Table 3.

A summary of notable toxicological findings associated with MPs/NPs in human cells. PS, polystyrene; PE, polyethylene; PVC, polyvinylchloride; NPs, nanoplastics (<1 µm); MPs, microplastics.

Human Cell Models	Properties of MPs/NPs Used	Cellular Uptake	Notes on Toxicological Observations	References
Significant Toxicity
Human Peripheral blood monocytic cells (PBMCs) U937 (human monocytic cell line) THP-1 (human monocytic cell line) DMBM-2 (mouse macrophage cell line)	Carboxylated PS NPs (20–1000 nm)	20 nm nanoparticles taken up passively, while larger ones taken up both actively and passively	• 20 nm NPs cytotoxic to U937 and THP-1 cells • 20 nm NPs stimulated IL-8 secretion in human monocytes and induced measurable oxidative burst in monocytes •  500 and 1000 nm NPs stimulated IL-6 and IL-8 secretion in monocytes and macrophages, chemotaxis and phagocytosis of bacteria by macrophages, and provoked an oxidative burst of granulocytes • At lower concentrations with no cytotoxicity, 20 nm NPs inhibited, while 500 and 1000 nm NPs increased phagocytosis of bacteria by DMBM-2	Prietl et al., 2014 [115]
T98G (human glioblastoma cell line) HeLa (human cervical adenocarcinoma cell line)	PE microparticles (3–16 µm) PS particles (10 µm)		• Induced ROS generation • Cytotoxic effect, with PE having a higher EC50 value compared to PS in both T98G and HeLa cells	Schirinzi et al., 2017 [116]
Caco-2 (human epithelial colorectal adenocarcinoma cell line)	PS particles (0.1 and 5 µm)	Cellular uptake of nanoparticles	• Low toxicity on cell viability, oxidative stress, and membrane integrity and fluidity • Disruption of mitochondrial membrane potential • Inhibition of plasma membrane ATP-binding cassette (ABC) transporter activity	Wu et al., 2019 [117]
Human dermal fibroblasts Peripheral blood mononuclear cells (PBMCs) HMC-1 (human mast cell line 1) RBL-2H3 (human basophilic leukemia cell line) RAW 264.7 (mouse macrophage cell line)	PP particles (~20 µm and 25–200 µm), either first dispersed in DMSO or used directly in culture media		• Some degree of cytotoxicity at high dosages of the smaller size 20 µm particles • Low degree of induction of proinflammatory cytokines IL-6 and TNF-α from PBMCs • Increased histamine release from HMC-1 and RBL-2H3 cells • Some degree of ROS induction at high dosages of the smaller size 20 µm particles	Hwang et al., 2019 [118]
BEAS-2B (human lung epithelial cells)	PS MPs (4.06 ± 0.44 µm at 1–1000 μg/cm2		• Cytotoxic effects • Oxidative stress and inflammatory responses • Disruption of epithelial layer	Dong et al., 2020 [120]
A549 (Human alveolar type II epithelial cell line)	PS nanoparticles (25 and 70 nm)	Cellular uptake of nanoparticles	• Decreased viability and induced cell cycle arrest • Upregulation of transcripts for NF-κB and some pro-inflammatory cytokines • Alteration of cell cycle and apoptosis-regulation related protein expressions	Xu et al., 2019 [121]
BEAS-2B (Human bronchial epithelial cells)	PS nanoparticles	Cellular uptake of PS nanopaticles	• PS NPs only cytotoxic at very high concentrations • Metabolomics analyses revealed autophagic and endoplasmic reticulum (ER) stress-related metabolic changes	Lim et al., 2019 [122]
Hs27 (Human fibroblasts)	PS nanoparticles (100 nm at 5–75 µg/ml)		• Stimulation of ROS production •  Genotoxic stress and DNA damage measured with the cytokinesis-block micronucleus (CBMN) assay	Poma et al., 2019 [119]
No or Insignificant Effects
Caco-2	Polyethylene terephthalate (PET) NPs (laser ablated, ca. 100 nm)	Cellular uptake of NPs	• No apparent toxic effect • Nano-PET are internalized into endo-lysosomal compartments • Nano-PET has high propensity to cross the Caco-2 intestinal barrier model	Magri et al., 2018 [113]
Caco-2 THP-1 monocytic line	PS microparticles (1, 4, and 10 µm)	Cellular uptake of PS microparticles	• Low crossing of the cell monolayer on Transwells even by 1 µm microparticles • No pronounce loss of cell viability except only at very high dosage of 1 µm microparticles • Microparticles uptake did not affect macrophage differentiation or polarization	Stock et al., 2019 [109]
Caco-2 and HT29-MTX-E12 (human colon epithelial cell) co-culture BeWo b30 (Human placental trophoblast cell)	Carboxy-modified PS nanoparticles (50 nm and 0.5 μm,	Cellular uptake of PS nanoparticles	• No significant cytotoxicity unless at very high concentrations • No significant transport across the in vitro intestinal and placental “barriers” but intercellular distribution was observed	Hesler et al., 2019 [114]