In an article published on January 3, 2022, in the peer-reviewed journal Food and Chemical Toxicology, Tao Huang from Nanchang University, China, and co-authors investigated the trans-generational effects of nanoplastics. The researchers exposed mice during gestation and lactation to 0.1, 1 and 10 mg/L of 100 nm-sized polystyrene (PS) particles (eight mice per concentration). Exploring the impacts on male offspring compared to the offspring of unexposed mice, Huang and co-authors reported PS nanoplastics impaired offspring development. While no effects on the small intestine and the kidney were found, effects of high PS particle concentrations on the pups’ liver included a reduced liver weight and size, an alteration in liver morphology, the induction of oxidative stress, and the promotion of an inflammatory response. Concerning male reproductive toxicity, maternal nanoplastics exposure induced testicular oxidative injury and a decrease in sperm count.
The authors highlighted that toxicity of naturally generated nanoplastics differs from commercial plastic particles used in laboratory studies and that “human health risk of exposure to nanoplastics requires further investigation.” However, their findings would “put forward new understanding into the detrimental effects of nanoplastics on mammalian offspring.” Two studies published in 2021 also evaluated the reproductive toxicity effects of microplastics in mice. In those studies, PS microplastics induced reproductive toxicity in male mice (FPF reported) as well as fetal losses of pregnant mice (FPF reported).
Asma Haddadi and colleagues from Université de Monastir, Tunisia, also assessed reproductive effects of PS particles, but of a larger size (5 µm in diameter) and using female adult Wistar rats. In the study published on January 18, 2022, in the journal Environmental Science and Pollution Research, 14 animals were orally exposed to 0.1 mg microplastics (1.5 × 106 particles) per day during four estrus cycles and impacts on ovarian function were analyzed.
Using microscopy and histological analysis, Haddadi and co-authors detected the florescent PS particles in the duodenum and different parts of the ovarian tissue. Reported effects on the ovaries include a reduction in relative ovarian weights and estradiol serum concentration, as well as “an abnormal estrous cycle and effective folliculogenesis.” According to Haddadi et al., the “defective ovarian function following PS-microplastics treatment might be due to the induction of oxidative stress.” The scientists also investigated microplastics’ effects on the cytoskeleton by using immunofluorescence and RT-PCR. They reported that the exposure decreased the expression of the two analyzed cytoskeleton proteins α-tubulin and disheveled-associated activator of morphogenesis (DAAM-1).
Zehua Yan and colleges from Nanjing University, China, analyzed potential health risks of microplastic ingestion on humans. The article was published on December 22, 2021, in the journal Environmental Science & Technology. The researchers collected fecal samples from 50 healthy participants and 52 participants with Inflammatory Bowel Disease (IBD) and compared the microplastics amounts and polymer types between the two groups.
Results of micro-Raman spectroscopy showed that microplastic concentrations were on average 28 items/g dm in healthy people compared to 42 items/g dm in feces from IBD patients. Fecal microplastic concentration and severity of IBD were found to be positively correlated. In both groups, sheet was the most prominent shape and polyethylene terephthalate (PET) was the most prominent polymer type detected. To analyze potential sources of microplastics, the participants were asked to complete a questionnaire on their drinking and dietary habits as well as their living and working conditions. Results of the 37 and 50 valid questionaries collected from IBD and healthy participants, respectively, showed that participants with higher consumption of bottled water, takeaway food, and those more often exposed to dust, had a higher concentration of microplastics in their feces. According to the authors, the study outcome “suggests that MP exposure may be related to the disease process or that IBD exacerbates the retention of MPs.”
Previous research has also assessed microplastics in human feces and detected them in the stool of adults (FPF reported) and infants (FPF reported). Small plastic particles have also been detected in the human placenta (FPF reported and here). Five Horizon 2020 projects are working to better understand the impacts of microplastic exposure to humans with one of the projects, AURORA, focusing on the effects of micro- and nanoplastics on early life health (FPF reported).
In a review published on September 29, 2021, in the journal Current Opinion in Toxicology, Michael F. Hughes and co-authors from the US Environmental Protection Agency, USA, summarized scientific knowledge on the sources of nanoplastics (1-1000 nm) as well as on their ingestion by humans, their cellular uptake, and potential effects on humans as well aquatic and terrestrial organisms. Since their small sizes allow nanoplastics to be absorbed by cells, the authors proposed that “research on these materials should be accelerated to properly assess their potential risks.”
In another review published on December 20, 2021, in the journal Advances in Nutrition, María-Carmen López de las Hazas from the Madrid Institute for Advanced Studies, Spain, and co-authors also discussed the potential impacts of plastic particles (microplastic and nanoplastics) on human health, but with a focus on the intestine and impacts on the systemic, cellular, and molecular level. The review further summarizes the ubiquity of plastic particles, also in food and beverages (FPF reported), as well as the epigenetic and transgenerational effects from micro- and nanoplastics exposure and the particles’ potential contribution to the dysregulation of molecular pathways.
The authors concluded that available animal models suggest microplastics cause short-term effects by damaging the intestine and changing microbiota composition (FPF reported) which leads to an inflammatory response. Further animal models would indicate that the small plastic particles “deregulate many cellular signaling pathways, responsible for cell proliferation and differentiation,” and induce epigenetic alterations. López de las Hazas and co-authors emphasized that “all these changes are typical phenotypes of metabolic disorders and include an increase in systemic inflammation, alteration in the cell cycle, and important metabolic disorders based on lipid and glucose metabolism alterations” and call for further research on human health effects of micro- and nanoplastics.
In an article published on January 14, 2022, in the journal Microplastics and Nanoplastics, Todd Gouin from the UK consultancy TG Environmental Research, and co-authors develop and apply a toxicity study assessment tool helping to evaluate potential human health implications of micro- and nanoplastics. The screening and prioritization tool is proposed to serve as tier 1 of a tiered approach evaluating the reliability and relevance of micro- and nanoplastic studies. The categories to be assessed in this tier 1 “include particle characterization, experimental design, and applicability for risk assessment; with critical and noncritical criteria.”
The authors identified 74 studies for evaluation, which represent oral or inhalation pathways, and found the majority to focus on PS, spherical shapes, and particles smaller than 5 µm. The analyzed in vivo studies received a total assessment score between 12 and 44 (possible maximum score: 52) and the in vitro studies between 16 and 34 (possible maximum score: 46). It was observed that studies often received a high score concerning “study design and applicability in risk assessment,” but fell short in the variety of particle types assessed. Of the 24 in vivo oral ingestion studies, 10 were prioritized for tier 2 while it was two for the 16 in vivo inhalation studies. As tier 2 the authors propose an expert evaluation. Gouin et al. further proposed needs to strengthen future studies on micro- and nanoplastics effects, including “the generation and access to standard reference materials representative of human exposure to micro-and nanoplastics for use in toxicity test systems and/or the improved characterization and verification of test particle characteristics, and the adoption of study design guidance.”
References
Gouin, T. et al. (2022). “Screening and prioritization of nano- and microplastic particle toxicity studies for evaluating human health risks – development and application of a toxicity study assessment tool.” Microplastics and Nanoplastics. DOI: 10.1186/s43591-021-00023-x
Haddadi, A. et al. (2022). “Exposure to microplastics leads to a defective ovarian function and change in cytoskeleton protein expression in rat.” Environmental Science and Pollution Research. DOI: 10.1007/s11356-021-18218-3
Hughes, F. M. et al. (2021). “Human and ecological health effects of nanoplastics: May not be a tiny problem.” Current Opinion in Toxicology. DOI: 10.1016/j.cotox.2021.09.004
Huang, T. et al. (2022). “Maternal exposure to polystyrene nanoplastics during gestation and lactation induces hepatic and testicular toxicity in male mouse offspring.” Food and Chemical Toxicology. DOI: 10.1016/j.fct.2021.112803
López de las Hazas, M-C. et al. (2021). “Untoward effects of micro- and nanoplastics: An expert review of their biological impact and epigenetic effects.” Advances in Nutrition. DOI: 10.1016/j.fct.2021.112803
Yan, Z. et al. (2021). “Analysis of Microplastics in Human Feces Reveals a Correlation between Fecal Microplastics and Inflammatory Bowel Disease Status.” Environmental Science & Technology. DOI: 10.1093/advances/nmab154
