Lead stabilization in a polluted calcareous soil using cost-effective biochar and zeolite amendments after spinach cultivation

Abstract

Biochar has been shown to be an effective organic soil amendment for the in situ immobilization of Pb. Little research has been done on the effects of biochar and zeolite interactions on Pb immobilization in contaminated calcareous soils. Therefore, the aim of this study was to investigate the effect of different levels of zeolite (2% and 4% w/w) and biochar (3% w/w) prepared from compost and poultry manure on the concentration of Pb in spinach shoots and Pb stabilization in contaminated calcareous soil after spinach cultivation using sequential extraction and release kinetics procedures. The results of this study show that the application of biochars derived from compost and poultry manure significantly decreased the Pb mobility factor (MF) (2.8% to 4.6%) and the release of cumulative diethylenetriamine pentaacetate (DTPA)-extractable Pb (16.8% to 20.1%) in calcareous soil. This benefit was further enhanced by the combined addition of zeolite (MF reduction of 4.4% to 8.4%; cumulative Pb release reduction of 24.8% to 28.6%). The enhancement of soil Pb immobilization is attributed to the properties of the amendments, such as high pH (10.0 to 11.0), ash content (39.0% to 43.5%), and P content (0.25% to 0.43%). The results of the soil Pb sequential extraction and Pb release kinetics were highly and significantly correlated with spinach shoot Pb concentration. Soil chemical data showed that the application of municipal waste biochar with 4% zeolite (MB+Z 2 ) was the most effective treatment for immobilizing Pb (8.4% reduction in MF, 28.6% reduction in cumulative DTPA-extractable Pb), which is in agreement with the results of the spinach shoot Pb concentration (89.0% reduction in uptake).