Fe₃O₄-based nano-fertilizers for simultaneous nutrient supply and remediation of contaminated soils

Soil pollution associated with heavy metals and organic contaminants is a significant barrier to sustainable agriculture, soil fertility, and global food security. Conventional fertilizers serve mainly as nutrient carriers, often exhibit low nutrient-use efficiency, and have limited potential to mitigate soil contamination. At the same time, Fe₃O₄-based nanofertilizers are considered a multifunctional approach to balance nutrient delivery and soil remediation. Magnetite (Fe₃O₄) nanoparticles have unique physicochemical features, with high surface area, redox properties, and magnetic response, that regulate essential intermediate reactions like ion exchange, surface complexation, and redox transformations. Under environmental conditions, these mechanisms account for controlled nutrient release, improved nutrient bioavailability, and enhanced plant uptake. Aside from nutrient delivery, Fe₃O₄ nanoparticles can modulate soil microbial processes, e.g., enzyme-dependent nutrient mineralization, iron cycling, and redox-active microbial interactions; however, these effects are highly condition-dependent and depend on soil chemistry, nanoparticle properties, and microbial community composition. Concurrently, Fe₃O₄ nanoparticles may adsorb, immobilize, or transform pollutants via electrostatic interactions, surface complexation, and redox reactions, thereby reducing their mobility and bioavailability. Their magnetic abilities also have the potential to help recovery or redistribution after pollutant binding. Notwithstanding these benefits, the evidence is still limited and, in some instances, inconclusive, and is based on laboratory or greenhouse investigations. There remain important uncertainties regarding mechanistic pathways at the field site, long-term environmental fate, and repercussions for soil biota. However, inadequate field-scale validation and unresolved ecotoxicological hazards are among the major hurdles to practical deployment, whereas cost, large-scale synthesis, and regulatory frameworks remain impeding barriers to applications. Filling these gaps requires holistic, global strategies, including long-term field studies, established risk-assessment methodologies, and life-cycle analyses. The development of Fe₃O₄-based nanofertilizers will also rely on a trade-off between agronomic benefits and environmental safety, through context-specific, evidence-supported design approaches.