Abstract
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.
Highlights
We proposed the hypotheses that the migration and transformation of Cd fractions are the essences of Cd aging in paddy soils, and its aging processes are influenced by intermittent irrigation with acid water
In1.brief, the Cd-ununcontaminated soil was composed of clay, 69.16%
Sand, which contaminated soil was composed of 10% clay, 69.16% silt and 19.93% sand, which pre2 /g specific surface area
Summary
Cadmium (Cd) is a kind of heavy metal with high toxicity, and Cd contamination in soil is a big concern [1–5]. Cd in soil can cause a threat to human health through the food chain. It may lead to kidney damage, cancer and other chronic diseases and even cause death when humans are exposed to Cd over long periods [6]. With the increase in mining activities, large amounts of Cd enter the paddy soil around mining areas due to the accumulation of Cd-containing slag and the drainage of acid mine, which seriously affects food security and the stability of the agricultural foundation. It is necessary to carry out research on Cd migration and transformation in paddy soils around mining areas. It is known to all that the mobility and toxicity of Cd are mainly
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