It’s fall, the weather is getting cooler, and the time is right for steaming, soothing cups of tea. But as you sip on your favorite brew, you may be unwittingly ingesting billions of microplastics, according to a new study in Environmental Science & Technology.
Many commercial teas are packaged in paper bags, but some premium brands have shifted to plastic pouches that have a silky quality, according to Emily Chung of the CBC. Nathalie Tufenkji, a professor of chemical engineering at McGill University in Montreal and co-author of the new study, recently found one of these bags inside a hot cup of tea that she had ordered from a coffee shop. She was not happy about it.
“I said, 'Oh God, I'm sure if it's plastic it's, like, breaking down into the tea,'" Tufenkji recalls in an interview with Chung.
She and her colleagues, led by McGill graduate student Laura Hernandez, decided to test the theory. They purchased four types of commercial loose leaf teas that are packaged in plastic bags, cut the bags open and removed the tea—so as to make sure that if any microplastics were found, they were coming from the bags and not the tea itself. Then the researchers dunked the tea bags in glass vials containing water heated to 95 degrees Celsius (203 degrees Fahrenheit), an average brewing temperature. Using electron microscopy, the team analyzed samples of the water and estimated that a single plastic tea bag steeped in hot water releases around 11.6 billion microplastics (which the study authors define as pieces that range from 100 nanometers to 5 millimeters in size) and 3.1 billion nanoplastics (pieces that are less than or equal to 100 nanometers in size).
“We think that it is a lot when compared to other foods that contain microplastics,” Tufenkji tells Adam Vaughan at New Scientist. “Table salt, which has a relatively high microplastic content, has been reported to contain approximately 0.005 micrograms plastic per gram salt. A cup of tea contains thousands of times greater mass of plastic, at 16 micrograms per cup.”
The researchers conducted a number of control experiments, among them testing uncut tea bags to ensure that slicing the bags open did not cause plastics to leach out. They found that “a significant number of particles are released even when the tea bags are uncut.” The team also analyzed water from tea that had been brewed with a metallic strainer and did not find any particles.
In recent years, it has become clear that microplastics are a persistent and ubiquitous presence: they’ve been found everywhere from oceans, to soils, to remote mountain airs, and to human stool. Microplastics seem to negatively impact animals; studies have shown that the particles impair reproduction and damage the digestive tracts of various species. But the risks to human health are not clear.
In August, for instance, a World Health Organization analysis of plastic in tap and bottled water found that the particles “don’t appear to pose a health risk at current levels,” but also noted that data is “extremely limited.”
As part of their study, the McGill team exposed water fleas, small aquatic organisms formally known as Daphnia magna, to various doses of microplastics and nanoplastics leached from tea bags. The little critters didn’t die, but they began to exhibit anatomical and behavioral abnormalities. They swam “crazily,” Tufenkji tells Chung, and their carapaces—or defensive shells—did not develop properly.
Again, we don’t know what this means for humans. The study authors acknowledge that the amount of plastics in a single cup of tea—around 16 micrograms—is not likely to pose any acute toxicity risks, but questions linger about the impacts of long-term exposure. “Overall, the knowledge on adverse effects of plastic particles on human health is still lacking,” the researchers write, “and there is an urgent need to investigate potential toxic mechanisms in higher vertebrates and humans.”