Table 1.

Basic characteristics of the studies reviewed

Particle type	Particle diameter	Particle dose	Exposure	Placenta model	Detection method	Major findings	Reference
Fluoresbrite polystyrene latex nanoparticles	50, 100 nm	0.5 mg/mL	24 h time course	In vitro model with BeWo b30 cells	Particle mass measurement, fluorescence measurement, confocal microscopy	- Smaller particles transported to fetal compartment at significantly higher rate - Cellular accumulation of 50-nm particles indicating transcellular transport	Cartwright et al. 2012 [29•]
Positive and negatively charged fluorescent polystyrene nanoparticles, negatively charged fluorescent carboxylated microspheres	50 nm	10 µg/mL	Single dose, 24-h time course	In vitro model with BeWo b30 cells	Fluorescence microplate reader	- Translocation of polystyrene nanoparticles not related to charge and not mediated by known active transporters - Positive NPs induced cytotoxicity of BeWo b30 cells	Kloet et al. 2015 [30•]
Plain fluorescent polystyrene nanoparticles	49, 70 nm	0.5 mg/ml 49 nm NPs, 50 µg/mL 70 nm NPs	Single dose, 24-h time course	In vitro models with BeWo b30 and HPEC-A2 cells	Particle mass measurement, fluorescent microplate reader	Limited translocation of 49-nm polystyrene particles, no translocation of 70-nm polystyrene particles	Aengenheister et al. 2018 [31•]
Rhodamine labeled carboxylated polystyrene particles	50, 500 nm	10, 100 µg/mL	Single dose, 24-h time course	In vitro co-culture model with BeWo b30 and HPEC-A2 cells	Asymmetrical flow field-flow fractionation	- No transport of polystyrene particles across the placental barrier - Polystyrene particles identified as weakly embryotoxic and non-genotoxic	Hesler et al. 2019 [9•]
Fluorescently labeled carboxylate-modified polystyrene beads	20, 40, 100, 200, 500 nm	300 µg	Intravenous injection on embryonic day 17, 4-h time course	In vivo mouse model	Histologic evaluation, HPLC, fluorescence microscopy	- All particle sizes tested observed to cross the placental barrier and distribute in fetal organs in pregnant mice - Uptake of 40 nm particles by 3A-Sub-E trophoblast cells - Cytotoxicity of 20- and 40-nm particles to 3A-Sub-E cells and primary cultures of trophoblasts from term placentas	Huang et al. 2015 [32•]
Carboxylated and PEGlyated fluorochrome labeled polystyrene nanoparticles	50–90 nm	330 µg/mL	Single intravenous injection on 10th and 15th post conception days, 5 min or 4-day time course	In vivo mouse model	Confocal microscopy, spectral imaging fluorescence microscopy	While NPs were detected in the lacunas of the placenta, no particles were found in the embryonic tissues indicating proper barrier function	Kenesei et al. 2016 [33•]
Rhodamine labeled polystyrene beads	20 nm	2.64 × 1014 particles	Intratracheal instillation on gestational day 19, 24-h time course	In vivo rat model	Fluorescent optical imaging, hyperspectral microscopy	Maternal pulmonary exposure to polystyrene nanoparticles results in translocation of nanoplastics to placental and fetal tissues and reduced placental and fetal weight	Fournier et al. 2020 [34••]
Fluorescently labeled polystyrene beads	50, 80, 240, 500 nm	25 µg/mL	180- and 360-min perfusion	Ex vivo human placental perfusion model	Fluorescence microplate reader; transmission electron microscopy	Nanoplastics up to 240 nm in diameter crossed the placental barrier without affecting placenta viability	Wick et al. 2010 [35•]
Fluorescently labeled plain and carboxylated polystyrene beads	50, 240, 300 nm	25 µg/mL	6-h perfusion	Ex vivo human placental perfusion model	Fluorescence microscopy, transmission electron microscopy	- Significant transport of polystyrene particles in the fetal-to-maternal direction with main mechanism likely to be an active, energy-dependent pathway - Accumulation of polystyrene particles in syncytiotrophoblast	Grafmueller et al. 2015 [21]
Fluorescent-labeled plain polystyrene particles	80 nm	40 µg/mL	6-h perfusion	Ex vivo human placental perfusion model	Fluorescence microplate reader, transmission electron microscopy	Dynamically forming protein corona significantly influenced transfer of particles across placenta	Gruber et al. 2020 [36•]
Pigmented microplastic fragments, some identified as polypropylene	5–10 µm			Observational study of human placentas	Raman microspectroscopy	Microplastics found in fetal side, maternal side, and chorioamniotic membranes in 4 out of 6 human placentas tested	Ragusa et al. 2021 [37••]