US study finds hundreds of thousands of nanoplastic particles in bottled drinking water

Each litre of bottled water contains 110,000 to 370,000 plastic particles — and about 90 per cent of them are nanosized (less than 1 micrometer in size), a new study has found. These nanoplastics are even smaller than microplastics and pose a greater risk to human health. 

The quantity of these particles in bottled water is 10 to 100 times greater than previous estimates, the research published in journal Proceedings of the National Academy of Sciences noted.

Most plastics divide into smaller and smaller particles of the same chemical composition and there is no theoretical limit to how small they can get.

Unlike microplastics (ranging between 5 millimeters and 1 micrometer), nanoplastics can move from the intestines and lungs directly into the bloodstream before reaching the heart and brain. This raises concern over the potential health impacts.

“However, our understanding of nanoplastics is limited by the lack of adequate analytical tools,” Beizhan Yan from Columbia University and one of the authors of the study, told Down To Earth.

While traditional techniques using pure plastics have confirmed the existence of nanoplastics, much remains unknown about their distribution, abundance, types in our environment and exposure levels, Yan added.

Yan and his colleagues analysed micro and nanoplastics in three popular brands of daily consumed bottled water using a technique called stimulated Raman scattering microscopy, which was co-invented by study coauthor Wei Min, who is also from Columbia University.

Stimulated Raman scattering microscopy is a powerful imaging technique that provides highly specific chemical information about a sample. 

The technique passes two lasers through the sample. It is particularly suitable for the identification of microplastics due to its ability to distinguish different types of plastics based on their molecular fingerprints. 

“It can be used to study tiny plastic particles from water bodies to biological tissues, thereby aiding in the assessment of environmental pollution and its potential impacts on ecosystems and human health,” Yan explained.

The team looked for seven common plastics: Polyamide, polypropylene, polyethylene, polymethyl methacrylate, polyvinyl chloride, polystyrene, and polyethylene terephthalate.  These chemicals are found likely to play a significant role in micro-nano plastics exposure from bottled waters, the paper noted.

“People developed methods to see nanoparticles, but they didn’t know what they were looking at,” the study’s lead author, Naixin Qian, a Columbia graduate student, said in a statement.

On average, the team detected some 240,000 detectable plastic fragments, 10 per cent of which were identified as microplastics and the remaining were nano-sized.

All seven of the plastic compounds were detected in the samples.  Polyethylene terephthalate, or PET, which is used in disposable beverage bottles, could leach into water when the bottle is squeezed or exposed to heat. 

The study also observed that PET was outnumbered by polyamide, a type of nylon. The researchers suspect that it could have been introduced by plastic filters that work to purify water. Polyamide is the most popular membrane material used in reverse osmosis.

Polypropene is widely used as equipment components or coagulant aids in water treatment. Polyvinyl chloride is identified as the most abundant polymer type in raw water, while polystyrene is used as backbone material for ion exchange resins (used to demineralise water) in the water purification process.

These seven plastics accounted for 10 per cent of all the nanoparticles they found in the samples. The remaining are unknown. Yan suspected that 90 per cent could be inorganic nanoparticles and might not be among the seven major types.

The study was conducted in the United States. The results, however, could vary between countries depending on the bottle materials and filtration techniques used, Yan highlighted.

“Further research is necessary to determine if drinking bottled water containing nanoplastics could lead to adverse health effects. If people are concerned about nanoplastics in bottled water, it's reasonable to consider alternatives like tap water,” he added.

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