When in need of an easy, hot meal, we may opt for a frozen meal from the grocery store or meal delivery service. After the frozen meal is finished heating in the microwave, we may eat the meal straight from the plastic meal tray or transfer the food content into different dinnerware. Heating microwaveable frozen meals in its original plastic container is conventional. Microwaveable meal trays are typically made with polypropylene, and polypropylene is regarded as a heat resistance and microwave safe plastic. It is debatable if there is any plastic including polypropylene that can safely contain food or beverage content when exposed to heat.
Recent research has found that microplastics and nanoplastics can be released from plastic containers into food or beverage content through realistic usage conditions, and the release of microplastics and nanoplastics is accelerated with increased heat exposure. A microplastic is defined as a synthetic polymer with the size less than or equal to five millimeters in length and the size of a nanoplastic ranges from 1 nanometer to 1 micrometer.1
A study published in Environmental Science and Technology conducted an experiment with two brands of food containers made of polypropylene and a food pouch made of polyethylene to determine if microplastics and nanoplastics could be released under different usage conditions. “The study examined the polypropylene food containers and polyethylene food pouch under different conditions including refrigeration (replicated at 20oC/68oF for 10 days), room temperature exposure (replicated at 40oC/104oF for 10 days), high temperature exposure (replicated at 2 hours at 70oC/158oF followed by 20oC/68oF for 10 days) and microwave heating for 3 minutes with maximum power of 1000 W. The results found thousands of microplastics and millions of nanoplastics were released under all usage conditions and the number of microplastics and nanoplastics increased as each condition exposed more heat. Microwave heating for 3 minutes produced the highest number of microplastics and nanoplastics in the polypropylene food containers with the first container releasing 425 thousand microplastics/cm2 and 169 million nanoplastics/cm2 and the second container releasing 4.22 million microplastics/cm2 and 1.21 billion nanoplastics/cm2. Additionally, the researchers conducted an in vitro cell viability study to further analyze how the collected microplastics and nanoplastics could impact human embryonic kidney cells. The study found that the highly concentrated microplastics and nanoplastics caused cell death of 76.70% and 77.18% after exposure of 48 and 72 hours.” 2 These results shed light that microplastics and nanoplastics directly released from plastic food containers have the potential to cause cytotoxicity to human cells.
A study published in Science Direct conducted an experiment using various plastic food takeout containers to determine if microplastics and nanoplastics could be released under realistic food takeout conditions. “The study examined the following types of food takeout containers: polyethylene packaging, polypropylene cups and transparent boxes, and polystyrene expandable boxes. To simulate realistic conditions of using these containers for hot food, the plastic containers soaked in 300 mL of hot water at 100oC/212oF for 60 minutes. The study classified the plastic particle sizes as submicrons (0.1 – 1 micron) and micro-particles (1-5000 microns). The study determined the polyethylene packaging released 1.07 million submicrons and 0.507 million micro-particles, the polypropylene cups released 1.44 million submicrons and 0.147 million micro-particles, the polypropylene transparent boxes released 2.24 million submicrons and 0.719 million micro-particles, and the polystyrene plastic container released 1.57 submicrons and 0.599 million micro-particles.” 3 These results should prompt food takeout consumers to be more conscious of the food's temperature ordered for takeout since the customer has no control over the type of takeout packaging used for the order. The hot liquid food content such as ramen or soup could be packaged in polypropylene, polystyrene, polyethylene lined container, or polyethylene terephthalate lined container. If a curry dish is ordered for takeout, the meal will likely be packaged in a polypropylene takeout container or a hot noodle dish could be packaged in a polystyrene takeout container. The list could go on with the variety of hot food items to be careful transporting in plastic containers, and when ordering takeout, it is out of the customers control how long the food content will soak in the plastic container until it arrives to the destination.
The research on the release of microplastics and nanoplastics from plastic food containers under realistic use conditions should start to open our minds to other circumstances that may be creating microplastics and nanoplastics for ingestion. Many people love a good cup of tea to either invigorate their day or help to wind the mind and body down. Have you ever stopped to wonder why the packaging instructions for individual teabags typically states to brew for no more than two to five minutes? It could be the optimal brewing time and temperature for a particular tea, but it could additionally be because many individual teabags on the market are made with different plastics and these instructions could be a form of precaution to limit the amount of microplastics and nanoplastics released into the beverage. A study published in Environmental Science & Technology assessed if plastic teabags could release microplastics and nanoplastics under realistic brewing conditions. The study found that “a single plastic teabag brewing for 5 minutes at 95 oC or 203 oF can release approximately 11.6 billion microplastics and 3.1 billion nanoplastics into a single cup of tea. The study noted small particles on the teabag before brewing and observed that these particles disappeared after brewing resulting in surface deterioration with dents and fractures on the teabags. The study confirmed the released particles matched the materials of the original teabags which was nylon and polyethylene terephthalate through X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FTIR).” 4 Similarly, another study published in Science Direct conducted an experiment to research if microplastics could be released from drip coffee bags. The study found “a single plastic coffee bag steeped at 95oC/203oF for 5 minutes could release more than 10,000 microplastics and 80% of the microplastics identified was rayon material.” 5 If a plastic teabag or drip coffee bag were to brew in a to-go beverage cup which is typically lined with polyethylene or polyethylene terephthalate, how many microplastics and nanoplastics would be present in the beverage for consumption but invisible to the naked eye?
Many food and beverage plastic containers and consumer products such as plastic teabags and drip coffee bags are advertised as safe to use for hot food or beverage content. It may be wise to avoid using plastic food and beverage packaging materials under realistic heat conditions in effort to minimize ingestion of microplastics and nanoplastics.
Sources:
Source (1) Lai, H., Liu, X., & Qu, M. (2022, April 11). Nanoplastics and human health: Hazard identification and Biointerface. Nanomaterials (Basel, Switzerland). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9026096/
Source (2) Li, Y., Schubert, M., Lu, Y., Fernandez-Ballester, L., Wang, B., Huang, X., Kuebler, J., Zhang, D., Okur, I., Romanova, S., & Hussain, K. A. (2023, June 21). Assessing the release of microplastics and nanoplastics from … Assessing the Release of Microplastics and Nanoplastics from Plastic Containers and Reusable Food Pouches: Implications for Human Health. https://pubs.acs.org/doi/10.1021/acs.est.3c01942
Source (3) Liu, G., Wang, J., Ying, R., Li, X., Hu, Z., & Zhang, Y. (2021, November 14). Disposable Plastic Materials Release Microplastics and harmful substances in hot water. Science of The Total Environment. https://www.sciencedirect.com/science/article/abs/pii/S0048969721067619
Source (4): Tufenkji, N., Maisuria, V. B., Tahara, R., Larsson, H. C. E., Xu, E. G., & Hernandez, L. M. (2019, September 25). Plastic Teabags Release Billions of Microparticles and Nanoparticles into Tea. ACS Publications. https://pubs.acs.org/doi/10.1021/acs.est.9b02540
Source (5) Wang, H.-P., Huang, X.-H., Chen, J.-N., Dong, M., Zhang, Y.-Y., & Qin, L. (2023, February 18). Pouring hot water through drip bags releases thousands of microplastics into coffee. Food Chemistry. https://www.sciencedirect.com/science/article/abs/pii/S0308814623003345
