Institute of Hydrogeology and Environmental Geology, Chinese Academy of Geological Sciences, Shijiazhuang 050061, China.
Hebei and China Geological Survey Key Laboratory of Groundwater Remediation, Shijiazhuang 050061, China.
Int J Environ Res Public Health. 2022 Mar 11;19(6):3339. doi: 10.3390/ijerph19063339.
Cadmium (Cd)-contaminated paddy soils are a big concern. However, the effect of irrigation with acid water on the migration and transformation of Cd and the effect of alternating redox conditions caused by intermittent irrigation on Cd aging processes in different depths of paddy soils are unclear. This study revealed Cd fractionation and aging in a Cd-contaminated paddy soil under four irrigation periods with acid water and four drainage periods, by applying a soil columns experiment and a sequential extraction procedure. The results showed that the dynamic changes of soil pH, oxidation reduction potential (ORP), iron (Fe) oxides and dissolved organic carbon (DOC) throughout the intermittent irrigation affected the transformation of Cd fractions. After 32 days, the proportion of exchangeable Cd (F1) to the total Cd decreased with a reduction of 24.4% and 20.1% at the topsoil and the subsoil, respectively. The labile fractions of Cd decreased, and the more immobilizable fractions of Cd increased in the different depths of soils due to the aging process. Additionally, the redistribution of the Fe and Mn oxide-bound Cd (F3) and organic matter and secondary-sulfide-bound Cd (F4) occurred at different depths of soils during the incubation time. Overall, the bioaccessibility of Cd in the subsoil was higher than that in the topsoil, which was likely due to the leaching and accumulation of soluble Cd in the deep soil. In addition, the aging processes in different depths of soils were divided into three stages, which can be mainly described as the transformation of F1 into F3 and F4.
镉（Cd）污染的稻田土壤是一个令人关注的问题。然而，用酸性水灌溉对镉的迁移转化的影响以及间歇性灌溉引起的交替氧化还原条件对不同深度稻田土壤中镉老化过程的影响尚不清楚。本研究通过土壤柱实验和连续提取程序，揭示了在镉污染稻田土壤中，经过四个酸化水灌溉期和四个排水期的交替过程后，镉的分馏和老化情况。结果表明，整个间歇性灌溉过程中土壤 pH 值、氧化还原电位（ORP）、铁（Fe）氧化物和溶解有机碳（DOC）的动态变化影响了镉形态的转化。32 天后，可交换态 Cd（F1）在表土和底土中的比例分别降低了 24.4%和 20.1%。由于老化过程，土壤中不同深度的 Cd 易变部分减少，更稳定的 Cd 部分增加。此外，在培养时间内，土壤不同深度的 Fe 和 Mn 氧化物结合态 Cd（F3）和有机物质及次生硫化物结合态 Cd（F4）发生了再分配。总体而言，底土中 Cd 的生物可利用性高于表土，这可能是由于深层土壤中可溶性 Cd 的淋溶和积累。此外，土壤不同深度的老化过程可分为三个阶段，主要表现为 F1 向 F3 和 F4 的转化。
