The widespread occurrence of microplastics (MPLs) and nanoplastics (NPLs), collectively abbreviated as M/NPLs, has markedly affected the ecosystem and has become a global threat to human health. Multiple investigations have shown that the chronic ingestion of M/NPLs negatively affects gut barrier function but the mechanism remains unclear. Herein, this research has investigated the toxic effects of pristine polystyrene (PS) M/NPLs, negatively charged carboxylated polystyrene M/NPLs (PS-COOH) and positively charged aminated polystyrene M/NPLs (PS-NH₂) of two sizes (70 nm and 5 μm in diameter) in mice. Gavage of these PS M/NPLs for 28 days caused obvious injuries to the gut tract, leading to the decreased expression of tight junction proteins. The toxicity of the M/NPLs was ranked as PS-NH₂ > PS-COOH > pristine PS. Oral administration of these M/NPLs resulted in marked gut microbiota dysbiosis. The M/NPLs-enriched genera generally contained opportunistic pathogens which are accompanied by a deteriorated intestinal barrier function, while most M/NPLs-decreased bacteria were beneficial microbes with known tight junction-promoting functions, implicating an important indirect toxic effect of gut microbiota dysbiosis in M/NPLs-induced gut barrier dysfunction. In conclusion, this research highlights the importance of gut microbiota in the toxicity of M/NPLs exposure on gut barrier function, providing novel insights into the adverse effects of M/NPLs exposure on human health.

Nanomaterials (NMs) display many unique and useful physico-chemical properties. However, reliable approaches are needed for risk assessment of NMs. The present study was performed in the FP7-MARINA project, with the objective to identify and evaluate in vitro test methods for toxicity assessment in order to facilitate the development of an intelligent testing strategy (ITS). Six representative oxide NMs provided by the EC-JRC Nanomaterials Repository were tested in nine laboratories. The in vitro toxicity of NMs was evaluated in 12 cellular models representing 6 different target organs/systems (immune system, respiratory system, gastrointestinal system, reproductive organs, kidney and embryonic tissues). The toxicity assessment was conducted using 10 different assays for cytotoxicity, embryotoxicity, epithelial integrity, cytokine secretion and oxidative stress. Thorough physico-chemical characterization was performed for all tested NMs. Commercially relevant NMs with different physico-chemical properties were selected: two TiO₂ NMs with different surface chemistry – hydrophilic (NM-103) and hydrophobic (NM-104), two forms of ZnO – uncoated (NM-110) and coated with triethoxycapryl silane (NM-111) and two SiO₂ NMs produced by two different manufacturing techniques – precipitated (NM-200) and pyrogenic (NM-203). Cell specific toxicity effects of all NMs were observed; macrophages were the most sensitive cell type after short-term exposures (24-72h) (ZnO>SiO₂>TiO₂). Longer term exposure (7 to 21 days) significantly affected the cell barrier integrity in the presence of ZnO, but not TiO₂ and SiO₂, while the embryonic stem cell test (EST) classified the TiO₂ NMs as potentially ‘weak-embryotoxic’ and ZnO and SiO₂ NMs as ‘non-embryotoxic’. A hazard ranking could be established for the representative NMs tested (ZnO NM-110 > ZnO NM-111 > SiO₂ NM-203 > SiO₂ NM-200 > TiO₂ NM-104 > TiO₂ NM-103). This ranking was different in the case of embryonic tissues, for which TiO₂ displayed higher toxicity compared with ZnO and SiO₂. Importantly, the in vitro methodology applied could identify cell- and NM-specific responses, with a low variability observed between different test assays. Overall, this testing approach, based on a battery of cellular systems and test assays, complemented by an exhaustive physico-chemical characterization of NMs, could be deployed for the development of an ITS suitable for risk assessment of NMs. This study also provides a rich source of data for modeling of NM effects.