Your Brain On... Microplastics

Ayesha Sherzai (0:00)

You may have seen the headlines, microplastics found in the human brain, levels increasing over time, higher concentrations in people with dementia. We covered that study, and a lot of people saw it. Then a chemical scientist, Dr. Michelle Wong, reached out to us and told us that the method used to measure those plastics may have been measuring brain fat instead. So we did what we said we'd always do. We went to the primary literature, we read the critique, and then Dr. Wong introduced us to someone who could explain it. Dr. Oliver Jones is a professor of analytical chemistry at RMIT University in Melbourne. He's a fellow of the Royal Society of Chemistry, a graduate of Imperial College London and Cambridge, and one of only 118 scientists around the world, named to the International Union of Pure and Applied Chemistry Periodic Table of Outstanding Younger Chemists.

He's spent over 20 years developing methods to measure what's actually in the world around us, and he was one of the first scientists to publicly flag the problem with this study. This is a conversation about what we know, what we assumed we knew, and what it looks like when the evidence shifts under a claim you've already made. This is Your Brain On Microplastics.

So, Ollie, when we put out this conversation about microplastics, one of our mutual acquaintances or your friend, Dr. Michelle Wong, reached out and said, hold on, there's more to this story than just that. So we went back and we read about it. And it was essentially about how the brain accumulates plastic in that. There is research that found plastic in the brain, and there were pictures of visible plastic pieces sitting in brain tissue, which was terrifying, to be honest with you. So give us an idea of what is actually being detected and how this study was brought about.

Oliver Jones (2:05)

Yeah, great question. So the thing is this study had a number of different approaches to measuring microplastics. And measuring microplastics, it's a very challenging field as in most analytical chemistry when you're trying to detect things that are really small amounts or really low concentrations. People often see something like NCIS or a show like that, and they're like, oh, you just put the sample in the instrument and press the button and it tells you the answer. And it doesn't work like that. This particular study was using a technique called pyrolysis gas chromatography mass spectrometry, which is a bit of a mouthful. But essentially how that works is if you think about a molecule of plastic, it's a polymer, right? So the long chains are repeating subunits. You could think of it like a bit like a Lego model almost. You can have all these little individual components and you can put them together to make longer chains or longer structures. Those polymer molecules are too big to go into a mass spectrometer. So the first thing you have to do is break them down, and that's where the pyrolysis step comes in. So you're essentially heating up your sample to a height average of several hundred degrees without oxygen, then you fragment these long chains into smaller subparticles or subchains, I should say. They then move into the chromatograph, which separates them based on size and polarity. So you've got a mixture of all these complex fragments. So you then move them through the chromatography and they separate out. And then they go into the mass spec where they're detected.

But what you're actually detecting is the breakdown products or any sort of reaction products that might have happened in the pyrolysis. So the pyrolysis destroys the original sample. And then the data that comes out of that, you're using that to infer what was in the original sample. And there's all sorts of things that can go wrong with a complex biological sample like brain tissue compared to a pure sample.

And the issue is that a plastic polymer chain, it's basically a long hydrocarbon chain, right? So you're breaking it down into a smaller hydrocarbon chain.

But if you have a biological sample, which is full of, say, fats, fats are also hydrocarbon chains. So the fragments of some plastics, to be fair, not all plastics, but some plastics look like the breakdown products of fats. So if you're using a fat-rich tissue, there's a potential that you might misidentify some of the compounds that you're, end products from your mass spectrometer as fats, when they're not actually fats at all, they're something else. So you got to be really sure that there's no other sort of interfering product that might look like the plastic, but it's actually something else.