Reproductive Risk Assessment of Bisphenol A and Its Substitutes on Estrogen Receptors (ERs) in Bivalves

As benthic filter feeders, bivalve mollusks serve as ideal biological indicators. Bisphenol A (BPA) and its substitutes (BPS, BPF, and BPAF) are endocrine disruptors with reproductive toxicity, targeting estrogen receptors (ERs). However, their binding sites and affinity for shellfish ERs remain unclear. This study aims to identify ER binding sites of BPA and its substitutes, compare toxicity via molecular docking, and validate results through exposure experiments. The full-length cDNA of <i>Corbicula fluminea</i> ER was cloned using the RACE technique for the first time, the sequence length is 2138bp. Homologous models of LBD sequences from <i>Danio rerio</i>, <i>C. fluminea</i>, <i>Azumapecten farreri</i>, and <i>Ruditapes philippinarum</i> ERs were constructed via homology modeling and screened for optimal fit. Hydrogen bonds were observed during the docking process, with interaction sites including Glu-66, Arg-177, and other amino acid residues. Exposure experiments (1, 10, and 100 μg/L) showed an enhancement in ER mRNA expression. Based on the docking energies and results of the exposure experiments, it was concluded that the toxicity of BPA and BPS is similar and greater than that of BPF and BPAF. This study provides data for a reproductive risk assessment and aquatic toxicological monitoring of bisphenols.