Silica-Based Encapsulation for Immobilizing Heavy Metal Mobility in Agricultural Soil

Stabilization and immobilization techniques have been applied to mitigate the mobility and bioavailability of metal(loid)s in agricultural soils. However, conventional chemical stabilizers alter soil physicochemical properties, potentially impairing plant growth. As an alternative, silica (Si), an abundant component of natural soils, has demonstrated potential in mitigating heavy metal toxicity in plants. This study introduces silica encapsulation of soil particles as an innovative stabilization approach to restrict the translocation of metal(loid)s from soil to crops. The application of silica encapsulation reduced the leachable concentrations of Pb, Zn, and Cu, as determined by the Toxicity Characteristic Leaching Procedure (TCLP), by up to 34.6%, 19.7%, and 11.8%, respectively. Bioaccessible concentrations also decreased by up to 12.0% (Pb), 15.6% (Zn), and 19.4% (Cu). Notably, silica encapsulation effectively reduced heavy metal mobility even under accelerated wet-dry aging conditions. The technique also enhanced the germination rates of Lactuca sativa and Hordeum vulgare by up to 11-fold in heavy metal-contaminated soils and decreased heavy metal accumulation in barley roots by as much as 97.3%. Furthermore, silica encapsulation demonstrated effectiveness across various soil types and contamination levels, underscoring its robustness as a stabilization strategy. These findings not only demonstrate the practical potential of silica encapsulation in mitigating heavy metal transfer but also provide new insights into the stabilization mechanisms involving silica layers on soil particles, thereby contributing to safer and more sustainable agricultural practices.