Biochar for soil remediation: synergizing pollution control and carbon sequestration: a critical review and outlook on green low-carbon assessment

Background Soil contamination and climate change represent dual environmental challenges requiring integrated solutions. Biochar, a carbon-rich material derived from biomass pyrolysis, has attracted growing interest for its potential to simultaneously immobilize soil pollutants and sequester carbon. However, existing reviews typically address pollutant remediation and carbon sequestration separately, and the synergies and trade-offs between these functions remain insufficiently synthesized. A standardized green low-carbon assessment framework for biochar-based soil remediation is also lacking. This review critically evaluates biochar application in contaminated soil, combining bibliometric analysis with systematic evaluation of pollutant immobilization, carbon sequestration potential, and their interrelationships. Main text Analysis of Web of Science literature confirms that biochar effectively immobilizes a wide range of heavy metals and organic pollutants, though efficiencies vary substantially with biochar properties, soil conditions, and contaminant types. For heavy metals, average removal rates range from 31 to 69%, with cationic metals most effectively immobilized and anionic metals least amenable. For organic pollutants, reported efficiencies span 28% to 86%, though the evidence base remains limited and dominated by short-term studies, raising concerns about long-term re-release upon aging. Carbon sequestration potential varies widely, with carbon abatement factors spanning 0.03 to 1.3 across feedstocks and production conditions, though uncertainties persist regarding long-term stability. Notably, the dual benefits carry inherent tensions: modifications and production conditions that enhance one dimension may compromise the other. Current research largely evaluates remediation and carbon effects independently, lacking integrated methodologies to quantify net environmental benefits. Conclusions This review identifies critical knowledge gaps and proposes two future directions: site-specific biochar customization to improve remediation quality and efficiency, and development of a comprehensive green low-carbon assessment framework with clear system boundaries, computable indicators, and uncertainty analysis. Advancing these fronts will facilitate quantification of biochar remediation efficacy and support broader field deployment, realizing the full potential of biomass waste conversion into a valuable environmental resource.