A Single Soil Washing with Humic Substance Can Achieve the Risk-Based Remedial Target for Nickel Contaminated Soil

Risk-based soil remediation and management have become a global environmental issue. Here, a nickel (Ni)-contaminated site was selected to conduct the risk-based remediation strategy. The Health and Environment Risk Assessment Software was used to calculate the human health risk and the remedial target value (RTV) of Ni. Soil highly contaminated with Ni (424.30 mg kg^-1) could cause an unacceptable carcinogenic risk (1.41 × 10^-6), which needs further remediation. Hence, a soluble humic substance (HS) was used as the washing agent to remove Ni. After a single wash at pH 4 and 8, the Ni concentrations in soil were reduced to 278.05 and 288.27 mg kg^-1, both below the RTV (300 mg kg^-1). Furthermore, sequential extraction analysis revealed that the residual Ni was maintained stably in the soil after HS washing. These findings suggested that HS is a promising washing agent for Ni-contaminated soil remediation under the guidance of risk control.