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土壤质量是农业生产中粮食安全的重要保障[1]. 随着工业的发展,土壤污染日益严重,其中重金属污染已成为社会广泛关注的土壤污染问题之一[2]. 工业三废的排放、矿产资源的开发以及农业生产中化肥、农药的过量施用是土地中重金属污染的主要来源[3]. 据资料显示我国农业耕地受重金属污染面积近20万km2,约占耕地总面积的20%[4]. 进入土壤的重金属会通过扬尘、饮水或食物链传递等途径在人体富集,进而损害人体器官、影响神经系统甚至会引发癌症[5].
矿产资源开发、金属冶炼与加工等过程中产生含重金属的“三废”以堆砌、沉降等形式进入土壤,是造成矿区及其影响区土壤重金属污染的主要来源之一,严重威胁生态系统和人体健康[6]. 内蒙古自治区矿产资源十分丰富,储量大、种类多、分布较为集中,据资料显示2015年全自治区已发现144种矿种,亚矿种有164种,占全国已发现矿种的83.72%,其中有43种矿产资源储量高居全国前三[7]. 据统计自治区现存有色金属采选业企业数量约140余家,包含多种矿物采选,其中铅锌矿采选企业数量最多. 从地域看自治区有色金属采选业企业主要分布于内蒙古东部地区,主要集中于赤峰市、锡林郭勒盟、呼伦贝尔市3个盟市,占全区企业数量的80%以上[8]. 矿产资源的开发、冶炼和加工造成矿区及其影响区土壤重金属污染. Hu等[9]研究发现,内蒙古赤峰市某典型有色金属矿区As、Cd、Cu、Pb和Zn的含量都超过了当地土壤背景值,潜在生态风险评价结果表明,矿区以及周边地带都处于中等风险水平. 郭伟等[10]研究发现,包头尾矿库区周边土壤都受到了重金属Pb、Cu、Zn、和Mn不同程度的污染,影响了周边的生态环境安全. 杨勇等[11]研究发现,锡林郭勒盟胜利煤田露天矿区土壤中重金属元素Cu含量高于内蒙古背景值. 周妍姿等[12]学者测定了内蒙古土壤剖面样品Ni、Mn、Cr、Cu、Zn、As和Pb重金属的浓度,结果表明,所有重金属类型变异性均较高,意味着影响土壤重金属含量的自然和人为因素的区域分异极为强烈.
虽然近些年关于内蒙古地区土壤重金属污染及生态风险评估的研究取得了一些进展,但大部分都是围绕有色金属矿区或矿区周边农田土壤展开的研究[13 − 15],而对于内蒙古草原地区土壤重金属来源途径、分布特征及生态风险评估相关的研究则鲜有报道. 内蒙古自治区拥有全国面积最大的草原,总面积为74.9185万km2[16]. 草原土壤的健康对于维持草原生产力和筑牢我国北方生态安全屏障至关重要. 内蒙古中东部地区主要的植被类型分为森林、典型草原、草甸草原和荒漠草原,几乎涵盖内蒙古地区的所有植被类型;而且内蒙古中东部地区人口相对密集,人类活动、资源开采等行为都会对土壤环境和理化性质产生一定影响. 因此开展内蒙古地区草原土壤中重金属元素污染特征和生态风险评估的研究具有重要的科学与实际意义. 本研究以内蒙古中东部草原土壤作为研究对象,按植被类型进行样带划分并进行采样,分析土壤中6种重金属元素(Cd、Cr、As、Zn、Pb和Cu)的含量及其空间分布特征,采用地累积污染指数法、潜在生态风险指数法和风险评估指数法对土壤中重金属的生态风险进行评价. 本文旨在揭示内蒙古地区草原土壤的重金属污染状况,为内蒙古地区生态环境保护和土壤污染防治提供科学依据.
内蒙古中东部地区草原土壤中重金属分布特征及生态风险评价
Distribution characteristics and ecological risk evaluation of heavy metals in grassland soils in the east-central region of Inner Mongolia
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摘要: 为探究内蒙古中东部地区草原土壤重金属污染特征及生态风险状况,采集四子王旗、苏尼特右旗、商都、锡林浩特、西乌旗、新巴尔虎左旗、鄂温克族自治旗等地区土壤,对其中重金属元素(Cd、Cr、As、Zn、Pb和Cu)的全量和有效态含量进行测定,运用空间插值法分析内蒙古草原土壤中重金属含量的空间分异特征;同时采用地累积指数法、潜在生态风险指数法和风险评估指数法对重金属元素的生态风险进行了评价. 结果表明,内蒙古中东部地区草原土壤全量重金属元素Cr、Cu、Pb的平均含量相对较低,而Cd、As和Zn全量的均值分别是背景值的3.58倍、1.53倍和1.98倍. 地累积指数评价结果显示Cd的污染程度最高,其它元素污染程度相对较低. 潜在生态风险指数评价结果显示Cd为研究区土壤中最主要的潜在生态危害因子,其次是As,其它元素则处于低生态危害. 风险评估指数法结果显示,研究区土壤中有效态重金属占重金属总量的百分含量不到10%,说明研究区土壤中重金属元素的生物可利用性较低,对环境构成的风险也相对较低. 综合来看,研究区土壤中Cd元素存在一定的潜在风险,需引起有关部门高度重视,加大监测力度.Abstract: To investigate the characteristics and ecological risk of heavy metal pollution in grassland soils in the east-central region of Inner Mongolia, soils were collected from Siziwang Banner, Sunit Right Banner, Shangdu, Xilinhot, Xiwuqi, Xinbahuzuo Banner and Ewenke Autonomous Banner. The total and available content of heavy metals (Cd, Cr, As, Zn, Pb and Cu) in soils were determined, the spatial variation characteristics of heavy metal contents in grassland soils of Inner Mongolia were analyzed using spatial interpolation method. The ecological risks of heavy metals were also evaluated using the geological accumulation index, the potential ecological risk index and the risk assessment index. The results showed that the average total contents of Cr, Cu and Pb in the grassland soil of the east-central region of Inner Mongolia were relatively low, while the average total contents of Cd, As and Zn were 3.58, 1.53 and 1.98 times of the background values respectively. The results of the evaluation of the ground accumulation index show that the pollution level of Cd is the highest, while those of other elements is relatively low. The evaluation results of potential ecological risk index showed that Cd was the most important potential ecological hazard factor in the soils of the study area, followed by As, and the other elements were in low ecological hazard. The results of risk assessment index method showed that the available heavy metals in the soils of the study area accounted for less than 10% of the total heavy metals content, indicating that the bioavailability of heavy metal elements in the soils of the study area is low and the risk posed to the environment is relatively low. In general, there is a certain potential risk of Cd in the soil in the study area, which needs to be highly valued by relevant departments and strengthened monitoring.
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Key words:
- inner Mongolia /
- grassland soil /
- heavy metal pollution /
- risk assessment.
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表 1 土壤采样信息表
Table 1. Soil sampling information table
编号
Number样带编号
Sample number纬度
Latitude经度
Longitude海拔/m
Altitude采样点数
Number of sampling points草原类型
Grassland type1 四子王旗样带1 111.9014 41.7850 1454.30 3 荒漠草原 2 四子王旗样带2 111.9933 41.9729 1498.20 6 荒漠草原 3 四子王旗样带3 111.9972 41.9778 1503.00 18 荒漠草原 4 四子王旗样带4 112.1908 42.1355 1347.76 18 荒漠草原 5 苏尼特右旗样带1 112.5493 42.6040 1163.06 3 荒漠草原 6 苏尼特右旗样带2 113.2477 43.5407 983.21 13 荒漠草原 7 锡林浩特样带1 116.6773 43.5634 1227.04 2 典型草原 8 锡林浩特样带2 116.5593 43.5432 1182.20 19 典型草原 9 锡林浩特样带3 116.6979 43.5844 1212.34 3 典型草原 10 锡林浩特样带4 116.6972 43.5824 1240.35 1 典型草原 11 西乌旗样带 119.1073 41.5543 990.95 3 典型草原 12 鄂温克族自治旗样带1 119.7077 48.5129 720.30 3 草甸草原 13 鄂温克族自治旗样带2 119.7132 48.5197 717.58 8 草甸草原 14 新巴尔虎左旗样带1 118.2716 48.1963 613.10 3 草甸草原 15 新巴尔虎左旗样带2 118.4293 48.1735 670.00 3 草甸草原 16 商都样带 113.3901 41.4881 1391.00 3 荒漠草原 表 2 研究区土壤中不同重金属元素总含量统计表(mg·kg−1)
Table 2. Total contents of different heavy metals in soil of the study area(mg·kg−1)
元素
Element最大值
Maximum最小值
Minimum平均值Average 背景值
Background标准差
Standard deviation变异系数
Coefficient of variation平均值/背景值
Average/Background valueZn 411.07 34.21 116.87 59.10 82.53 70.62% 1.98 Cr 60.84 8.49 27.14 41.40 10.22 37.67% 0.66 Cu 110.38 2.90 12.79 14.10 15.94 124.57% 0.91 As 44.41 4.21 11.51 7.50 44.18 71.76% 1.53 Cd 1.10 0.03 0.19 0.053 0.11 60.98% 3.58 Pb 18.04 3.84 11.50 17.20 3.60 31.32% 0.67 表 3 研究区土壤中不同重金属元素有效态含量统计表(mg·kg−1)
Table 3. Statistical table of available state contents of different heavy metal elements in soil of the study area(mg·kg−1)
元素
Element平均值
Average最大值
Maximum最小值
Minimum标准差
Standard deviation变异系数
Coefficient of variationRAC/% Zn 2.63 6.89 1.40 0.02 44.05 2.25 Cr 0.94 1.32 0.68 0.00 10.43 3.46 Cu 1.84 8.53 0.84 0.08 60.19 7.07 As 3.21 3.63 2.41 0.05 9.55 6.22 Cd 0.03 0.05 0.02 0.24 32.41 1.06 Pb 0.99 2.30 0.54 0.03 42.63 2.93 -
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