Fate of per-and polyfluoroalkyl substances (PFAS) in a mega-city wastewater treatment network: The ‘Precursor Paradox’in transitioning to 100% water reclamation
By Francesca Nyega Otim and Ochan Otim
Sci Total Environ
June 16, 2026
DOI: 10.1016/j.scitotenv.2026.181939
As municipalities strive to replace potable water with recycled sources in their effort to transition toward 100% wastewater recycling, understanding exposure to contaminants that wastewater treatment plants (WWTPs) were not designed to remove is important for environmental and public health. Per- and polyfluoroalkyl substances (PFAS) are such contaminants. They are man-made chemicals that persist in the environment and are known to bioaccumulate in living tissues with adverse effects. In this context, the occurrence of 31 PFAS in the sprawling network of four municipal WWTPs serving 4 million people in Los Angeles (USA) is examined comprehensively in this study. With 3252 pieces of data collected over four calendar quarters, results show that the network, on average, receives 202 g and discharges 107 g of PFAS on a daily basis. In terms of species however, the network releases more PFAS than it receives, suggesting that influents from the WWTPs contain unidentified PFAS precursor. Reverse osmosis filtration (RO), used in the production of recycled water, is able to remove 99% of the 31 PFAS from treated wastewater. While that is laudable, RO concentrates PFAS in brine, up to 40-fold at a time when no safe disposal method exists for the PFAS-laden brine. Managing this concentrate is therefore key in protecting exposure level and water quality. More work is needed to identify the presumed PFAS precursors in influent to prevent unintened introduction of PFAS into the environment via the water reclamation processes. And while the data used here is centered on Los Angeles, the implications are universal.
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