Study on the migration pathway and isotopic composition of Zn in soil, plant and water in mining area

Abstract

Isotopic tracing has been widely used to identify the sources and migration processes of Zn in diverse environments. However, Zn isotope fractionation during the migration process within the mining area poses challenges to the accuracy of isotopic tracing. To address this issue, a representative Pb-Zn mining area in the karst region of southwestern China was selected as the study area, given its long-term tailings’ pollution history and the extensive spatial distribution of Zn migration. End-member samples and environmental media (soil, plants, river water and groundwater) were systematically collected, and heavy metal concentrations and isotopic signatures were analyzed. The migration pathways of Zn and associated isotopic fractionation from end members to surrounding environments were comprehensively investigated. Results indicated that tailings constitute the dominant source of Zn, with ZnS weathering being the primary driver of Zn isotopic variability in soils. Eluviation process, characterized by selective transport of soluble Zn²⁺ enriched in heavy isotopes, was identified as the key mechanism governing Zn migration across the soil-plant-river continuum. Retention processes (adsorption by organic matter, plant uptake, and mineral interactions) exhibited minimal influence on soil Zn isotopic composition. These findings advance the understanding of Zn and Zn isotope cycling in karst ecosystems and provide a scientific basis for formulating pollution control strategies in mining areas.