Using advanced imaging technology, researchers have ascertained the number of nanoplastics – bits of plastic smaller than a micrometer – in bottled water, finding that, on average, a liter contains 240,000 detectable fragments. The study provides invaluable information to address rising concerns about micro- and nanoplastic toxicity.

Microplastics – ranging from less than a quarter inch (5 mm) down to a micrometer – are formed when plastics break down into progressively smaller bits. And, in recent years, concerns have been raised that microplastics are showing up literally everywhere on Earth – from the bottom of oceans to the top of mountains.

These plastic particles are consumed by humans and other creatures, with research now looking into the potentially harmful effects of this consumption. However, these studies are predominantly concerned with microplastics. Now, researchers from the Columbia Climate School, New York, have used advances in imaging technology to investigate the ‘spawn’ of microplastics – nanoplastics, less than a micrometer in size – to see how prevalent they are in the bottled water we drink.

“Previously, this was just a dark area, uncharted,” said Beizhan Yan, one of the study’s corresponding authors. “This [study] opens a window where we can look into a world that was not exposed to use before.”

The researchers developed a technique called stimulated Raman scattering (SRS) microscopy, which involves probing samples with two simultaneous lasers that are tuned to make specific molecules resonate. The technique allows micro- and nanoplastic analysis at the single-particle level, providing high chemical specificity and throughput. Focusing on seven common plastics, the researchers created a data-driven algorithm to interpret the results.

Testing three popular brands of bottled water sold in the US (they declined to name them), the researchers analyzed them for the plastic particles present down to just 100 nanometers in size, which had previously been invisible under conventional imaging. They observed 110,000 to 370,000 plastic fragments in each liter (33.8 fl oz), 90% of which were nanoplastics. The rest were the larger – but still very small – microplastics. They determined which of the seven specific plastics they were and charted their shapes, information which could be relevant to biomedical research.

Polyethylene terephthalate (PET) was common, which is not unusual as it’s what many water bottles are made of. PET probably enters the water when the bottle is squeezed, exposed to heat, or when the cap is screwed off and on. However, compared to PET, the researchers found higher amounts of polyamide, a type of nylon that, ironically, probably comes from plastic filters used to purify the water before it’s bottled. The other commonly seen plastics included polystyrene, polyvinyl chloride and polymethyl methacrylate, all of which are used in various industrial processes.

“Our results confirm the plastic fragmentation beyond the micron level by unambiguously detecting nanoplastics in real-life samples,” said the researchers. “Similar to many other particle size distributions in the natural world, there are substantially more nanoplastics, despite being invisible or unidentified under conventional particle imaging techniques, than previously counted large micron ones.”

Somewhat concerningly, the seven plastics tested accounted for only about 10% of all the nanoplastics the researchers found in the bottled water. They had no idea what the others were and whether they are, in fact, nanoplastics. Assuming that they are nanoplastics, the researchers say, means they could number in the tens of millions per liter.

A study published in 2022 noted growing evidence of ingested microplastics accumulating in mammalian tissues and organs and negatively affecting endocrine function, reproduction, gut microbiota, and immune responses in rats and mice. The authors of that study concluded that it was essential for further studies to be conducted to determine the potential hazards posed by micro- and nanoplastics.

The researchers here say that the association between particle shape and chemical composition has “profound implications” for toxicological concerns. Studies have started to indicate that toxicity induced by micro- and nanoplastics is not only dose-dependent, but it is related to the particles’ physical and chemical characteristics and their effect on cellular interactions and uptake. They say that single-particle imaging data such as that gathered by their research provides indispensable information to address the rising concerns relating to toxicity.

Next, the researchers plan to look beyond bottled water to other potential sources of nanoplastics, including tap water.

“It is not totally unexpected to find so much of this stuff,” said Naixin Qian, the study’s lead author. “The idea is that the smaller things get, the more of them there are.”

The study was published in the journal PNAS.

Source: Columbia Climate School