This paper is the result of environmental geological survey engineering.

Objective This study aims to systematically reveal the distribution characteristics, pollution degree and potential pollution sources of heavy metals in soils across different zones of the Lanmuchang mercury-thallium mining area in southwestern Guizhou Province.

Methods The concentrations of nine heavy metals (Tl, Hg, Cd, As, Pb, Cu, Ni, Cr, and Zn) in soil, ore, and smelting slag samples were quantitatively analyzed using inductively coupled plasma mass spectrometry (ICP-MS). The obtained analytical data were subsequently employed to conduct a comprehensive assessment of heavy metal pollution status and ecological risks in the mining area soils through an integrated approach incorporating the Nemerow comprehensive pollution index, enrichment factor analysis and potential ecological risk index methods. Furthermore, a sophisticated source apportionment investigation was performed by applying the positive matrix factorization (PMF) model in conjunction with multivariate statistical techniques, including correlation analysis and principal component analysis, to identify potential pollution sources and quantify their respective contribution rates.

Results The pollution and ecological risks assessment showed that the soil of study area was of obvious heavy metal pollution and showed serious potential ecological risks. The main contaminating elements were Tl, Hg, As and Cu, while Cd, Pb, Ni, Cr and Zn were all in the degree of less pollution. In addition, the results of PMF source analysis showed that there were three main pollution sources of heavy metals in the soil of the study area: 1) Mining activities (primarily Tl, Hg, As, and Pb), contributing for 41.1%; 2) Agricultural activities (characterized by Cd), accounting for 21.0%; and 3) Natural sources (including Cu, Pb, Ni, Cr, and Zn), accounting for 37.9% of the total contamination.

Conclusions The soils in the study area were severely contaminated by Tl, Hg, and As, with mining activities identified as their primary source, necessitating targeted remediation and risk control measures.