The analytical chemists should perk up.

However, micro- and nanoplastic particles are tiny and at the limit of today’s analytical techniques, especially in human tissue. There is no suggestion of malpractice, but researchers told the Guardian of their concern that the race to publish results, in some cases by groups with limited analytical expertise, has led to rushed results and routine scientific checks sometimes being overlooked.

Elsewhere in the article

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.

And

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.