Utilization of Biochar Alone and in Combination with Compost for Removal of Potentially Toxic Metals Accumulated in Soils Associated with Land-use Patterns

Background: Potentially toxic metals in soils are a threat to food security and human health because it enters the food chain through crop uptake. Hence, it is critical to understand the levels of potentially toxic metals in soils due to agricultural land use patterns and the approach to remove them from the soil. Objective: This review discussed the effect of different land-use patterns on heavy metal accumulation and their removal using biochar. Methods: A desktop review employing preferred reporting items for systematic review and meta-analysis was used to analyse information from peer-reviewed papers including journal articles, books, thesis, and reports. Results: It was shown that potentially toxic metals mainly found in the soil include arsenic (As), copper (Cu), cadmium (Cd), zinc (Zn), chromium (Cr), cobalt (Co), nickel (Ni), antimony (Sb), mercury, thorium (Th), lead, silicon (Si), and selenium (Se). The sources of these potentially toxic metals accumulation in soils were the application of organic and inorganic fertilizers, irrigation, use of pesticides and weedicides, and atmospheric deposition. However, different land-use patterns (greenhouse field, vegetable field soils, forest field, and maize field soil) had a significant accumulation of heavy metals (Cr, Ni, Cu, As, Cd, and Zn) due to increasing crop yield after the use of fertilizers and pesticides. Biochar was found to be effective in the removal of 18 to 40% of these potentially toxic metals from the soil. The mechanisms of removal included precipitation, physical sorption, complexation, ion exchange, and electrostatic interaction. Conclusion: Biochar applied alone or with compost is highly stable to remove heavy metals accumulated in soils due to land use patterns.