Transformation of endocrine disrupting compounds in estuarine sediments under dry-wet cycles: Shift in metabolic pathways driven by microbial salinity dependence

Salinity fluctuations and dry-wet cycles caused by seawater incursion can reshape microbial communities and influence the fate of endocrine disrupting compounds (EDCs) in estuarine sediments. In this study, controlled water-sediment microcosms were established to investigate how salinity gradients under dry-wet cycles affect the transformation of two typical EDCs (bisphenol A (BPA) and nonylphenol (NP)) in sediments. The results indicate that biodegradation is the predominant pathway in the transformation process of the above substances. Compared to continuously submerged sediments, dry-wet cycles significantly shortened the half-life of BPA and NP ( p < 0.05), increased microbial diversity, and enriched various BPA- and NP-degrading bacteria with salinity preference, including Stutzerimonas, Sphingomonas, and Pusillimonas . As salinity increased, the half-life of BPA continuously decreased, whereas that of NP first decreased and then increased. At moderate salinity (10‰), the microbial transformation of both BPA and NP was enhanced. However, at high salinity (20‰), NP degradation by Stutzerimonas via the long-chain alkylcatechol pathways was inhibited. In contrast, BPA transformation was further enhanced through potential cross-feeding among Pusillimonas, Sphingomonas , and Stutzerimonas . This was attributed to the BPA transformation pathway shifts from 4-carboxy-2-hydroxymuconate semialdehyde to β-carboxy-muconate-mediated route, thereby enhancing resistance to salinity stress. These findings provide new insights into the contamination and control of in-situ EDCs in estuarine environments under salinity stress.