Tracking of [ ¹⁴ C]Polystyrene Nanoplastics in Pregnant Mice

Micro- and nanoplastics (MNP) are increasingly reported in the reproductive and maternal organs and tissues, yet their translocation and accumulation during pregnancy remain poorly quantified - often the material used as MNP is heavily modified. Herein, we have used unmodified polystyrene (PS) nanoparticles of three sizes (33 ± 11, 246 ± 81, and 1052 ± 189 nm) with covalent ¹⁴C backbone labels to track biodistribution in late-gestation mice after intranasal (IN) or intravenous (IV) administration. Tissue collection after administrations revealed exposure route-dependent nanoplastic accumulation. After IN exposure, the majority of the nanoplastics were retained in the lungs or excreted through the GI tract, whereas IV administration exhibited size-dependent accumulation in the liver and spleen, and a lung uptake consistent with microvascular interactions. We did not detect PS in placentae or fetuses after IN administration. Placentae exhibited low concentrations of PS (0.10%-0.15% of the injected dose) after IV administration, indicating restricted transplacental transfer even after direct intravenous exposure to relatively large amounts of nanoplastics. These findings indicate that exposure route and particle size principally govern early disposition during pregnancy. Importantly, the covalently incorporated radiolabel (¹⁴C) allows quantitative tracking of unmodified pure polystyrene particles and preserves the material's intrinsic behavior.