Three research studies analyzed how micro- and nanoplastics may affect humans and other organisms by performing in vitro and in vivo experiments with human cells and mice. One source of human exposure to microplastics is via food when particles are released from food packaging. Xuejun Zhou and colleagues from Zhejiang Institute of Product Quality and Safety Science, Hangzhou, China, investigated microplastics (MP) released from takeaway food containers in China and calculated monthly microplastic ingestion. In an article published on April 20, 2022, in the journal Molecules, the authors described their approach using focal plane array (FPA)-based micro-Fourier transform infrared (FT-IR) imaging to measure MP generation. The authors analyzed seven types of commonly used takeaway food containers, such as tea bags and juice cups, purchased in China and made of different polymers, including polystyrene (PS). After simulating food packaging use in real life, they detected that all containers but one released between 29 and 552 plastic particles. Zhou et al. calculated that “people who order takeaway food 5–10 times monthly may ingest 145–5520 pieces of microplastics from these containers.”
Once ingested, microplastic may be taken up in different types of human cells and change their normal functioning. In an article published on May 14, 2022, in the journal Chemosphere, Marcella Bonanomi, and co-authors from ISBE. IT/ Centre of Systems Biology, Milan, Italy, investigated whether PS micro- and nanoplastics affect human colon cells. For their study, the authors exposed normal human intestinal CCD-18Co cells to fluorescent carboxylate-modified polystyrene beads of an average size of 0.5 µm (=nanoplastics) in concentrations of 3.6*107 particles/ml or 2 µm (microplastics) in concentrations between 1 and 20 µg/ml for 48 h or 28 days. They analyzed particle uptake in the cells and potential effects on cell proliferation, cytotoxicity, mechanisms, and different metabolites.
Bonanomi and co-authors found that the analyzed PS particles were internalized in the human colon cells and led to metabolic changes. This metabolic rewriting occurred both after short (48 h) and long-term (24 days) exposure and included the induction of oxidative stress, an increase in “glycolysis via lactate to sustain energy metabolism and glutamine metabolism to sustain anabolic processes.” The scientists reported that the observed changes in the metabolic pathway are comparable to those induced by the carcinogenic agent azoxymethane (AOM; CAS 25843-45-2) and HCT15 colon cancer cells. Therefore, they concluded that “chronic polystyrene exposure could act as a cancer risk factor for human health.”
Others have studied the cytotoxic and genotoxic potential of PS particles in different cell lines and Devojit Kumar Sarma from the National Institute for Research in Environmental Health, Bhopal, India, and co-authors used human blood lymphocytes for their analysis. Their research was published on May 20, 2022, in the journal Nanomaterials. They exposed peripheral blood lymphocyte cells against 50 nm-sized particles in concentrations of 500, 1000, and 2000 µg/mL. Performing chromosomal aberration and cytokinesis-block micronucleus assays, they reported that nanoplastics triggered several effects indicating “the induction of chromosomal damage and genomic instability in lymphocyte cell.” The scientists further found their results to indicate PS nanoplastics induce cytotoxicity mediated by oxidative stress and DNA damage. They highlighted the need for further studies to evaluate the toxicodynamics and mechanisms of particle-induced cytotoxicity and genotoxicity. Previous studies with human cells have already reported that microplastics affect cytotoxicity and further found the particles to affect oxidative stress, immune response, and barrier attributes (FPF reported).
In an article published on April 30, 2022, in the peer-reviewed journal Environment International, Chunzhen Shi from Beijing Technology and Business University, China, and co-authors went one step further by exploring whether inflammation induced by microplastics may cause further disease development. In contrast to Sarma and Bonanomi, they orally exposed mice for one or two weeks to 1 µm sized microplastics in concentrations reflecting highly exposed populations (106 particles/day). Afterwards, they analyzed the effects on hepatic metabolites, gut microbiota, and histopathology of the liver and colon.
After two weeks of exposure the liver and intestine were observed to be significantly damaged, e.g., tissues were infiltrated with inflammatory cells. Shi and co-authors further identified gut and liver metabolites to be dysregulated in microplastic exposed mice and the gut-liver axis to be affected. They reported, “that the crosstalk between the gut and liver ultimately leaded to insulin resistance and even diabetes.” In addition, fasting blood glucose and insulin levels were significantly increased in mice exposed to microplastics which verified their results. The scientists emphasized that “further studies need to be conducted to verify potential disease outcomes in human cohorts.”
Better understanding micro- and nanoplastics impacts on human health is also the aim of five Horizon 2020 research projects (FPF reported) which have been running for around one year. One of the projects (AURORA) is specifically focusing on the assessment of microplastics’ effects on the placenta and the developing fetus.
References
Bonanomi, M. et al (2022). “Polystyrene micro and nano-particles induce metabolic rewiring in normal human colon cells: A risk factor for human health.” Chemosphere. DOI: 10.1016/j.chemosphere.2022.134947
Sarma, K. et al (2022). “The Biological Effects of Polystyrene Nanoplastics on Human Peripheral Blood Lymphocytes.” Nanomaterials. DOI: 10.3390/nano12101632
Shi, C. et al. (2022). “Disturbed Gut-Liver axis indicating oral exposure to polystyrene microplastic potentially increases the risk of insulin resistance.” Environment International. DOI: 10.1016/j.envint.2022.107273
Zhou X. et al. (2022). “Analysis of Microplastics in Takeaway Food Containers in China Using FPA-FTIR Whole Filter Analysis.” Molecules. DOI: 10.3390/molecules27092646
