Removing microplastics from drinking water, as simple as putting the kettle on

Human-made plastics degrade into fragments over time and are now ubiquitous in our soil, air, and water – threatening drinking water safety. 

But Chinese researchers have found that simply boiling “hard” tap water could help remove nearly 90% of the nano- and microplastics (NMPs) . 

Because the effects of these tiny particles on human health remains poorly understood, simple inexpensive methods to reduce their consumption are needed. 

The new solution has been outlined in a paper in Environmental Science & Technology Letters

“Micro- and nano- plastics are coming into our water supply system. However our drinking water treatment systems are not designed to face this challenge,” corresponding author Dr Zhanjun Li, from the School of Biomedical Engineering in Guangzhou Medical University, told Cosmos

“Many advanced technologies [have been] found effective [in] removing these particle pollutants, yet they are expensive and need professional skills. 

“Boiling water is an old tradition in many Asian countries, [where] they drink boiled water even without tea. In the past, this habit helps prevent pathogens and some epidemic diseases. And now, our study shows that boiling water can help remove plastic pollutants.” 

Li and his team team collected hard tap water from Guangzhou, China, and spiked the samples with different amounts of polystyrene, polyethylene and polypropylene NMPs. After boiling the samples for 5 minutes and allowing them to cool for 10, the team then measured the free-floating plastic content.  

Calcium and magnesium carbonate salts are what makes water “hard”, these minerals come from rocks like limestone so places that use groundwater often have harder tap water. Boiling hard water causes a white chalky deposit called limescale, or calcium carbonate (CaCO3), to form – you’ve probably seen it on the bottom of your kettle! 

Artist's impression of a stovetop kettle pouring boiled water into a glass. Inside the kettle is a representation of the process that traps nano- and microplastics in limescale particles
Boiling tap water can trap nano- and microplastics inside limescale particles, which can be easily filtered out. Credit: Eddy Zeng

As water temperature increases, the researchers found that CaCO3 forms crystalline structures called incrustants that encapsulate NMPs. Over time, these incrustants build up like typical limescale and can be scrubbed away. Any that remain floating in the water can also be removed by pouring through a simple household filter – like a coffee filter. 

The efficiency of this process increases with water hardness – the amount of CaCO3 per litre of water. They found 34% of NMPs were removed at 80mg of CaCO3/L, 84% at 180 mg/L, and 90% at 300 mg/L.  

Drinking water hardness varies significantly between regions, but even boiling soft water (less than 60mg/L) can remove more than 25% of MNPs. 

So, can people at home use this method to remove NMPs from their own drinking water? Li says the answer is “an absolute yes”. 

“There [are] no specific requirements on the kettle. There [are] no technical secrets or any difficulty on boiling water,” he says. 

Li suggests leaving the kettle to stand for 5-10 minutes after boiling to allow the incrustants time to precipitate to the bottom and for the water to cool down enough before drinking. 

And, if you have the choice, “try to use a kettle with a rough internal surface, it will help the generation of incrustants,” Li adds. 

The team are now looking to study the role of incrustant formation in removing other anthropogenic trace pollutants from drinking water. 

“We believe that the benefits of simply drinking boiled water is beyond your imagination,” says Li. 

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