Spatial heterogeneity of soil Cd and Pb driven by combined effects of pedogenesis and anthropogenic activities: A case study in the mountainous and hilly region of Fujian Province, China

Soil is a vital and fragile natural resource in the Earth's surface system, with the accumulation of potentially toxic elements (PTEs), such as Cd and Pb, drawing global environmental concern. Soil convergent evolution may lead to the homogenization of major elemental compositions; however, the main mechanisms controlling the distributions of PTEs in soils remain insufficient. Furthermore, the combined effects of pedogenesis and anthropogenic activities on the geochemical behaviors of PTEs are still poorly understood. The results exhibited a high degree of development of the studied soils, with the median Cd and Pb concentration were 0.143 and 47.40 mg/kg in topsoil, respectively. The exceedance rates of Pb in topsoil is 18.22 % indicating that Pb posed broader pollution risks than Cd. The soil Cd concentration exhibited a gradual accumulation at lower slope positions, whereas Pb reached its highest concentration in mid-upper slope areas. Results from Positive Matrix Factorization (PMF) analysis revealed that rock weathering is the primary sources of Cd and Pb, contributing approximately 69.6 % and 70.3 %, respectively. Terrain played a key role in influencing soil physicochemical properties, consequently leading to Cd and Pb spatial heterogeneity. Moreover, mountain barriers facilitated Cd and Pb accumulation on windward slopes along prevailing wind direction. Mining activities accelerated the release and diffusion of PTEs, with airborne pollutants further dispersing PTEs on a large scale. This study provides critical insights into the mechanisms governing soil PTE s pollution from pedogenesis perspective, offering valuable guidance for long-term soil quality monitoring and management in high-altitude and hilly regions.