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

Abstract

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:① The 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. ② Kriging interpolation results showed that the spatial distribution characteristics of Cd, Ni, Pb, and Zn in farmland soils were similar, and high-content 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. ③ Taking 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).