湖南省某典型流域农用地土壤重金属污染及影响因素

Heavy Metal Pollution and Influencing Factors of Agricultural Land in a Typical Watershed in Hunan Province

农田土壤环境直接关系到农产品质量安全,是维系“菜篮子”工程、保障“吃的放心”的重要基础,近年来受到广泛关注.为探明农田土壤重金属污染分布特征及主要影响因子,以污染问题突出、地势起伏较大、水网密布的我国湖南省某典型流域为研究区,以流域主干河流沿线的农田土壤为研究对象,借助单因子指数、内梅罗指数和潜在生态危害指数,综合评价土壤Cd、Hg、As、Pb、Cr这5种重金属的污染状况;结合多元统计分析与地统计分析的方法,分析土地利用类型、地形因子与重金属含量的关系,并对土壤重金属空间分布和污染来源进行探究.结果表明:①研究区土壤Cd、Hg、As、Pb、Cr的平均含量分别为1.59、0.19、33.01、229.95、72.78 mg kg.其中,Cd、As、Pb的平均含量均超过研究区土壤背景值.②内梅罗指数分析显示,研究区中77.16%的土壤点位评价结果为重度污染;与GB 15618—2018《土壤环境质量农用地土壤污染风险管控标准(试行)》中农用地土壤污染风险管制值相比,土壤点位中Cd、As、Pb超标现象突出,主要分布于流域上游西部;综合潜在生态危害评价结果表明,3.05%的土壤点位表现为强生态风险及以上.③不同土地利用类型中,土壤重金属含量存在显著差异.旱地、水田、果园土壤中Cd、Hg、As、Pb的含量依次降低.高程与各重金属(除Hg外)含量均呈显著相关(P<0.05),坡度、坡向与各重金属含量的相关性均不显著(P<0.05).④源解析结果表明,流域农田土壤中Cd、As、Pb受到工业生产活动、交通运输、农业活动的综合影响,Hg、Cr主要来源于成土母质等自然因素.研究显示,研究区土壤中重金属存在一定程度的污染,重金属富集受土地利用类型、高程及人为因素的影响较明显.

The soil environment of farmland directly affects the quality and safety of agricultural products.It is an important foundation for maintaining the‘vegetable basket’project and ensuring‘safe eating’,and has received widespread attention in recent years.To determine the distribution characteristics and main influencing factors of heavy metal pollution in farmland soil,a typical watershed in Hunan Province and farmland soil along the main watershed river were studied.The watershed has prominent pollution problems,large terrain fluctuations,and a dense water network.The pollution status of Cd,Hg,As,Pb,and Cr in the soil was comprehensively evaluated using the single factor Nemerow index and potential ecological hazard index.Combining multivariate statistical analysis and geostatistical analysis,the relationship between land-use types,terrain factors,and heavy metal content was concurrently analyzed,and the spatial distribution of soil heavy metals and sources of pollution were explored.The results showed that:(1)The average concentrations of Cd,Hg,As,Pb,and Cr in the soil were 1.59,0.19,33.01,229.95 and 72.78 mg kg,respectively.Among them,the average content of Cd,As,and Pb was higher than the background values in the study area.(2)The Nemerow index showed that 77.16%of the soil sample points were seriously polluted.Compared with the Soil Environmental Quality Risk Control Standard for Soil Contamination of Agricultural Land(GB 15618-2018),Cd,As,and Pb substantially exceeded the standard and were mainly distributed in the western upper reaches of the river basin.The comprehensive potential ecological hazard evaluation results showed that 3.05%of the soil samples had significant ecological risks.(3)The difference in land use resulted in significant differences in heavy metal content in the soils.The heavy metal contents of Cd,Hg,as and Pb in dry land,paddy field and orchard decreased in turn.There was a significant correlation between the elevation and content of heavy metals(except Hg)(P<0.05),and there was no significant correlation between slope and aspect and heavy metal content(P<0.05).(4)The source analysis results showed that Cd,As,and Pb in farmland soil of the basin were affected by the combined effects of industrial production activities,transportation,and agricultural activities.Hg and Cr are mainly came from natural activities such as parent soil material.This study has shown heavy metal pollution in the soil of the study area.The accumulation of heavy metals is significantly affected by land use type,elevation and human factors.