The Guardian has identified seven studies that have been challenged by researchers publishing criticism in the respective journals, while a recent analysis listed 18 studies that it said had not considered that some human tissue can produce measurements easily confused with the signal given by common plastics.
“Levels of microplastics in human brains may be rapidly rising” was the shocking headline reporting a widely covered study in February. The analysis, published in a top-tier journal and covered by the Guardian, said there was a rising trend in micro- and nanoplastics (MNPs) in brain tissue from dozens of postmortems carried out between 1997 and 2024.
However, by November, the study had been challenged by a group of scientists with the publication of a “Matters arising” letter in the journal. In the formal, diplomatic language of scientific publishing, the scientists said: “The study as reported appears to face methodological challenges, such as limited contamination controls and lack of validation steps, which may affect the reliability of the reported concentrations.”
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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.
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.
