Green solutions to soil pollution: a review on natural extracts for heavy metal remediation, current challenges, and future directions

Heavy metal contamination of soils remains a persistent global concern, yet translation of remediation technologies from laboratory studies to field implementation remains limited. Natural extracts-including organic acids, biosurfactants, and humic substances-are increasingly promoted as sustainable alternatives to synthetic chelators such as EDTA. However, existing reviews largely report removal efficiencies without critically assessing stability, soil dependency, scalability, or regulatory feasibility. This bibliometric-mechanistic synthesis analyzes research published between 2000 and 2025 to evaluate technological maturity, normalization inconsistencies, and long-term durability of natural extract-based remediation. Fewer than 15% of studies progressed beyond laboratory scale, and reported efficiencies (often 70%-90%) were strongly dependent on soil pH, organic matter content, and experimental system (aqueous vs soil-solid matrices). By integrating soil chemistry constraints, thermodynamic stability, and mass balance considerations, this review proposes a comparative framework distinguishing mobilization-based extraction from stabilization-oriented immobilization strategies. A Technology Readiness Level (TRL) perspective and regulatory benchmarking are introduced to assess field applicability. The analysis indicates that while natural extracts demonstrate strong short-term kinetic performance, long-term remobilization risk and multi-season validation remain insufficiently addressed, limiting real-world deployment.