Algal communities mediate hydroxylated polybrominated diphenyl ethers formation in mangrove surface sediments

Bromophenols (BPs) are critical precursors in the biosynthesis of hydroxylated polybrominated diphenyl ethers (OH-PBDEs) by marine algae. However, the roles of algal communities in the environmental occurrence of BPs and OH-PBDEs, as well as their interactions with these compounds, remain poorly understood. This study investigated the distribution patterns, algal community associations, and ecological risks of BPs and OH-PBDEs in the surface sediments from Xiwan mangrove wetland. Five target compounds were detected, including 4-bromophenol (4-BP), 2,4-dibromophenol (2,4-DBP), 2,4,6-tribromophenol (2,4,6-TBP), 2'-hydroxy-2,3',4,5'-tetrabromodiphenyl ether (2'-OH-BDE-68), and 6-hydroxy-2,2',4,4'- tetrabromodiphenyl ether (6-OH-BDE-47). BPs constituted over 90 % of total quantified compounds. Total BPs concentrations were significantly higher in winter (14.04 - 35.99 ng g^-1 dw) than in summer (6.99 - 16.01 ng g^-1 dw). Conversely, OH-PBDEs exhibited higher concentrations in summer (22.97 - 48.24 pg g^-1 dw). Furthermore, the greater algal diversity in summer correlated with the variations in BPs and OH-PBDEs concentrations observed between these two seasons. Chlorophyta and Bacillariophyta were the predominant algal groups in the surface sediments, and their distributions showed significant associations with the concentrations of both BPs and OH-PBDEs throughout the mangrove ecosystem. Ecological risk assessment identified invertebrates as the most sensitive trophic level. Furthermore, the risks posed by detected BPs were low. These findings highlight the algal-mediated biotransformation processes and potential ecological risks associated with BPs and OH-PBDEs in vulnerable mangrove ecosystems.