Bottled water is often marketed as a pure alternative to what comes out of the tap, but a new report has found it's often anything but.
Researchers in the US tested more than 250 bottles from 11 different brands, and found they can contain up to thousands of tiny pieces of plastic each, reports Washington DC-based data journalism organisation Orb Media. The bottles came from various countries, including the US, China, Mexico, Thailand and Brazil.
On average, they found bottled water contains 10.4 pieces of plastic per litre around the 0.1mm size - about double what they found in tap water sourced from around the globe. For even tinier pieces, they found more than 300 per litre in bottles.
"Some of the bottles we tested contained so many particles that we asked a former astrophysicist to use his experience counting stars in the heavens to help us," Orb's Christopher Tyree and Dan Morrison wrote.
One bottle they found had more than 10,000 microplastics in it, per litre.
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The most common type of plastic found was polypropylene - the kind used to make bottle caps. Others had nylon and polyethylene terephthalate, used to make polyester.
The brands tested included Evian, Dasani, Aquafina, Nestle Pure Life, Gerolsteiner, Minalba, San Pellegrino, Wahaha, Epura and Bisleri. The cleanest brand was San Pellegrino, with a maximum 74 microparticles per litre. The worst was Nestle Pure Life, with up to 10,390.
Nestle denied the report, saying its own testing showed a maximum of five microparticles per litre - far less than 10,390. Gerolsteiner said its own testing also showed far fewer than Orb's.
Coca-Cola, which makes Dasani, told BBC News that microplastics "appear to be ubiquitous and therefore may be found at minute levels even in highly treated products". Pepsi, which makes Aquafina, said the science behind microplastics was "emerging", and needed further research to determine if it was a true health risk.
The research has not been peer-reviewed or published in a scientific journal. Orb quoted scientists who backed its research methods, and the testing was carried out at the State University of New York.
The results have convinced the World Health Organization to look closer at the impacts microplastics might have on health.
The effect of plastic microparticles on health is largely unknown. While much of it is believed to pass through the digestive system, it's suspected smaller particles may get lodged in the gut.
"We don't have actual experimental data to confirm that assumption," Zurich-based food scientists Jane Muncke told Orb.
"We don't know all the chemicals in plastics, even... There's so many unknowns here. That, combined with the highly likely population-wide exposure to this stuff - that's probably the biggest story here. I think it's something to be concerned about."
The United Nations is also concerned by the report.
"Please name one human being on the entire planet who wants plastic in his or her bottle," Erik Solheim, executive director of the United Nations Environment Program, told Orb. "They will all hate it."
Around 480 billion disposable plastic drink bottles are bought every year, and it's estimated fewer than half of them are recycled.