Since the phase-out of long-chain perfluorinated substances by the multinational company 3M in 2000, long-chain perfluoroalkyl carboxylic acids (PFCAs), perfluoroalkane sulfonic acids (PFSAs) and their potential precursors have been gradually replaced by shorter-chain perfluorinated chemicals. However, there is little knowledge about the identity, production volumes and applications of these alternatives in the public domain. In a review published October 1, 2013 in the peer-reviewed scientific journal Environment International, researchers from the Swiss Federal Institute of Technology ETH Zurich, Switzerland identified 20 fluorinated substances used in six different areas, including food contact materials (FCM) (Wang et al. 2013). In addition, Wang and colleagues investigated the environmental releases, persistence and exposures of these known fluorinated alternatives of long-chain perfluorinated chemicals.
Wang and colleagues distinguished in their analysis between fluorinated alternatives used in fluoropolymer manufacture, surface treatment of textile, leather and carpets, surface treatment of food contact materials (FCMs), metal plating, fire-fighting foams, and other commercial and consumer applications. According to the analysis of publicly available sources, producers of fluorochemical alternatives include 3M, the former main producer of perfluorooctane sulfonate (PFOS, see figure 1), DuPont, Solvay, Asahi, Daikin, Miteni and several unknown Chinese manufacturers. Most of the identified fluorinated alternatives are based on 6:2 fluorotelomer raw materials, functionalized perfluoropolyethers (PFPEs) and perfluorobutane sulfonyl fluoride (PBSF). In fluoropolymer manufacture different functionalized PFPEs are used as alternatives to the processing aids including ammonium perfluorononanoate (APFN), and ammonium and sodium perfluooctanoate (APFO and NaPFO). Alternative surface treatments of textiles are polymers based on short-chain, highly purified fluorotelomer raw materials, polyfluoroalkyl alcohols and PFPEs. Problematic alternatives are those based on perfluorohexane sulfonyl fluoride (PHxSF) as they may degrade into perfluorohexane sulfonate (PFHxS, Figure 2), a long-chain, highly persistent and bioaccumulative substance. For metal (chromium) plating, 6:2 fluorotelomer sulfonic acid (6:2 FTSA) is used as alternatives to the PFOS salts, but they can only be used in decorative plating due to higher surface tension. Other alternatives include PBSF-based substitutes. Current alternative fire-fighting foams are based on a gaseous fluorinated ketone and others based on a PBSF-derivative as well as substances based on pure 6:2 fluorotelomer raw materials are being developed to replace earlier mixtures of long-chain fluorotelomer raw materials. For surface treatments of FCMs the researchers identify 8 substances of which are mostly based on 6:2 fluorotelomer raw materials (see table 1.).
Table 1: Fluorinated alternative substances known to be used in surface treatment of FCMs
|CAS number||Commercial name||Producer||Chemical basis||Source|
|357624-15-8||DuPont||6:2 fluorotelomer||US FDA, 2013|
|1071022-26-8||DuPont||6:2 fluorotelomer||US FDA, 2013|
|1071022-25-7||DuPont||6:2 fluorotelomer||US FDA, 2013|
|1158951-85-9||Daikin||6:2 fluorotelomer||US FDA, 2013|
|1206450-09-0||Daikin||6:2 fluorotelomer||US FDA, 2013|
|1206450-09-0||Daikin||6:2 fluorotelomer||US FDA, 2013|
|1345817-52-8||Asahi||6:2 fluorotelomer||US FDA, 2013|
Wang et al. identified wastewater, disposal of resins, and air emissions as evidence of the environmental release of new fluorinated alternatives. Further, they stressed that that 6:2 fluorotelomer- and PBSF-based alternatives can undergo degradation processes into short-chain PFCAs and PFSAs that are equally persistent as previously used long-chain homologues. It is still unclear about the degradation of PFPEs in the environment and biota. Several non-functionalized PFPEs in the product Galden® HT70have been observed to have half-lives around 46 years (reaction with Cl and OH radicals) and 800 years (photolysis) in the air. Furthermore, perfluorohexane sulfonate (PFHxS, see figure 2) has an equally long half-life in rodent serum as PFOS that has been listed as a persistent organic pollutant (POP) under the Stockholm Convention and is being phased out globally.
Nevertheless, the presence of PFBS and PFHxS in human serum has undergone a marked increase over the past decade, pointing to increased industrial usage and subsequent environmental releases. As it takes decades for global environmental levels of those fluorinated chemicals to respond to reductions, it is important that associated risks are discovered and regulatory action is taken. Currently, actual production, use and emission volumes of the fluorinated alternatives remain unknown and their environmental fate, toxicity and bioaccumulation are insufficiently studied to presume safety. The researchers suggest a transparent knowledge exchange amongst stakeholders as to develop accurate analytical techniques and more sophisticated environmental fate, toxicity and bioaccumulation study designs. Finally, Wang and colleagues propose the development of an industrial ecology allowing the latest scientific findings to be easily implemented as to produce materials with minimal hazardous properties.
Wang et al. (2013). “Fluorinated alternatives to long-chain perfluoroalkyl carboxylic acids (PFCAs), perfluoroalkane sulfonic acids (PFSAs) and their potential precursors.” Environmental International, 60, 242-248.