Role of Biochar-based Nanocomposites in Soil Remediation: Heavy Metal Immobilization and Ecological Safety

Heavy metal contamination presents a pervasive threat to soil health and ecosystem integrity globally. Biochar-based nanocomposites represent an innovative class of materials designed for effective in-situ remediation by immobilizing toxic metals. This review provides a comprehensive overview of these materials and explores the critical interplay between biochar characteristics, influenced by feedstock selection and pyrolysis conditions, and the functional enhancements achieved through integration with various nanomaterials like metal oxides and carbon nanostructures. Different fabrication strategies are discussed in detail, including in-situ generation during pyrolysis and ex-situ deposition onto pre-formed biochar. A main theme is the elucidation of contaminant sequestration mechanisms, including electrostatic adsorption, surface complexation, ion exchange, and precipitation/co-precipitation, with particular attention to the influence of environmental factors such as soil pH and the presence of competing ions in multi-metal systems. Impressively, we assess the ecological footprint of these amendments, examining potential risks like nanoparticle leaching and evaluating impacts on soil microbial communities and fauna through ecotoxicity studies. Insights are also provided from field trials demonstrating practical efficacy in reducing metal phytoavailability and facilitating site revegetation. Furthermore, it highlights the environmental significance of biochar-based nanocomposites as multifunctional, low-carbon, and field-deployable tools that align with the principles of sustainable remediation and circular resource use—addressing one of the most persistent threats to global soil health.