Influence of green waste compost on Pb-polluted soil remediation, soil quality improvement, and uptake by Pakchoi cabbage (Brassica campestris L. ssp)

Green waste compost (GWC) has been widely used as organic mulches, growing media, soil organic fertilizer, and amendment in Beijing, China. The aim of this study is to determine the remediation efficiency of GWC on the Pb concentration in soil and uptake by pakchoi cabbage and to assess the activities of dehydrogenase, urease, and catalase after applying GWC. Original soil samples were spiked with Pb (NO3)2 of 500 mg/kg, and greenhouse pot experiment was carried out. Three seedlings of pakchoi cabbage (Brassica campestris L. ssp) were planted in plastic pots with mixture of soil amended with three levels of GWC (2%, 5%, and 10%, w/w). Soil and plant samples were collected over 45-day growth, after which Pb concentration and enzyme activities were assessed by laboratory analysis. The available Pb in soil and total Pb in roots and leaves of pakchoi cabbage greatly decreased after adding GWC, associated with significant increases in organic matter, water soluble organic carbon, total nitrogen, and available K and P, whereas pH was not a main factor controlling Pb speciation in this study. Activities of dehydrogenase, urease, and catalase were promoted with addition of GWC because physical properties, high organic matter, and organic carbon content rose by 9-fold, 40%, and 37% at 10% application rate, respectively. In conclusion, GWC could be an alternative option for the remediation of Pb-contaminated soil because of soil quality improvement and Pb reduction in soils and plants, without introducing extra heavy metals compared with other organic amendments.