Quantitative analysis of heavy metal contamination in agricultural soils at the northern foot of the Qinling Mountains, China

Heavy metals in agricultural soils pose risks to ecosystems and public health, influenced by industrial emissions, atmospheric deposition, and agricultural practices. This study assesses contamination in reforested farmlands following unauthorized development removal in conservation areas of Baoqizhai and Dayangyu (Jiaodai Town, Lantian County, Xi’an City, northern Qinling foothills, China). Spatial distributions of chromium (Cr), arsenic (As), nickel (Ni), cadmium (Cd), lead (Pb), copper (Cu), and zinc (Zn) were quantified using inductively coupled plasma optical emission spectrometry (ICP-OES). Pollution levels were evaluated with the geo-accumulation index (Igeo) and potential ecological risk index (PERI). Mean concentrations were 65.4 mg/kg (Cr), 12.1 (As), 29.8 (Ni), 0.36 (Cd), 32.7 (Pb), 42.5 (Cu), and 110.3 mg/kg (Zn), generally below China’s Grade II standards except for Cd, which approached limits and contributed the highest risk. Igeo values indicated unpolluted to moderately polluted conditions (maximum Cd Igeo = 0.28), while PERI showed low to moderate overall risk (RI = 62.02), primarily from Cd (Er = 36.0). Atmospheric deposition, sewage irrigation, and industrial/agricultural activities were identified as the main sources through correlation and principal component analysis. The study evaluates reforestation’s effects on legacy pollution and recommends ongoing Cd monitoring and phytoremediation to protect soil health and biodiversity in this ecologically sensitive region.