title: Factors controlling the rate of perfluorooctanoic acid degradation in laccase-mediator systems: The impact of metal ions.
abstract: This study investigated the factors that regulated the degradation of perfluorooctanoic acid (PFOA) in laccase-catalyzed oxidative humification reactions with 1-hydroxybenzotriazole (HBT) as a mediator. The reaction rates were examined under conditions with key factors varied, including initial PFOA concentrations, laccase and HBT dosages, and the ionic contents of the reaction solutions. The PFOA degradation followed pseudo-first order kinetics, and the rate constants (k) were similar for the high (100 μmol L-1) and low (1.00 μmol L-1) initial PFOA concentrations, respectively at 0.0040 day-1(r2= 0.98) and 0.0042 day-1(r2= 0.86) under an optimum reaction condition tested in this study. The metal ions contained in the reaction solution appeared to have a strong impact on PFOA degradation. Differential UV-Vis spectrometry revealed that Cu2+can complex with PFOA, which plays an essential role to enable PFOA degradation, probably by bridging the negatively charged PFOA and laccase, so that the free radicals of HBT that are released from laccase can reach and react with PFOA. It was also found that Fe3+plays a similar role as Cu2+to enable PFOA degradation in the laccase-HBT reaction system. In contrast, Mg2+and Mn2+cannot complex with PFOA under the investigated conditions, and do not enable PFOA degradation in the laccase-HBT system. Fluoride and partially fluorinated compounds were detected as PFOA degradation products using ion chromatography and high resolution mass spectrometry. The structures of the products suggest the reaction pathways involving free-radical initiated decarboxylation, rearrangement, and cross-coupling.
authors.affiliation: Interdisciplinary Toxicology Program, Department of Crop and Soil Sciences, University of Georgia, Griffin, GA 30223, USA.
authors.forename: Qi
authors.initials: Q
authors.lastname: Luo
authors.affiliation: School of the Environment, Nanjing University, Nanjing, Jiangsu 210023, PR China.
authors.forename: Zunyao
authors.initials: Z
authors.lastname: Wang
authors.affiliation: School of the Environment, Nanjing University, Nanjing, Jiangsu 210023, PR China.
authors.forename: Mingbao
authors.initials: M
authors.lastname: Feng
authors.affiliation: AECOM Inc., Remediation Technology, Atlanta, GA 30309, USA.
authors.forename: Dora
authors.initials: D
authors.lastname: Chiang
authors.affiliation: AECOM Inc., Remediation Technology, Mechanicsburg, PA 17055, USA.
authors.forename: David
authors.initials: D
authors.lastname: Woodward
authors.affiliation: Interdisciplinary Toxicology Program, Department of Crop and Soil Sciences, University of Georgia, Griffin, GA 30223, USA.
authors.forename: Shangtao
authors.initials: S
authors.lastname: Liang
authors.affiliation: College of Resources and Environmental Science, Nanjing Agricultural University, Nanjing, Jiangsu 210095, PR China.
authors.forename: Junhe
authors.initials: J
authors.lastname: Lu
authors.affiliation: Interdisciplinary Toxicology Program, Department of Crop and Soil Sciences, University of Georgia, Griffin, GA 30223, USA. Electronic address: qhuang@uga.edu.
authors.forename: Qingguo
authors.initials: Q
authors.lastname: Huang
mesh_terms: D002210:Caprylates / Q000737:chemistry*; D002384:Catalysis; D005466:Fluorocarbons / Q000737:chemistry*; D042845:Laccase / Q000737:chemistry* / Q000378:metabolism; D008670:Metals / Q000737:chemistry*; D010084:Oxidation-Reduction; D020076:Pleurotus / Q000737:chemistry*; D014230:Triazoles / Q000737:chemistry*
chemical_list: D002210:Caprylates; D005466:Fluorocarbons; D008670:Metals; D014230:Triazoles; C023036:perfluorooctanoic acid; C011852:1-hydroxybenzotriazole; D042845:Laccase
keywords: Enzyme catalyzed oxidative humification reactions; Hydroxybenzotriazole mediator; Laccase; Metal ions; Perfluorooctanoic acid