This paper is the result of environmental geological survey engineering.

Objective This study aims to characterize the heavy metal content in soil, assess topsoil pollution risk and apportion the sources of topsoil heavy metals, thereby providing a scientific basis for green agriculture development, soil heavy metal pollution prevention and land resource management in Tiandong County, Guangxi.

Methods A total of 2779 topsoil and 704 subsoil samples were collected systematically, which were formed into 704 topsoil and 176 subsoil analysis samples. The content of As, Cd, Cr, Cu, Hg, Ni, Pb and Zn was determined. Statistical analysis methods were applied to analyze the characteristics of heavy metal content. For paddy fields, drylands, orchards, and towns with strong human activity impacts, topsoil heavy metal pollution risk was assessed against the “Soil Environmental Quality Risk Control Standard for Soil Contamination of Agricultural Land (Trial)” (GB15618—2018) and “Soil Environmental Quality Risk Control Standard for Soil Contamination of Construction Land (Trial)” (GB36600—2018). For forest land, shrub land, other woodlands, other grasslands, other orchards, and bare land with weak human activity impacts, topsoil heavy metal pollution risk was assessed by using the single−factor pollution index and the Nemerow comprehensive pollution index, with subsoil metal content as the background. The heavy metal sources were analyzed using correlation analysis, factor analysis, and the Absolute Principal Component−Multiple Linear Regression (APCS−MLR) model.

Results The average content of heavy metals in topsoil and subsoil was both significantly higher than the corresponding national background values. The average content of heavy metal elements in karst soil were significantly higher than that in non-karst soil. The risk assessment for paddy fields, dry land, orchards, and towns showed that the dry land posed the highest pollution risk. In dry land, 33.59% of soil samples exceeded Cd pollution risk screening value. The risk assessment for forest land, shrub land, other woodlands, other grasslands, other orchards, and bare land showed that pollution by heavy metals other than Cd was largely absent or mild. The proportions of samples with mild, moderate and severe Cd pollution were 15.06%, 19.20% and 10.74%, respectively. Topsoil heavy metals in the study area originated from soil parent material and anthropogenic sources, contributing 78.58% and 21.42%, respectively.

Conclusion Soil heavy metals in the study area exhibited high content. Cd was the primary pollution prevention and control element in the study area. The heavy metal content was primarily controlled by the geological background, with human activities contributing to their further accumulation.