Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, PR China; University of Chinese Academy of Sciences, Beijing 100049, PR China.
Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, PR China.
Water Res. 2021 Nov 1;206:117721. doi: 10.1016/j.watres.2021.117721. Epub 2021 Sep 30.
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 (DOM*), singlet oxygen (O), 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 DOM* and OH were comparable, while quantum yields of O 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 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 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.
尽管近年来已经广泛研究了地表水的光化学行为及其对污染物转化的影响，但稻田水的光化学仍知之甚少。在这项研究中，我们研究了在水稻的四个不同种植阶段采集的稻田水样中的光化学过程。三重态溶解有机物（DOM*）、单线态氧（O）和羟基自由基（OH）被发现是主要的反应中间体（RIs），并定量了它们的表观量子产率和稳态浓度。与典型的地表水相比，DOM和 OH 的量子产率相当，而 O 的量子产率比地表水高 2.4-6.7 倍。荧光发射-激发矩阵（EEM）光谱、傅里叶变换离子回旋共振质谱（FTICR-MS）和统计分析表明，DOM 特性和亚硝酸盐浓度是影响 RIs 生成的主要因素。结果表明，分子量和腐殖化程度较低的 DOM 生成更多的 RIs，亚硝酸盐贡献了 23.9%-100%的 OH 生成。EEM 和 FTICR-MS 数据表明，在辐照下，具有更多饱和和较少芳构化公式的 DOM 可以产生更多的 DOM，而 DOM 的多酚成分抑制了 RIs 的形成。此外，RIs 显著增强了砷酸盐（As(III))氧化，在稻田水中的氧化速率提高了 1.8-4.1 倍，OH 和 DOM*是导致 As(III)氧化的主要 RIs。这项研究为稻田土壤和水中砷酸盐的非生物转化途径提供了新的见解。
