Abstract:
In nature, carbonate rocks are a type of parent rock with relatively low concentrations of trace elements such as cadmium (Cd). However, in karst areas, soils with significantly enriched Cd are commonly found, exhibiting typical geological high background characteristics. The source of Cd in the soil is unknown, and the mechanism of its enrichment is unclear, which has attracted considerable attention and systematic research from the academic community. Considering the widespread
in situ weathering of carbonate rocks into soil, most studies are based on this, combining theories such as two-stage weathering, metasomatic dissolution, and isovolumetric replacement. They use methods such as soil profiles, leaching and dissolution experiments, and natural parent material research to reveal the migration and transformation patterns of Cd in karst areas under the combined effects of primary inheritance and secondary adsorption. The Cd enrichment effect in karst soil is not continuous during weathering: (1) The formation and evolution of parent material is the main stage of Cd enrichment. During this stage, Cd enrichment is mainly attributed to the high Cd source provided by the parent material during the early stages of soil formation, as well as the adsorption of Cd by apatite, clay minerals, and Fe-Mn oxides. (2) During soil formation, Cd exhibits leaching behavior, and the leaching and hydrolysis of carrier minerals serve as the main driving forces for Cd leaching. The consequent activation of Cd also presents potential environmental risks to karst areas with high geological background. Currently, the macroscopic patterns of Cd migration during the weathering and pedogenesis process in karst regions are relatively well-established. However, the relevant research methods and analytical testing can still be further optimized. The suggestion is that research efforts should ensure the continuity and integrity of the weathering process. Based on an understanding of macro-level patterns, micro-level mechanisms should be further explored to provide a scientific basis for establishing a theoretical framework for Cd accumulation in karst soils. This research also aims to offer new approaches and methods for the management of land resources and the scientific conservation of the ecological environment in karst areas with high geological background.