title: Evidence for photochemical production of reactive oxygen species in desert soils.
abstract: The combination of intense solar radiation and soil desiccation creates a short circuit in the biogeochemical carbon cycle, where soils release significant amounts of CO2 and reactive nitrogen oxides by abiotic oxidation. Here we show that desert soils accumulate metal superoxides and peroxides at higher levels than non-desert soils. We also show the photogeneration of equimolar superoxide and hydroxyl radical in desiccated and aqueous soils, respectively, by a photo-induced electron transfer mechanism supported by their mineralogical composition. Reactivity of desert soils is further supported by the generation of hydroxyl radical via aqueous extracts in the dark. Our findings extend to desert soils the photogeneration of reactive oxygen species by certain mineral oxides and also explain previous studies on desert soil organic oxidant chemistry and microbiology. Similar processes driven by ultraviolet radiation may be operating in the surface soils on Mars.
authors.affiliation: Department of Biology, University of Patras, Patras 26504, Greece.
authors.forename: Christos D
authors.initials: CD
authors.lastname: Georgiou
authors.affiliation: Desert Research Institute, Las Vegas, Nevada 89119, USA.
authors.forename: Henry J
authors.initials: HJ
authors.lastname: Sun
authors.affiliation: NASA Ames Research Center, Moffett Field, California 94035, USA.
authors.forename: Christopher P
authors.initials: CP
authors.lastname: McKay
authors.affiliation: Department of Biology, University of Patras, Patras 26504, Greece.
authors.forename: Konstantinos
authors.initials: K
authors.lastname: Grintzalis
authors.affiliation: Department of Biology, University of Patras, Patras 26504, Greece.
authors.forename: Ioannis
authors.initials: I
authors.lastname: Papapostolou
authors.affiliation: Department of Biology, University of Patras, Patras 26504, Greece.
authors.forename: Dimitrios
authors.initials: D
authors.lastname: Zisimopoulos
authors.affiliation: Department of Biology, University of Patras, Patras 26504, Greece.
authors.forename: Konstantinos
authors.initials: K
authors.lastname: Panagiotidis
authors.affiliation: Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou 73000, China.
authors.forename: Gaosen
authors.initials: G
authors.lastname: Zhang
authors.affiliation: Laboratory of Electron Microscopy and Microanalysis, University of Patras, Patras 26500, Greece.
authors.forename: Eleni
authors.initials: E
authors.lastname: Koutsopoulou
authors.affiliation: Department of Mineral Resources Engineering, Technical University of Crete, Chania 73100, Greece.
authors.forename: George E
authors.initials: GE
authors.lastname: Christidis
authors.affiliation: Department of Biology, University of Patras, Patras 26504, Greece.
authors.forename: Irene
authors.initials: I
authors.lastname: Margiolaki
mesh_terms: D003889:Desert Climate; D008670:Metals / Q000737:chemistry; D010084:Oxidation-Reduction; D010545:Peroxides; D055668:Photochemical Processes; D017382:Reactive Oxygen Species / Q000737:chemistry*; D012987:Soil / Q000737:chemistry*
chemical_list: D008670:Metals; D010545:Peroxides; D017382:Reactive Oxygen Species; D012987:Soil