典型锰矿区周边农田土壤-农作物重金属污染特征及生态风险评价

Pollution Properties and Ecological Risk Assessment of Heavy Metals in Farmland Soils and Crops Around a Typical Manganese Mining Area

以湖南省某典型关停锰矿区为研究对象,采集了矿区周边(污染区)和远离矿区(对照区)的农作物及其对应的土壤样品,测定了Cr、Mn、Ni、Cu、Zn、As、Cd和Pb等8种重金属含量,利用ArcGIS空间插值和主成分分析法分析了土壤重金属的分布及主要来源,重点探讨了土壤及对应农作物间重金属迁移规律,采用单因子、综合污染指数法以及潜在生态风险指数法进行了生态风险评价.结果表明,污染区存在严重的Cd、Zn、As和Mn污染,其中旱田中的平均含量分别为6.22、612.28、37.72和1506.2 mg·kg^(-1),相较农用地风险筛选值,Cd、Zn和As超标率分别为88.41%、94.2%和84.06%,Mn的平均含量是湖南土壤背景值的3倍,水田污染相对较轻.由主成分分析可知农田土壤中Cd、Zn和Mn的来源与锰矿开采有关,As可能来源于农业活动.污染区为重污染等级,Cd、Mn和Zn是主要的污染因子,土壤中Cd存在极强的潜在生态风险,其余重金属具有轻微的潜在生态风险.研究区农作物主要存在Cr、Pb和Cd超标且超标率在1.1%~37.3%,其中,玉米中各超标重金属含量均值均高于大米,叶菜类蔬菜中各重金属含量均值均高于根茎类蔬菜.农田土壤污染程度会影响作物的富集能力,且不同作物对重金属的富集能力不同,蔬菜和玉米中8种重金属以及大米中Cd和As与对应土壤中重金属呈现正相关.

In order to assess the ecological risks of heavy metals and explore the pattern of heavy metal migration between farmland and corresponding crops in a typical and closed manganese mining area in Hunan province,farmland soils and crops surrounding the mining area(pollution area)and away from the mining area(control area)were collected,and then the contents of Cr,Mn,Ni,Cu,Zn,As,Cd,and Pb were analyzed.The sources and distribution of heavy metals in farmland soils were analyzed using Kriging spatial interpolation and principal component analysis,and the ecological risk was evaluated using the single factor index,comprehensive pollution index,and potential ecological risk index.The results showed that the surrounding farmland soils in the closed Manganese mining area presented serious pollution of Cd,Zn,As,and Mn,in which the average contents of the above heavy metals in the dry land soil in the polluted area were 6.22,612.28,37.72,and 1506.2 mg·kg^(-1),respectively.Compared with the soil risk screening value of agricultural land,the over-standard rates of Cd,Zn,and As were 88.41%,94.20%,and 84.06%,respectively,and the average content of Mn in the farmland soil was three times that of the background value in the Hunan soil;however,the heavy metal pollution in the paddy field was relatively light.The principal component analysis showed that the sources of Cd,Mn,and Zn in the farmland soil were related to the manganese ore mining,whereas the source of As in the farmland soil might originate from agricultural activities.The pollution area was at a heavy pollution level,and the main pollution factors were Cd,Mn,and Zn.The Cd in the farmland soil could pose a strong potential ecological risk,but the rest of the heavy metals presented only a slight potential ecological risk.The content of Cr,Pb,and Cd in the crops in the study area exceeded the standard,and the exceeding standard rate was between 1.1%and 37.3%,where the average content of over-standard heavy metals in corn was higher than that in rice,and the average content of heavy metals in leafy vegetables was higher than that in root vegetables.The soil pollution degree of heavy metals could affect the accumulation ability of crops,and different crops had different accumulation abilities.For instance,leafy vegetables and root vegetables easily accumulated Cd and Zn;however,rice and corn separately enriched Cd and Cr,as well as Zn and Cu.The contents of heavy metals in dryland soils had a positive correlation with the content of heavy metals in corresponding crops.The contents of Cd and As in the paddy field and rice presented a positive correlation,but the remaining six heavy metal contents in rice(i.e.,Cr,Mn,Ni,Cu,Zn,and Pb)did not correlate with the content of the paddy fields.