title: Production of Abundant Hydroxyl Radicals from Oxygenation of Subsurface Sediments.
abstract: Hydroxyl radicals (•OH) play a crucial role in the fate of redox-active substances in the environment. Studies of the •OH production in nature has been constrained to surface environments exposed to light irradiation, but is overlooked in the subsurface under dark. Results of this study demonstrate that abundant •OH is produced when subsurface sediments are oxygenated under fluctuating redox conditions at neutral pH values. The cumulative concentrations of •OH produced within 24 h upon oxygenation of 33 sediments sampled from different redox conditions are 2-670 μmol •OH per kg dry sediment or 6.7-2521 μM •OH in sediment pore water. Fe(II)-containing minerals, particularly phyllosilicates, are the predominant contributor to •OH production. This production could be sustainable when sediment Fe(II) is regenerated by the biological reduction of Fe(III) during redox cycles. Production of •OH is further evident in a field injection-extraction test through injecting oxygenated water into a 23-m depth aquifer. The •OH produced can oxidize pollutants such as arsenic and tetracycline and contribute to CO2 emissions at levels that are comparable with soil respiration. These findings indicate that oxygenation of subsurface sediments is an important source of •OH in nature that has not been previously identified, and •OH-mediated oxidation represents an overlooked process for substance transformations at the oxic/anoxic interface.
authors.affiliation: State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences , 388 Lumo Road, Wuhan 430074, P. R. China.
authors.forename: Man
authors.initials: M
authors.lastname: Tong
authors.affiliation: State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences , 388 Lumo Road, Wuhan 430074, P. R. China.
authors.forename: Songhu
authors.initials: S
authors.lastname: Yuan
authors.affiliation: State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences , 388 Lumo Road, Wuhan 430074, P. R. China.
authors.forename: Sicong
authors.initials: S
authors.lastname: Ma
authors.affiliation: State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences , 388 Lumo Road, Wuhan 430074, P. R. China.
authors.forename: Menggui
authors.initials: M
authors.lastname: Jin
authors.affiliation: State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences , 388 Lumo Road, Wuhan 430074, P. R. China.
authors.forename: Deng
authors.initials: D
authors.lastname: Liu
authors.affiliation: State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences , 388 Lumo Road, Wuhan 430074, P. R. China.
authors.forename: Dong
authors.initials: D
authors.lastname: Cheng
authors.affiliation: State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences , 388 Lumo Road, Wuhan 430074, P. R. China.
authors.forename: Xixiang
authors.initials: X
authors.lastname: Liu
authors.affiliation: State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences , 388 Lumo Road, Wuhan 430074, P. R. China.
authors.forename: Yiqun
authors.initials: Y
authors.lastname: Gan
authors.affiliation: State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences , 388 Lumo Road, Wuhan 430074, P. R. China.
authors.forename: Yanxin
authors.initials: Y
authors.lastname: Wang
mesh_terms: D001151:Arsenic / Q000032:analysis / Q000737:chemistry; D005290:Ferric Compounds / Q000032:analysis / Q000737:chemistry; D019015:Geologic Sediments / Q000737:chemistry*; D060587:Groundwater / Q000737:chemistry; D017665:Hydroxyl Radical / Q000032:analysis* / Q000737:chemistry; D010084:Oxidation-Reduction; D014874:Water Pollutants, Chemical / Q000032:analysis* / Q000737:chemistry
chemical_list: D005290:Ferric Compounds; D014874:Water Pollutants, Chemical; D017665:Hydroxyl Radical; D001151:Arsenic