In Situ Immobilization of Potentially Toxic Elements in Arable Soil by Adding Soil Amendments and the Best Ways to Maximize Their Use Efficiency

Soil contaminated by potentially toxic elements (PTE) can cause enormous human health and environmental concerns. Hence, it has become a hot topic worldwide, right now. The immobilization of PTE by soil amendments is one of the crucial chemical processes trapping their mobility and bioavailability. In this review, the most used soil amendments for arable soil remediation, such as lime, gypsum, biochar, bone meal, fly ash, and iron (oxyhydr)oxides, are presented along with descriptions in terms of their typical chemical composition, PTE retention mechanisms, interaction with PTE, and ability for improvement of arable soil quality. In addition, the retention mechanisms of PTE such as cationic metals (Cd, Cu, Pb, and Zn) and anionic metalloids (As) are reviewed. Typical mechanisms of surface adsorption, complexation and precipitation, and electrostatic reactions are responsible for PTE immobilization by soil amendments but vary greatly with metal ion species, mineral composition, and properties of reactive soils. Moreover, since the geochemical behavior of cationic and anionic metals is generally opposite, simultaneous remediation becomes challenging. Considering these points, a blended application of soil amendments could be recommended to achieve better performance and optimum synergistic effects for metal immobilization and soil management. Herein, this review summarizes the combined application of soil amendments with high potential for simultaneously improving soil quality and PTE immobilization based on numerous research findings, which will provide better insights and approaches to remediate PTE-contaminated agricultural soils effectively.