This review critically analyzes the key mechanisms of stabilization of soil organic carbon by biochar.

Antimony micro/nanoparticles (Sb MNPs) are key environmental Sb species that enter the human body via inhalation, ingestion, and dermal contact, posing potential health risks. Their complex transformation across multiple Sb species hinders accurate quantification, leaving their in vivo transformation mechanisms poorly understood. In this study, in vitro respiratory, gastrointestinal, and sweat models were established to investigate Sb MNP biotransformation, and the gastrointestinal model incorporated human fecal suspension to better mimic in vivo conditions. Transformation dynamics showed that simulated gastric fluid dissolved Sb₂O₃, Sb₂S₃ and Sb₂O₅ MNPs into ionic Sb without altering valence states, while Sb ions remained at low levels. Gastric-derived Sb(III) was oxidized to less toxic Sb(V) in the intestinal phase. In simulated sweat, Sb(III) concentrations increased but accounted for only 1.75% of total exposure, indicating low dermal risk. Notably, Sb₂O₃ MNPs exhibited lability in simulated lung fluids, particularly artificial lysosomal fluid (ALF), where dissolved Sb(III) reached 1276.7 μg/L with an ionic release rate of 63.8%. The low pH of ALF and formation of stable soluble complexes with citrate, lactate, and Cl⁻ might drive Sb₂O₃ dissolution, suggesting high inhalation risk. This study advances the quantitative understanding of Sb MNP biotransformation and thus for human health risk assessment.