Transformation of roxarsone during UV disinfection in the presence of ferric ions

Photolysis of Roxarsone in Aqueous Solutions Containing Goethite under Simulated Sunlight Irradiation: Kinetics, Mechanism, and Degradation Pathways

“…However, the presence of anions inhibited the degradation of ROX. Anions in the solution could competitively scavenge the ROS formed and occupy the sorption sites on the α-FeOOH surface to inhibit the reaction between ROX and ROS. , Since H 2 PO 4 – can form a stable complex with iron species to reduce the formation of HO • and to quench the HO • formed (HO • + H 2 PO 4 – → HPO 4 •– , which is a weaker oxidant than HO • ), , H 2 PO 4 – dramatically inhibited the degradation of ROX (Figure a). The presence of SWRHA and SWRNOM inhibited the photodegradation of ROX in pure water and in the presence of α-FeOOH (Figure b), which could be explained by the combined effects of light shielding, scavenging of the ROS formed, and competitive adsorption on the α-FeOOH surface brought by organic matter .…”

“…Since most of the ROX (5.0 μM) (>96%) can be adsorbed on the α-FeOOH (2.2 mM) within minutes, the presence of Fe­(III) barely enhanced the adsorption of ROX (Figure S12). Also, the enhancement of ROX degradation in the presence of Fe­(III) could be mainly attributed to the formation of HO • (FeOH 2+ + h v → Fe 2+ + HO • ; Fe 2+ + H 2 O 2 → Fe 3+ + HO • + HO – ) and inhibition of the recombination of electron holes. , Meanwhile, the photodegradation of ROX was not completely quenched in the presence of KI, in which KI was preabsorbed on the α-FeOOH surface for 24 h and used as a scavenger of surface HO • (Figure c) . Together, these results suggest that both α-FeOOH and the released iron ions are crucial for the photodegradation of ROX.…”

“…Moreover, a natural water sample collected from the Jinjiang River, Changsha, China was used as a water matrix to investigate the degradation of ROX under realistic conditions. The r init of ROX degradation decreased from 6.5 ± 0.5 × 10 –1 μM·h –1 in pure water (pH initial = 7.2) to 2.0 ± 0.2 × 10 –1 μM·h –1 in natural water (Figure c and Table S5), similar to the results obtained in the presence of 5.0 or 10.0 mg·L –1 SWRNOM, confirming the negative effect of natural dissolved organic matter (TOC: 7.1 mg·L –1 ) on ROX photodegradation …”

“…Photochemical transformation is an important route in deciding the fate of organic pollutants in surface water. ROX can be photodegraded under UV irradiation in the lab, and As­(III) and As­(V) are the main arsenic-containing products. , Ferric ions (Fe­(III)) enhance the UV photodegradation of ROX through the formation of reactive oxygen species (ROS) (i.e., HO • , O 2 •– ) . However, they failed to disclose the fate of ROX in natural water under simulated sunlight/solar light irradiation (λ> 290 nm).…”

Photodegradation of roxarsone in the aquatic environment: influencing factors, mechanisms, and artificial neural network modeling

“…Because ROX is water-soluble, the land application of poultry litter can result in the transformation of ROX into receiving waters after rain events (Cortinas et al, 2006;Liu et al, 2015;Yang et al, 2016). In the aquatic environment, ROX is degraded into inorganic arsenics (arsenite (As(III) and arsenate (As(V)), which are more toxic and mobile than ROX (Chen et al, 2019;Lei et al, 2019;Mangalgiri et al, 2015;Nguyen et al, 2019;Rutherford et al, 2003;Su et al, 2019;Tang et al, 2019;Wang et al, 2021;Zheng et al, 2014), and part of inorganic arsenics is converted into volatile arsenics (Tang et al, 2020;Tang et al, 2019).…”