Photochemical characterization of paddy water during rice cultivation: Formation of reactive intermediates for As(III) oxidation. (1st November 2021)

• Record Type: Journal Article
• Authors: Zeng, Yu; Fang, Guodong; Fu, Qinglong; Dionysiou, Dionysios D.; Wang, Xiaolei; Gao, Juan; Zhou, Dongmei; Wang, Yujun
• Is Part Of: Water research. Volume 206(2021)
• Publication Date: 2021-11-01
• Subjects: Paddy water -- Reactive intermediate -- Dissolved organic matter -- Nitrite photochemistry -- Arsenite oxidation; Water -- Pollution -- Research -- Periodicals; 363.7394
• DOI: 10.1016/j.watres.2021.117721
• Languages: English
• ISSNs: 0043-1354

Abstract

Highlights: Reactive intermediates (RIs) generated from paddy water during the rice growing. 3 DOM*, 1 O2 and OH were found to be the dominant RIs. Quantum yields of 1 O2 were about 2.4-6.7 times higher than those of surface water. DOM and NO2 − were main responsible for RIs generation. 3 DOM* was dominant RIs for As(III) oxidation in paddy water Abstract: Although the photochemical behavior of surface water and its effects on pollutant transformation have been studied extensively in recent years, the photochemistry of paddy water remains largely unknown. In this study, we examined the photochemical processes involving paddy water samples collected at four different cultivation stages of rice. Triplet dissolved organic matter ( 3 DOM*), singlet oxygen ( 1 O2 ), and hydroxyl radicals ( OH) were found to be the dominant reactive intermediates (RIs), and their apparent quantum yields and steady-state concentrations were quantified. Compared with the typical surface water, quantum yields of 3 DOM* and OH were comparable, while quantum yields of 1 O2 were about 2.4-6.7 times higher than those of surface water. Fluorescence emission-excitation matrix (EEM) spectra, Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS), and statistical analysis revealed that DOM properties and nitrite concentration were the main factor influencing RIs generation. The results suggest that DOM with lower molecular weight and humification extent generated more RIs, and nitrite contributed to 23.9%–100% of OH generation. EEM and FTICR-MS data showed that DOM with more saturated and less aromatic formulas could produce more 3 DOM* under the irradiation, while the polyphenolic components of DOM inhibited the formation of RIs. Moreover, RIs significantly enhanced arsenite (As(III)) oxidation with oxidation rate increased by 1.8–4.1 times in paddy water, and OH and 3 DOM* were the main RIs responsible for As(III) oxidation. This study provides new insight into the pathways of arsenite abiotic transformation in paddy soil and water. Graphical abstract: Image, graphical abstract