PFAS screening in municipal wastewater effluents and mixed liquor – using TOP assay as a sum parameter

Wastewater treatment plants (WWTPs) are a point source for the release of per- and polyfluorinated alkyl substances (PFAS) into the environment. In our study we investigated wastewater effluent and mixed liquor samples for PFAS in order to obtain information on the current PFAS contamination in municipal WWTPs in Bavaria, Germany. In addition to PFAS target analysis, the total oxidizable precursor (TOP) assay was used as a PFAS sum parameter to obtain information on the precursor concentration in the samples. The sewersheds of the investigated wastewater treatment plants were characterized according to the industrial sectors that discharge into the public sewer system using the Statistical Classification of Economic Activities in the European Community (NACE) code. Known PFAS were detected in all effluent samples, except one, and in concentrations up to 4.700 ng L^-1. The concentrations in effluent samples varied widely between the different sampling dates at the individual WWTPs and also between the different WWTPs. The PFAS concentration in the effluent of 65 % of the WWTPs investigated increased significantly by a factor of 2.9 on average after the TOP assay. In the mixed liquor samples, the PFAS concentration ranged between 56 and 440 μg kg^-1 dw. The concentration varied less than in the effluent samples. After the TOP assay the PFAS concentration in the mixed liquor samples increased on average by a factor of 4. The NACE codes alone cannot be used to determine whether low or high PFAS concentrations are to be expected in a municipal WWTP. However, they can provide an indication of PFAS dischargers and help to prioritize further investigations. Without the TOP assay, the PFAS concentration in the effluent and the mixed liquor samples is clearly underestimated. Our investigations identified hotspots with very high PFAS concentrations in the WWTP effluents. Measures must be taken at the sources to prevent the further release of PFAS into the environment via municipal WWTPs.