Size-dependent translocation of polystyrene nanoplastics across biological barriers in mammals

Nanoplastics (NPs) pose health concerns worldwide. However, robust quantitative data on their absorption, distribution, and excretion in mammals remain scarce. Here, we provide a comprehensive assessment of polystyrene (PS) NP biodistribution and elimination in rats using ¹⁴C-radiolabeling, the most accurate and quantitative method available. Pregnant rats were exposed to ¹⁴C-labeled 20 nm or 100 nm PS NPs (PS₂₀ or PS₁₀₀) via oral gavage, intratracheal aerosolization, or intravenous injection, and tissue distribution and excretion were determined by radioactivity measurements. We found that PS NPs were exclusively excreted through faeces, irrespective of the exposure routes, without urinary elimination. Both PS₂₀ and PS₁₀₀ crossed multiple biological barriers, yet only PS₂₀ reached the brain. Maternal transfer of PS₂₀ occurred through both placenta and milk, while PS₁₀₀ transferred solely via milk. A physiologically based toxicokinetic model further simulated accumulation kinetics across tissues. This study establishes the most comprehensive and reliable quantitative profile of PS NP biodistribution in mammals to date, revealing distinct size-dependent translocation patterns that provide a robust foundation for evaluating their health impacts.