A deluge of research has painted a picture of our world being drowned in tiny, inescapable microplastics. Our guilt over plastic particles being found in even the most remote regions on Earth turned into paranoia once scientists started discovering them in our own bodies, too — riddling our blood streams, organs, and even our brains, stoking a rush of scientific inquest.
But now, there’s a growing contingent in the scientific community that’s casting significant doubts on these claims, The Guardian reports, criticizing the methodologies used in some of the most notable papers behind them.
One study published in the journal Nature Medicine last February claimed to have documented a rise in micro and nanoplastics (MNPs) in human brain tissues by autopsying preserved cadavers of people who had died between 1997 and 2024. But in November, another group of researchers contested the findings in a letter published in the same journal, criticizing them for “limited contamination controls and lack of validation steps,” per The Guardian.
“The brain microplastic paper is a joke,” coauthor of the letter Dušan Materić, from the Helmholtz Centre for Environmental Research in Germany, told the newspaper. “Fat is known to make false-positives for polyethylene. The brain has [approximately] 60 percent fat.”
In reality, Materić suggests that rising obesity rates could explain the trend.
“That paper is really bad, and it is very explainable why it is wrong,” he added, warning that there’s serious doubts over “more than half of the very high impact papers” over microplastics in tissues.
One core issue arises from the prevailing method for measuring the mass of micro and nanoplastics. Called Py-GC-MS, it involves pyrolyzing the sample, or heating it in an oxygen free environment until it vaporizes. The fumes this process produces are then separated and measured so the nature of the original substance can be analyzed.
But as it turns out, the same fume signatures for the materials used in microplastics like polyethylene can also be produced from the fats present in human tissue. And while studies purport to chemically remove the tissues before subjecting the samples to pyrolysis, critics are skeptical that some traces aren’t being left over and producing false positives. This led University of Queensland environmental chemist Cassandra Rauert to conclude in a January 2025 paper that Py-GC-MS “is not currently a suitable technique for identifying polyethylene or PVC due to persistent interferences.” In all, the paper points to 18 studies that didn’t properly account for the risk of false positives.
“I do think it is a problem in the entire field,” Rauert added to The Guardian. “I think a lot of the concentrations [of MNPs] that are being reported are completely unrealistic.”
Another problem is that while the field of analytical chemistry has guidelines on how to analyze certain samples, these guidelines don’t exist yet for microplastics, according to Frederic Béen at Vrije Universiteit Amsterdam.
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