Characteristics and interactions of heavy metals with humic acid in gold mining area soil at a upstream of a metropolitan drinking water source

The concentrations of heavy metals were measured in the mine soil and humic acids extracted from the soil in the depth of 0 cm to 20 cm and 20 cm to 40 cm in the upstream area of Miyun reservoir, Beijing. The results show that the average concentrations of V, Cr, Co, Ni, Cu, Zn, Cd and Pb in the soils at 0 cm to 20 cm are higher than 20 cm to 40 cm. The average concentrations of Cr and Cd in the humic acids at 0 cm to 20 cm are lower than that at 20 cm to 40 cm and the average concentrations of other metals are higher at 0 cm to 20 cm. Depth affects the heavy metal association with humic acids. The enrichment factor analysis indicates that Cu has a greater affinity for humic acids and V, Cr, Ni, Zn and Pb have a weaker affinity for humic acids. The concentrations of V, Cr, Co, Ni, Cu, Zn and Pb have a stronger enrichment in the humic acid at 0 cm to 20 cm than 20 cm to 40 cm, while Cd has a stronger enrichment in the humic acids at 20 cm-40 cm. It indicates that humic acids from different depths have different characteristics.