A single plastic-containing tea bag steeped in near-boiling water releases approximately 11.6 billion microplastic particles and 3.1 billion nanoplastic particles into the cup. That finding, from a 2019 study at McGill University, remains one of the most striking single-source microplastic exposures ever measured. The research also quantified, for the first time, nanoplastic release from a common consumer product.
What the 2019 McGill study measured
The study, “Plastic Teabags Release Billions of Microparticles and Nanoparticles into Tea” by Hernandez and colleagues, was published in Environmental Science and Technology, a peer-reviewed journal of the American Chemical Society. The researchers purchased four brands of premium pyramid-shaped tea bags from commercial retailers in Montreal, removed the tea leaves (to isolate the bag as the source), then steeped the empty bags in water at 95 C, the standard brewing temperature for black tea.
Using electron microscopy and spectroscopic analysis, they identified two types of synthetic material: polyethylene terephthalate (PET, the same plastic used in water bottles) and nylon. They then quantified the number of particles released from a single bag into a single cup of hot water. The figure was 11.6 billion microplastic particles (defined as 100 nanometres to 5 millimetres) and 3.1 billion nanoplastic particles (smaller than 100 nanometres) per bag. Both figures are orders of magnitude higher than microplastic release previously reported from other food contact items.
Biological effects in Daphnia
Beyond the measurement, the McGill team exposed water fleas (Daphnia magna, a standard aquatic toxicology model) to the tea-bag-derived particle suspensions. Exposed Daphnia showed anatomical and behavioural abnormalities including distorted swimming and altered growth, at particle concentrations comparable to what a human could ingest by drinking a single cup.
The study did not establish direct human health effects, and the authors noted that translation from Daphnia toxicity to human biology is uncertain. What it did establish is that the particles released from pyramid tea bags are biologically active in at least one model organism, which is more than can be said of many other microplastic exposure routes.
What the bags are actually made of
The silky pyramid bags that drove the marketing appeal of premium tea brands around 2010 are most commonly made of one of three materials. Polyethylene terephthalate (PET): used for its strength, clarity, and ability to be heat-sealed into the pyramid shape. Nylon (polyamide): used for similar structural reasons with slightly different handling. Polylactic acid (PLA): a plant-based bioplastic, marketed as compostable, but still releases particles when heated. PLA does biodegrade under specific industrial composting conditions; in a hot cup of water it behaves as a plastic and sheds particles similarly.
Conventional paper tea bags often contain polypropylene as a sealing agent. Research sampling paper tea bags from multiple brands has confirmed polypropylene in the heat-sealed seams of most samples. Particle release is lower than from pyramid bags but is non-zero.
Alternatives that eliminate the exposure
Loose leaf tea with a stainless steel or ceramic infuser is the highest-evidence solution and also generally produces a better cup, because loose tea has more room to expand during steeping. A stainless steel basket infuser costs roughly $10 to $20 and lasts indefinitely. String-and-staple style plain paper tea bags (the old-fashioned rectangular format) typically do not have polypropylene seals, because the bag is folded and stapled rather than heat-sealed. This is not universal across brands, but it is a reasonable default. Checking the manufacturer's specification or looking for a plastic-free certification is the safer route. Hemp, unbleached cotton muslin and abaca fibre reusable tea bags are also available.
The broader picture
The McGill study matters less for any single cup of tea and more for what it established about particle release from heated synthetic food contact materials. The same mechanism of heat-induced particle shedding is now believed to apply to plastic baby bottles (a 2020 study in Nature Food found roughly 16 million particles per litre from polypropylene infant feeding bottles prepared at standard temperature), plastic-lined takeaway cups, and plastic kettles.
Heat and time drive particle release across the category. Hot beverages brewed or served in plastic-containing vessels consistently produce particle counts several orders of magnitude higher than cold-water exposure from the same material. The practical implication: replacing the plastic contact points in the daily hot beverage routine (tea bags, kettle, travel mug lid) achieves a large reduction in measured microplastic intake for relatively little cost. A single stainless steel infuser and a loose tea habit eliminates the single largest measured microplastic exposure from a common consumer product. Few other interventions offer a comparable effect size.