Occurrence and point source characterization of perfluoroalkyl acids in sewage sludge

• High spatial and temporal variability of PFAA concentrations among different WWTPs.
• Metal plating, aqueous firefighting foams (AFFF), and landfill leachates are significant point sources for PFSAs.
• Carpet and textile protection are most relevant for the emissions for PFCAs.
• Temporal trends between 2008 and 2011 show a decrease of PFOS levels.

The occurrence and levels of perfluoroalkyl acids (PFAAs) emitted from specific pollution sources into the aquatic environment in Switzerland were studied using digested sewage sludges from 45 wastewater treatment plants in catchments containing a wide range of potential industrial emitters. Concentrations of individual PFAAs show a high spatial and temporal variability, which infers different contributions from industrial technologies and activities. Perfluorooctane sulfonic acid (PFOS) was generally the predominant PFAA with concentrations varying between 4 and 2440 μg kg−1 (median 75 μg kg−1). Elevated emissions were especially observed in catchments capturing discharges from metal plating industries (median 82 μg kg−1), aqueous firefighting foams (median 215 μg kg−1) and landfill leachates (median 107 μg kg−1). Some elevated perfluoroalkyl carboxylic acids (PFCAs) levels could be attributed to emissions from textile finishing industries with concentrations up to 233 μg kg−1 in sewage sludge. Assuming sorption to sludge for PFOS and PFCAs of 15% and 2%, respectively, concentrations in wastewater effluents up to the low μg L−1 level were estimated. Even if wastewater may be expected to be diluted between 10 and 100 times by the receiving waters, elevated concentrations may be reached at specific locations. Although sewage sludge is a minor compartment for PFAAs in WWTPs, these investigations are helpful for the identification of hot-spots from industrial emitters as well as to estimate monthly average concentrations in wastewater.