TORONTO -- While your plastic tea bag steeps in hot water, it could also be secreting billions of microplastics into your cup, according to a new Canadian study.

The McGill University research found that a single plastic tea bag brewed at 95 C released more than 11 billion microplastics and more than 3 billion nanoplastics into a single cup.

Such bags often look like silk and are called “silky or silken” on the packaging, but are more structured and use plastic to keep their shape.

That’s the highest level of tiny plastic particles found in any food or beverage item tested for microplastics to date, the researchers told The particles measured no larger than 200 micrometres in size and equaled 16 micrograms per cup.

We were expecting to see maybe a couple hundred or a couple thousand particles. We were shocked when we saw billions of particles being released into a single cup,” said chemical engineering professor and lead researcher Nathalie Tufenkji.

Even in room temperature water, the tea bags secreted high levels of plastic, though it was about 300 times less than brewing temperature, according to the results published in the journal Environmental Science & Technology.

The researchers tested four brands of common plastic tea bags, including their loose-leaf varieties, which didn’t release any plastic into the cup. “We bought the same brand loose leaf tea and we didn’t see anything like this,” said Tufenkji.

They also conducted experiments on cut and emptied tea bags to determine that the particles originated in the tea bag material, not the tea itself.

In the steeped tea bags, they found nylon and polyethylene terephthalate, or PET, which is widely used to help some tea bags hold their shape.

“It’s the exact same material that the tea bag is made of,” she said, adding that many might be surprised the bags are even plastic at all. Tufenkji herself was surprised when she got the inspiration for the study on her way to work one morning. The bag in her cup of tea looked plastic, which puzzled her.

“That doesn’t really make sense to put plastic into hot water,” she recalled thinking. So she went back to her McGill lab and launched the study with PhD student Laura Hernandez and collaborator Hans Larsson.

They have decided not to disclose the brand names tested because they can’t be sure if the plastic variety of tea bag will stay on the market in the midst of a global movement to reduce and ban plastic use. Last year, Co-op Food announced a move to bio-degradable bags and PG Tips switched to plastic-free corn starch tea bag products.

More extensive research is needed to understand potential health risks of ingesting microplastics. A toxicity test on water fleas in the McGill study found that the particles caused significant behavioural and development effects, but didn’t kill them. “It points to the need for more studies,” said Tufenkji.