Background: Plastic is everywhere. It is used in food packaging, storage containers, electronics, furniture, clothing, and common single-use disposable items. Microplastic and nanoplastic particulates are formed from bulk fragmentation and disintegration of plastic pollution. Plastic particulates have recently been detected in indoor air and remote atmospheric fallout. Due to their small size, microplastic and nanoplastic particulate in the atmosphere can be inhaled and may pose a risk for human health, speci cally in susceptible populations. When inhaled, nanosized particles have been shown to translocate across pulmonary cell barriers to secondary organs, including the placenta. However, the potential for maternal-to-fetal translocation of nanosized-plastic particles and the impact of nanoplastic deposition and accumulation on fetal health remain unknown. In this study we investigated whether nanopolystyrene particles can cross the placental barrier and deposit in fetal tissues after maternal pulmonary exposure. Results: Pregnant Sprague Dawley rats were exposed to 20 nm rhodamine-labeled nanopolystyrene beads (2.64 x 10 14 particles) via intratracheal instillation on gestational day (GD) 19. Twenty-four hours later on GD 20, maternal and fetal tissues were evaluated using uorescent optical imaging. Fetal tissues were xed for particle visualization with hyperspectral microscopy. Using isolated placental perfusion, a known concentration of nanopolystyrene was injected into the uterine artery. Maternal and fetal e uents were collected for 180 minutes and assessed for polystyrene particle concentration. Twenty-four hours after maternal exposure, fetal and placental weights were signi cantly lower (7% and 8%, respectively) compared with controls. Nanopolystyrene particles were detected in the maternal lung, heart, and spleen. Polystyrene nanoparticles were also observed in the placenta, fetal liver, lungs, heart, kidney, and brain suggesting maternal lung-to-fetal tissue nanoparticle translocation in late stage pregnancy. Conclusion: These studies con rm that maternal pulmonary exposure to nanopolystyrene results in the translocation of plastic particles to placental and fetal tissues and renders the fetoplacental unit vulnerable to adverse effects. These data are vital to the understanding of plastic particulate toxicology and the developmental origins of health and disease. Background Plastics are ubiquitous in modern society, used worldwide in a variety of applications ranging from manufacturing, packaging materials, personal products, and medical devices. Growing production and post-consumer plastic waste disposal contribute to the accumulation of plastic in land lls, waterways, and oceans [1]. In the natural environment, material fragmentation of bulk plastic waste by a combination of physical, chemical, and biological processes produces smaller particles referred to as microplastics (< 5 mm in a single dimension [2]) and nanoplastics (< 100 nm in a single dimension). Recent literature identi ed microplastics ...