Exploring the variability of PFAS in urban sewage: a comparison of emissions in commercial versus municipal urban areas†

Per- and polyfluoroalkyl substances (PFAS) are recognized for their persistence and ubiquitous occurrence in different environmental compartments. Conventional wastewater treatment plants (WWTPs) cannot effectively remove PFAS from wastewater, and a better understanding of the occurrence and sources of PFAS in this medium would enable effective source abatement. We compared sewage from urban areas exhibiting differentiating characteristics with respect to activities in their catchments. These included a sewer that serves primarily a municipal area, with no commercial activities involving PFAS emissions being identified, another sewer with a strong influence of commercial activities potentially related to PFAS emissions, and the influent of the whole city sewage network. The year-long monitoring campaign consisted of flow-proportional, monthly composite samples and targeted analysis of 29 PFAS compounds. Principal component analysis was used to investigate the relationships between selected PFAS and standard water quality parameters such as ammonium, a known tracer of urine and thus of typical municipal wastewater. Notable findings were seen for PFOS and 6:2 FTS, whose concentrations were most negatively correlated with ammonium. Ammonium concentration data allowed for a normalized per-person median load calculation, which resulted in loads of the observed PFAS ranging from below 0.4 up to 4.7 μg per person per day. Both the commercial area sewer and the city influent exhibited significantly higher (p < 0.05) median loads (>0.9 μg per person per day) in the case of 6:2 FTS and PFOS, compared to the municipal sewer (<0.6 μg per person per day). No statistically significant difference was found for other compounds, such as PFBA, PFHxA, PFOA, and PFHxS. We argue that this approach demonstrates that PFAS can differ in speciation and quantity within an urban wastewater setting, and consideration of both municipal and commercial activities is needed for a proper understanding of sources and emission pathways within the urban environment.