Peroxidase-mediated Degradation of Perfluorooctanoic Acid

• Published in: Environmental toxicology and chemistry 2009-02, Vol.28 (2), p.264-271
• Main Authors: Colosi, Lisa M, Pinto, Roger A, Huang, Qingguo, Weber, Walter J. Jr
• Format: Article
• Language: English
• Subjects: Aliphatic compounds; By products; Byproducts; Caprylates - metabolism; Caprylates - toxicity; Carbon dioxide; Chain reactions; Chains; chemical reactions; Chemicals; Confidence intervals; Contaminants; Copyrights; Decarboxylation; Degradation; Depletion; Fluorides; Fluorocarbons - metabolism; Fluorocarbons - toxicity; Fragmentation; Health hazards; horseradish; Hydrogen peroxide; Mass spectrometry; organic compounds; Organic contaminants; Parents; Perfluorooctanoic acid; Peroxidase; Peroxidases - metabolism; PFA; Phenols; Pollutant removal; Polymerization; Presses; Radicals; Rate constants; reaction kinetics; Reactors; remediation; Surface water; Toxicity; Transformations; water pollution
• ISSN: 0730-7268; 1552-8618
• DOI: 10.1897/08-282.1

Concentrations of aqueous-phase perfluorooctanoic acid (PFOA), a representative perfluorinated aliphatic (PFA) compound, are shown to be reduced effectively via reaction with horseradish peroxidase (HRP), hydrogen peroxide, and a phenolic cosubstrate (4-methoxyphenol). Reaction rate profiles are pseudo-first order, yielding an apparent best-fit removal rate constant of k₁ = 0.003/min (r² = 0.96, n = 14). Approximately 68% depletion of the parent compound and 98% depletion of its related acute aquatic toxicity are achieved in 6 h. Because no PFOA removal is observed in the absence of cosubstrate and/or following consumption thereof, we conclude that radical intermediate species generated during reaction between HRP and 4-methoxyphenol mediate nonspecific depletion of PFOA and that these intermediates may be sufficiently reactive to sever the extremely stable C-F bonds of PFOA. These results are consistent with measurements of reaction by-products, including fluoride ion and various aliphatic species of shortened chain length. Based on these findings, we conclude that PFA degradation may occur via one of two mechanisms: Kolbe decarboxylation followed by stepwise conversion of -CF2 units to CO₂ and fluoride ion, or radical abstraction from a double bond with subsequent fragmentation. Our results indicate that under appropriate conditions, enzymatic degradation may comprise a natural transformation pathway for PFAs. Moreover, we anticipate that appropriately engineered enzymatic processes may hold promise for treatment of PFOA-contaminated waters. This, to the best of our knowledge, is the first report to substantiate the efficacy of HRP-catalyzed reactions for contaminant removal via degradative reactions versus polymerization reactions.