相山铀矿尾矿区植物根际土壤稀土元素和铀、钍生物富集特征

Bioaccumulation of rare earth elements,uranium and thorium in plant-rhizosphere soil in Xiangshan uranium tailings areas

本文采集了相山铀矿尾矿库不同地方(库内、坝上和库下游)8种优势植物及其根际土壤,通过野外实地调查和室内分析相结合的方法,研究了植物根、茎、叶、穗和根际土壤REEs及U、Th的生物地球化学行为。结果表明,植物稀土元素总量(∑REEs含量)总体表现为根际土壤>根>茎和叶(穗)。归一化结果显示,库内植物根与根际土壤具有相似的重稀土元素(HREEs)富集、铕(Eu)负异常配分模式,坝上及下游则演变平坦配分模式且铈(Ce)负异常,茎、叶和穗出现轻稀土元素(LREEs)富集配分模式,指示REEs在土壤根体系及植物体内转运过程中发生了分异。根际土壤DTPA萃取实验表明HREEs优先于LREEs被生物吸收利用,且Gd的生物有效性相对于其他REEs更差。Person相关分析表明土壤pH、Fe、Mn矿物吸附和有机质是影响REEs生物有效性的重要因素;灰色关联分析显示U、Th和REEs在根际土壤与根中的灰色关联度普遍大于叶茎穗,指示土壤U和Th对REEs含量的影响在根中大于叶茎穗。芒萁叶REEs的富集系数(BCF=6.09)和转运系数(TF=8.25)均大于1,茎和根部的转运系数和富集系数也优于其他植物,指示芒萁可作为REEs的环境修复植物,水稻的根部对REEs和Th、U均有较强的富集作用,可作为植物联合修复的考虑对象。

Eight dominant plants and their rhizosphere soils were collected from different parts of the Xiangshan uranium tailings areas(in the tailing pond,on the dam,and downstream of the tailing pond).The bioaccumulation behavior and spatial isomerism characteristics of rare earth elements(REEs),uranium(U),and thorium(Th)in the roots,stems,leaves,spikes,and rhizosphere soils of the plants were studied through field investigation and laboratory analysis.The results showed that the total REE(∑REEs)contents were highest in the rhizosphere soils,followed by the roots,stems,and leaves(spikes).REE normalization indicated that,for plants in the pond,the roots exhibited similar patterns to the rhizosphere soils,showing enrichment of heavy rare earth elements(HREEs)and a negative europium(Eu)anomaly.In contrast,for plants collected from the dam and downstream of the pond,the roots and rhizosphere soils had relatively flat patterns with a negative cerium(Ce)anomaly,while the stems,leaves,and spikes showed enrichment of light rare earth elements(LREEs).This indicated that fractionation of REEs occurred during the transport from soils to roots in the soil-root systems and within the plant tissues.A DTPA extraction experiment with the rhizosphere soils showed that HREEs were preferentially taken up by plants compared to LREEs,and the bioavailability of gadolinium(Gd)was lower than that of other REEs.Pearson correlation analysis revealed that soil pH,Fe/Mn mineral adsorption,and organic matter were important factors affecting the bioavailability of REEs.Grey correlation analysis showed that the grey correlation coefficients of U,Th,and REEs were generally higher between rhizosphere soil and root as compared to those between rhizosphere soil and leaf,stem,and spike,reflecting that the influence of soil U and Th concentration on REEs was greater in root than that in leaf stem,and spike.The REEs Bioconcentration Factor(BCF=6.09)and Translocation Factor(TF=8.25)of Dicranopteris dicthotoma leaves were both greater than 1,and BCF and TF of its stems and roots were also higher than other plants.This indicated that Dicranopteris dicthotoma could be used as an accumulator for REEs.The rice roots were strongly accumulated with REEs,Th and U,which meat that rice could be considered as the candidate for joint-contamination phytoremediation.