Because of their persistence, bioaccumulation potential, and (eco)toxicity, long-chain perfluoroalkyl substances (PFASs) are being replaced with short-chain PFASs and fluorinated alternatives. However, almost no information exists about the behavior of fluorinated alternatives during drinking water treatment. The objective of this research is to identify parameters that control the adsorption of PFASs, including 10 traditional PFASs (7 carboxylic acids, 3 sulfonic acids) and 6 emerging perfluoro(poly)ethers (PFPEs), by a thermally activated wood-based powdered activated carbon (PAC). Adsorbability of PFASs was determined in batch kinetic tests and adsorption isotherm experiments that were conducted in ultrapure water and in North Carolina surface water. PFASs were either natively present in the surface water or spiked at environmentally relevant concentrations (500-1000 ng/L). PFASs were quantified by a large-volume direct injection liquid chromatography-tandem mass spectrometry method using an isotope dilution approach. The removal of PFPEs, for which no authentic standards were available, was studied by changes in relative peak areas instead of concentrations. The adsorbability of PFASs increased with increasing number of perfluorinated carbons, and, for a given number of perfluorinated carbons, sulfonic acids were more adsorbable than carboxylic acids. When containing the same number of carbons as the corresponding perfluorocarboxylic acid, monoethers had a lower affinity for PAC. For example, a six-carbon monoether, CF3(CF2)2OCF(CF3)COOH, exhibited an adsorbability that fell between the five-carbon and six-carbon perfluorocarboxylic acids. In contrast, the adsorbability of polyethers was higher than that of perfluorocarboxylic acids with the same number of carbon atoms. For example, a six-carbon/four-ether-oxygen PFPE, CF3(OCF2)4COOH, exhibited an adsorbability similar to the eight-carbon perfluorocarboxylic acid. Similarly, a five-carbon/three-ether-oxygen PFPE, CF3(OCF2)3COOH, exhibited an adsorbability similar to the six-carbon perfluorocarboxylic acid. For the PFASs investigated in this study, affinity for PAC was related to the number of perfluorinated carbon atoms and the octanol/water partition coefficient (log D). This relationship can be a useful tool to predict the adsorbability of emerging PFASs by activated carbon.

Adsorption of traditional and emerging perfluoroalkyl substances by powdered activated carbon

251st National Meeting (2016)

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