Degradation Of Perfluorooctane Sulfonate Research Articles

Fluorine mass balance in electrolytic degradation of perfluorooctane sulfonate in aqueous solution

Perfluorinated chemicals (PFCs) have been widely used in various household products. Because of inactive C–F bond within its structure, most PFCs cannot be biologically degraded and tend to accumulate in the ecosystems once discharged into the environment through sewage effluent etc., necessitating low-cost treatment technologies for PFCs. We have worked on the electrolysis method in which PFCs in water are decomposed at moderate cost, and found that perfluorooctane sulfonate, considered to be the most recalcitrant chemical among PFCs, can be decomposed by electrolysis. The decomposition products, however, remained unknown although we used various advanced analytical techniques (mass spectrometry for analysis of organic substances in liquid and gas samples, and combustion-ion chromatography for total fluorine analysis) to identify the products. The emanation of volatile low-molecular fluorine compounds was suspected. The present report summarizes our trial to identify the unknown decomposition products by analytical instruments cited above, and the application of PIXE/PIGE analysis to track the fluorine compounds lost from the solution by concentrating the gaseous compounds in low temperature (–100°C) activated charcoal.

Removal of perfluorooctanoic acid and perfluorooctane sulfonate via ozonation under alkaline condition

The elimination of recalcitrant, ubiquitous perfluoroalkyl acids (PFAAs) such as perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) is desirable for reducing potential human health and environmental risks. We here report the degradation of PFOA and PFOS by 85–100% via ozonation under alkaline condition being studied at environmentally relevant contaminant concentrations of 50μgL−1 to 5mgL−1, with enhanced removal rates by addition of hydrogen peroxide. Enhanced removal is achieved by ozonation pretreatment for 15min at the ambient pH (i.e. 4–5), followed by elevation of pH to 11 and continued ozonation treatment for 4h. The ozonation pretreatment resulted in increased degradation of PFOA by 56% and PFOS by 42%. The results indicated hydroxyl radical-driven degradation of PFOA and PFOS in both treatments by ozone and peroxone under alkaline conditions. Wastewaters from electronics and semiconductor fabrication plants in the Science Park of Hsinchu city, Taiwan containing PFOA and PFOS have been readily treated by ozonation under alkaline condition. Treatment of PFAAs by ozone or peroxone proves to be efficient in terms of energy requirement, contact time, and removal rate.

Behavior and Fate of PFOA and PFOS in Sandy Aquifer Sediment

AbstractMicrocosms were constructed with sediment from beneath a landfill that received waste containing PFOA (perfluorooctanoic acid) and PFOS (perfluorooctane sulfonate). The microcosms were amended with PFOA and PFOS, and sampled after 91, 210, 343, 463, 574, and 740 d of incubation. After 740 d, selected microcosms were extracted to determine the mass of PFOA and PFOS remaining. There was no evidence for degradation of PFOA or PFOS. Over time, the aqueous concentrations of PFOA and PFOS increased in the microcosms, indicating that PFOA and PFOS that had originally sorbed to the sediment was desorbing. At the beginning of the experiment, the adsorption coefficient, Kd, averaged 0.27 L/kg for PFOA and 1.2 L/kg for PFOS. After 740 d of incubation, sorption of PFOA was not detectable and the Kd of PFOS was undetectable in two microcosms and was 0.08 L/kg in a third microcosm. During incubation, the pH of the pore water in the microcosms increased from pH 7.2 to pH ranging from 8.1 to 8.8. The zeta potential of the sediment decreased with increasing pH. These observations suggest that the sorption of PFOA and PFOS at near neutral pH was controlled by the electrostatic sorption on ferric oxide minerals, and not by the sorption to organic carbon. Accurate predictions of PFOA and PFOS mobility in ground water should be based on empirical estimates of sorption using affected aquifer sediment.

Kinetics and Mechanism of the Sonolytic Conversion of the Aqueous Perfluorinated Surfactants, Perfluorooctanoate (PFOA), and Perfluorooctane Sulfonate (PFOS) into Inorganic Products

The perfluorinated surfactants perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) are recognized as widespread in the environment as well as recalcitrant toward most conventional water treatment technologies. In this study, acoustic cavitation as driven by high-frequency ultrasound is shown to be effective in the degradation of aqueous solutions of PFOS and PFOA and effective over a wide range of concentrations from 10 nM to 10 muM for a given compound. Sulfur, fluorine, and carbon mass balances indicate that mineralization occurs immediately following the degradation of the initial perfluorinated surfactant. Near complete conversion of PFOS and PFOA to CO, CO2, F-, and SO42- occurs due to pyrolytic reactions at the surface and vapor phase of transiently collapsing cavitation bubbles. The initial PFOS or PFOA pyrolytic degradation occurs at the bubble-water interface and involves the loss of the ionic functional group leading to the formation of the corresponding 1H-fluoroalkane or perfluoroolefin. The fluorochemical intermediates undergo a series of pyrolytic reactions in the bubble vapor leading to C1 fluoro-radicals. Secondary vapor-phase bimolecular reactions coupled with concomitant hydrolysis converts the C1 fluoro-radicals to carbon monoxide, carbon dioxide, and HF, forming a proton and fluoride upon dissolution. Sonochemical half-lives, which are calculated from high-temperature gas-phase kinetics, are consistent with kinetic observations and suggest that mineralization occurs shortly after initial perfluorinated surfactant interfacial pyrolysis.

Reductive Defluorination of Perfluorooctane Sulfonate

Perfluorooctane sulfonate (PFOS) is under increased scrutiny as an environmental pollutant due to recent reports of its worldwide distribution, environmental persistence, and bioaccumulation potential. The susceptibility of technical PFOS and PFOS branched isomers to chemical reductive dehalogenation with vitamin B12 (260 microM) as catalyst and Ti(III)-citrate (36 mM) as bulk reductant in anoxic aqueous solution at 70 degrees C and pH 9 was evaluated in this study. Defluorination was confirmed by fluoride release measurements of 18% in technical PFOS, equivalent to the removal 3 mol F-/mol PFOS, and 71% in PFOS branched isomers equivalent to the removal of 12 mol F-/mol PFOS. Degradation of PFOS was further confirmed by monitoring the disappearance of PFOS compounds with reaction time by suppressed conductivity ion chromatography, LC-MS/MS, and 19F NMR studies. The PFOS compounds differed in their susceptibility to reductive degradation by vitamin B12Ti(III) citrate. Chromatographic peaks corresponding to branched PFOS isomers disappeared whereas the peak corresponding to linear PFOS was stable. To our knowledge this is the first report of reductive dehalogenation of PFOS catalyzed by a biomolecule.