重庆溶溪锰矿区土壤重金属污染评价及植物吸收特征

对重庆溶溪锰矿尾渣堆积区土壤、优势植物以及周边农田土壤的重金属含量(Mn、Cd、Cu、Zn和Pb)进行测定分析,并以重庆市土壤背景值为评价标准,应用Hakanson潜在生态危害指数法对土壤中重金属的潜在生态危害进行了评价。结果表明:该锰矿尾渣堆积区土壤中Mn、Cd、Cu、Zn和Pb的平均含量分别为48382.5、3.91、79.97、131.23和80.68 mg/kg,受到Mn、Cd的严重污染,Mn为强或很强生态危害,Cd为极强生态危害,而Cu、Zn、Pb为轻微生态危害,各尾矿渣堆积区的综合潜在生态危害指数(RI)均远大于720,为极强生态危害。对优势植物重金属含量的分析显示,绝大部分植物地上部Mn、Cd含量都超出正常范围的上限值,而Cu、Zn和Pb含量基本都在正常范围内;根据植物对重金属的吸收特征,将植物分为三类:将重金属主要累积于地上部分的富集型,如垂序商陆(Phytolacca americana L.)和酸模叶蓼(Polygonum lapathifolium Linn.),适用于重金属复合污染土壤的植物修复;将重金属主要累积于根部的根部囤积型,如芒(Miscanthus sinensis Anderss.)和乌蕨(Stenoloma chusanum Ching);重金属含量较低的规避型,如黄花蒿(Artemisia annua L.)、长波叶山蚂蝗(Desmodium sequax Wall.)及钻形紫苑(Aster subulatus Michx.);后两种类型的植物可种植在重金属污染严重且使用价值相对较低的矿山废弃地上,同时规避型植物对于研究植物的重金属排斥机理具有重要价值。溶溪锰矿区周边农田土壤主要受到Cd的严重污染,Cd为很强或极强生态危害。

Assessment of heavy metal pollutions in soils and bioaccumulation of heavy metals by plants in Rongxi Manganese mineland of Chongqing

Mining activities are producing waste tailings that pose serious environmental impacts to aquatic and terrestrial ecosystems. In most mining activities, these waste tailings are left without proper management. The negative impact of these mining activities on the surroundings is m ainly due to the presence of high volumes of tailing. These tailings are usually unfavorable to the surrounding environment, contributing to the contamination of soil substrates, destruction of soil texture, short of nutrient, destruction of ecological diversity. Heavy metals are considered highly hazardous to ecosystems and humans, not only because of their direct toxicity to organisms but also due to their potential for bioaccumulation along the food chain. This is a global concern. Studies of natural and man-made environmental interaction of metals after mining have become increasingly important to society. Xiushan County is located in southwest China and is rich in Mn ore. Rongxi Manganese mine is one of the biggest mines in Xiushan County. This region is economically underdeveloped where mining is the most important pillar industry. Mining activities in this region has deleterious effects on the local environment due to deposition of large volumes of wastes on the soil. Finding out tolerant plants, which can adapt to the local climate and soil conditions, is a premise for soil remediation and vegetation restoration. The aim of this study is to examine the heavy metal concentrations in soils and dominant plants, and to determine plant-soil relationships for the various native species that grow directly on the mining tailings in the Rongxi Mn mine. This information can be used to establish guidelines in order to assess further revegetation options by selecting the most suitable plant species to revegetate the tailings. The contents of heavy metals (Mn, Cd, Cu, Zn and Pb) in soils and dominant plants were measured in Rongxi Manganese mine. Hakanson's ecological risk index and single-factor pollution index were employed to evaluate the heavy metal pollutions in soils and vegetables, respectively. The results showed that the average contents of Mn, Cd, Cu, Zn and Pb in soils collected from Manganese mining tailing were 48382.5, 3.91, 79.97, 131.23 and 80.68 mg/kg, respectively. Cd and Mn posed heavily ecological risks, while Cu, Zn and Pb posed light potentially ecological risk. The contents of Mn and Cd in the dry shoots of most dominant plants exceeded the upper limit of the normal range, while the contents of Cu, Zn and Pb fell within the normal range. According to the plant-soil relationships, plants were classified into three groups: accumulators, excluders and compartments. Accumulators such as Phytolacca americana L. and Polygonum lapathifolium Linn. absorbing high concentrations of heavy metals in the shoots are suitable to clean up the compound pollution of heavy metals. Compartments like Miscanthus sinensis Anderss. and Stenoloma chusanum Ching store high levels of heavy metals in the roots and transfer little to shoots. Excluders including Artemisia annua L., Desmodium sequax Wall., and Aster subulatus Michx. are the plants accumulating little heavy metals in their bodies though they grow on the severely polluted soil. The latter two can be used to remediate mine soils with higher heavy metals levels and low use value, and excluders had an important value in the study of plant heavy metal exclusion mechanism. The surrounding farmland soils were also mainly polluted by Cd.