In an article published on April 20, 2022, in the journal Environmental Science & Technology, Christopher D. Zangmeister and colleagues from the National Institute of Standards and Technology, Gaithersburg, United States, analyzed single-use plastic food contact materials (FCMs) for the release of nano-sized particles under normal conditions of use.
The scientists purchased “multiple” single-use hot beverage cups lined with low-density polyethylene (LDPE) as well as single-component food-grade nylon bags approved for baking in the United States. They filled the cups with 300 mL of 100 °C or room temperature ultra-pure water for 20 min and bags with 1 L holding them at 22 or 90 °C for 1 h. Subsequently, they measured the released particles comparing the numbers to untreated ultra-pure water. Zangmeister et al. reported that the analyzed FCMs “release nanometer-sized plastic particles at number densities >1012 per L when exposed to water.” The nylon bags released seven times more particles than the LDPE-lined cups.
To put their results into perspective, the authors calculated that “the ingestion of 13 cups of hot water from a fresh 300 mL single-use beverage cup releases the equivalent of one particle for each cell in the human body (1.5 × 1013 cells).” For the tested nylon bags, this amount is reached already in 0.5 L of water exposed to the bag at 90 °C. Sizes of measured particles were between 15 and 325 nm with a mean size between 30 and 80 nm. This is within the size range that vertebrates can take up via endocytosis. According to the data, both the materials and the temperature influence particle release, which was higher for nylon compared to LDPE and increased with temperature.
Another study, published on April 20, 2022, in the Journal of Hazardous Materials, also assessed the release of plastic particles from FCMs. Jingyu Deng from Nanyang Technological University and co-authors purchased a plastic beverage cup, cling wrap, disposable cup, and a food container made from polyethylene terephthalate (PET), LDPE, polypropylene (PP), and polystyrene (PS), respectively, form grocery stores in Singapore. As opposed to Zangmeister et al., they cut the products into squares before exposing them to 95°C hot water for 10 min. PP and PET were repeatedly exposed for four times.
Deng and co-authors reported that the food containers released >10 million particles/mL of water. While PET and PP samples contained >5 × 107 particles/mL, unexposed control water contained < 1 × 105/mL. LDPE and PS samples had approximately 10-times particles/mL more than the control. The sizes and shapes of released particles differed between the four packaging types. For instance, PET, LDPE, and PS particles shared a similar size with a mean of around 400 nm while PP particles were larger with a mean size of 723 nm. Moreover, the researchers found that particle release continues over repeated heat treatment: The PP plastic consistently released similar particle amounts over the four heating cycles but PET particles decreased from 50 million to 600,000/mL. It has to be considered that the numbers in real-world scenarios, where products are not cut before use, may be different. Performing in vitro engulfing experiments with RAW264.7 murine macrophages, Deng et al. further showed that microplastics are readily taken up and suppress the lysosomal activity of macrophages.
Previous studies have reported that plastic tea bags release over 14 billion particles per bag during brewing (FPF reported) and polypropylene baby bottles up to 16.2 million particles per liter over 21 days (FPF reported).
Nano- and microplastics are not only present in foodstuff but also in the air. Lauren C. Jenner from the University of Hulland, United Kingdom, and co-authors investigated whether these airborne microplastics can be inhaled by humans being deposited in the lung. For their research, published on March 29, 2022, in the peer-reviewed journal Science of the Total Environment, the scientists collected 13 peripheral human lung tissue samples from surgical procedures of 11 patients with a mean age of 63. After isolating the plastic particles from the lung tissues, they chemically characterized all particles down to 3 µm in size using micro Fourier Transform Infrared (μFTIR) spectroscopy. The researchers also controlled for procedural and laboratory particle contamination, by analyzing several blank samples.
Jenner and co-authors reported a mean of 0.69 ± 0.84 microplastics/g of lung tissue which comprised fibers, fragments, and films. The lengths and widths of the plastic particles ranged from 12 to 2475 μm and from 4 to 88 μm, respectively. Concerning polymer types, PP (23%) and PET (18%) were the most abundant, but in total 12 different polymer types were identified. Particles were found in all regions of the lung with the highest levels in the lower lung, followed by the middle and the upper lung. The authors summarized that their “results support inhalation as a route of exposure for environmental microplastics” and suggested that their findings can be used to design realistic laboratory exposure experiments and study the health impacts of microplastic inhalation such as cytotoxicity.
Small plastic fragments may not only enter the lung but also the brain. This has recently been demonstrated for mice orally exposed to 20 µm-sized PE particles (FPF reported). In an article published on April 11, 2022, in the Journal of Hazardous Materials, Timothy Hua and co-authors from Florida State University, Tallahassee, US, were aiming to understand the potential impacts of microplastics on the human brain. The researchers differentiated human iPSC cells into forebrain cortical spheroids to imitate human cerebral cortex development and exposed the cells to 5, 50, and 100 µg PS microplastics/mL. They compared the effects of 1 and 10 µm microplastics and short-term exposure (during days 4-10) and long-term exposure (during days 4-30).
Hua and co-authors reported that “short-term microplastics exposure promotes cell proliferation and neural progenitor gene expression” while “long-term MP exposure reduces cell viability and downregulates more mature neuronal marker and cortical layer VI marker expression.” Long-term exposure was also found to reduce cell viability. Furthermore, the scientists observed that the effects of PS microplastics on developing forebrain cerebral spheroids were size- and concentration-dependent. They hypothesize that these effects “may induce high intercellular/intracellular stress and adversely affect cortical layer differentiation.“
Another four research studies published in April 2022, focused on potential health consequences of exposure to plastic particles by performing experiments looking at mice. These studies reported that particle exposure led to fetal growth restriction, affected hormonal and immunological profiles as well as animal behavior, and changed gut morphology and microbiota composition. Moreover, they found that patients with an intestinal immune imbalance may be more sensitive to microplastic exposure since mice with intestinal immune imbalance showed increased particle accumulation and enhanced colonic inflammation. Also previously published mice studies have linked microplastic exposure to several effects, such as an alternation of gut function and microbiota composition (FPF reported), the induction of autism spectrum disorder (FPF reported) as well as reproductive toxicity (FPF reported and here). A review published on April 21, 2022, summarizes the knowns and unknowns regarding micro- and nanoplastics distribution, bioaccumulation, and effects in rodent models.
References
Deng, J. et al. (2022). “Microplastics released from food containers can suppress lysosomal activity in mouse macrophages.” Journal of Hazardous Materials. DOI: 10.1016/j.jhazmat.2022.128980
Hua, T. et al. (2022). “Microplastics exposure affects neural development of human pluripotent stem cell-derived cortical spheroids.” Journal of Hazardous Materials. DOI: 10.1016/j.jhazmat.2022.128884
Jenner, L., C. et al. (2022). “Detection of microplastics in human lung tissue using μFTIR spectroscopy.” Science of the Total Environment. DOI: 10.1016/j.scitotenv.2022.154907
Zangmeister, C., D. et al. (2022). “Common Single-Use Consumer Plastic Products Release Trillions of Sub-100 nm Nanoparticles per Liter into Water during Normal Use.” Environmental Science & Technology. DOI: 10.1021/acs.est.1c06768
