Micro‐ and nanoplastics are generated from plastics and have negative impacts on the environment due to their high level of fragmentation. They can originate from various sources such as fragments, fibers and foams. The large proportion of the waste and resistance to degradation means micro‐ and nanoplastics have become a serious global environmental problem, but there are few studies on their potential toxicity for human health. In this review, we discussed routes of exposure and the potential effects of micro‐ and nanoplastics to human health. Human beings could mainly be exposed to micro‐ and nanoplastics orally and by inhalation. The possible toxic effects of plastic particles are due to the potential toxicity of plastics themselves, and their combined toxicity with leachable additives and adsorbed contaminants. The potential risks for human health focused on their gastrointestinal toxicity and liver toxicity. The toxic mechanisms could involve oxidative stress, inflammatory reactions and metabolism disorders. More studies are needed to carry out and explore the potential toxicological mechanisms of micro‐ and nanoplastics and evaluate the combined toxicity of their adsorbed contaminants.

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This study evaluated the biodistribution and organ oxidative effects of silver nanoparticles (AgNPs) coated with/without polyvinylpyrrolidone (PVP) (AgNP‐20 and AgNP‐PVP) in mice; these were administered by gavage at a dose of 10‐250 mg/kg body weight per day for 28 days. The results showed that both the AgNPs could induce subacute toxicity and oxidative damage to mice and were mainly accumulated in the liver and spleen and excreted by feces. AgNPs could be absorbed into blood and might cross the blood‐brain barrier, and be distributed extensively in mice. The malondialdehyde content in the liver, lungs and kidneys increased in both AgNP groups, while the content of glutathione decreased, and the activity of superoxide dismutase increased at first and then decreased along with the increased doses. Inflammatory pathological changes in the lung and liver at high dose of both AgNPs were consistent with increases in glutamate pyruvic transaminase, glutamate oxaloacetic transaminase and the total protein in serum detection. The Ag content was detected in organs, with the highest content in the liver, followed by spleen, while the Ag content in feces was about 500 times higher than that in urine. AgNP‐PVP could induce higher oxidative stress and subacute toxicity than AgNP‐20 at the same dose, which might be related to the higher concentrations and more Ag+ ions released in mice after AgNP‐PVP exposure. The data from this research provided information on toxicity and biodistribution of AgNPs following gavage administration in mice, and might shed light for future application of AgNPs in daily life.

With the development of nanotechnology, metal-containing nanoparticles are used widely in the diagnosis, monitoring and treatment of central nervous system (CNS) diseases. The neurotoxicity of these nanoparticles has drawn attention. Glial cells (particularly microglial cells and astrocytes) have important functions in the CNS. Neural disorders are related to functional/histologic damage to glial cells. Dysfunctions of microglial cells or astrocytes injure the brain, and cause the neurodegeneration seen in Alzheimer's disease and Parkinson's disease. We have summarized the route of access of metal-containing nanoparticles to the CNS, as well as their neurotoxicity and potential molecular mechanisms involved in glial cells. Metal-containing nanoparticles cross or bypass the blood-brain barrier, access the CNS and cause neurotoxicity. The potential mechanisms are related to inflammation, oxidative stress, DNA and/or mitochondrial damage and cell death, all of which are mediated by microglial cell activation, inflammatory factor release, generation of reactive oxygen species, apoptosis and/or autophagy in glial cells. Moreover, these processes increase the burden of the CNS and even accelerate the occurrence or development of neurodegenerative diseases. Some important signaling pathways involved in the mechanism of neurotoxicity in glial cells caused by nanoparticles are also discussed.