Advanced imaging reveals bottled water nanoplastics

Whereas microplastics are defined as fragments ranging from 5mmdown to 1μm, nanoplastics are classified as particles below 1μm and are measured in nanometres (billionths of a metre). The presence of these tiny particles in virtually every environment on Earth and all aspects of food chains has only recently been confirmed, with the effects on human health largely unknown.

Using stimulated Raman scattering microscopy - which was co-developed by Columbia biophysicist and study co-author Wei Min - the team probed water samples with two simultaneous lasers tuned to make specific molecules resonate. Targeting seven common plastics, the researchers created a data-driven algorithm to interpret the results.

“Previously this was just a dark area, uncharted. Toxicity studies were just guessing what’s in there,” said study co-author 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.”

The team tested three popular brands of bottled water sold in the United States, analysing plastic particles down to just 100 nanometres in size. Each litre was found to contain between 110,000 to 370,000 plastic particles, 90 per cent of which were nanoplastics, with the rest comprising microplastics. The work is published in the Proceedings of the National Academy of Sciences

Unsurprisingly, PET (polyethylene terephthalate) was one of the most common particles found, it being the most widely used plastic for disposable water and soft drink bottles. However, PET was outnumbered by polyamide, a type of nylon. According to the Columbia team, it is likely the prevalence of polyamide comes from plastic filters designed to purify the water before bottling.

Other common plastics found include polystyrene, polyvinyl chloride and polymethyl methacrylate. The seven plastic types the team searched for accounted for only around 10 per cent of all the nanoparticles found in samples, with the researchers unsure what the remaining 90 per cent of particles were.

The Columbia team is now setting its sights beyond bottled water and will use the technique to examine tap water and laundry wastewater, as well as snow collected by a British expedition in Western Antarctica.   

“There is a huge world of nanoplastics to be studied,” said Min. “It’s not size that matters. It’s the numbers, because the smaller things are, the more easily they can get inside us.”