Efficiency of biochar and compost (or composting) combined amendments for reducing Cd, Cu, Zn and Pb bioavailability, mobility and ecological risk in wetland soil

Biochar and compost are two inexpensive and effective in situ remediation materials for heavy metal contaminated soils. The interaction between biochar and compost (or composting material) calls for further studies to maximize the potential benefits of both. In this study, we examined the short-time efficiency of compost (C), biochar (B), a mixture of compost and biochar (B + C), composted biochar (Bced) and biochar-composting material (BCing, biochar and biomass mixed before composting) for reducing bioavailability, mobility and ecological risk of Cd, Cu, Zn and Pb in wetland soil. Adding these amendment materials to the contaminated soil changed the total organic carbon (TOC), waterextractable organic carbon (WEOC) and pH. All the materials decreased the available Cd, Cu, Zn and Pb concentrations in the soil (compost increased the available Cu concentration) and Cd, Cu, Zn and Pb concentrations in pore water. As a whole, soil with Bced and BCing had the biggest decrease in these concentrations. These results indicated that all the materials reduced the bioavailability and mobility of heavy metals (compost improved the bioavailability of Cu), and Bced and BCing had the greatest capacity for that. The materials improved soil microbial biomass and BCing created the biggest improvement, which suggested all the amendment materials reduced the ecological risk of heavy metals and BCing had the greatest capacity for that.