桂西南地球化学异常区农田重金属空间分布特征及污染评价

Spatial Distribution Characteristics and Pollution Assessment of Heavy Metals on Farmland of Geochemical Anomaly Area in Southwest Guangxi

为了解桂西南地球化学异常区土壤Cd、Cu、Ni、Pb和Zn的空间分布特征及污染状况,共采集自然土壤和农田土壤256个并分析重金属含量.结果表明:①自然土壤Cd、Cu、Ni、Pb和Zn背景值分别为0.890、32.58、51.50、55.57和168.1mg·kg^-1.农田土壤(n=193)pH值在4.8~7.9之间,Cd、Cu、Ni、Pb和Zn几何均值分别为0.637、30.76、27.04、39.59和123.9 mg·kg^-1;②Kriging插值结果显示农田Cd、Ni、Pb和Zn空间分布特征较为相似,高含量区主要集中在崇左—龙州一带;田林县、凌云县、百色市和田阳县农田Cu含量最高;③以《土壤环境质量农用地土壤污染风险管控标准》(GB 15618^-2018)和土壤基线值为标准,农田Cd、Cu、Ni、Pb和Zn的超标率分别为57.5%、6.2%、0.5%、3.6%、10.9%和4.1%、14.0%、0.5%、2.1%和2.1%.综合污染指数表明,天等县、隆安县、大新县、龙州县和崇左市表现出较严重的复合污染特征.研究区地层发育时代齐全,构造性质复杂,矿床种类繁多,母质(岩)自身具有较高含量重金属,进而在风化成土过程土壤继承母质(岩)中的重金属,是桂西南地球化学异常区土壤具有较高背景值(特别是Cd元素)的最主要自然因素.

To understand spatial distribution characteristics and pollution status of Cd,Cu,Ni,Pb,and Zn in soils within geochemical anomaly areas in southwestern Guangxi,256 natural and farmland soils were collected,and heavy metal contents in soils were analyzed.The results show the following:①The background values of Cd,Cu,Ni,Pb,and Zn in natural soils were 0.890,32.58,51.50,55.57,and 168.1 mg·kg^-1,respectively.The pH value of farmland soil(n=193)ranged from 4.8 to 7.9.The geometric mean values of Cd,Cu,Ni,Pb,and Zn were 0.637,30.76,27.04,39.59,and 123.9 mg·kg^-1,respectively.②Kriging interpolation results showed that the spatial distribution characteristics of Cd,Ni,Pb,and Zn in farmland soils were similar,and highcontent areas were mainly concentrated in Chongzuo^-Longzhou area.The highest content of Cu was found in Tianlin County,Lingyun County,Baise City,and Tianyang County.③Taking the"Standard for Risk Control of Soil Pollution in Agricultural Land of Soil Environmental Quality"(GB 15618^-2018)and soil baseline values as evaluation criteria,the above^-standard rates of Cd,Cu,Ni,Pb,and Zn in farmland were 57.5%,6.2%,0.5%,3.6%,10.9%,and 4.1%,14.0%,0.5%,2.1%,and 2.1%,respectively.The comprehensive pollution index shows that Tiandeng County,Longan County,Daxin County,Longzhou County,and Chongzuo City have severe combined pollution characteristics.The most important reason behind the high background value(particularly the Cd element)in the geochemical anomaly area of southwestern Guangxi is that the topography of the study area is complex,and the types of heavy metal deposits are numerous,which means that the parent material(rock)itself has a high content of heavy metals,which is weathered into soil.This soil inherits heavy metals from the parent material(rock).