title: Investigation of humic substance photosensitized reactions via carbon and hydrogen isotope fractionation.
abstract: Humic substances (HS) acting as photosensitizers can generate a variety of reactive species, such as OH radicals and excited triplet states ((3)HS*), promoting the degradation of organic compounds. Here, we apply compound-specific stable isotope analysis (CSIA) to characterize photosensitized mechanisms employing fuel oxygenates, such as methyl tert-butyl ether (MTBE) and ethyl tert-butyl ether (ETBE), as probes. In oxygenated aqueous media, Λ (Δδ(2)H/Δδ(13)C) values of 23 ± 3 and 21 ± 3 for ETBE obtained by photosensitization by Pahokee Peat Humic Acid (PPHA) and Suwannee River Fulvic Acid (SRFA), respectively, were in the range typical for H-abstraction by OH radicals generated by photolysis of H2O2 (Λ = 24 ± 2). However, (3)HS* may become a predominant reactive species upon the quenching of OH radicals (Λ = 14 ± 1), and this process can also play a key role in the degradation of ETBE by PPHA photosensitization in deoxygenated media (Λ = 11 ± 1). This is in agreement with a model photosensitization by rose bengal (RB(2-)) in deoxygenated aqueous solutions resulting in one-electron oxidation of ETBE (Λ = 14 ± 1). Our results demonstrate that the use of CSIA could open new avenues for the assessment of photosensitization pathways.
authors.affiliation: Department of Isotope Biogeochemistry, Helmholtz Centre for Environmental Research-UFZ , Permoserstrasse 15, 04318 Leipzig, Germany.
authors.forename: Ning
authors.initials: N
authors.lastname: Zhang
authors.forename: Janine
authors.initials: J
authors.lastname: Schindelka
authors.forename: Hartmut
authors.initials: H
authors.lastname: Herrmann
authors.forename: Christian
authors.initials: C
authors.lastname: George
authors.forename: Mònica
authors.initials: M
authors.lastname: Rosell
authors.forename: Sara
authors.initials: S
authors.lastname: Herrero-Martín
authors.forename: Petr
authors.initials: P
authors.lastname: Klán
authors.forename: Hans H
authors.initials: HH
authors.lastname: Richnow
mesh_terms: D002244:Carbon; D002247:Carbon Isotopes; D005591:Chemical Fractionation / Q000379:methods*; D003903:Deuterium; D005019:Ethyl Ethers / Q000737:chemistry*; D006812:Humic Substances; D006859:Hydrogen; D006861:Hydrogen Peroxide / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D017665:Hydroxyl Radical; D007700:Kinetics; D008738:Methyl Ethers / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry; D055668:Photochemical Processes; D010782:Photolysis; D012395:Rose Bengal / Q000737:chemistry
chemical_list: D002247:Carbon Isotopes; D005019:Ethyl Ethers; D006812:Humic Substances; D008738:Methyl Ethers; D012395:Rose Bengal; C043243:methyl tert-butyl ether; D017665:Hydroxyl Radical; C098546:ethyl tert-butyl ether; D002244:Carbon; D006859:Hydrogen; D003903:Deuterium; D006861:Hydrogen Peroxide; D010100:Oxygen