Biochar applications enhance the phytoextraction potential of Salix smithiana [Willd.] (willow) in heavily contaminated soil: potential for a sustainable remediation method?

Purpose The combination of chemostabilization and phytoextraction provide an affordable and environmentally effective remediation technology for the heavy metals in contaminated soils. The purpose of this study was to investigate how biochar applications in heavily contaminated alluvium soils reduced the toxic effects of heavy metal (Cd, Pb, Zn) and their transport through the soil profile. Materials and methods The 3-year experiment was conducted under controlled conditions in greenhouse. Extremely contaminated soil required high doses (5, 10, and 15% w/w) of biochar. Biochar was prepared from wood by high-temperature pyrolysis (800 degrees C). Salix smithiana Willd. was chosen as a model plant. Leachate describing the mobility of metals was collected five times during each vegetative period. Leachate was collected. Results and discussion Biochar application enhanced the phytoextraction potential of willow plants in the first and second year of a pot experiment. High biochar applications (5, 10, and 15% w/w) reduced the phytotoxicity of metals in soil solution, improved biomass growth in Salix smithiana, and enhanced heavy metal uptake by plants in the amendment treatments. In the 3rd year, the pH of both the soil and leachate decreased by 1 unit. The decrease of pH led to the increase of Cd and Zn in the leachate and/or limited the growth of plants. Conclusions Biochar seems to be an effective tool for heavy metal immobilization; however, further research is necessary to evaluate the mechanisms of biochar behavior and subsequent utilization for remediation of extremely contaminated alluvial soils.

Automated summary

The combination of chemostabilization and phytoextraction is an affordable and environmentally effective remediation technology for heavy metals in contaminated soils. Biochar application enhanced the phytoextraction potential of willow plants and improved biomass growth, but also led to a decrease in soil and leachate pH which affected plant growth and metal uptake in the long term. Further research is needed to evaluate biochar behavior mechanisms and its utilization for remediation of contaminated soils.