Bioavailability, mobility, and toxicity of Cu in soils around the Dexing Cu mine in China

Total concentration is not a reliable indicator of Cu mobility or its bioavailability in soils. The chemical fraction determines the behavior of Cu in soils and hence its toxicity for terrestrial biota. We used the sequential extraction procedure and barley toxicity tests to examine the transfer of Cu in soils around the Dexing Cu mine and to make an ecological risk assessment of Cu in this area. The bioavailable Cu (exchangeable Cu and carbonate-bound Cu) in each soil profile did not change significantly with soil depth, indicating that the Cu itself was vertically mobile and thus potentially a higher risk to the environment. Cu toxicity and bioaccumulation in plants varied with the soil physicochemical characteristics [e.g., pH, clay content, and cation exchange capacity (CEC)] and the level of bioavailable Cu. Multiple regression analysis revealed that bioavailable Cu and CEC could be used to predict Cu toxicity to barley and that other characteristics (such as soil pH, clay content, or total organic carbon) did not predict the risk of toxicity as well as CEC. For the soil to be suitable for agriculture use, treatment of the local soil contamination with guest soil reclamation and phytoremediation with heavy metal-resistant plants would be necessary.