This project aimed to develop the X-ray absorption spectroscopic (XAS) method to determine the chemical speciation of copper (Cu) in contaminated farmland soils before and after the soils were remediated using the tillage method. The information was further used to evaluate the potential Cr risk in the soils after the remediation. Soil samples were collected from different locations in two contaminated farmlands in Taoyuan and Changhua before and after remediation. The XAS results of the soils showed that the predominant Cu species in the soils are humic-acid associated Cu, and Cu sulfate and sulfite. The chemical speciation and fractionation, obtained using XAS and sequential extraction methods, showed similar trends in terms of their spatial distributions in the contaminated sites. The contents of the residual phase were relatively constant over the contaminated sites, while those of the other species and phases with higher mobility and availability increased with decreasing the distance from the irrigation water inlets of the farmlands or soil depth. The highest contents of mobile species in the soils near the irrigation water inlets revealed the input of Cu from anthropogenic sources through irrigation water. After remediation, the total content and the chemical speciation/fractionation in the soils at different locations became similar, and the solubility of Cu in the surface soils decreased. These results indicated the positive effects of the tillage remediation method on reducing the bioavailability and associated risk of soil Cu contamination. However, further investigation is required to consider the potential release of Cu from mobile species at deeper soils after tillage remediation. The complementary information from combining the XAS and sequential extraction method allows the effective identification of the predominant Cu-associated phases in soils and the understanding of their chemical transformation under certain conditions in the environment.

Heavy metals, Soil copper contamination, X-ray absorption spectroscopy, Sequential extraction, bioavailability, Chemical speciation, Spatial distribution