水稻根系锑吸收过程的同位素分馏效应与机制

Antimony (Sb) is a carcinogenic and toxic environmental pollutant. It can be accumulated by plants such as rice, possessing potential risks to human beings via food consumption. Understanding the mechanisms underlying the complex transport and transfer of antimony from paddy soil to the root system of rice and its translocation within the plant is key to the development of strategic schemes for better pollution prevention and management in antimony contaminated paddy farms. However, few prior studies have focused on this topic. For example, root plaques are known to adsorb heavy metals and inhibit their uptake by rice plant, but whether heavy metals such as antimony adsorbed on plaques could remain bioavailable to rice remains unknown. In this project we propose to employ stable isotope geochemistry methodologies to study the mechanisms underlying uptake and translocation of antimony within the soil-root system. We will quantify stable Sb isotopic fractionation during 1) Sb uptake by rice roots in the absence of iron plaques, 2) in the presence of iron plaques, and 3) Sb adsorption on ferrihydrite, the main mineralogical constituent of the plaque. The systems 1) and 2) will be hydroponically grown rice and system 3) will be the mineral synthesized in lab following standard procedures. Both the distinct difference in isotope fractionation patterns and Sb distributions in different phases or compartments, along with the physiological characteristics of rice will be used to quantify the sources of Sb (either from growth medium or partially from adsorbed plaque phase) uptaken by rice root systems. The study will help answer whether Sb adsorbed on iron plagues of external root surfaces could be absorbed by root during growth of rice, which is key to assessing the role of the iron plaque in reduction of Sb by rice. It will provide strong scientific support for developing pollution control technologies aiming at reducing Sb uptake by rice via stimulation of iron plaque growth on root systems. Our study will not only help develop the stable isotope geochemistry methodologies for investigating the mechanisms of uptake, translocation, and metabolism of Sb by rice plant, but also may stimulate motivation in scientific community for broadening the applications of stable metal isotope-based methodologies (e.g., cadmium) in pollution control of paddy soils.

锑是致癌有毒重金属，能在水稻等农作物中富集，威胁粮食安全。水稻根系能从土壤中吸收锑并在其植物体内转运和代谢，同时水稻根际自然生长的铁膜能吸附锑并可以降低锑被水稻吸收，然而这个降低锑吸收的过程及其影响机制尚不明确。本项目将以土壤中主要存在形态五价和三价锑为对象系统研究1）水培水稻有、无铁膜条件下根系对锑吸收的生物地球化学过程中锑同位素分馏和2）铁膜主要成分水铁矿对锑吸附的物理化学过程中锑同位素分馏，通过甄别同位素分馏特征差异，并分析锑在体系中各部位的分布，结合植物生理资料，定量解析有铁膜的水稻根系所吸收的锑来源。本研究将为铁膜吸附态锑能否被水稻根系直接吸收（即铁膜阻隔锑吸收）这一关键科学问题提供答案，为研发以促进根系铁膜生长为基础的稻田阻隔修复技术提供科学依据，同时为发展稳定同位素地球化学方法在水稻等农作物锑的吸收、转运和代谢机理研究奠定基础，并为该方法在研究农田其它重金属污染提供参考。

锑是致癌有毒重金属，能在水稻等农作物中富集，威胁粮食安全。水稻根系能从土壤中吸收锑，同时水稻根际自然生长的铁膜能吸附锑并可以降低锑被水稻吸收，然而这个降低锑吸收的过程及其影响机制尚不明确。利用锑稳定同位素方法研究水稻根际锑的生物地球化学过程的根本和关键是过程的同位素分馏效应与机制研究。因此，研究水稻根系吸收锑及其在植物体内的转运和代谢过程与机理。. 本项目主要研究了水稻根际铁膜的主要形态之一水铁矿对锑的吸附动力学和吸附过程的锑同位素分馏机制，除水铁矿外，还对比研究了针铁矿对锑的吸附动力学和吸附过程的同位素分馏研究，探讨了两种吸附剂对锑同位素分馏的差异。初步研究了无铁膜水稻的锑暴露实验研究，通过残留营养液锑同位素组成，推算出水稻锑的同位素组成；利用同位素分馏规律，结合分馏模型，初步探讨了铁膜对锑吸附过程的同位素分馏机制和水稻吸收过程的对锑同位素分馏的影响。吸附动力学研究表明：吸附在水铁矿上的Sb形成了内层表面吸附结构，包括共边和双角构型，Sb作为八面体吸附在针铁矿表面，与Fe(OH)6八面体在针铁矿表面倾向于形成共边内吸附络合物，吸附过程都是单层化学吸附。同位素分馏研究表明：pH值和溶解的Sb浓度等环境条件对吸附和Sb分馏因子有影响。在所有条件下，较轻的Sb同位素优先吸附在水铁矿和针铁矿表面，使溶液中Sb相对于初始Sb原液同位素较重。封闭平衡体系模型适合描述所有吸附实验数据，表明Sb水溶液与表面吸附的Sb之间存在平衡同位素交换。水铁矿的锑同位素分馏系数αsolid-solution平均值为0.99957，针铁矿的锑同位素分馏系数为0.99950。水铁矿吸附的Sb同时形成了分边和双分角配合物，而针铁矿吸附的Sb只形成了分边表面配合物。Sb配合物的差异可能是水铁矿与针铁矿吸附Sb同位素分馏差异的原因。以上研究结果对根际铁膜吸附和水稻的生物吸收过程进行系统研究，明确根际铁膜吸附作用和水稻根锑吸收机制，有着现实而重要的意义。