphenol analogues differ substantially in their mode of action and biological effects. While BPA displayed clear obesogenic properties, most replacement bisphenols reduced lipid storage and altered endocrine-regulated pathways. These findings indicate that BPA substitutes cannot be assumed to represent safer alternatives and highlight the need for a broader evaluation of their ecological impacts in aquatic organisms.