You’ve heard of microplastics, now get ready for nanoplastics

They seem to be everywhere, and yet scientists are still struggling to understand microplastics: plastic fragments between a micrometre and a few millimetres in size.

But plastic can break up into even smaller pieces – nanometre-sized – and at this size, they are even less well understood.

Nanoplastics are fragments of plastic which are between roughly one nanometre in size (or a few atoms), to one micrometre in size (or about bacterium-sized).

According to Associate Professor Melanie MacGregor, a chemist at Flinders University, scientists still need to find out where these nanoplastics are, and what risks they might pose.

MacGregor talked about nanoplastics at the Cosmos Science City session held on World Environment Day.

“We are a bunch of scientists from different fields, trying to answer the questions: where else do we find them? How many are there? When do they actually become toxic? What do we do about it?” she says.

“People from all sorts of science, engineering, biology, chemistry, physics, we’re all coming together to try and work out what to do next, basically, from the scientific point of view.”

The most popular, and fastest, methods of detecting microplastics tend not to work for nanoplastics.

“Everything that’s based on optical detection, you can’t use,” says MacGregor.

This is because nanoplastics are usually smaller than the “diffraction limit” of light: light waves are too big for them.

“You need to use different types of microscopes, such as scanning electron microscopes, which are slower and more expensive,” says MacGregor.

Researchers tend to use completely different methods to study nanoplastics. One method involves burning samples with pyrolysis and analysing the remains with mass spectrometry, which can identify which molecules might have been in the sample.

Because they’re so difficult to study, it’s not yet clear what the environmental and health effects of nanoplastics are.

“We’re still at the point of identifying it. I think that’s really what we need to keep working on, especially: is it actually a real threat? There’s not enough data yet to say something that is that small, is actually still toxic, or if we can, you know, eliminate it naturally without it causing much trouble,” says MacGregor.

This is particularly pertinent after research published last year has found nanometre-sized plastics in human blood.

“That’s one thing, but then the bloodstream goes through the kidneys. So what happens there? Are they filtered by the kidney? Do we find them in urine afterwards, and we don’t need to worry about it further, or do they accumulate in the kidney?” says MacGregor.

One of her new PhD students is working on this exact problem.

It’s also not yet clear what we could do to prevent nanoplastics from getting into our waterways and our bodies – other than, of course, drastically reducing plastic production.

Filters that target microplastics based on size can’t simply be downsized – filters with nanometre-sized holes would slow down the water you could push through significantly.

Researchers are still working on solutions. MacGregor says that one way around this is to build filters that target polymeric materials specifically, so they’d stick to plastics but not other things.

“That way you still can keep a flow, but you’re capturing the things that you don’t want to have in your water.”