Canadian researchers found that some plastic tea bags shed high levels of microplastics into water.
Microplastics have widely been found in the environment, in tap and bottled waters, and in some foods.
The World Health Organization (WHO) says such particles in drinking water do not appear to pose a risk.
But the WHO said the findings were based on “limited information” and it called for greater research on the issue.
The researchers, from McGill University in Montreal, Canada, also called for more investigation into the health effects of microplastics, defined as small (less than 5mm in length) pieces of any kind of plastic debris.
For the study, they bought four different commercial teas packaged in plastic teabags.
Most teabags are made from paper, but some premium brands have switched to using a type of plastic mesh instead for their product.
The researchers removed the tea and placed the empty teabags in water heated to 95C (203F), as if they were brewing tea.
They found that a single plastic teabag released about 11.6bn microplastic and 3.1bn smaller nanoplastic particles into the hot water. The particles are completely invisible to the naked eye.
The level of “particles released from the teabag packaging are several orders of magnitude higher than plastic loads previously reported in other foods”, according to the study, which was published by the journal of Environmental Science and Technology.