Speciation and bioavailability of metals in soil under different land use from a coal mine area in Bijie, southwest of China

In different land types near coal mining areas, the migration and speciation of heavy metals may have different characteristics, and the impact on the ecological environment and human health is also different. In order to further explore this difference, total amount and speciation of six heavy metals (Cd, As, Cu, Zn, Pb, and Ni) in soil samples from the agricultural land, forest land, wasteland, and coal mine land were analyzed. The results indicated that (1) the heavy metals Cd, Cu, and Pb are higher than the background values of Guizhou Province, and the content of heavy metals in mining area is higher than other land use types. (2) Heavy metals As, Ni, and Zn exist mainly in residual state, while Cd, Cu, and Pb exist mainly in non-residual state. (3) The results of the bioavailability test indicate that Cd had the highest bioavailability and certain risks to the human body. The potential ecological risk assessment results suggested that Cd was at medium ecological risk, while other heavy metals were at low risk. (4) The health risk assessment results based on bioavailability indicated that the noncarcinogenic risk in the study area was less than 1, with low-risk level and certain carcinogenic risk. However, within the acceptable range, the health risk assessment results corrected by bioavailability were less than the evaluation results based on the total amount of heavy metals. Heavy metals cannot be completely absorbed by the human body, so it is more meaningful to use bioavailability for health risk assessment.