title: Mechanism, kinetics, and pathways of self-sensitized sunlight photodegradation of phenylarsonic compounds.
abstract: Being highly water-soluble, phenylarsonic feed additives discharged in animal wastes can easily accumulate in surface water bodies. The photodegradation mechanism, kinetics, and pathways of p-arsanilic acid (p-ASA), 4-hydrophenylarsonic acid (4-HPAA), and phenylarsonic acid (PAA) in water under simulated and natural sunlight irradiation were investigated. The -AsO(OH)2 group was cleaved from the aromatic ring during photodegradation, and p-benzoquinone and p-hydroquinone were formed as the major organic degradation intermediates. Experimental results did not indicate any significant direct photolysis of the phenylarsonic compounds under simulated and natural sunlight irradiation, but consistently showed that they sensitized the formation of singlet oxygen, which was responsible for their photodegradation and oxidation of the As(III) released. A simple (1)O2-based "heterogeneous" model was developed, which could well describe the kinetics of (1)O2 formation and phenylarsonic compound photodegradation under various conditions. Indirect photolysis caused by inorganic ions commonly present in natural waters was negligible, while natural organic matter could significantly inhibit their photodegradation. The half-lives of p-ASA, 4-HPAA, and PAA photodegradation under simulated sunlight irradiation (765 W m(-2), 25 °C) were 11.82 ± 0.19, 20.06 ± 0.10, and 135 ± 6.0 min, respectively, while their degradation rates under natural sunlight in the Pearl River Delta of southern China were 5 times slower due to lower irradiation intensity and water temperatures (19-23 °C).
authors.affiliation: State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China; University of Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Xiande
authors.initials: X
authors.lastname: Xie
authors.affiliation: School of Water Resources and Environment, China University of Geosciences (Beijing), Beijing 100083, China.
authors.forename: Yuanan
authors.initials: Y
authors.lastname: Hu
authors.affiliation: MOE Laboratory for Earth Surface Processes, College of Urban and Environmental Sciences, Peking University, Beijing 100871, China. Electronic address: hefac@umich.edu.
authors.forename: Hefa
authors.initials: H
authors.lastname: Cheng
mesh_terms: D016227:Benzoquinones; D007700:Kinetics; D010782:Photolysis; D013472:Sunlight; D014874:Water Pollutants, Chemical
chemical_list: D016227:Benzoquinones; D014874:Water Pollutants, Chemical
keywords: Inorganic arsenic; Natural organic matter; Phenylarsonic compounds; Self-sensitized photolysis; Singlet oxygen; “Heterogeneous” kinetic model