镉同位素分馏及其在示踪土壤镉来源和迁移转化过程中的应用进展

土壤镉污染已成为危害人体健康的主要因素之一，要实现精准、快速和有效地防治土壤镉污染，首先必须厘清土壤中镉的来源及其迁移转化行为。近年来，随着镉同位素分析技术的进步及其分馏机制认识的深入，镉同位素在土壤镉示踪中展示出了巨大的应用潜力。本文在前人研究的基础上，归纳了土壤样品镉同位素分析前处理方法以及测试技术的研究进展。对于基质复杂的土壤样品，高温高压密闭消解和微波消解可以满足其镉同位素测试要求。在分离纯化镉回收率足够、干扰元素去除彻底的情况下，应用多接收电感耦合等离子体质谱(MC-ICP-MS)分析镉同位素并采用标准-样品匹配法、外标法或双稀释剂法进行质量歧视校正，均可获得较高精度的土壤镉同位素组成数据。同时，本文概括了土壤多个潜在镉源的镉同位素组成以及典型过程(风化淋滤、吸附、沉淀/共沉淀、络合)镉同位素分馏方向与程度。结合最新研究成果，总结了镉同位素在示踪土壤镉来源及其迁移转化过程中的应用。在未来的工作中，需进一步开发和优化高精度镉同位素分析方法，建立土壤镉同位素指纹图谱，揭示土壤多组分、多界面过程中的镉同位素分馏机制和特征。

Cadmium Isotope Fractionation and Its Applications in Tracing the Source and Fate of Cadmium in the Soil: A Review

BACKGROUND: Soil cadmium pollution has become one of the main factors that endanger human health. Rapid and effective remediation of Cd pollution soil requires a fundamental understanding of Cd sources and geochemical cycling. With the advancement of Cd isotope analysis technology and the in-depth understanding of its fractionation mechanism, Cd isotopes provide new perspectives for understanding the source and fate of Cd in the soil.OBJECTIVES: To systematically summarize the cadmium isotope analysis method, and emphasize the research progress, problems, and potential application of Cd isotopes as tracers in soil.METHODS: Sample digestion methods, such as high-temperature digestion bombs, microwave acid digestion, ashing, and acid extraction, are reviewed here with ion-exchange separation and multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS).RESULTS: Based on previous studies, this review systematically summarizes the fundamental principle and methodology of Cd isotopic analysis methods. For the soil samples, the high-temperature digestion bombs method and microwave acid digestion can meet its cadmium isotope analysis requirements. With sufficient recovery and complete removal of interfering elements, standard-sample bracketing, external normalization, and double-spike techniques can be used for mass bias correction to obtain accurate and reliable Cd isotope data. In addition, the theoretical basis of soil cadmium isotope tracing was reviewed. This review summarizes the cadmium isotopic composition of multiple potential cadmiumsources in soil and the direction and extent of cadmium isotope fractionation in typical processes (weathering leaching, adsorption, precipitation/co-precipitation, complexation). Combined with the latest research results, the application of cadmium isotopes in tracing soil cadmium sources and their migration and transformation processes is summarized.CONCLUSIONS: In the future, we should further develop and optimize the high-precision cadmium isotope analysis method, construct the fingerprint map of soil cadmium isotope, and reveal the cadmium isotope fractionation mechanisms in the processes of multi-component and multi-interface.