Organophosphate flame retardants and their metabolites in the Pearl River Estuary: Occurrence, influencing factors, and ecological risk control strategies based on a mass balance model

[Display omitted] •OPFRs and their metabolites exhibited seasonal variation in seawater rather than in sediments in the PRE.•In comparison to vertical migration, horizontal migration accounted for the majority of OPFR transport.•The majority of the riverine-input OPFRs in the PRE have transitioned to the open sea.•Multi-scenario control strategies for the ecological risk of EHDPHP have been proposed. Estuaries serve as crucial filters for land-based pollutants to the open sea, but there is a lack of information on the migration and fate of organophosphate flame retardants (OPFRs) within estuaries. This study focused on the Pearl River Estuary (PRE) by examining the co-occurrence of OPFRs and their metabolites and quantifying their transport fluxes using a mass balance model. The seawater concentrations of OPFRs and their metabolites exhibited significant seasonal variations (p