土壤-水稻系统中硫代砷的研究进展

Research advances of thioarsenates in the soil⁃rice system

硫代砷是土壤-水稻系统中砷的重要形态之一,其形态转化对砷的生物地球化学循环具有重要意义,同时也对环境和人类健康构成潜在威胁.总结了近年来国内外有关水稻土中硫代砷的定量检测方法、存在形态、影响因素、生物地球化学过程与水稻吸收机制方面的研究进展,旨在为后续研究提供方法参考与理论依据.为减少在环境样品分析之前硫代砷的形态转化,可向样品中加入二乙基三胺五乙酸(DTPA),将样品快速冷冻后低温避光保存.离子色谱串联电感耦合等离子体质谱法(IC-ICP-MS)适用于环境样品中硫代砷的分离与定量检测.无机硫代砷与甲基硫代砷在形成条件、环境行为以及水稻吸收方面存在显著差异.水稻土中硫代砷的含量受pH、氧化还原环境以及还原态硫等因素的影响,环境条件的变化会驱使不同形态硫代砷之间以及硫代砷与非硫代砷之间的相互转化.相较于(亚)砷酸盐,硫代砷在铁矿物表面的吸附能力通常较弱,且在土壤氧化还原条件变化时表现出更高的不稳定性.硫代砷可被水稻吸收并在籽粒中积累,其中二甲基一硫代砷酸盐(DMMTA)具有高吸收、高转运和高毒性,广泛存在于全球水稻籽粒与商品大米中.目前尚未明确水稻对硫代砷的吸收、转运与解毒机制,值得进一步深入探索以准确评估硫代砷对水稻生长、食品安全与人类健康所带来的潜在风险.

Thioarsenates have been proved to be important species of arsenic in the soil⁃rice system,their transformations playing a crucial role in the biogeochemical cycle of arsenic and posing a potential threat to the environment and human health.This article provides a comprehensive overview of the latest research progress on quantitative detection methods,species,influence factors,biogeochemical processes and rice uptake mechanisms of thioarsenates in paddy soil,in an effort to provide methodological references and theoretical foundation for future research.To minimize the transformations of thioarsenates before analysis,diethylenetriamine⁃pentaacetic acid(DTPA)can be added to the sample,which can be flash⁃frozen and stored in the dark at low temperature.Ion chromatography coupled to inductively coupled plasma–mass spectrometry(IC⁃ICP⁃MS)is suitable for the separation and quantitative determination of thioarsenates in environmental samples.There are significant differences between inorganic and methylated thioarsenates in their formation conditions,environmental behaviors and rice uptake.Concentrations of thioarsenates in paddy soil are affected by many factors such as pH,redox environment and reduced sulfur.Changes of environmental conditions can facilitate transformations between various thioarsenates or between thioarsenates and non⁃thioarsenic species.Notably,the adsorption capacities of thioarsenates on iron minerals are usually weaker compared with arsenite and arsenate,and thioarsenates show higher instability with the changes of the soil redox conditions.Thioarsenates can be absorbed by rice and accumulated in grains.Dimethymonothioarsenate(DMMTA)exhibits high uptake,transport,and toxicity in rice,and it exist in rice grains and commercial rice globally.Currently,the mechanisms of uptake,transport and detoxification of thioarsenates in rice remain unclear,which is worthy of further research to accurately assess the potential risks of thioarsenates on rice growth,food safety,and human health.