研究报告
张良东,杨建军,夏星,Sajjad Hussain.Eh耦合的稻田土壤镉、砷释放机制[J].环境科学学报,2020,40(5):1828-1835
Eh耦合的稻田土壤镉、砷释放机制
- Eh-coupled release mechanisms of cadmium and arsenic in a contaminated paddy soil: A microcosm and synchrontron-based spectroscopic study
- 基金项目：国家重点研发计划（No.2018YFD0800305）；农业部农业环境重点实验室应用基础研究项目（No.Y2017PT53）；中国农业科学院科技创新工程项目（2016—2021）
- 作者
- 单位
- 张良东
- 中国农业科学院农业环境与可持续发展研究所, 北京 100081
- 杨建军
- 1. 中国农业科学院农业环境与可持续发展研究所, 北京 100081;2. 农业农村部农业环境重点实验室, 北京 100081
- 夏星
- 中国农业科学院农业环境与可持续发展研究所, 北京 100081
- Sajjad Hussain
- 1. 中国农业科学院农业环境与可持续发展研究所, 北京 100081;2. 北京林业大学水土保持学院, 北京 100081
- 摘要：镉（Cd）、砷（As）是稻田土壤的主要重（类）金属污染物，稻田土壤Cd、As的释放与其氧化还原电位（Eh）密切相关，但Eh耦合的稻田土壤砷、镉释放机制仍不清楚.本实验利用高精度土壤微反应器模拟Eh梯度变化过程（-250、-50、170 mV），研究其耦合的土壤Cd、As及相关元素（Fe、Al、Ca、S、P、DOC）的释放特征，并结合同步辐射微区X射线荧光光谱技术（μ-XRF）探讨了不同Eh（-250、-50、170 mV）条件下稻田土壤As释放机制.结果表明：随着供试体系Eh从-250 mV升高至170 mV，土水混合液中DOC和pH值逐步下降，但Cd、As及相关Al、S、P、Fe元素浓度则同时升高.其中，Cd与S、Al增长均呈先缓后快特征，而As与P、Fe增长则呈先快后缓趋势，说明在Eh升高过程中Cd与S，以及As与Fe间密切相关.同步辐射μ-XRF分析发现，在低Eh条件下，土壤颗粒上As、Fe和S的高含量点信号重合，As-S及As-Fe的可决系数分别在Eh为-250 mV和170 mV条件下最高，说明在低Eh条件下As很可能主要受硫化铁控制，但在高Eh条件下则受铁氧化物影响.综上可知，低Eh条件下，As、Cd主要受到硫化铁的控制.随着Eh的升高，土壤Cd的活性逐渐升高，As的活性则受到铁氧化物控制.本研究结果可为理解土壤Cd、As共同释放机制及调控土壤Cd、As活性提供重要理论依据.
- Abstract：Cadmium (Cd) and arsenic (As) are identified as major contaminants in paddy fields, which was characteristic of frequently soil redox potential (Eh). However, Eh-coupled release mechanisms of Cd/As in contaminated paddy soils remains unclear. In this experiment, the combination of advanced microcosms and synchrotron-based X-ray fluorescence spectroscopy (μ-XRF) were applied to investigate the release mechanisms of As in the contaminated paddy soil at varied Eh conditions (-250, -50, 170 mV). The results indicated the concentrations of Cd, As, Al, S, P and Fe increased but DOC and pH decreased with the Eh increase from -250 mV to 170 mV. Cd/S/Al exhibited similar increasing pattern, with fast increase from -250 mV to -50 mV (Eh Range 1, EhR1), but slow increase from -50 mV to 170 mV (Eh Range 2, EhR2). However, As/Fe/P showed slow increase during EhR1 but fast increase during EhR2. Those suggested Cd and As were probably mainly correlated with S and Fe, respectively, during Eh changes. Moreover, μ-XRF analysis found As tended to overlap with Fe and S rather than K and Ca in the investigated soil for all Eh values, and the correlation coefficients of As-Fe and As-S were much higher at -250 mV and 170 mV compared to -50 mV. These results indicated As was probably associated with iron sulfide at low Eh condition but Fe hydroxides at high Eh condition. Collectively, iron sulfide was expected to be as the predominant sorbents for Cd/As sequestration at the low Eh condition, while the release of Cd increased but that of As mainly depended on the transformation of Fe hydroxides with Eh changes from reducing to oxidation conditions. This study provides new insights on the co-release mechanisms of Cd/As in contaminated paddy soils, thus benefitting the control of rice contamination in paddy soils.
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