Phosphorus (P)-containing passivators have a stabilizing effect on cadmium (Cd)-contaminated agricultural soils to be safely used, offering good potential for risk control of Cd-contaminated agricultural soils to be strictly controlled. In this study, an incubation experiment was conducted to evaluate the risk control effects of using hydroxyapatite (HAP) and monocalcium phosphate (MCP) on Cd-contaminated agricultural soils to be strictly controlled.
Materials and methodsSamples of topsoil were collected (0–20 cm) from agricultural land near a lead–zinc mine in Southwestern China containing 32.07 mg kg?1 Cd with a pH of 7.28. The amounts of passivators added were equal to approximately 3% of the soil by weight. The soil Cd content, physicochemical properties, enzyme activity, and microbial community were analyzed.
ResultsThe results showed that the application of HAP and MCP decreased the activity and mobility of Cd in soils to be strictly controlled. HAP was more effective in decreasing the exchangeable Cd (CdEx) than MCP (rate of decrease was 48.1% for HAP and 24.4% for MCP). According to the results of the geometric mean (GMean) and the integrated total enzyme activity (TEI) index, the total soil enzyme activity of the HAP treatment was higher than that of CK and MCP treatment. HAP and MCP significantly decreased the Chao and Shannon bacterial community indices and the Shannon index of the soil fungal community. HAP increased Actinobacteria abundance, which is beneficial to soil fertility enhancement and plant growth, and MCP increased Rhizobiales abundance, which promotes soil P cycling and plant growth. Primary driving factors for the changes in bacterial and fungal community composition in the stabilized soils were CEC and CdEx for bacteria and Cd bound to carbonates (CdCar) and residual Cd (CdRes) for fungi.
ConclusionsHAP is more suitable for risk control of Cd-contaminated agricultural soils to be strictly controlled than MCP from the perspective of soil Cd activity and mobility, soil enzyme activity, and diversity and composition of the soil microbial community.
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