Microplastics in the brain are likely laboratory contamination

icroplastics are small bits of degraded plastic with diameters between one nanometer and 5 millimeters. Most are microscopic; the pictures of people holding handfuls of “microplastics” you see on the Internet are not microplastics, but ground-up plastic shown for effect. They are unrealistic.

In this article, I will discuss the possibility that the presence and health effects of microplastics have been exaggerated. In many cases, it is likely that microplastics are not even real, but artifacts of sample processing. Only scientific articles not behind paywalls will be cited here, but paywalled ones contain similar information. Microplastics have been ‘implicated’ in cancer ^[1], cardiovascular disease ^[2], mitochondrial disorders ^[3], asthma and COPD ^[4], autism ^[5], Parkinson's disease ^[6], Alzheimer's disease ^[7][8], anxiety and depression ^[9], skeletal dysplasia ^[10], frontotemporal dementia, amyotrophic lateral sclerosis and sleep disorders ^[11], and many others.

“Implicated” is a term used by scientists to mean that there's a possibility that a correlation may exist, but causality remains to be proved. It's commonly found in grant applications where the researchers want to build a case that something might be real. If they send it to the National Cancer Institute, they'll say it's implicated in cancer. If the same grant goes to NINDS, they'll say it's implicated in neurological disorders. And so on.

One article ^[11] tried to pre-empt criticism of their findings by saying “Denial is not an option,” as if it were a political issue. It's certainly impossible to rule out all these effects categoric­ally, but a claim that one thing is responsible for every disease with an unknown cause is a classic sign of a solution looking for a problem.

Microplastics can go where no other substance can go

Microplastics are said to be everywhere. They're in Antarctica ^[11], in sea birds ^[12], and floating in the atmosphere. The authors of one paywalled article wrote “Microfibers were found to be the predominant particle form, constituting approximately 80% of the particles detected at each sampling point.”

They're in the bloodstream ^[13] and even in the human brain ^{[14][15][16][17]}. Of course, it's plausible to find them in the digestive tract: humans will eat anything, which is why companies have to write “Do not eat” on all their products. But when people claim to see them in the brain, it sets off alarm bells.

The general view is that it's impossible for anything with a molecular weight over 1000 Daltons (Da) to cross the blood-brain barrier (BBB). Big pharma companies go to elaborate lengths to shrink bifunctional antibodies, which have a molecular weight of 150,000, to make them small enough to cross the BBB in the hopes of treating brain diseases. If they found out they could get six grams of a drug with a molecular weight of 180,000,000,000 into the brain just by making it out of plastic, they'd be overjoyed.

A typical 50 kDa protein, about 1/3 the size of an antibody, has a radius of 2.4 nm.^[18] A microplastic with a radius of 0.5 mm has a radius 208,000 times bigger and 9.05 × 10¹⁵ times more volume. The point is: if a therapeutic protein can't cross the BBB due to its size, the odds of a hunk of plastic getting across are infinitesimal.

One article ^[13] claimed that microplastics could block blood flow in the brain. Unfortunately, this study simply injected microparticles into the mouse's blood. They merely showed that you can create a vascular occlusion by injecting mice with large insoluble particles.

Several papers, noting how microplastics can go where no molecule has gone before, have proposed them as carriers to transport drugs to cancer cells and to get anticancer drugs, antibiotics, and anti-Alzheimer drugs into the brain.

A crisis

The earlier claim that microplastics absorb toxins from the environment and release them in the cell seems to have been abandoned. If it were true, microplastics would make excellent home filtration systems. They'd absorb all the plasticizers and organic pollutants we keep hearing about. Since plastic is insoluble, it would be easily contained in a filter cartridge.

By now, most people know that calling something a crisis is a common ploy designed to elicit funding. I've reviewed dozens of grant proposals. Very few fail to call their topic a ‘crisis’ or a ‘major public health problem.’ The reason is simple. They have no choice: if someone wrote that something was not a big problem, it would not get funded.

There are ready-made solutions waiting to go

As we saw with the ozone hole crisis, where chemical companies were happy to ban CFCs because they had new refrigerants still under patent, the plastics industry has stated that the only reason they haven't switched to biodegradable plastics is that they're waiting for regulations that force them to do it. It's unlikely that a blanket ban on plastic would ever happen. The most likely outcome is that plastic items would get more expensive and it would be illegal to get rid of any plastic stuff you already have.

If microplastics aren't real, what are they?

One recent review study by Roslan et al. ^[20] reviewed 26 articles on microplastics. Nine claimed high health risk, three claimed unclear risk, and 14 claimed low risk. They concluded that the data for health risks are still unclear and that standard meth­ods for detection are not established. They advised researchers to run blanks in parallel to check for contamination.

That's about as strong an admission as you can make in academia that they suspect everyone is looking at artifacts. Academics get very defensive when their source of funding is challenged, so it's necessary to hedge. Hard sciences tend to be more open to chal­len­ges, but nobody likes to hear they've made a mistake.

Roslan et al. described microplastics as blue, red, yellow, purple, transparent, or black fragments, films, and fibers.^[20] Most often they were identified as nitrocellulose (aka cellulose nitrate), polyethylene, polyether­sulfone, PET, polypropylene, PVC, cellulose acetate, nylon, PMMA, and similar materials.

This gives us the Big Clue we need. Polyethylene, polystyrene, PMMA, and polypropylene are ubiquitous in the laboratory. The other materials—Teflon, nitrocellulose, nylon, and cellulose acetate—are components of filters that researchers use to sterilize their solutions.

Cytiva is one of many companies that sell such membrane filters. (The membrane is the part of the filter that the solution passes through.)

Sterilizing your solutions is essential in the lab because an unsterilized solution will rapidly become overgrown with algae, bacteria, and myco­plasma. In the old days, people used to sodium azide for this purpose. Azide is, of course, highly toxic, and it would kill your cells (and maybe also the investigator). It is also unstable, so you have to keep adding it every month or so. So everyone switched to filtration instead.

Colored fibers and chunks are of plastic are readily produced by filtration. To get the solution through the filter, you have to apply suction or pressure, which dislodges bits of the filter. Syringe filters are the worst, and you will find pieces of cellulose, nylon, or Teflon in your samples. Even pre-washing the filter to remove any loose plastic doesn't help: the pressure just creates new ones. The image above shows several examples of particles found in plain water or buffer solution caused by passage through a syringe filter.

I have even found red, green, and blue colored fibers in cultured ganglia from invertebrates. The quantity of fibers was far too high to be from pollution. The cause again was filtered solutions. Most people, of course, run blanks. The trick is to run an appropriate blank. They might not consider that a combination of two lab supplies is something that can cause an artifact. I didn't at first when I discovered them in my cultured cells and post-mortem brain samples and got suspicious.

Microplastics in decedent human brains

Nihart et al. ^[14] claimed to find “shard-like fragments” and irregular-shaped particles of polyethylene in postmortem brain samples. They claimed that there were more particles in decedent brain samples from patients with dementia. They also claimed that brains from 2016 had fewer particles than brains from 2024. The result is statistically significant, but not convincing due to the high variability. The levels were highest in brain, about 4917 micrograms per gram in samples from brain, compared to about 400 in the liver—the exact opposite of what you'd expect.

This number of 4917 μg/ml works out to 6.3 grams in a 1300 cc brain. The press accurately described it as a ‘spoonful.’ If true, it would mean that the human brain is nearly 0.5% plastic. The authors say the amount of plastics did not correlate with age at death, ruling out accumulation over a lifetime. They also say they measured blanks by checking plastic tubes and pipette tips, but make no mention of filtration steps, which is where the microplastic particles are coming from.

The answer is clear: in this study, as in most others, most of these microplastics are most likely artifacts of sample processing. Researchers need to address the issue of laboratory contamination before any conclusions about microplastics can be drawn.

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