Spatial variability and environmental controls of trace elements (Co, Cu, Mo, Ni and Zn) in topsoils in northern Vietnam

Understanding the distribution and controlling factors of trace elements in soils is essential for evaluating soil quality and potential environmental risks. This study investigated the concentrations, spatial distribution, enrichment characteristics, and environmental controls of trace elements (Co, Cu, Mo, Ni, and Zn) in surface soils of Cao Bang Province, northern Vietnam. The concentrations ranged from 0.00–278.11 mg kg⁻¹ for Co, 0.26–269.32 mg kg⁻¹ for Cu, 0.00–15.12 mg kg⁻¹ for Mo, 0.00–482.58 mg kg⁻¹ for Ni, and 0.02–947.05 mg kg⁻¹ for Zn. Spatial interpolation revealed considerable variability across the study area, although most soils exhibited low to moderate concentrations. Enrichment factor (EF) values were generally below 3, indicating minimal to moderate enrichment and suggesting that these elements mainly originate from natural lithogenic sources. Principal component analysis showed strong associations among Co, Cu, Ni, and Zn, whereas Mo displayed a distinct behavior. Statistical analyses indicated that topography and parent materials had no significant influence ( p  > 0.05) on trace element concentrations, while elevation showed a weak but significant effect on Ni ( p  = 0.049). Overall, the distribution of trace elements in Cao Bang soils is largely controlled by natural geochemical processes and long-term weathering, with limited evidence of significant anthropogenic contamination. These results provide important baseline information for soil environmental assessment and future monitoring in northern Vietnam.