Hidden Contaminants in Tea Bags: Using Analytical Spectroscopy to Characterize Microplastics and Nanoplastics (MNPLs)

Microplastics and nanoplastics (MNPL) are pervasive in society. These small plastic particles, usually 5 mm or smaller, have been found in many differing environments, such as the ocean and desert (1,2). Recently, it was observed that MNPLs are routinely transported via air, allowing MNPLs to find themselves in remote environments and, as a result, go undetected by researchers and people (2).

However, it is not only the environment that is seeing the impact of MNPLs and the negative effects they can cause. Lately, researchers have been uncovering the presence of MNPLs in many commonly consumed food items, which directly impacts human health. Now that scientists are aware of MNPLs corrupting our food supply, the question becomes how MNPLs manage to get into our food and beverages.

A recent study published in Chemosphere explored this question by examining tea bags (3). Tea is one of the most popular drinks worldwide, with approximately 6.7 million tons of tea produced as of 2022 (4). This year, it is expected that the global tea market will reach $134.4 billion (4).

White tea bags with mint leaves | Image Credit: © Sklyarov - stock.adobe.com

As a result, many consumers worldwide make tea on a regular basis. The study, led by researchers Ricard Marcos, Alba Hernandez, and Alba Garcia-Rodriguez representing the Universitat Autònoma de Barcelona, explored how polymer-based teabags contribute to MNPL release and their possible health implications (3).

The study examined three commercially available teabags made from nylon-6 (NY6), polypropylene (PP), and cellulose (CL). By simulating typical tea preparation, they extracted and characterized the MNPLs released during the process using advanced analytical techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), attenuated total reflectance Fourier transform infrared spectroscopy (ATR FT-IR), dynamic light scattering (DLS), and nanoparticle tracking analysis (NTA) (3). These methods provided a comprehensive profile of the particles, which ranged from microfibers to nano-scale plastic fragments.

All three tea bag materials showed MNPL release. In particular, NTA analysis revealed high particle concentrations in the aqueous phase: for polypropylene (PP), it was 1.20 × 10⁹ particles/mL (average size 136.7 nm); for cellulose (CL), it was 1.35 × 10⁸ particles/mL (average size 244 nm); and for nylon-6 (NY6), it was 8.18 × 10⁶ particles/mL (average size 138.4 nm) (3).

For the second part of the study, the researchers assessed the health effects of ingested MNPLs. For this part of the study, three types of human intestinal cells—Caco-2, HT29, and HT29-MTX—were exposed to the MNPL particles. The findings revealed that PP-NPLs showed the highest uptake in HT29-MTX cells, which produce large amounts of mucus (3).

Meanwhile, CL-NPLs were internalized by both HT29 and HT29-MTX cells, and NY6-NPLs exhibited preferential uptake in Caco-2 cells, which model intestinal epithelial absorption (3).

The results show that mucus plays a role in MNPL absorption (3). As a result, the researchers concluded that prolonged exposure to such particles could pose health risks, particularly to individuals with high mucosal activity (3).

The study’s findings contribute to the growing body of evidence on the pervasive nature of plastic pollution and its potential human health impacts. As plastics continue to dominate food packaging, understanding the pathways of MNPL exposure has become increasingly critical (3).

Moreover, the research highlights the need for standardized methodologies to evaluate both the release and toxicological effects of MNPLs. Such insights are essential for informing regulatory policies aimed at minimizing plastic contamination in food contact materials and protecting public health (3).

As MNPL contamination becomes an ever-growing concern, this study serves as a wake-up call for consumers, manufacturers, and policymakers alike. The world’s largest producers of tea, which include Kenya, Sri Lanka, China, and India, will have to bear this in mind as they continue to export their tea around the world (4).

References

1. Wetzel, W. Microplastics in the Desert: A Growing Concern in Phoenix Soils. Spectroscopy. Available at: https://www.spectroscopyonline.com/view/microplastics-in-the-desert-a-growing-concern-in-phoenix-soils (accessed 2025-01-02).
2. Wetzel, W. Measuring Microplastics in Remote and Pristine Environments. Spectroscopy. Available at: https://www.spectroscopyonline.com/view/measuring-microplastics-in-remote-and-pristine-environments (accessed 2025-01-02).
3. Banaei, G.; Abass, D.; Tavakolpournegari, A.; et al. Teabag-derived Micro/Nanoplastics (true-to-life MNPLs) as a Surrogate for Real-life Exposure Scenarios. Chemosphere 2024, 368, 143736. DOI: 10.1016/j.chemosphere.2024.143736
4. Fleck, A. Who Drinks Tea? Statista. Available at: https://www.statista.com/chart/29582/share-of-people-that-drink-tea-in-selected-countries/#:~:text=Tea%20is%20the%20second%20most,ten%20people%20regularly%20drinking%20tea. (accessed 2025-01-02).