A tough nut to crack! How to destroy PFOS/PFOA? Activated Persulfate Oxidation as a Remediation Technology for Perfluorooctane Sulfonate and Perfluorooctanoic Acid Ian Ross (Ph.D.) Adventus Environmental Solutions Team Perfluorooctane sulfonate (PFOS) and Perfluorooctanoic acid (PFOA) which can be generally termed perfluorinated compounds (PFCs) are emerging environmental pollutants attracting significant attention due to their global distribution, persistence, toxicity and tendency to bioaccumulate. There are a number of scientific reports now published reporting that activated persulfate has the capacity to destroy PFOS and thus there is immense potential for remediation of PFOS and PFOA impacted soil and groundwater using this versatile oxidative technology. Currently hydraulic containment seems to be the only option for PFOS/PFOA impacted soil and groundwater. However, this article describes potentially robust and versatile technologies to cause destruction of PFOS/PFOA on site (in situ and/or ex situ), with the power to alleviate long term liabilities by providing innovative risk management solutions. Introduction Fluorinated compounds are classified as being perfluorinated when all the hydrogen atoms are substituted by fluorine atoms. The structure of PFOS is shown below. Structure of Perfluorooctane sulfonate (PFOS) Perfluorinated compounds (PFC’s) have been used extensively in the electronic, engineering, chemical and medical industries, due to their unique high surface activity, thermal and acid resistance and both hydro- and lipophobic properties (Lewandowski et. al., 2006). PFC’s were nigh production volume chemicals used in a variety of industrial and consumer applications since the 1950’s and used in the manufacture of leather, paper, textiles, sealants, paint, semiconductors and aviation hydraulic fuels. PFOS was used in the production of aqueous film forming foams (AFFFs) for fire fighting activities, hydraulic aviation fuels and substances used in the chrome plating and photography industries, so has had a wide array of industrial applications. Hence there are multiple activities which could result in loss of PFC’s to soil and groundwater, but one of the more notable uses of PFC’s has been in extinguishing fires, such that fire fighting activities such as fire fighting training areas can be impacted with significant concentrations of PFC’s from repeat application of AFFF during multiple training exercises, or specific fires which extinguish with AFF can lead to a source of PFC’s is soil and groundwater. The substitution of hydrogen for fluorine in perfluorinated surfactants contributes to the persistence of perfluorocarbons relative to hydrocarbon analogues (Key, 1996 and Key et al., 1997), due to the electronegativity of the fluorine, as well as the overlap between the 2s and 2p orbitals of fluorine and the corresponding orbitals of carbon. The highly polarised C-F bond is the strongest known covalent bond, and fluorination usually also strengthens the adjacent C-C bonds (Kissa, 1994; Hudlicky & Pavlath, 1995). This means that PFOS is highly persistent, and difficult to degrade. Therefore, PFC’s are extremely stable and are considered almost un-degradable by nature (Key et al., 1997) with the only report of reductive defluorination by OchoaHerrera et al. (2008), and their results show Ti(III) citrate successfully defluorinating PFOS, but the reaction kinetics are slow. PFOS meets the EU “Persistent‟ and “Very Persistent‟ criteria. It is of note that no degradation of PFOS by hydrolysis, photolysis or biodegradation has been observed in any environmental condition tested, as described by the OECD (OECD 2002). Toxiciological studies examining PFC’s have suggested neurotoxic and immunotoxic effects (Johansson et al., 2009, Liu et. al., 2010). A recent study by researchers at the University of California, Los Angeles (UCLA) has found that women who took longer to become pregnant were more likely to have higher blood levels of PFOS and PFOA (Potera ,2009). During the Buncefield fire in the UK in 2005 a significant amount of PFC foam was used to extinguish the flames, which lead to the collection of immense volumes toxic firewater which required treating (Sample, 2006). The PFC components of the waste water represented the most significant challenge as compared to the hydrocarbons which are amenable to biodegradation. The key features of these PFCs include:    Extremely persistent Soil, groundwater, sediment and surface water are key environmental compartments High water solubility (PFOS solubility 570 mg/L) but bioaccumulative and able to partition into organic matter (i.e. soils and sediments) Therefore, innovative solutions to cause destruction of PFOS/PFOA in wastewater, soil , sediment and groundwater have been researched over the last few years. Some of the more successful technologies are described below. Oxidation of PFOS/PFOA There are a number of reports showing that oxidation with activated persulfate is effective for destruction and mineralization of PFOS/PFOA. The versatility of the activation methodologies should make activated persulfate ideal for in situ and/or ex situ remediation of PFOS / PFOA impacted soils, sediments and groundwater, however only laboratory based trials have been reported to date. Advanced oxidation processes using activated persulfate are characterized by the high reactivity of the sulfate (SO4 ) and hydroxyl radicals (OH ) in driving oxidation processes. Several different variation of oxidation processes such as Fenton’s reagents and persulfate (S2O82-)have been tested and show the most promising results in degrading PFOS/PFOA (Hori et al., 2005, 2008). Hori et al. (2005) found that use of persulfate produced highly oxidative sulfate radical anion (SO4-), which efficiently degrades PFOA to F- and CO2 as major products, whilst minor amounts of shorter chain perfluorocarboxylic acids (PFCA’s) were formed, indicating further oxidation would cause complete mineralization. Hori et al., reported that PFOA at a concentration of 1.35 mM was completely decomposed by a light activated persulfate system with 50 mM S2O82- and 4 hours of irradiation. Further work (Hori et al., 2008) showed that heat activated persulfate could effectively decompose PFOA, as when an aqueous solution containing perfluorooctanoic acid (PFOA, 374 μM) and S2O82- (50.0 mM) was heated at 80 °C for 6 h. PFOA concentration in the aqueous phase fell below 1.52 μM (detection limit), and the yields of F- ions [i.e., (moles of F- formed) /(moles of fluorine content in initial PFOA)] and CO2 [i.e, (moles of CO2 formed) /(moles of carbon content in initial PFOA) ] were 77.5% and 70.2%, respectively, demonstrating significant mineralization of PFOA. Further to these reports, Lee et al.., 2010 demonstrated that persulfate could be activated using iron at heat to cause decomposition of PFOA. Kingshott (2008) assessed differing methods to activate persulfate to treat PFOS, but adapted methodologies to use persulfate activation methods which can be used more easily to treat contaminated soils, sediments and groundwater. Treatments that can most successfully destroy PFOS including Fenton’s reagent, Fenton’s reagent activated persulfate, H2O2 activated persulfate and heat activated persulfate, all of which showed >97.5% PFOS destruction. Some evaluation of strong reductants was also attempted, but this further work using reduction by sodium dithionite and sodium hypophosphate resulted in incomplete degradation of PFOS. Some of the results from this research work are shown below. Conclusions Review of available studies show that oxidation based technologies such as activated persulfate and Fenton’s reagent have huge potential to treat PFOS/PFOA impacted soil and groundwater. However, more in depth bench studies and pilot test are needed before active application of these technologies in field. Scale up from laboratory tests to a site pilot are required to allow confidence to develop in application of oxidants for on site destruction of PFC’s. Oxidation technologies represent a giant leap forward in managing the risks posed from PFC’s including PFOS and PFOA. References Hori, H., Yamamoto, A., Hayakawa, E., Taniyasu, S., Yamashita, N. and Kutsuna, S. (2005) Efficient decomposition of environmentally persistent perfluorocarboxylic acids by use of persulfate as a photochemical oxidant, Environ. Sci. Technol., vol. 39, no. 7, pp. 2383- 2388. Hori, H., Nagaoka Y., Murayama M. and Kutsuna S. (2008) Efficient Decomposition of Perfluorocarboxylic Acids and Alternative Fluorochemical Surfactants in Hot Water, Environ. Sci. Technol, 42, 7438–7443 Hudlicky, M. & Pavlath, A. E. (1995), Chemistry of Organic Fluorine Compounds II: A Critical Review, Washington, DC: American Chemical Society Johansson N., P. Eriksson, H. Viberg, (2009) Neonatal exposure to PFOS and PFOA in mice results in changes in proteins which are important for neuronal growth and synaptogenesis in the developing brain, Toxicol. Sci. 108 412-418 Key, B. D. 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