干湿交替作用下水稻土铊的形态转化及机制研究

铊（Tl）是一种剧毒重金属，在自然界有两种形态Tl(I)和Tl(III)，两者的化学活性、迁移性和毒性存在巨大差异。我国南方部分水稻土受Tl污染较为严重，危害农产品安全和人体健康。干湿交替作用下，水稻土的水热条件和氧化还原电位发生强烈变化，使铁循环加快，但其对土壤Tl的形态、迁移和生物有效性的影响及其机制尚不清楚。本项目以Tl为目标物，以干湿交替作用为切入点，利用传统化学提取技术(BCR), 原位高分辨率分析特性的新型梯度扩散薄膜技术(DGT)和原位微区分析技术等，通过野外试验和室内模拟试验，研究周期性淹水-落干过程土壤铁矿物形态和结构的变化，明确氧化铁在Tl转化、活化与固定中的作用及其与Tl的耦合关系，揭示干湿交替作用下土壤Tl形态转化和生物有效性的主控因素及机制。本项目的实施可望丰富和深化对Tl的环境行为的认识，为有效防控农田Tl污染提供理论依据，有重要的科学研究价值和实际指导意义。

Thallium (Tl) is a highly toxic heavy metal. As we know, Tl exists as Tl(I) and Tl(III) in natural environment, and different valence states exhibit significantly reactivity, mobility, toxicity and bioavailability. The paddy soil in Southern China is heavily polluted by Tl, which endangers the safety of agricultural products and human health. Dramatic changes of hydrothermal conditions and oxidation-reduction potential of paddy soil due to wetting/drying cycle could accelerate the iron cycle process, however, to date, its effect on the speciation, migration and bioavailability of Tl in paddy soil are still unclear. This project takes Tl as the target and uses the wetting/drying cycles as the driving force for redox reactions. The classic chemical extraction technology (BCR), an in-situ high-resolution diffusive gradients in thin films (DGT), X-ray fluorescence spectroscopy (XRF), X-ray diffraction (XRD), high-resolution scanning transmission electron microscopy (STEM-EDS) and X-ray photoelectron spectroscopy (XPS) are comprehensively used during the field experiment and simulation experiment. The main purposes of this project are (1) to characterize the structure and speciation of iron oxide in paddy soil under the wetting/drying cycle, (2) to clarify the iron oxide function and its coupling relationship with the transformation, activation and immobilization of Tl, and (3) to explore the main controlling factors and mechanisms of speciation transformation and bioavailability of Tl in paddy soil under the wetting/drying cycle. The implementation of this project is expected to enrich and deepen the understanding of environmental behavior of Tl, and provides a theoretical basis for the effective prevention and control of Tl pollution in farmland.