Key Laboratory for Environmental Factors Control of Agro-product Quality Safety, Ministry of Agriculture and Rural Affairs, Tianjin 300191, China; Agro-Environmental Protection Institute, Ministry of Agriculture and Rural Affairs, Tianjin 300191, China.
Agro-Environmental Protection Institute, Ministry of Agriculture and Rural Affairs, Tianjin 300191, China.
Sci Total Environ. 2022 Apr 15;817:152898. doi: 10.1016/j.scitotenv.2021.152898. Epub 2022 Jan 11.
Speciation changes in Fe and Mn during the soil flooding-drainage process strongly affect the Cd and As bioavailability in paddy soils. However, owing to a lack of in-situ dynamic monitoring technology, the regularity and mechanism of synergetic changes in Fe, Mn, Cd, and As in paddy soils have not been sufficiently studied. Diffusive gradients in thin films (DGT) were used to investigate the dissolution/transformation process of FeMn oxides and their effects on the bioavailability of Cd and As in three contaminated paddy fields that underwent incubated flooding for 40 d followed by a 20 d oxidation period. In-situ monitoring showed that the labile Cd concentrations decreased rapidly upon flooding but bioavailability of As increased significantly, with As and Cd concentrations largely depending upon Fe (II) content. We discovered that the transformation pathway of Iron Oxide-LDH (Fe-Fe)-Goethite was the key process in reducing the activity of soil Cd. A higher Mn/Fe ratio and lower organic matter content delayed the Fe reduction process, which subsequently delayed Cd immobilization. Mobilization of Cd upon soil drainage was caused by a decrease in soil pH resulting in the release of Cd from secondary minerals.
在土壤淹水-排水过程中，铁和锰的分异变化强烈影响了稻田土壤中镉和砷的生物有效性。然而，由于缺乏原位动态监测技术，尚未充分研究稻田中铁、锰、镉和砷协同变化的规律和机制。扩散梯度薄膜（DGT）被用来研究 FeMn 氧化物的溶解/转化过程及其对三种受污染稻田中镉和砷生物有效性的影响，这些稻田经历了 40 天的培养淹水期，随后进行了 20 天的氧化期。原位监测表明，淹水后可利用的镉浓度迅速下降，但砷的生物有效性显著增加，而砷和镉的浓度主要取决于二价铁（Fe(II)）含量。我们发现，氧化铁-层状双氢氧化物（Fe-Fe）-针铁矿的转化途径是降低土壤镉活性的关键过程。较高的 Mn/Fe 比和较低的有机质含量会延迟铁的还原过程，从而延迟镉的固定。土壤排水时镉的迁移是由于土壤 pH 值降低，导致次生矿物中镉的释放。
