State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, PR China.
National-Regional Joint Engineering Research Center for Soil Pollution Control and Remediation in South China, Guangdong Key Laboratory of Integrated Agro-environmental Pollution Control and Management, Institute of Eco-environmental and Soil Sciences, Guangdong Academy of Sciences, Guangzhou 510650, PR China.
J Hazard Mater. 2022 Aug 15;436:129048. doi: 10.1016/j.jhazmat.2022.129048. Epub 2022 May 4.
Sequential flooding and draining substantially alter Cd mobilization in paddy fields, primarily due to redox-driven changes in Fe-Mn (hydro)oxides and Cd-sulfides. However, the impacts of carbonates on Cd mobilization during flooding-drainage alternations remain poorly understood. In this study, Cd isotope compositions were analyzed in soils and plants at three growth stages, and the results show a pH-dependent Cd mobilization and isotope fractionation. Sequential extraction shows the Cd mainly binds to the exchangeable fraction and carbonates, and their amounts vary with pH. Exchangeable Cd with light isotopes coprecipitates into carbonates due to increased pH during flooding (tillering and panicle initiation). Whereas in drained soils (maturity), the carbonate-bound Cd releases with decreased pH. Light isotopes are enriched in rice compared with exchangeable Cd, but this enrichment is insignificant at maturity. This difference is mainly caused by the change in Cd isotope composition of exchangeable Cd pool due to carbonate coprecipitation during flooding. Limited isotope fractionation between roots and aboveground tissues is found at tillering, whereas significant isotope fractionation is observed at two other stages, suggesting the nodes might work during Cd translocation between tissues. These findings demonstrate alternating flooding-drainage impacts the mobilization of carbonate-bound Cd and, consequently, isotope fractionation in soil-rice systems.
连续淹水和排水会极大地改变稻田中 Cd 的迁移，这主要是由于 Fe-Mn（氢）氧化物和 Cd-硫化物的氧化还原驱动变化所致。然而，碳酸盐在淹水-排水交替过程中对 Cd 迁移的影响仍知之甚少。在这项研究中，分析了三个生长阶段土壤和植物中的 Cd 同位素组成，结果表明存在依赖于 pH 值的 Cd 迁移和同位素分馏。连续提取表明，Cd 主要与可交换部分和碳酸盐结合，其数量随 pH 值而变化。在淹水期间（分蘖和抽穗初期），由于 pH 值升高，轻同位素的可交换 Cd 与碳酸盐共沉淀。而在排水土壤中（成熟阶段），随着 pH 值降低，碳酸盐结合的 Cd 释放。与可交换 Cd 相比，水稻中富集了轻同位素，但在成熟时这种富集并不显著。这种差异主要是由于淹水期间碳酸盐共沉淀导致可交换 Cd 库中 Cd 同位素组成的变化造成的。在分蘖期，发现根系和地上组织之间的同位素分馏有限，而在另外两个阶段则观察到显著的同位素分馏，这表明节点可能在 Cd 在组织间转移过程中起作用。这些发现表明，交替淹水和排水会影响土壤-水稻系统中碳酸盐结合 Cd 的迁移，从而影响同位素分馏。
