Oxidative Conversion as a Means of Detecting Precursors to Perfluoroalkyl Acids in Urban Runoff Erika F. Houtz and David L. Sedlak* Department of Civil and Environmental Engineering, University of California at Berkeley, Berkeley, California, 94720-1710 * S Supporting Information ABSTRACT: A new method was developed to quantify concentrations of difficult-to-measure and unidentified precursors of perfluoroalkyl carboxylic (PFCA) and sulfonic (PFSA) acids in urban runoff. Samples were exposed to hydroxyl radicals generated by thermolysis of persulfate under basic pH conditions and perfluoroalkyl acid (PFAA) precursors were transformed to PFCAs of related perfluorinated chain length. By comparing PFCA concentrations before and after oxidation, the concentrations of total PFAA precursors were inferred. Analysis of 33 urban runoff samples collected from locations around the San Francisco Bay, CA indicated that PFOS (2.6-26 ng/L), PFOA (2.1-16 ng/L), and PFHxA (0.9-9.7 ng/L) were the predominant perfluorinated compounds detected prior to sample treatment. Following oxidative treatment, the total concentrations of PFCAs with 5-12 membered perfluoroalkyl chains increased by a median of 69%, or between 2.8 and 56 ng/L. Precursors that produced PFHxA and PFPeA upon oxidation were more prevalent in runoff samples than those that produced PFOA, despite lower concentrations of their corresponding perfluorinated acids prior to oxidation. Direct measurements of several common precursors to PFOS and PFOA (e.g., perfluorooctanesulfonamide and 8:2 fluorotelomer sulfonate) accounted for less than 25% of the observed increase in PFOA, which increased by a median value of 37%. Exposure of urban runoff to sunlight, advanced oxidation processes, or microbes could result in modest, but measurable, increases in concentrations of PFCAs and PFSAs. ■ INTRODUCTION For more than fifty years, perfluoroalkyl and polyfluoroalkyl substances (PFASs) have been manufactured and used as surfactants, processing aids, and oil and water repellent coatings in consumer products and industrial applications. 1 Two classes of recalcitrant PFASs, the perfluoroalkyl sulfonic acids (PFSAs) and perfluoroalkyl carboxylic acids (PFCAs), have been widely detected in human sera, 2-4 wildlife, 5 municipal wastewater, 6-8 and surface waters. 8-11 PFCAs and PFSAs enter the environ- ment from direct emission and through transformation of precursor compounds. 1 PFASs containing 8-carbon (C8) perfluoroalkyl chains were historically produced in the largest quantities, leading to widespread distribution of the C8 perfluoroalkyl acids, perfluorooctane sulfonate (PFOS), and perfluorooctanoate (PFOA). 2-11 Concern over the potential health effects of PFOS and PFOA on humans and wildlife resulted in a manufacturing shift in the early 2000s toward PFASs containing shorter perfluoroalkyl chains that have a lower potential for bioaccumulation. 12 Urban runoff is a significant source of PFASs in surface waters. For example, urban runoff and wastewater effluent were estimated to contribute approximately equal masses of PFASs to rivers in urbanized regions of Japan. 10 PFASs also have been detected in urban runoff and runoff-receiving waters in Zü rich, 13 Albany, New York, 14 Toronto, 15 and Singapore. 16 Most prior efforts to quantify PFASs in runoff and runoff- receiving waters have focused on the PFSAs and PFCAs and a small number of C8- perfluoroalkyl sulfonamide-containing fluorochemicals, such as perfluorooctanesulfonamide (FOSA) and 2-(N-methylperfluorooctanesulfonamido) acetic acid (N- MeFOSAA). Measured concentrations of C8 perfluoroalkyl sulfonamides in runoff and surface waters were typically 1-2 orders of magnitude lower than those of PFOS and PFOA. 14-16 In Singaporean surface waters receiving wet weather discharge, similar concentrations of 6:2 fluorotelomer sulfonate (6:2 FtS) and individual PFCA congeners were detected. 16 To date, 8:2 and shorter fluorotelomer compounds have rarely been measured in runoff. Despite low concentrations of C8 perfluoroalkyl sulfona- mides in runoff, results from several studies have suggested that polyfluorinated substances that can be converted to PFCAs and PFSAs might be present in runoff at appreciable concen- trations. 14,17,18 For example, PFOS concentrations in Tokyo groundwater were consistently higher than PFOS concen- trations measured in the two most likely sources of contamination, wastewater and urban runoff. 17 Supporting the Received: June 6, 2012 Revised: August 1, 2012 Accepted: August 6, 2012 Article pubs.acs.org/est © XXXX American Chemical Society A dx.doi.org/10.1021/es302274g | Environ. Sci. Technol. XXXX, XXX, XXX-XXX