Effects of Compound Materials on Bioavailability of Cadmium and Lead in Contaminated Soil and Accumulation of Cadmium and Lead in Maize

Purpose To study the immobilization effects of compound materials on cadmium (Cd) and lead (Pb) contaminated soils.

Methods Soil from Cd and Pb contaminated farmland around a mining area in Yunnan Province was collected, and indoor pot experiments were carried out to study the effects of two pairs of materials (0.10% lime, 1.00% sepiolite, 0.07% calcium-magnesium phosphate fertilizer and 1.00% humus organic fertilizer) on soil chemical properties, Cd and Pb form and availability, and Cd and Pb content in maize.

Results Compound materials increased soil pH (4.8%-24.3%) and cation exchange capacity (23.6%-86.1%); significantly increased the distribution ratio of Cd and Pb in soil colloids by 35.8%-87.3% and 43.1%-87.4%, respectively; increased the proportion of low-activity forms of Cd and Pb in the soil, among which, lime+sepiolite reduced weak acid extracted state Cd (14.5%) while increasing residual Cd (22.5%), whereas lime+calcium-magnesium phosphate fertilizer decreased weak acid extracted state Pb (16.1%) and increased residual Pb (28.8%). Compared with CK, the lime+calcium-magnesium phosphate fertilizer treatment exhibited optimal immobilization efficiency, reducing DTPA-extractable Cd and Pb by 16.6% and 18.9%, respectively, and decreasing the Cd and Pb content in above-ground part of maize by 23.2% and 9.1%, respectively; lime+humic organic fertilizer treatment had the best effect on maize growth, increasing the biomass of root and stem by 22.8% and 56.9%, respectively. Correlation analysis showed that soil available Cd and Pb content was significantly and negatively correlated with soil pH; content of soil weak acid extracted state Cd and Pb was significantly or extremely significantly positively correlated with the Cd and Pb content in above-ground part of maize.

Conclusion Compound materials can improve the physicochemical properties of contaminated soil, reduce the bioavailability of Cd and Pb in soil and the content of Cd and Pb in maize plants. Among them, the application of lime+calcium-magnesium phosphate fertilizer can transform Cd and Pb in soil into low active forms, significantly reduce the content of active Cd and Pb in soil and the content of Cd and Pb in the above-ground part of maize, and can be used as better choice for the remediation of Cd and Pb contaminated soil.