Attribute-Driven Maternal–Fetal Transfer of Atmospheric Magnetite Nanoparticles Revealed by Single-Particle Analysis

Atmospheric magnetite nanoparticles (MNPs) are an important yet understudied component of PM_2.5, with potentially significant systemic and developmental health impacts. Here, using a whole-body inhalation model in pregnant C57BL/6 mice, we investigated the biodistribution and maternal–fetal transfer of atmospheric MNPs. Following gestational exposure, MNPs were magnetically extracted from maternal and fetal organs and characterized by high-resolution TEM and single-particle mass spectrometry. Exogenous MNPs in multiple maternal and fetal organs were investigated by TEM. Quantitative analysis revealed pronounced accumulation of MNPs in maternal serum, liver, spleen, placenta, and lung, accounting for 93% of the total burden. Approximately 0.7% of MNPs were transferred from the maternal compartment to the fetus, with over 60% of these transferred particles retained in the fetal liver. Single-particle analysis demonstrated selective enrichment of fine-sized MNP subcategories, enriched with potentially toxic metals (especially Zn and Pb), in fetal organs (like heart and brain). Multimodal network analysis further identified particle size and elemental composition as key determinants governing systemic transport and placental transfer. Our results demonstrate that inhaled atmospheric MNPs cross the placental barrier and accumulate in fetal organs, underscoring their contribution to early life exposure risks and the need for particle-specific air quality standards.