Efficient Degradation of Organoarsenic by UV/Chlorine Treatment: Kinetics, Mechanism, Enhanced Arsenic Removal, and Cytotoxicity

Abstract

Roxarsone (ROX) has been widely used as an organoarsenic additive in animal feeding operations and poses a risk to the environment. Here, we first report the efficient degradation of ROX by UV/chlorine, where the kinetics, removal of total arsenic (As), and cytotoxicity were investigated. The kinetics study presented that reactive chlorine species (RCS) and HO• were the dominant species to react with ROX. Furthermore, the degradation rate of ROX can reach the maximum value at pH 7.5 due to the formation of more RCS. The degradation of ROX was affected by the amount of chlorine, pH, and water matrix. Through product analysis and Gauss theoretical calculation, two possible ROX degradation pathways were proposed. The free radicals attacked the As–C bond of ROX and resulted in releasing arsenate (As­(V)). It was the reason that for an enhancement of the removal of total As by ferrous appeared after UV/chlorine, and over 98% of the total As was removed. In addition, cytotoxicity studies indicated that the cytotoxicity significantly enhanced during the degradation of ROX by UV/chlorine. However, by combination of UV/chlorine and adsorption, cytotoxicity can be greatly eliminated, probably due to the removal of As­(V) and chlorinated products. These results further demonstrated that UV/chlorine treatment could be an effective method for the control of the potential environmental risks posed by organoarsenic.

Light- and H2O2-Mediated Redox Transformation of Thallium in Acidic Solutions Containing Iron: Kinetics and Mechanistic Insights

“…Fe­(III) mainly existed as FeCl 2 + in the presence of Cl – . The processes of FeCl 2 + activation via UV light or H 2 O 2 can both give rise to • Cl, which rapidly reacts with Cl – to form • Cl 2 – , which is less reactive than • OH. , The role of • Cl 2 – was further confirmed by the experiments with the addition of TBA, which reacts quickly with • OH at a rate constant of 6.0 × 10 8 M –1 s –1 but slowly with • Cl 2 – at 7 × 10 2 M –1 s –1 . The addition of 25 mM TBA only partially inhibited the oxidation rate of Tl­(I) in the presence of Cl – (Figure S29), indicating that • OH and • Cl 2 – both contributed to Tl­(I) oxidation in the presence of Cl – .…”

“…80,81 The role of • Cl 2 − was further confirmed by the experiments with the addition of TBA, which reacts quickly with • OH at a rate constant of 6.0 × 10 8 M −1 s −1 but slowly with • Cl 2 − at 7 × 10 2 M −1 s −1 . 82 The addition of 25 mM TBA only partially inhibited the oxidation rate of Tl(I) in the presence of Cl − (Figure S29 ) to be photocatalyzed in the UV irradiation system and the slow rate of H 2 O 2 decomposition in the H 2 O 2 system; 52,84 and (ii) the formation of the SO 4…”

Transformation mechanisms of iopamidol by iron/sulfite systems: Involvement of multiple reactive species and efficiency in real water

“…S18). The peaks around 711 and 725 eV could be attributed to Fe 2p3/2 and Fe 2p1/2 (Richardson and Johnston, 2007;Yang et al, 2021).…”

DFT Calculation of Nonperiodic Small Molecular Systems to Predict the Reaction Mechanism of Advanced Oxidation Processes: Challenges and Perspectives

“…However, since corresponding products cannot be detected experimentally, several studies selectively ignored these O atoms on the basis that they cannot undergo further oxidation. 11,17,39,40,54,62,91,116,117 In fact, the electrophilic attack of free radicals on the oxygen atom may result in the destruction of adjacent sites. Therefore, it is unreasonable to disregard the high reactivity of the oxygen atoms.…”

“…Frontier electron density (FED) is the electron density function corresponding to the frontier orbital (HOMO or LUMO), which is calculated for each atom in predicting reaction sites. ,,,,− It can also be referred to as “frontier atomic population”. The calculation method of FED is: 2 normalF normalE normalD normalH normalO normalM normalO 2 = 2 × normalΘ normalA normalH normalO normalM normalO normalF normalE normalD normalH normalO normalM normalO 2 + normalF normalE normalD normalL normalU normalM normalO 2 = normalΘ normalA normalH normalO normalM normalO + normalΘ normalA normalL normalU normalM normalO where Θ A HOMO and Θ A LUMO are the contributions of the HOMO and LUMO of atom A, respectively.…”