Nylon tea bags: cooling changed the result

What they found

In 2019 a Montreal lab reported that one plastic tea bag steeped at 95 °C put about 11.6 billion microplastics and 3.1 billion nanoplastics into a cup. At the EU Joint Research Centre, a team steeped empty nylon tea bags at 95 °C for 10 minutes and poured the water through a filter with pores 20 nanometres wide (a nanometre is a millionth of a millimetre). What got through depended on temperature.

Filtered hot, all the nylon that had dissolved out of each bag passed through: 1.13 mg. Filtered after cooling to room temperature, only 0.71 mg got through, so about 35% had turned into particles too big for the pores. Reheated to 95 °C, 1.01 mg passed again. The "nanoplastic" appeared as the water cooled and mostly dissolved again when reheated. EFSA, Europe's food safety agency, says this effect largely explains the billions-per-cup counts. The 2019 team counted specks in dried extract under an electron microscope without identifying each; drying turns dissolved material into solids. Germany's risk agency BfR judges its 2.3 million larger specks probably 100 to 1,000 times too high.

Evidence against: Strong

Why it matters

Plastic tea bags still put real plastic into the cup. Checking each particle by micro-Raman (a laser test of what it is made of), a German team including the risk agency BfR found 5,800 to 20,400 plastic particles over a thousandth of a millimetre per nylon bag after 5 minutes in boiling water, mostly loose bits already on the bag. A lab in China, also using Raman, found 80 to 1,288 per bag.

Evidence: Emerging

The swap

Switch to loose leaf

Brew loose tea in a stainless-steel infuser or a teapot with a strainer, so there is no bag in the cup at all. If you prefer bags, plain paper ones contain less plastic, though some include polypropylene. In one research group's tests, rinsing a bag three times in room-temperature water before brewing cut the plastic in the tea by three-quarters or more. No need to throw out tea you already have: use it up, then switch.

Cost: ~$5-10 · Swap rating: Likely

What we don't know yet

Every figure is a lab test on a few bag types; nobody has measured tea brewed at home. Two labs that identified each particle differ 16- to 70-fold; a third, counting only fibres, estimated 10-19 per serving. The German and fibre counts were read only in BfR and EFSA reports; the Chinese study, rinsing included, only in summary. The EU test used one bag type and 20 times less water than a cup.