Perfluoroalkyl compounds

Perfluoroalkyl and polyfluoroalkyl substances (PEASs) are persistent organic pollutants with nearly ubiquitous occmrence in environmental samples. PEASs have anthropogenic origins over the period 1951 to 2004, it has been estimated that up to 7300 tons (i.e., 6.6 x 10 kg) of PEASs have been released into the environment [145]. PEASs are used in the manufacture of industrial materials and consmner products. The compounds are characterized by a nonpolar fluorinated hydrocarbon chain with a polar end group, and they exhibit both lipophobic and hydrophobic properties. Principal applications include uses as srufactants, nonstick coatings, and stain repellants. The compoimds are also precursors in the synthesis of fluoroelastomers and fluoropol)uners and are used in the 

Three subcategories are commonly used to classify PFASs per-fluoroalkyl sulfonic acids (PFSAs), perfluoroalkylcarboxylic acids (PFCAs), and fluorotelomer alcohols (FTOHs). Historically, PFSAs and PFCAs have been prepared by electrochemical fluorination, whereas fluorotelomer alcohols are s)mthesized by telomerization [146]. The electrochemical fluorination process results primarily in straight chain homologs, but branched chain isomers are known to be present. Branched chain isomers can also be s)mthesized through telomerization s)mthesis with the use of branched chain telogen precursors. FTOHs have an even number of carbon atoms and contain a nonfluorinated ethylene group adjacent to the polar end group. Pathways for the conversion of FTOHs fo PFCAs in the environment have been proposed [147,148]. 

Perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) are the two most commonly measured PFASs however, analytical methods have been developed to determine other, shorter and longer chain PFSAs and PFCAs (see Table 13.2 for a list of common PFASs and abbreviations). Recommended terminology and abbreviations have been described by Buck et al, [146]. 

These compounds have been determined in a wide range of samples t3 es, which include human biological fluids, fish and other marine organisms, water samples, and food. Advances in analytical instrumentation that occurred over the past decade now permit the determination of PFAAs in environmental samples at pg/g levels [149,150]. A survey of PFOS and PFOA levels reported for various samples is provided in Table 13.3. 

Health risks associated with PFASs are not yet well established however the assessment of potential risks is the subject of numerous studies [151—153]. Knovm or suspected risks include chronic toxicity, carcinogenic activity, endocrine effects, and bioaccumulation—biomagnification. PFASs are included in the National Health and Nutrition Examination Survey (NHANES) conducted by the Centers for Disease Control and Prevention (CDC) [154], and the National Toxicology Program has included various PFASs in their assessment of toxicity, carcinogenicity, and persistence in human blood [155]. 

Naomi L. Stock Derek C. G. Muir and Scott Mabury Currently at Wonfold Water Quality Centre, Trent University, Peterborough, 

Perfluoroalkyl compounds (PFCs) consist of a perfluoroalkyl chain (where all hydrogen atoms are replaced with fluorine atoms) and a hydrophilic end group, with the general strucmre F(CF2) R. The perfluoroalkyl chain may be of varying lengths, typically k = 4 to 15. Several specific classes of PFCs are discussed below. As research in this field continues and analytical standards and methods evolve, the number of PFCs observed in environmental samples continues to increase. 

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Photolysis of the carbon-iodine bond in iodo-perfluoroalkyl compounds has been employed to enable the formation of the corresponding pefluoroalkyl radical [37]. Different perfluorinated alkyl chains can thus be covalently bound to the CNT. Interestingly, the authors reported that no change in solubility of the nanotubes was noted after the perfluoro-alkylation. 

Harrad S, de Wit CA, Abdallah MAE, Bergh C, Bjorklund JA, Covad A, Damerud PO, de Boer J, Diamond M, Huber S, Leonards P, Mandalakis M, Oestman C, Haug LS, Thomsen C, Webster TF (2010) Indoor contamination with hexabromocyclododecanes, polybrominated diphenyl ethers, and perfluoroalkyl compounds an important exposure pathway for people Environ Sci Technol 44 3221-3231... 

The very high ionization potential and the low polarizability of the fluorine atom imply that fluorinated compounds have only weak intermolecular interactions. Thus, perfluoroalkylated compounds have very weak surface energies, dielectric constants, and refracting indexes. 

The number of 1,2,4,5-tetrazines used in these cycloaddition reactions is limited. The most frequently used are the 3,6-dicarboxylates, the 3,6-diphenyl, 3,6-dimethyl, 3,6-di(2-pyridyl) and bis(perfluoroalkyl) compounds a few others have also been used. The most reactive substances seem to be the 1,2,4,5-tetrazinedicarboxylates, possessing the extra electron-withdrawing effect of the two carboxylate groups. 

For many organic compounds that accumulate in lipids, bio accumulation potential can be estimated from the Kow. Since perfluoroalkyl compounds are inherently oleophobic, and do not partition preferentially to lipid rich tissues [67], the K0w is not a useful predictor of bioaccumulation and direct evidence derived from the laboratory or field is required. Additionally, tissue concentrations of perfluoroalkyl substances should never be lipid normalized. The dietary accumulation, bioconcentration, and biomagnification potential of various perfluoroalkyl carboxylates and sulfonates have been assessed in the laboratory and in the Great Lakes food web (Table 4). 

Perfluoroalkyl compounds have been manufactured since the 1950s.The total production of fluorinated surfactants (anionic, cationic and neutral) was 2001 in 1979, whereas in 2000 the total production of PFOS (perfluorooctane sulfonate) alone was nearly 3000t (Shoeib et al., 2004). Together with PFOA (perfluoroocta-noic acid), PFOS is used in refrigerants, surfactants, fire retardants, stain-resistant coatings for fabrics, carpets and paper and insecticides. Surface treatments, such as protection of clothing and carpets constitute the largest volume of PFOS production (Moriwaki, Takata and Arakawa, 2003). PFOA as well is present in several... 

Bjorklund, J.A., Thuresson, K., et al (2009) Perfluoroalkyl compounds (PECs) in indoor dust concentrations, human exposure estimates, and sources. Environmental Science and Technology, 43(7) 2276-2281. 

Table I. Renin Inhibitory Activity of the Perfluoroalkyl Compounds...

There are a number of SF5L and SF4L2 species (Table 12). Perfluoroalkyl compounds are formed by oxidative fluorination of thiols. F NMR provides a simple and quick method for establishing the stereochemistry in the bis compounds there does not appear to be any fluxionality. 

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