Soil Metal Immobilization in Agricultural Land Contaminated with Cadmium and Lead: A Case Study of Effectiveness Evaluation in Lanping, Southwest China

The growth of edible crops on land that is highly polluted with potentially toxic elements is prohibited in many developed countries, but the growth of fiber or energy crops may be permitted. Here, we have evaluated metal immobilization in a maize field polluted with cadmium (Cd) and lead (Pb) to determine the thresholds of soil CaCl 2 -extractable Cd and Pb and to assess management options designed to maximize food safety. Based on geographical and statistical methods we found that when the soil pH was increased from 5.24 to 6.24, the soil CaCl 2 -extractable Cd and Pb values decreased by 47.8 and 74.7%, respectively. Soil CaCl 2 -extractable Pb concentrations need to be < 2.14 mg kg −1 in order to comply with the Chinese maximum permissible grain Pb concentration (< 0.2 mg kg −1 ). Immobilization increased the percentage of samples that were below permissible levels from 77.4% to 96.2% (grain Cd) and 90.6% to 96.2% (grain Pb) during the period 2017 to 2019. To avoid excessive or inadequacy immobilization, the spatial distribution of correlation coefficients of soil pH, CaCl 2 -extractable or grain Cd/Pb may be helpful in the precise management of immobilization for long-term remediation.