Emerging investigator series: identification and transformation of per/polyfluoroalkyl substances (PFASs) in residential wastewater and effluent from alternative treatment systems

Onsite wastewater treatment systems (OWTSs) are designed for the removal of pathogens and nutrients from septic effluent. However, many other contaminants are widespread in wastewater including pharmaceuticals, personal care products, and other trace organic chemicals. We analyzed per/polyfluoroalkyl substances (PFASs) in residential septic effluent and investigated their fate in nitrogen-removing biofilters (NRBs), an innovative and alternative type of OWTS. We measured concentrations of 22 targeted PFASs in septic effluent pre- and post-NRB treatment in nine residential OWTSs. We measured total PFAS in septic effluent ranging from 42 to 9795 ng L⁻¹ and in NRB effluent ranging from 72 to 2575 ng L⁻¹, corresponding to estimated effluent loads of 39 to 1423 mg PFASs per household per year. Perfluoroalkyl carboxylates (PFCAs) were generally enriched in NRB effluent versus influent while perfluoroalkyl sulfonates appeared to be partially removed during NRB treatment. Grab sampling results were highly variable but passive sampling (microporous polyethylene tubing containing WAX sorbent) consistently showed greater PFAS levels post-NRB treatment. High-resolution mass spectrometry screening of composited grab samples using two different workflows (suspect screening and untargeted analysis with ion mobility spectrometry) resulted in tentative identifications of 40 additional PFASs not included on the target list. The average mass defect of features identified as potential PFASs was significantly lower (p = 0.014) in post-NRB samples. This, along with increasing concentrations of PFCAs in effluent, suggested transformation of precursors to end products with greater fluorinated character in the NRB.