In situ immobilization of potentially toxic elements in soil using agricultural byproducts and wastes: A review

Potentially toxic elements (PTEs) such as As, Cd, Cr, Cu, Hg, Ni, Pb and Zn pose a considerable threat to ecosystems, food safety, and human health due to their toxicity, bioaccumulative nature, and environmental persistence. In situ immobilization using soil amendments has emerged as a cost-effective remediation strategy by reducing PTEs mobility and bioavailability and enhancing the soil quality. However, the long-term stability, ecological impacts, and economic viability of these amendments remain key challenges. This review critically examines scientific papers published from 2000 to 2025 on the use of agricultural byproducts and waste-derived materials such as manure, compost, biochar, and fishery residues, for the in-situ immobilization of PTEs. The dominant immobilization mechanisms (surface adsorption, precipitation, and complexation) and the influence of soil properties, amendment characteristics, and PTEs speciation on the immobilization efficiency are presented. By synthesizing current knowledge and identifying knowledge gaps, this review provides a framework for selecting appropriate, low-cost amendments for long-term, environmentally sound remediation of PTE contaminated soils.