Ellen Phiddian
Cosmos science journalist
Bottled water is filled with even more microplastics and smaller nanoplastics than previously thought, according to a new study from US researchers.
It’s well known that bottled water has more microplastics in it than tap water, both from the bottles and the processing. But a study published in PNAS has used newer technology to find 10 to 100 times more microplastic than older estimates.
These plastic fragments, which are smaller than 5mm, are typically counted by hand, making their detection a laborious process.
Nanoplastics, which are smaller than a micrometre – about the thickness of a human red blood cell – are even more difficult to track.
The researchers developed a technique called stimulated Raman scattering microscopy, which in combination with computer algorithms, allowed them to identify microplastics faster.
After testing 3 off-the-shelf bottled water brands, they found a litre of bottled water contained, on average, 240,000 plastic fragments. Concentrations ranged from 110,000 fragments per litre to 370,000 fragments per litre.
Most of these fragments – 90% – were nanoplastics, the remaining 10% were microplastics.
“It is not totally unexpected to find so much of this stuff,” says lead author Naixin Qian, a graduate student in chemistry at Columbia University. “The idea is that the smaller things get, the more of them there are.”
Because they’re so difficult to track, the health effects of microplastics and particularly nanoplastics are poorly understood.
“Previously this was just a dark area, uncharted. Toxicity studies were just guessing what’s in there,” says co-author Dr Beizhan Yan, an environmental chemist at Columbia University.
“This opens a window where we can look into a world that was not exposed to us before.”
Their new method, which involves firing lasers through the water to collect light signatures, searched for 7 common types of plastic.
The most common plastic in the water was polyamide. This, says Yan, likely comes from the filters used to purify bottled water. Ironic.
Another common type of plastic was PET, or polyethylene terephthalate, which is what most bottles are made of.
Most of the fragments spotted in water weren’t any of these 7 types of plastic. In fact, the researchers found fragment concentrations of more than one million parts per litre, with the identified plastics making up only 10% of these.
While these unidentified fragments could be plastics, it’s also possible they’re organic matter.
The researchers are aiming to investigate micro and nanoplastics in tap water next, alongside looking at the health effects of these tiny particles.
