Fluorotelomer carboxylic acids

The fluorotelomer carboxylic acids (FTCAs) and fluorotelomer unsaturated carboxylic acids (FTUCAs) are degradation products of FTOHs with the general structure F(CF2) CH2CH00H and F(CF2) CHCOOH respectively, where usually n = 6, 8 or 10 (Table 3.1). Similar to FTOHs, FTCAs and FTUCAs are also named based on the ratio of fluorinated carbons to hydrogenated carbons in the molecule. Although the acid dissociation constants are not known for the FTCAs and the FTUCAs, it is assumed they will also dissociate in the natural environment ... 

Ellis DA, JW Martin, AO De Silva, SA Mabury, MD Hurley, MPS Andersen, TJ Wallington (2004) Degradation of fluorotelomer alcohols a likely atmospheric source of perfluorinated carboxylic acids. Environ Sci Technol 38 3316-3321. 

Fig. 2 a Overall metabolic scheme for the perfluoroalkylsulfonamide alcohols based on rat and fish studies. Presumably the conversion of the alcohol to the corresponding acetates (e.g., N-EtFOSAA and FOSAA) proceed via the aldehyde intermediate though this has yet to be identified. Secondary metabolites for the alcohols (e.g., glucoronide and sulfate) and the carboxylic acids have been omitted, b Overall metabolic scheme for fluorotelomer alcohols (FTOH) derived from published work from microbial and rat studies [52-54,85]... 

Polyfluorinated compounds comprise hundreds of chemicals characterized by hydrophobic linear alkyl chains partially or fully fluorinated (as the perfluorinated compounds [PFCs]) and containing different functional groups. Polyfluorinated compounds include perfluoroalkyl sulfonamides (PFASAs), fluorotelomer alcohols (FTOHs), polyfluorinated alkyl phosphates (PFAPs), fluorotelomer unsaturated carboxylic acids (FTUCAs), perfluoroalkyl acids (PFAAs), and their salts. The most common PFAAs are perfluoroalkyl carboxylic acids (PFCAs) and perfluoroalkyl sulfonic acids (PFASs). In particular, PFASs contain one or more fluorinated alkyl chains bonded to a polar head, which at neutral pH can be charged (anionic, cationic, and amphiphilic surfactants) or noncharged (nonionic surfactants). 

However, most metabolites including those of fluorinated substances are ionic or at least highly polar, such as carboxylic acids. Thus, they are not compatible with GC analysis due to their non-volatility. Some fluorotelomer-based metabolites, such as fluorotelomer ketones [16] or secondary alcohols [17], are volatile and have been first described after detection by GC-MS. 

Perfluoro chemicals are present in the environment and have been detected all over the globe [6-14], whereby fluorotelomer alcohols may act as highly mobile precursors for perfluorinated carboxylic acids [8]. PFC are present in drinking water resources, where they probably persist for a long time due to their high environmental stability. Thus drinking water suppliers have to deal with the possibility of elevated PFC concentrations in their raw water and thereby need to consider treatment strategies as barriers for PFC. 

Similar experiments for the degradation of the 8-2-fluorotelomer alcohol on the basis of microbial communities of a domestic wastewater treatment plant revealed a different pattern of metabolite formation. There, no formation of perfluorinated carboxylic acids like PFOA or PFHxA has been observed [61] suggesting that in this case the biological community of the industrial wastewater may be more adapted to fluorinated chemicals as a potential substrate. 

Perfluoroalkyl acids (PFAs) are synthetic, perfluorinated, straight- or bran-ched-chain organic acids characterized by a carboxylate or sulfonate moiety [1]. PFAs are manufactured directly but can also be formed through transformation of many precursor molecules containing a perfluoroalkyl moiety [2], These include fluorotelomer alcohols (FTOHs) and perfluoroalkyl-sulfonamides (Table 1, Fig. 1), however, others likely exist. Collectively, this family of chemicals including PFAs and their polyfluorinated precursors will be referred to in this document as perfluoroalkyl substances (PFSs). 

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