Your kettle, your coffee, and microplastics

Most kitchen-audit stories about microplastics start at the cup: the paper filter, the takeaway lid, the disposable coffee tumbler. But there's an earlier step that gets less attention. If your electric kettle has a plastic body, or a plastic lid, spout, or water window, boiling water is sitting against plastic every morning before your first sip.

A 2025 study took a careful look at what that actually shakes loose. Here’s what the researchers found, and what you can do with the information.

1. The first boil is not like the hundredth

A team at the University of Queensland ran polypropylene kettles through 150 back-to-back boils and measured what came out each time [1]. The pattern wasn't a steady drip. It was a sharp decline.

The very first boil shed the most. By the tenth boil, particle release had already fallen by roughly two-thirds. By the 150th, it had dropped about 97% and settled into a low, steady background.

Think of it this way: manufacturing leaves a thin layer of loose, thermally weakened plastic on the inside wall of a new kettle. That’s the low-hanging fruit that comes off first. Once it’s gone, release slows to whatever the bulk material is doing.

That’s genuinely useful to know if you just unboxed a plastic kettle. It's also easy to misread. A 97% drop from the first cycle is not the same as a kettle that has stopped shedding. The plateau is above zero, and nobody has yet followed a single kettle to the end of its life to see whether wear or scale flaking eventually restarts the curve.

2. Heat is the real driver, not the shape of the vessel

The kettle isn’t unusual. It’s one shape of a bigger pattern.

The same Queensland group tested polypropylene food containers and found nanoplastic release much higher in 90 °C water than at room temperature [6]. A separate study on disposable plastic containers found that a single exposure to boiling water released more than a million submicron particles per milliliter [4]. Simulation work on common food packaging under 100 to 121 °C conditions reached the same conclusion [7]. And a 2025 survey of 155 UK-market beverages found hot drinks carried noticeably more microplastics than cold ones, with hot tea averaging around 60 particles per liter [5].

The through-line is simple. Hot water plus plastic tends to release particles. What that plastic is shaped into matters less than the temperature and contact.

3. Hard water changes the picture — but doesn’t erase it

The most interesting finding in the 2025 paper is the one most people miss. Shi’s team ran the experiment twice — once with ultrapure lab water, and once with hard tap water at the mineral level typical of a lot of municipal supplies. Hard water released far fewer nanoplastics into the cup [1].

The mechanism is limescale. Calcium and bicarbonate come out of solution at boiling temperatures and coat the polypropylene wall, physically trapping plastic fragments as they release [1]. A separate group at Trinity College Dublin reported the same effect earlier, with common drinking-water minerals reducing microplastic release by roughly 89 to 99.8% compared to deionized water [2,8].

So does hard water solve the kettle problem? Not exactly. The particles are moving from the water into the scale. There they can end up in the flakes you dislodge when descaling, or in the residue you scrub out with a sponge. Where those particles eventually go hasn’t been characterized. And on soft-water or reverse-osmosis systems, this natural trapping barely happens at all [3].

4. Three simple swaps that sidestep the mechanism

If you’d rather just keep hot water off polypropylene in the first place, a few small changes do most of the work:

• Switch to a stainless-steel or glass kettle. Both keep boiling water in contact with materials that don’t shed plastic. If you keep the plastic kettle for now, at least make sure you didn’t just buy it yesterday. The first several boils are when release is highest, and dumping the first few boils before drinking (a practice water testers already use with new kettles) is a small hedge.
• Use a French press or pour-over with a glass or metal carafe. These skip the plastic-lined coffee-maker basket and heating chamber entirely. Water contacts glass, metal, and coffee grounds — nothing else.
• Drink out of ceramic, glass, or stainless steel. Not just the mug — the travel cup, the shaker bottle, the water bottle. Every time hot liquid sits in a plastic-lined vessel, the same heat-driven leaching applies.

None of these swaps require you to declare any product unsafe. They just quietly cut one exposure route while the research keeps landing.

Notes on the science

The kettle study measured what enters the water using pyrolysis gas chromatography–mass spectrometry, a technique that identifies polymer mass directly. Two useful caveats: the study tested Australian-market kettles, and formulations in the U.S. or E.U. use different additives that haven't been directly compared. And nobody has quantified the chemical additives — antioxidants, slip agents — that may leach alongside the particles. A 2025 European Food Safety Authority review looking at the wider literature reached a similar summary: individual worst-case lab measurements likely overstate real-world release, and wear or descaling can matter as much as heat [9].

Where Winnow fits in

The kettle isn’t the whole story — it’s one input in a much longer chain of food-contact plastic exposure. Small, boring changes to the equipment on your counter are one of the more useful moves an ordinary person can make while researchers work on the bigger questions. Winnow’s probiotic strains have been shown in laboratory testing to bind micro- and nanoplastics within the gut lumen — one targeted piece of a much broader response, not a replacement for reducing exposure at the source.

Sources

[1] Shi, K. et al. Release of nanoplastic from polypropylene kettles. npj Emerg. Contam. 1, 16 (2025).

[2] Shi, Y. et al. The influence of drinking water constituents on the level of microplastic release from plastic kettles. J. Hazard. Mater. 425, 127997 (2022). https://pubmed.ncbi.nlm.nih.gov/34986566/

[3] Yu, Z., Wang, J.-J., Liu, L.-Y., Li, Z. & Zeng, E. Y. Drinking Boiled Tap Water Reduces Human Intake of Nanoplastics and Microplastics. Environ. Sci. Technol. Lett. 11, 273–279 (2024).

[4] Liu, G. et al. Disposable plastic materials release microplastics and harmful substances in hot water. Sci. Total Environ. 818, 151685 (2022). https://pubmed.ncbi.nlm.nih.gov/34785231/

[5] Al-Mansoori, M., Harrad, S. & Abdallah, M. A.-E. Synthetic microplastics in hot and cold beverages from the UK market: Comprehensive assessment of human exposure via total beverage intake. Sci. Total Environ. 996, 180188 (2025). https://pubmed.ncbi.nlm.nih.gov/40752223/

[6] Shi, K. et al. Release of Nanoplastics from Polypropylene Food Containers into Hot and Cold Water. J. Agric. Food Chem. 73, 27038–27047 (2025). https://pubmed.ncbi.nlm.nih.gov/41084274/

[7] Wang, Y., Wang, Z., Lu, X., Zhang, H. & Jia, Z. Simulation and Characterization of Nanoplastic Dissolution under Different Food Consumption Scenarios. Toxics 11, 550 (2023). https://pubmed.ncbi.nlm.nih.gov/37505516/

[8] Shi, Y. et al. Real-world natural passivation phenomena can limit microplastic generation in water. Chem. Eng. J. 428, 132466 (2022).

[9] European Food Safety Authority. Literature review on micro- and nanoplastic release from food contact materials during their use. EFSA Support. Publ. 22, (2025).