‘A bombshell’: doubt cast on discovery of microplastics throughout human body

Exclusive: Some scientists say many detections are most likely error, with one high-profile study called a ‘joke’

the Guardian

One of the team behind the letter was blunt. “The brain microplastic paper is a joke,” said Dr Dušan Materić, at the Helmholtz Centre for Environmental Research in Germany. “Fat is known to make false-positives for polyethylene. The brain has [approximately] 60% fat.” Materić and his colleagues suggested rising obesity levels could be an alternative explanation for the trend reported in the study. Materić said: “That paper is really bad, and it is very explainable why it is wrong.” He thinks there are serious doubts over “more than half of the very high impact papers” reporting microplastics in biological tissue.

But the brain study is far from alone in having been challenged. One, which reported that patients with MNPs detected in carotid artery plaques had a higher risk of heart attacks and strokes than patients with no MNPs detected, was subsequently criticised for not testing blank samples taken in the operating room. Blank samples are a way of measuring how much background contamination may be present. Another study reported MNPs in human testes, “highlighting the pervasive presence of microplastics in the male reproductive system”. But other scientists took a different view: “It is our opinion that the analytical approach used is not robust enough to support these claims.”

Further challenged studies include two reporting plastic particles in blood – in both cases the researchers contested the criticisms – and another on their detection in arteries. A study claiming to have detected 10,000 nanoplastic particles per litre of bottled water was called “fundamentally unreliable” by critics, a charge disputed by the scientists. The doubts amount to a “bombshell”, according to Roger Kuhlman, a chemist formerly at the Dow Chemical Company. “This is really forcing us to re-evaluate everything we think we know about microplastics in the body. Which, it turns out, is really not very much. Many researchers are making extraordinary claims, but not providing even ordinary evidence.” While analytical chemistry has long-established guidelines on how to accurately analyse samples, these do not yet exist specifically for MNPs, said Dr Frederic Béen, at Vrije Universiteit Amsterdam: “But we still see quite a lot of papers where very standard good laboratory practices that should be followed have not necessarily been followed.”

A key way of measuring the mass of MNPs in a sample is, perhaps counterintuitively, vaporising it, then capturing the fumes. But this method, dubbed Py-GC-MS, has come under particular criticism. “[It] is not currently a suitable technique for identifying polyethylene or PVC due to persistent interferences,” concluded a January 2025 study led by Dr Cassandra Rauert, an environmental chemist at the University of Queensland in Australia. “I do think it is a problem in the entire field,” Rauert told the Guardian. “I think a lot of the concentrations [of MNPs] that are being reported are completely unrealistic.” “This isn’t a dig at [other scientists],” she added. “They use these techniques because we haven’t got anything better available to us. But a lot of studies that we’ve seen coming out use the technique without really fully understanding the data that it’s giving you.” She said the failure to employ normal quality control checks was “a bit crazy”. Py-GC-MS begins by pyrolysing the sample – heating it until it vaporises. The fumes are then passed through the tubes of a gas chromatograph, which separates smaller molecules from large ones. Last, a mass spectrometer uses the weights of different molecules to identify them. The problem is that some small molecules in the fumes derived from polyethylene and PVC can also be produced from fats in human tissue. Human samples are “digested” with chemicals to remove tissue before analysis, but if some remains the result can be false positives for MNPs. Rauert’s paper lists 18 studies that did not include consideration of the risk of such false positives. Rauert also argues that studies reporting high levels of MNPs in organs are simply hard to believe: “I have not seen evidence that particles between 3 and 30 micrometres can cross into the blood stream,” she said. “From what we know about actual exposure in our everyday lives, it is not biologically plausible that that mass of plastic would actually end up in these organs.” “It’s really the nano-size plastic particles that can cross biological barriers and that we are expecting inside humans,” she said. “But the current instruments we have cannot detect nano-size particles.”