Effects of biochar on heavy metal speciation and microbial activity in red soil at a mining area

With the development of the mining and metallurgy industries, heavy metal emissions are rising and increasingly polluting the soil. Heavy metals cause soil degradation, reductions in crop yield and quality, and the sustainability of land resources, and threaten regional biodiversity and human health. Accordingly, soil heavy metal pollution and remediation are attracting increasing global attention. Biochar is an excellent fixation agent that has been widely used in the remediation of heavy metal-contaminated soils. In this study, the feasibility of biochar remediation was explored by adding various doses of it to contaminated soil. Five treatments were explored: contaminated soil (controls), and contaminated soil with biochar doses of 1%, 2%, 4% and 10%. The influences of biochar on the forms and contents of soil heavy metals and microbial activity were determined. Biochar was found to passivate heavy metals, reduce the contents of acid-soluble and reducible Cd, Pb, Cu, and Zn, increase the contents of oxidizable and residual Cd, Pb, Cu, and Zn, increase soil basal respiration and microbial carbon, reduce microbial respiration entropy, reduce fluorescein diacetate (FDA) hydrolase activity, and increase the activities of dehydrogenase, catalase, and urease. Biochar clearly affected the forms and availability of heavy metals in red soil and soil microbial activity. Biochar is an ideal conditioner for the remediation of heavy metal-contaminated red soil in mining areas, for which the present study provides a theoretical basis and practical guidance.