The majority of tea bags are still made from paper, but a study suggests plastic tea bags might be a harmful trend.

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Reducing the use of plastics has been a popular environmental cause as of late—whether it’s giving the boot to plastic straws or eliminating plastic toys from fast food kids meals. But while eliminating the plastics we can see is an easy idea to rally behind, eliminating the ones we can’t see is trickier. Microplastics—the miniscule plastics that sneak into our food chain—can be tough to control because, unlike a Burger King toy, it’s not always clear where they come from. Here’s a fresh example: Canadian researchers recently discovered that a single plastic tea bag can release billions of tiny particles of plastic into your cuppa.

Though the vast majority of tea bags are still made from paper, as the American Chemical Society (ACS)—who published the research—points out, some tea brands have been moving towards plastic tea bags. What scientists at McGill University in Montreal found is that “steeping a single plastic teabag at brewing temperature (95 °C) releases approximately 11.6 billion microplastics and 3.1 billion nanoplastics into a single cup of the beverage.” The study assured that these plastics were coming specifically from the bags by removing the tea beforehand and then matching the particles to the tea bags “using Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS)” afterward. All four tea bags tested were purchased commercially—meaning they are brands that can be found in grocery stores.

Making matters worse, the study found that the levels of plastics coming from the bags were thousands of times higher than found in other foods. Then, the big question becomes whether or not consuming these plastics is harmful to humans. Though the answer remains unknown, these researchers did test this plastic tea bag water on water fleas. The tiny crustaceans survived, but “they did show some anatomical and behavioral abnormalities,” according to the ACS.

Meanwhile, this focus on microplastics overlooks a (literally) larger point: Opting for plastic tea bags to begin with contributes to more plastic waste even before these bags add more microplastics into the water the supply—not to mention that single-use tea bags are themselves a bit wasteful when you can buy tea in bulk. As a result, the takeaway from this study would seem to be pretty obvious: If you are trying to cut down on the impact of plastic on the environment, ditching plastic tea bags seems like an easy choice.