Exploring Per- and Polyfluoroalkyl Substances (PFAS) in Microestuaries: Occurrence, Distribution, and Risks

Microestuaries have a crucial role in supporting biodiversity and human life quality in heavily populated areas. They are also the last barrier controlling fluxes of pollutants from the land to sea. Here, we report the occurrence and distribution of per- and polyfluoroalkyl substances (PFAS) during the dry season in three microestuaries. The total PFAS concentration (n = 12) at the studied estuaries was very high from a global perspective with maximum and median concentrations of 17.4 and 3.4 μg L^-1, respectively. These concentrations significantly exceed the recommended benchmarks for recreational activity. Our analysis reveals that a major fraction of PFAS originated from wastewater effluents, whereas point source pollution dominated when the estuary met an industrial zone containing refinery facilities. In the case of limited dilution by natural riverine water, we suggest using carbamazepine as a steady indicator for the identification of PFAS originating from wastewater. Although the three studied microestuaries exhibit similar characteristics (morphology, precipitation, watershed size, water volume, etc.), changes in water input and connectivity to the sea, along with local anthropogenic activity, dramatically alter the occurrence, concentrations, and distribution of PFAS. This study suggests that microestuaries are subjected to high ecological risk from PFAS pollution due to intensive anthropogenic activity.