螯合诱导植物修复铀污染土壤的研究进展

Research Progress on Chelating Agent Induced Phytoremediation of Uranium-Contaminated Soils

土壤中的铀植物可利用性低,这会限制植物提取对铀污染土壤的修复效果。螯合剂可以使土壤中铀的赋存形态由难被植物吸收利用态转化为易被植物吸收利用态,达到活化铀的效果,从而辅助根系吸收铀。然而,植物往往难以在短时间内吸收大量被活化了的铀,可能导致植物中毒,并增加土壤铀淋溶进入地下水的风险,造成二次污染。本文对1996-2023年螯合诱导植物修复重金属和放射性核素污染土壤的研究进行文献计量学分析,归纳了螯合诱导植物修复技术的潜在环境风险,并针对螯合剂活化土壤铀速率过快的问题提出应用缓释技术,达到控制螯合剂在土壤中释放速率的目的,同时进一步梳理了代表性生物降解缓释载体材料和缓释螯合剂的释放机理,探讨了缓释螯合诱导植物修复的效果及其发展趋势,以期为缓释螯合剂在铀污染土壤植物修复领域的应用提供新的途径。结果表明:①目前在螯合诱导植物修复技术领域应用广泛的螯合剂包括以EDTA(乙二胺四乙酸)和EDDS(乙二胺二琥珀酸)为代表的氨基多羧酸类螯合剂,以及以柠檬酸为代表的低分子量有机酸类螯合剂,应用广泛的富集植物包括印度芥菜、向日葵和黑麦草等,其中黑麦草对铀具有较好的富集能力。②螯合剂虽然可以提高植物提取土壤铀的效率,但螯合剂本身的毒性作用及其在土壤中的残留效应可能导致植物中毒、干扰微生物群落,降低土壤质量;此外,施用螯合剂后产生的大量不能被及时吸收的活化铀可能会增加土壤铀淋溶进入地下水的风险。③代表性生物降解缓释载体材料可分为天然聚合物、合成聚合物和无机材料三大类,其中单一材料作为缓释载体均存在机械强度较差的缺点,需要通过改性延长缓释周期。④缓释螯合剂的释放机理分为水吸附、涂层/基质膨胀、水扩散3个阶段。⑤现有缓释螯合剂的制备过程往往加入多种有毒有害化学试剂。今后需要研发绿色合成技术制备生物降解缓释螯合剂,确保绿色可持续修复过程。

The low bioavailability of insoluble uranium to plants limits the applicability of phytoremediation for decontaminating uraniumcontaminated soil.Chelating agents can change the non-absorbable and unusable form of uranium in soil to a state that can be easily absorbed and utilized by plants,thereby helping the roots absorb the mobilized uranium.However,it is often difficult for plants to absorb large amounts of mobilized uranium in a short period of time,which may lead to plant poisoning and increase the risk of uranium leaching into groundwater,causing secondary pollution.In this study,we conducted a bibliometric analysis of the chelating agent-induced phytoremediation of heavy metal and radionuclide contaminated soils from 1996 to 2023.Moreover,the potential environmental risks of chelating agent-mediated phytoremediation were summarized.In order to reduce the rate of uranium mobilization in soil,a slow-release technique was proposed to control the release rate of chelating agents.Therefore,a review was conducted on representative biodegradable slow-release carrier materials,and the release mechanism of slow-release chelating agents was investigated.Finally,the development trends and effects of slow-release chelating agent-induced phytoextraction technology were discussed with the aim of providing an approach for applying such chemical agents in the phytoremediation of uranium-contaminated soils.The following points were concluded from the obtained results.(1)The most widely used chelating agents include those based on aminopolycarboxylates(represented by ethylenediaminetetraacetic acid and ethylenediaminedisuccinic acid)and low-molecular-weight organic acids(represented by citric acid)and the most widely used hyperaccumulators include Indian mustard,sunflower,and ryegrass with uranium enrichment abilities.(2)Although chelating agents can improve the efficiency of uranium phytoextraction,their toxicity and residual effects may lead to plant poisoning,interference with microbial communities,and decrease in soil quality.Additionally,plants are unable to absorb a large amount of mobilized uranium in a short period of time,which may increase the risk of heavy metals leaching from soil into groundwater.(3)Representative biodegradable slow-release carrier materials can be categorized as natural polymers,synthetic polymers,and inorganic materials.Because a single carrier material has the disadvantage of poor mechanical strength,it is necessary to modify it to extend its slow-release period.(4)The release mechanism of slow-release chelating agents can be divided into three stages:water adsorption,coating/substrate expansion,and water diffusion.(5)The processes used to prepare existing slow-release chelating agents involve a variety of toxic and harmful chemicals.The research show that developing a green synthesis technology for preparing biodegradable slow-release chelating agent is needed to ensure a green and sustainable remediation process.