Spatial distribution and migration of lead and zinc and the influence of parent materials in typical paddy soils of Hunan Province, China

Abstract To establish a clear understanding of the distribution and migration characteristics of lead (Pb) and zinc (Zn) in paddy soil in Hunan Province, a representative sampling design was employed. Specifically, the study selected 63 sampling points from various soil formations with paddy soil development in the province, and 343 soil samples were collected from different soil profiles. These soil samples were analyzed for various parameters, such as total Pb and Zn content, pH, organic matter, soil particle size, cation exchange capacity, and free Fe2O3 content. The objective of the comprehensive study was to examine the spatial distribution of Pb and Zn, their migration patterns, and the impact of soil formation on their concentration levels. The results revealed that the surface layer of paddy soil had Pb and Zn content ranging from 17.62 to 114.07 mg/kg and 44.98 to 146.84 mg/kg, respectively. Notably, Pb was found to be more influenced by human activities than Zn, and the comprehensive quality impact evaluations for both Pb and Zn indicated safety. The horizontal distribution maps demonstrated that high-content sampling points were mainly located downstream of the Xiangjiang River. Moreover, the vertical distribution of samples showed four predominant trends, including surface enrichment, sub-surface enrichment, surface, and bottom layer enrichment, and fluctuation. Interestingly, it was observed that Zn had a stronger migration ability than Pb. Additionally, the soil formation was found to have the greatest impact on Pb and Zn content in the bottom soil layer.