In recent years, scientists have become increasingly worried about the role micro- and nanoplastics are playing in our health. Since the 1950s, plastic has become an increasingly important feature of our everyday lives and conveniences. In 2021, around 390.7 million tonnes of plastic was produced across the world, and we know that much of the plastic waste we discard is now contaminating soil and water sources with tiny flakes, as well as invading our bodies through the air we breathe and the food we eat.

The more we learn about micro- and nanoplastics (MNPs), the more we find them in various parts of our bodies, raising questions and concerns about what this is doing to our health.

In the new study, researchers explored the amounts of MNPs in the livers, kidneys, and brains of autopsy specimens taken from people who died in 2016 and 2024, with supplementary analysis of brain samples taken from as far back as 1997. In total, the team explored 52 brain specimens, 28 from 2016 and 24 from 2024.

They used various methods to measure the concentrations of MNPs in these tissue samples, including pyrolysis gas chromatography, mass spectrometry, attenuated total reflectance, Fourier transform infrared spectroscopy, and electron microscopy with energy-dispersive spectroscopy. These complementary methods confirmed the presence of these tiny plastic pieces – mostly polyethylene, which is used in plastic bags, food wraps, bottles, containers, and plastic films – in all these organs, with lesser but still significant concentrations of other polymers.

During their analysis, the team found that concentrations of MNPs were significantly higher in brain samples (all derived from the frontal cortex) than in the liver and kidneys.

“Brain tissues harbor higher proportions of polyethylene compared to the composition of the plastics in liver or kidney, and electron microscopy verified the nature of the isolated brain MNPs, which present largely as nanoscale shard-like fragments,” the team write in their study.

More worryingly, the results showed a substantial increase in MNP concentrations in human brains across time. In particular, between 2016 and 2024, the median concentration of MNPs increased from 3,345 micrograms per gram to 4,917 micrograms per gram. This is nearly a 50 percent increase.

While examining the findings in relation to specific neurological conditions, the researchers also examined 12 brain samples from people who had dementia. They found that the amounts of plastic in these brains were higher than other samples. However, the team were keen to stress that these results do not imply a causal relationship at this stage.

“Atrophy of brain tissue, impaired blood–brain barrier integrity and poor clearance mechanisms are hallmarks of dementia and would be anticipated to increase MNP concentrations; thus, no causality is assumed from these findings,” they write.

The results show that plastic concentrations in the sample tissues were not influenced by age, sex, race, or the original cause of death. This is a strange finding, raising questions about why some people have higher levels in their bodies than others and how accumulation can be avoided.

These results continue to add to our understanding of MNP concentrations in human bodies, but their overall health implications remain unknown. The study itself has some limits too. Firstly, the sample size was pretty small, while the possibility of some sample contamination over the last 30 years cannot be completely ruled out.  

“However, given the consistent nature of handling and processing across all organ samples within objectively clean clinical and forensic settings, the significant accumulation of MNPs in the brain cannot be dismissed as an artifact of contamination,” the authors write.

“Furthermore the 2016 samples were stored for 84–96 months compared to only 2–4 months for the 2024 samples, which exhibited greater concentrations of polymer. Thus, contamination from plastic storage vessels should not influence the conclusions.”

Other experts not directly involved in the research have also called for caution when interpreting the study’s results.

“I can see this paper getting a lot of attention due to its scary-sounding title, but I’d urge caution. Before we get headlines like ‘Our brains are now made of plastics,’ we need to step back and look at how this study was conducted and what that might mean for the results,” said Oliver Jones, Professor of Chemistry at RMIT University in Melbourne, Australia, in a comment to Science Media Exchange. 

“The press release says the authors tested 28 brain samples from 2016 and 24 from 2024, which is only 52 samples in total. There is not enough data to make firm conclusions on the occurrence of microplastics in New Mexico, let alone globally.”

“The main analytical method used in this study was pyrolysis gas chromatography-mass spectrometry. This method can give false results when used to measure plastics because fats (which the brain is mainly made of) give the same pyrolysis products as polyethylene (the main plastic reported). The authors did try to address this concern but I am not certain they were able to account for everything.”

To be sure, the subject of MNPs in human bodies continues to raise concerns, so this latest study continues to stress just how important it is for us to investigate further.

“Overall, the work is interesting,” Jones added, “but the low sample numbers and potential analytical issues mean that care should be taken when interpreting the results. While it is not impossible that there are microplastics in the brains of some people, this study does not prove that this occurs, and, as the authors themselves note, there is as yet no strong evidence of any health effects.”

The study is published in Nature Medicine.