1.中国科学院南京土壤研究所土壤与农业可持续发展国家重点实验室;2.Institute of Soil Science Chinese Academy of Sciences
1.State Key Laboratory of Soil and Sustainable Agriculture,Institute of Soil Science,Chinese Academy of Sciences;2.Institute of Soil Science Chinese Academy of Sciences
砖红壤铬（Cr）的背景值和锰氧化物的含量均较高，当土壤中Cr溶出或者受到Cr(III)污染，可能被氧化生成毒性较高的Cr(VI)，从而对周围的环境造成威胁。为考察砖红壤中Cr的环境风险，以云南、海南和广东采集的部分砖红壤为对象，研究土壤中Cr的溶出和外源Cr(III)的氧化。连二亚硫酸钠-柠檬酸钠-重碳酸钠法提取和电子探针扫描分析的结果表明，砖红壤中的Cr主要与铁氧化物和硅酸盐矿物结合，呈非活性状态。盐酸和柠檬酸的酸化和络合作用促进了Cr的溶出，但即使1 mol?L-1的盐酸也仅使海南3和广东9砖红壤中3.68%和3.54%的Cr溶出。向砖红壤中添加Cr(III)并培养42 d，发现少量添加的Cr(III)氧化为Cr(VI)，但不同土壤中Cr(VI)的生成量与亚锰的净产生量不一致，说明土壤中Cr(III)氧化生成的Cr(VI)可能会被土壤有机质重新还原为Cr(III)。去除土壤有机质后，一次平衡实验中观察到外源添加的Cr(III)氧化为Cr(VI)，氧化量与土壤易还原锰的含量一致。随着溶液pH的增加，Cr(III)的氧化量呈先上升后降低的趋势，在pH4.5时Cr(III)氧化量达最大值，但Cr(III)的氧化转化量在Cr(III)添加量中的占比很小，外源Cr(III)在土壤中氧化转化的风险也很低。虽然砖红壤的背景Cr和易还原锰的含量较高，但自然条件下Cr的溶解和Cr(III)的氧化反应很难发生，Cr(III)不易转化为Cr(VI)，因此不需要过度担忧砖红壤中Cr的风险。
【Objective】The contents of background chromium (Cr) and manganese (Mn) oxides in latosols are high. The dissolution of Cr and subsequent oxidation of Cr(III) in the soils may occur to produce Cr(VI) with high toxicity, thus, posing a threat to the surrounding environment and humans. Therefore, this study aimed to study the dissolution of Cr and the oxidation of Cr(III) in latosols collected from Yunnan, Hainan, and Guangdong Provinces to understand the ecological and environmental risks associated with chromium in latosols.【Method】The dissolution of Cr was investigated using batch experiment , while both batch and incubation experiments were used to investigate the oxidation of Cr(III) in the soils. The concentration of Cr in extractants was determined by an atomic absorption spectrometer. Also, sodium hydrosulfite-sodium citrate-sodium bicarbonate (DCB) extraction and electron probe scanning were used to examine the forms of Cr in the soils.【Result】The results of DCB extraction and electron probe scanning showed that Cr in latosols was mainly combined with iron oxides and silicates. Acidification by hydrochloric acid and complexation by citric acid promoted the dissolution of Cr from the soils. However, even in 1 mol?L-1 hydrochloric acid, only 3.68% and 3.54% of total Cr was dissolved from the latosols of Hainan 3 and Guangdong 9, respectively, suggesting that Cr in latosols is stable and presents a low environmental risk. The oxidation of Cr(III) was observed in the soils during a 42-day incubation experiment. Based on the net production of Mn(II), Cr(VI) content, and organic matter content, it is probable that the Cr(VI) generated in the soils might be reduced to Cr(III) again by soil organic matter. The results of the batch experiment showed that the exogenous Cr(III) was oxidized to Cr(VI) in the latosols with organic matters removed, and the amount of Cr(III) oxidized was determined by the content of easily reducible Mn(III/IV) oxides in the soils. With the increase of suspension pH, the oxidized amount of Cr(III) increased firstly, reached the largest amount at pH 4.5 and then decreased. At this pH, only 1.48% of Cr(III) added was oxidized to Cr(VI). Although exogenous Cr(III) can be oxidized to Cr(VI) by soil Mn(III/IV) oxides in the latosols, the percentage of Cr(III) oxidized to Cr(VI) in the latosols was small, indicating that the risk of exogenous Cr(III) oxidization in the soils was very low.【Conclusion】Despite the high contents of background Cr and easily reducible Mn(III/IV) oxides in the latosols, the dissolution of Cr and oxidation of Cr(III) were difficult. This shows that under the experimental conditions, it was not easy to convert Cr(III) to Cr(VI) through oxidation reactions, therefore, the risk of background Cr in latosols is low.
Yang-xiao-xiao Shi, Jiang, Ke-wei Li, Ren-kou Xu. Dissolution of chromium and oxidation of exogenous trivalent chromium in latosol[J]. Acta Pedologica Sinica,,[In Press]