Seasonal distribution and ecological risk of bisphenols in the Indo-Pacific humpback dolphin habitats from the Northern South China Sea

High levels of bisphenols (BPs) have been identified in the vulnerable Indo-Pacific humpback dolphin (Sousa chinensis), yet the ecological risks associated with these compounds in dolphin habitats remain poorly understood. This study investigates the seasonal distribution characteristics of six BPs in seawater from the Pearl River Estuary of the Northern South China Sea during wet and dry seasons. Our results reveal a significant increase in BP concentrations compared to historical data, with a notable decline in bisphenol A (BPA) proportions and a corresponding rise in bisphenol S levels. BP concentrations were higher during the wet season than in the dry season. Furthermore, BPA, bisphenol B, bisphenol AF, and bisphenol P demonstrated strong bioconcentration potential within marine food webs. Environmental factors significantly influence the presence of BPs in dolphin habitats. The frontal processes may indirectly modulate the distribution and apparent bioavailability of BPs by altering environmental fields such as salinity, chlorophyll a. Elevated BP levels pose substantial risks to ecosystem health, particularly due to their toxicity to marine invertebrates and humpback dolphin calves. These findings deepen our understanding of the ecological risks of BPs on coastal ocean ecosystem, while also highlighting the ongoing threat that BPA alternatives pose to the conservation of cetaceans.