title: Evidence for the generation of reactive oxygen species from hydroquinone and benzoquinone: Roles in arsenite oxidation.
abstract: Natural organic matter (NOM) significantly affects the fate, bioavailability, and toxicity of arsenic in the environment. In the present study, we investigated the oxidation of As(III) in the presence of hydroquinone (HQ) and benzoquinone (BQ), which were selected as model quinone moieties for NOM. It was found that As(III) was oxidized to As(V) in the presence of HQ or BQ at neutral conditions, and the oxidation efficiency of As(III) increased from 33% to 92% in HQ solutions and from 0 to 80% in BQ solutions with pH increasing from 6.5 to 8.5. The oxidation mechanism was further explored with electron spin resonance (ESR) technique. The results showed that semiquinone radicals (SQ(-)) were generated from the comproportionation reaction between BQ and HQ, which mediated the formation of superoxide anion (O2(-)), hydrogen peroxide (H2O2) and hydroxyl radical (OH). Both the SQ(-), H2O2 and OH contributed to the oxidation of As(III). The increase of pH favored the formation of SQ(-), and thus promoted the generation of reactive oxygen species (ROS) as well as As(III) oxidation. Increasing concentrations of HQ and BQ from 0.1 to 1.0 mM enhanced As(III) oxidation from 65% to 94% and from 10% to 53%, respectively. The findings of this study facilitate our understanding of the fate and transformation of As(III) in organic-rich aquatic environments and highlight quinone moieties as the potential oxidants for As(III) in the remediation of arsenic contaminated sites.
authors.affiliation: Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China; University of Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Wenxiu
authors.initials: W
authors.lastname: Qin
authors.affiliation: Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China. Electronic address: yjwang@issas.ac.cn.
authors.forename: Yujun
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China.
authors.forename: Guodong
authors.initials: G
authors.lastname: Fang
authors.affiliation: Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China; University of Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Tongliang
authors.initials: T
authors.lastname: Wu
authors.affiliation: Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China.
authors.forename: Cun
authors.initials: C
authors.lastname: Liu
authors.affiliation: Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China. Electronic address: dmzhou@issas.ac.cn.
authors.forename: Dongmei
authors.initials: D
authors.lastname: Zhou
mesh_terms: D018053:Arsenites / Q000737:chemistry*; D016227:Benzoquinones / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D006861:Hydrogen Peroxide / Q000737:chemistry; D006873:Hydroquinones / Q000737:chemistry*; D016877:Oxidants / Q000737:chemistry; D010084:Oxidation-Reduction; D017382:Reactive Oxygen Species / Q000737:chemistry*; D013481:Superoxides / Q000737:chemistry
chemical_list: D018053:Arsenites; D016227:Benzoquinones; D006873:Hydroquinones; D016877:Oxidants; D017382:Reactive Oxygen Species; D013481:Superoxides; C025232:semiquinone radicals; D006861:Hydrogen Peroxide; C015001:arsenite; C031927:hydroquinone
keywords: Arsenite oxidation; ESR; Reactive oxygen species; Semiquinone radical