Biochar ameliorates heavy metals and polycyclic aromatic hydrocarbons in the soil-plant interface

Biochar (BC), a carbon-rich material produced through the pyrolysis of organic feedstocks, offers a promising approach for remediating soils contaminated with heavy metals (HMs) and polycyclic aromatic hydrocarbons (PAHs). This review focuses the role of BC in ameliorating HMs and PAHs contamination at the soil-plant interface. Biochar incorporation enhances soil health by improving physico-chemical properties (e.g., water retention, nutrient availability, cation exchange capacity) and stimulating microbial activity. Moreover, it mitigates the phytotoxicity of HMs and PAHs by immobilizing them through direct adsorption, complexation, and precipitation, thereby reducing their bioavailability to plants. A notable knowledge gap remains concerning contaminant mobilization and residual effects following BC application. However, this review primarily emphasizes the sorption capabilities of BC, while providing limited exploration of its multifaceted effects on plant growth under co-contaminated soil conditions. Furthermore, variations in feedstock type, pyrolysis conditions, and application rates lead to inconsistent outcomes, limiting large-scale field adoption. Also, this review highlights the need for future research to: (i) evaluate BC's long-term performance in diverse agroecosystems, (ii) assess the potential ecological risks and food safety concerns, (iii) explore synergistic applications of BC with other soil amendments, and (iv) develop standardized protocols. Addressing these knowledge gaps will facilitate the safe and effective integration of BC into sustainable agricultural practices and environmental remediation strategies.