This paper is the result of environmental geological survey engineering.

Objective This study aims to investigate the vertical distribution characteristics of heavy metals in the soils of a lead-zinc concentrator and to assess the associated heavy metal pollution risk in a scientific and reasonable manner.

Methods Taking a lead-zinc concentrator in Delingha City, Qinghai Province, as a case study, a grid-based sampling layout was implemented in the field. A total of 132 surface soil samples were collected from the 0-20 cm layer, 43 vertical soil profiles were established, and 242 deep soil samples were collected at varying depths of 20-700 cm. The concentrations of As, Cd, Cr⁶⁺, Cu, Pb, Hg, Ni and Zn in soils at different depths were determined. By comparing the variations in heavy metal concentrations within the 0-7 m buried-depth interval of the concentrator soils, the vertical distribution characteristics of these heavy metals were analyzed. The single-factor index method, the Nemerow comprehensive pollution index method, and the potential ecological risk assessment index method were then applied to evaluate the degree of heavy metal pollution and the potential ecological risk in the concentrator soils, respectively.

Results (1) As, one of the heavy metals exceeding the standard limits in the concentrator, is mainly distributed in the tailings pond, with its vertical enrichment range concentrated within 0-2 m below the ground surface; Pb is mainly distributed in the tailings pond, the circulating water pond, and the beneficiation area, with its vertical enrichment range concentrated within 0-6 m below the ground surface. (2) The average concentrations of heavy metals in the concentrator soils decrease in the order of Pb > Zn > Cu > As > Cr⁶⁺> Ni > Cd > Hg. (3) In terms of pollution degree, five heavy metals in the concentrator soils remain at a clean (non-pollution) level, whereas As and Pb reach the heavy pollution level in 33.33% and 34.85% of the surface soil samples, respectively. (4) The potential ecological risk index results show that the concentrator as a whole is subject to a strong potential ecological risk: Cd and Hg pose extremely strong risks, Pb a strong risk, As a moderate risk, and Cr, Ni, Zn, and Cu slight risks.

Conclusions (1) The vertical enrichment of As, a heavy metal exceeding the standard limit in the concentrator, is mainly confined to the interval of 0-2 m below the ground surface, and that of Pb is mainly confined to 0-6 m below the ground surface. (2) The concentrator as a whole is at a heavy pollution level with a correspondingly high degree of ecological risk. The standard-exceeding elements As and Pb originate mainly from production activities during lead–zinc beneficiation, such as tailings leaching, downward infiltration of circulating water, and deposition of production dust.