In this study we identified the translocation of nanopolystyrene particles from the maternal lungs, across the placenta, into fetal tissues. Elevated fluorescence from our rhodamine-labeled particles was measured in the maternal lung, heart, spleen, and uterus and fetal placenta, liver, and heart. Nanopolystyrene particles were observed in the fetal liver, lung, kidney, heart, and brain in late-stage pregnancy using dark-field microscopy. Furthermore, using an ex vivo placental perfusion system, we observed the transfer of nanopolystyrene particles from the maternal uterine circulation, across the placenta to the fetal circulation. As is pertains to fetal health, we observed reduced fetal weight, reduced placental weight, and an increase in reabsorption sites 24 hours after maternal nanopolystyrene particle pulmonary exposure.
In this study, we visualized nanopolystyrene translocation from the maternal lungs to the fetal compartment and deposition in the fetal, liver, heart, kidney, and brain on GD 20, within 24 hours of maternal exposure. Our study represents a snapshot of time during gestation, providing evidence that nanoplastic particles can reach fetal tissues after maternal pulmonary exposure. As it pertains to nanoplastic particle deposition, it remains unclear if the nanopolystyrene particles have been taken up by the fetal cells, remain in the fetal vasculature, migrate to the interstitial space, or are returned to the maternal circulation. It is plausible that these particles would remain in the fetus after birth as the nanoplastic particles passaged across the placental barrier and may be taken up by fetal cells. Endothelial cell exposure to engineered nanomaterials enhances endothelial barrier permeability [28, 29, 30], which offers accessibility to the interstitial space between cells within systemic tissues. Reports pertaining to the development and function of the blood brain barrier in a fetus are inconclusive [31, 32]. Therefore, the blood-brain barrier may not yet be fully formed, rendering the fetal brain susceptible to particle sedimentation. We, and others, have identified that maternal exposures to metallic and carbonaceous ENM during gestation can initiate developmental onset of disease within the maturing fetus. In laboratory studies, young and adult offspring have been reported to exhibit coronary dysfunction [33, 34, 35, 36, 37, 38], vascular perturbations [38, 39], negative reproductive health outcomes [40, 41, 42], and neurological outcomes [43, 44, 45] after maternal inhalation of engineered nanomaterials during pregnancy. It is also plausible that these findings represent a snapshot of time, wherein the particles reach the fetal tissues within 24 hours of exposure but are removed from the fetal circulation prior to birth. Therefore, particle deposition during fetal development may impact offspring health after birth and into adulthood.
Furthermore, the uptake and passage of nanosized materials is highly dependent on the physio-chemical properties of the particles including size, functionalization, chemical construct, and surface charge . Cellular uptake and subsequent toxicity of nanoplastic particles is dependent on the unique protein and chemical corona that forms on the surface during contact with biological fluids (e.g. pulmonary surfactant, interstitial fluid, plasma) and environmental chemicals; in the case of plastics these chemicals may be adsorbed and serve and a vehicle for chemical transport . Chemical additives adsorbed to the surface or added to plastics during the polymerization process can leach or be transferred from polystyrene products with normal use. These additives may include carcinogens or endocrine disrupting factors (e.g., vinyl chloride, phthalates) [47, 48]. Fundamental studies of plastics toxicology identify and refer to the potential for chemical leakage from polystyrene products after the addition of hot, cold, or boiling water . Recently, studies identify the propensity for polycyclic aromatic hydrocarbons, specifically pyrene, to dissociated from after aquatic exposure to microplastic particles in a biological environment . Together, these outcomes indicate the possibility of chemical release from particles within an organism. Fetal nanoplastic deposition could lead to life-long localized low-level exposure to these additives or adsorbed chemicals. Future studies are planned to examine chemical release from plastic nanomaterials within a biological environment and to assess the impact of a chronic exposure to nanoplastic particles on fetal growth and development are also required for a comprehensive understanding of the health hazards associated with airborne nanoplastics.
We quantified an elevation in fluorescently labeled nanopolystyrene particles in the umbilical vein within 90 minutes of bolus infusion to the uterine artery. These levels were significantly higher within 150 minutes of exposure. These results confirm the capacity of 20 nm nanopolystyrene plastic particles to pass from the maternal to the fetal compartment. Interestingly, while fluid flow from the maternal to fetal compartment decreased after both saline control and nanopolystyrene injection, this was not to significance. This suggests no reduction in blood flow through the placenta within 180-minutes of particles reaching the uterine artery.
Similarly, Grafmueller et al. demonstrated the placental transfer of fluorescently-labeled nanopolystyrene particles from the maternal to the fetal compartment [20, 21]. Upon further study utilizing the ex vivo human placental perfusion model, the authors identified a bidirectional, size-dependent transfer of nanopolystyrene beads without cytotoxicity . In this study, heightened polystyrene particle transfer from the fetal to the maternal compartment was observed instead of a concentration equilibrium evident of passive transport . Therefore, Grafmueller et al. speculated that nanopolystyrene translocation across the placenta likely involves energy-dependent uptake, material transfer, and particle efflux as opposed to passive transport . It is recognized that the concentration of particles that translocate from the primary site of exposure to the fetal compartment and tissues is low  and that the human placental perfusion methodology is not without limitation .
The results of our current study also corroborate data from previous nanotoxicological investigations from our group and others that have shown reduced fetal weight, or restricted fetal growth, after chronic maternal inhalation of nano-titanium dioxide particles [39, 52]. We have previously postulated that diminished fetal development after maternal nanoparticle exposure is associated with indirect vascular deficiencies leading to uteroplacental ischemia in late-stages of pregnancy [39, 53, 54]. These vascular deficiencies are also evident after a single exposure to nano-titanium dioxide particles during pregnancy [53, 54]. We have also observed decreased fluid flow during ex vivo placental perfusion after gold nanoparticle infusion . Interestingly, we identified reductions in fetal weight, placental weight, and increased number of fetal reabsorptions after an acute maternal nanoplastic pulmonary exposure in this study, but did not observe a reduction in fluid flow to the fetal compartment after direct infusion of nanopolystyrene particles into the uterine artery. Therefore, future studies of uteroplacental function are necessary to clarify if the differences in these outcomes are based on differences between single, acute, or chronic nanopolystyrene exposure or if these changes are mitigated only by metallic nanomaterials.