School of Nuclear Science and Technology, Lanzhou University, Lanzhou 730000, China.
Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou 730000, China.
Environ Sci Process Impacts. 2023 May 25;25(5):954-963. doi: 10.1039/d3em00052d.
Previous research studies have confirmed that Zn and Cd are the most predominant heavy metals in the Baiyin district, Gansu province, China. Furthermore, the speciation of Zn and Cd is a key factor in controlling the mobility, bioavailability, and toxicity of metals in Zn/Cd co-contaminated soil. In this study, the speciation of Zn and Cd in different types of agricultural soils including the Yellow River irrigated soil (s3) and sewage irrigated soil (s1 and s2) was investigated and compared by a combination of sequential extraction, bulk X-ray absorption fine structure (XAFS), and micro-X-ray fluorescence (μ-XRF) techniques. The results of the speciation quantified by XAFS were in general agreement with those obtained by sequential extraction, and the combination of both approaches allowed a reliable description of Zn/Cd speciation in soil. The speciation of Zn in the s1 soil exposed around the smelter was similar to speciation of Zn in the sewage irrigated s2 soil. In both soils, Zn was predominantly present as Zn-Al LDH (31-36%), Zn adsorbed on calcite (37-47%), and primary minerals (14-18% sphalerite and 9% franklinite). In contrast, the proportions of organic Zn (23%) and Zn-Al LDH (53%) were significantly higher in the Yellow River irrigated s3 soil, while that of Zn-calcite (24%) was lower. This indicated that Zn in s3 was less mobile and bioavailable than that in s1 and s2 soils. The content of bioavailable Zn in s3 was much lower than the background value and Zn did not pose a threat to the Yellow River irrigated soil. In addition, Cd was strongly correlated with Zn content and exhibited a simpler speciation. Cd adsorbed on illite and calcite was found as the major species in both soil types, posing higher migration and toxicity to the environment. Our study reported the speciation and correlation of Zn/Cd in sierozem soil for the first time and provided a significant theoretical basis for remediation actions to minimize Zn/Cd risks.
先前的研究已经证实，中国甘肃省白银地区的主要重金属是 Zn 和 Cd。此外，Zn 和 Cd 的形态是控制 Zn/Cd 复合污染土壤中金属迁移性、生物可利用性和毒性的关键因素。在这项研究中，采用连续提取、全反射 X 射线吸收精细结构（XAFS）和微束 X 射线荧光（μ-XRF）技术相结合的方法，研究了黄河灌溉土（s3）和污水灌溉土（s1 和 s2）等不同类型农业土壤中 Zn 和 Cd 的形态，并进行了比较。XAFS 定量的形态结果与连续提取法的结果基本一致，这两种方法的结合可以对土壤中 Zn/Cd 的形态进行可靠描述。冶炼厂周围暴露的 s1 土壤中的 Zn 形态与污水灌溉 s2 土壤中的 Zn 形态相似。在这两种土壤中，Zn 主要以 Zn-Al LDH（31-36%）、Zn 吸附在方解石上（37-47%）和原生矿物（14-18%闪锌矿和 9%铁闪锌矿）的形式存在。相比之下，黄河灌溉 s3 土壤中有机 Zn（23%）和 Zn-Al LDH（53%）的比例明显更高，而 Zn-方解石（24%）的比例较低。这表明 s3 土壤中的 Zn 迁移性和生物可利用性低于 s1 和 s2 土壤中的 Zn。s3 土壤中生物可利用 Zn 的含量远低于背景值，且 Zn 对黄河灌溉土壤没有威胁。此外，Cd 与 Zn 含量密切相关，形态较为简单。在两种土壤类型中，发现 Cd 吸附在伊利石和方解石上是主要的存在形式，对环境具有更高的迁移性和毒性。本研究首次报道了黑钙土中 Zn/Cd 的形态和相关性，为采取修复行动以降低 Zn/Cd 风险提供了重要的理论依据。
