Application of biochar for attenuating heavy metals in contaminated soil: potential implications and research gaps

The increasing anthropogenic activities are contributing toward increased contamination of heavy metals in soils on a global scale. Heavy metals can stick in the environment for long periods. Owing to their nondegradable nature, they pose severe threats to the environment, soil quality, plant, and human health, particularly due to their high accumulation in food chains. Therefore, heavy metals remediation in contaminated soils has received colossal attention. Various techniques, including physical, chemical, and biological methods, have been recognized to abate heavy metals contaminations and their movement in the soil-plant system. The application of soil amendments for an in-situ immobilization of environmental pollutants has shown great remediation potential. Biochar, a carbon-rich compound pyrolyzed under no or little oxygen supply with a large specific surface area, and cation exchange capacity can sorb heavy metals onto its surface, reducing their mobility and availability in contaminated soils. Besides, biochar can decrease heavy metals availability by precipitation or electrostatic interactions. This chapter mainly focuses on the impact of biochar application on heavy metals abatement, emphasizing biochar-heavy metals interactions in soil. Critical factors dictating the retention ability of biochar have also been critically evaluated. Finally, we intend to identify specific research gaps and future research themes to promote the sustainable application of biochar as a green remediation agent.