Some tea bags release microplastic particles into the water Antagain/Getty Images

Tea drinkers have been urged to avoid plastic tea bags after tests found that a single bag sheds billions of particles of microplastic into each cup.

A Canadian team found that steeping a plastic tea bag at a brewing temperature of 95°C releases around 11.6 billion microplastics – tiny pieces of plastic between 100 nanometres and 5 millimetres in size – into a single cup. That is several orders of magnitude higher than other foods and drinks.

“We think that it is a lot when compared to other foods that contain microplastics,” says Nathalie Tufenkji at McGill University. “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.”


Potential toxicity

Tufenkji’s team bought four different tea bags from shops and cafés in Montreal, cut them open and washed them, steeped them in 95°C water and analysed the water with electron microscopes and spectroscopy. A control of uncut tea bags was used to check it wasn’t the cutting that was causing the leaching of microplastics.

While microplastics are increasingly found in drinking water, the World Health Organization says there is no evidence of a health risk for humans. To test the potential toxicity of the particles released by plastic tea bags, Tufenkji and her colleagues exposed water fleas to the contaminated water.

“The particles did not kill the water fleas, but did cause significant behavioural effects and developmental malformations,” she says. However, she says that more research is needed to understand possible health impacts in humans.

In the meantime, Tufenkji suggests New Scientist readers avoid plastic tea bags. “Tea can be purchased in paper tea bags or as loose-leaf tea, which eliminates the need for this single-use plastic packaging.”

Journal reference: Environmental Science & Technology, DOI: 10.1021/acs.est.9b02540