Phosphatic rock weathering and agricultural activities driving the dynamics of potentially toxic elements in surface soil of weathered zone.

Phosphatic rock weathering and agricultural activities may pollute soils with potentially toxic elements (PTEs) in phosphate-rich regions. However, the behavior of PTEs during rock weathering and their subsequent fate under agricultural influence remain poorly understood. Therefore, the natural weathering profile and farmland soil in a typical phosphatic zone were selected as the subjects for investigating the behavior characteristics of PTE during weathering, as well as PTE bioavailability and sources in surface soil under the influence of agricultural activities. The investigation into natural weathered profiles demonstrated that the weathering of phosphatic rock could generate a significant geological background of cadmium (Cd), lead (Pb) and mercury (Hg) due to their geochemical fractions in minerals. The agricultural activities were associated with elevated levels and increased bioavailability of PTE, particularly lead (Pb), copper (Cu) and zinc (Zn). In farmland topsoil, mean Cd and Pb concentrations reached 0.86 and 151 mg/kg, respectively, with 87% and 70% of samples classified as seriously polluted. The correlation analysis indicated that iron oxide was the predominant controlling factor for the bioavailability of PTE in farmland soil. The results of sources based on Pb isotope and positive matrix factorization (PMF) model suggested that the presence of Cd and Pb in farmland soil was mainly caused by the pesticide use and fertilization, respectively, with PMF attributing approximately 81% and 74% of their totals to these anthropogenic sources. Our study reveals that severe PTE pollution in the phosphatic zone stems from the synergistic effects of natural rock weathering and agricultural activities. This research served as a valuable reference for the prevention and control of PTE in the phosphatic zone.