轻稀土尾矿库区植被修复的镧、铈富集植物筛选

Selection of La and Ce Hyper-Tolerant Plants for Vegetation Rehabilitation in Light Rare Earth Tailing

【目的】测定我国北方某轻稀土尾矿库区的土壤轻稀土元素含量及植物中镧、铈元素含量和分布,分析植物对轻稀土元素镧、铈的转移系数和吸收系数,筛选镧、铈富集植物,以期发现轻稀土富集植物,为尾矿库景观生态恢复提供理论依据。【方法】以稀土尾矿库区尾矿坑的边缘绿地为研究样地,依据风向将采样点设置在东南、西北、东北和西南4个方向,从矿坑边缘由近及远依次设置在50,100和300m边坡处,共计12个采样点。利用五点采集-四分法收集0~20cm表层土壤样品,在采样点采集修复工程栽植的6种植物(梭梭、小叶锦鸡儿、花棒、胡枝子、白刺和毛白杨)地上器官和根部样品。采用ICP法测定土壤中轻稀土元素镧La、铈Ce、镨Pr、钕Nd、钐Sm、钷Pm和铕Eu含量及植物中镧和铈含量。采用N.L.Nemerow综合指数法分析轻稀土尾矿库周边土壤单因子污染指数平均值,采用生物转移系数评价植物转移效率,采用生物吸收系数评价植物吸收土壤中镧和铈的能力。【结果】轻稀土尾矿库土壤中La,Ce,Pr,Nd,Sm,Pm和Eu的平均含量分别为2762.46,5440.42,1308.42,1604.11,133.96,28.12和40.53mg·kg-1,镧、铈含量之和占测试样品轻稀土总量的72%;各方位表层土壤中轻稀土含量表现为东南>东北>西南>西北,且高于内蒙古土壤含量几何平均值(背景值)25.10~230.56倍,且各方向土壤的单因子污染指数均大于3,确定研究区土壤属重度污染;东南单因子污染指数平均值为69.06~544.10,污染值最高,西北单因子污染指数平均值为5.99~19.75,污染值最低,东北和西南单因子污染指数平均值相似;梭梭、胡枝子和白刺体内La和Ce含量均表现为地上器官>根,小叶锦鸡儿、花棒和毛白杨体内La和Ce含量均表现为根>地上器官;梭梭、胡枝子和白刺的镧、铈转移系数为1.03~1.76,胡枝子的镧、铈吸收系数为1.00~1.72,只有胡枝子的镧、铈转移系数和吸收系数均大于1。【结论】胡枝子是轻稀土元素镧、铈的富集植物,可用于轻稀土污染土壤修复,其他5种植物可作为轻稀土元素的耐受性植物应用。

【Objective】The paper was intended to measure the contents of light rare earth elements in the soil and the contents of La and Ce and their distributions in plant in a light rare earth tailings in north China, Biological Transfer Coefficient (BTC) and Biological Absorption Coefficient (BAC) of the plants for La and Ce absorptions were calculated for the selection of La and Ce hyper-tolerant plants,in order to provide a scientific basis for landscape restoration in the tailings.【Method】Study site was selected at the edge of the rare earth tailings and 12 sampling plots were set up in 4 directions of south-east,north-west,north-east,and south-west according to the wind direction at 50,100 and 300 m from the mine pit.Firstly,the 0 to 20 cm surface soil samples were collected using the 5-points collection and quarter-division method,and plant samples were collected from the above-ground organs and the roots of the trees planted by the rehabilitation program ( Haloxylon ammodendron,Caragana microphylla,Hedysarum scoparium,Lespedeza bicolor,Nitraria tangutorum,and Populus tomentosa ).Secondly,the contents of light rare earth elements La,Ce,Pr,Nd,Sm,Pm,and Eu in the soil and the contents of La and Ce in the plants were measured by ICP.Furthermore,the average of the single factor pollution index of soil in the surrounding areas of the tailings was analyzed with the N.L.Nemerow comprehensive index method.Lastly,the plant transfer efficiency was evaluated by the BTC and the plant absorbing ability of La and Ce was evaluated by BAC.【Result】The average contents of La,Ce,Pr,Nd,Sm,Pm,and Eu in the soil of the light rare earth tailings were 2 762.46,5 440.42,1 308.42,1 604.11,133.96,28.12 and 40.53 mg ·kg -1 respectively,and the contents of La and Ce accounted for 72% of total contents.The order of these contents in the surface soil of all directions was south-east> north-east> south-west> north-west,all the values of which were 25.10 to 230.56 times higher than the geometric mean value (background value) of Inner Mongolia.Also,the single factor pollution indices of all directions were greater than 3,which could ascertain that the surrounding areas of the light rare earth tailings were seriously polluted.Then,the average values of the single factor pollution index in the south-east direction were 69.06 to 544.10,which were the highest.By contrary,the values in northwest were 5.99 to 19.75,which were the lowest. Meanwhile,the values in the north-east and south-west directions were similar.On the one hand,the La and Ce contents of the above-ground organs of H.ammodendron,L.bicolor and N.tangutorum were all higher than those in the roots.On the other hand,the La and Ce contents of the roots of C.microphylla,H.scoparium and P.tomentosa were all higher than those in the above-ground organs.At last,the BTC of La and Ce of H.ammodendron,L.bicolor and N.tangutorum ranged from 1.03 to 1.76.The BAC of La and Ce of L.bicolor ranged from 1.00 to 1.72.Only the BTC and BAC of L.bicolor were both greater than 1.【Conclusion】 L.bicolor was the hypertolerant plant of La and Ce,which might be significant for the remediation of light rare earth polluted soil.The other 5 plant species can be used as tolerant to light rare earth elements.