Characteristics and source analysis of soil heavy metal pollution around the Luanchuan molybdenum–lead–zinc mine area

This paper is the result of environmental geological survey engineering.

Objective Mineral resource development is one of the major drivers for heavy metal contamination in terrestrial ecosystems, posing substantial risks to agricultural sustainability and to human health. Luanchuan County, located in a key molybdenum-lead-zinc metallogenic zone of China, has undergone prolonged and large-scale mining activities. This study aims to systematically assess the contamination status, ecological risk levels, and potential sources of soil heavy metals in this region, thereby providing a scientific basis for regional environmental management and pollution abatement.

Methods A total of 471 surface soil samples were collected, and concentrations of eight heavy metals (Cd, Zn, Pb, Cu, Hg, Cr, Ni, and As) were analyzed. The extent of contamination was evaluated using the geo-accumulation index (I_geo), the Nemerow comprehensive pollution index, and the potential ecological risk index (RI). Source analysis was performed by Positive Matrix Factorization (PMF) integrated with Principal Component Analysis (PCA) to elucidate the origin and contribution of each heavy metal.

Results Cd, Zn, Pb, and Cu are the predominant pollutants in the study area, with mean I_geo values of 2.09 (moderate pollution), 0.74, 0.69, and 0.50 (slight pollution), respectively. The average Nemerow index is 0.86, reflecting a clean to slightly polluted level for most of the region. However, the mean RI value reaches 390.00, suggesting a high potential ecological risk, predominantly driven by Cd (66.09%) and Hg (19.22%). Spatial analysis indicates strong consistency among the three indices, with high-risk zones concentrated in areas of intensive mining activity, and pollution levels attenuate with increasing distance from these hotspots. PMF results identify mining activities as the primary sources of Cd (71.60%) and Zn (61.50%). Pb is primarily attributed to traffic emissions (84.70%) and mining sources (7.80%), while Cu originates from natural sources (60.50%) and mining activities (29.10%). Furthermore, Cr and Ni are mainly derived from natural geological sources, contributing 83.00% and 81.40%, respectively.

Conclusions The primary pollution in soils surrounding the mining areas is Cd, Pb, Zn, and Cu. Mineral resource development is the core driver of heavy metal accumulation in regional soils.