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Source: United Kingdom – Executive Government & Departments

February 3, 2025

A study published in Nature Medicine looks at microplastic accumulation in human organs. 

Prof Oliver Jones, Professor of Chemistry, RMIT University, said:

“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. 

“There are two main questions to consider with this study: 1) Are the results correct (exceptional claims need exceptional evidence)? 2) If so, what would that mean for human health? 

“Let’s look at the data first. I have questions here.

“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. 

“Only data from two years – 2016 and 2024 are presented. It is not explained why only these two years were studied, but regardless, you simply can’t make a trend from data from just two years. Data from 2017-2023 would be needed to say if there was an actual trend or if it was just a random variation. 

“The concentrations of microplastics in brain samples from 2024 have much less variation than any of the other data. This does not seem likely to me, but it is not explained. Similarly, in 2016, the kidney samples seemed to contain a more diverse range of plastics than liver samples, but in 2024, the liver had a more diverse range. The brain samples are consistent at both time points. This also seems odd but is not discussed.

“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) [1]. The authors did try to address this concern but I am not certain they were able to account for everything. 

“It is also challenging to properly account for potential contamination while handling or analysing samples in microplastic studies. This paper says that the findings are not likely to be lab contamination because samples were consistently handled and processed. I don’t think this is necessarily true. After all, consistent protocols could potentially result in consistent contamination. Even standard lab equipment, such as disposable lab gloves, can give false microplastic readings [2]. We also don’t know what happened to the samples during the original autopsy (bodybags are made of polyethylene, for example). There is also the issue of background contamination in any laboratory that needs to be controlled for [3]. Plastic contamination is almost everywhere, so how can we be confident that any particles found are evidence that plastic is crossing membranes in the human body or if it is just contamination from plastic in the clothes or lab equipment or background contamination in the air, etc?

“But let’s assume there are plastics in our brains. What would that mean? 

“There is a suggestion that microplastics might be associated with brain disease based on testing the brains from 12 people with dementia. This is not enough data to base this conclusion on (the patients didn’t all have the same kind of dementia). 

“To get to the brain, microplastics would need to cross the gut wall (which is relatively thick and well-regulated), be transported in the blood, and then cross the blood-brain barrier, which is also very well-regulated. Certainly, more work would be needed to see if this was even possible. 

“If microplastics could get into the brain, then theoretically, so could other small particulates that we are exposed to every day, e.g. from air pollution. If so any actual effects might be down to those substances – but the authors only tested for microplastics.

“We don’t know if microplastics or any other particles would stay in the brain or if they would be removed by the body. Again more work would be needed to test this.

“Overall, the work is interesting, 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.”

[1] Rauert C. et al. Extraction and pyrolysis-GC-MS analysis of polyethylene in samples with medium to high lipid content. Journal of Environmental Exposure Assessment 2022. 1(2): p. 13. http://dx.doi.org/10.20517/jeea.2022.04  

[2] Witzig C.S. et al. When good intentions go bad—false positive microplastic detection caused by disposable gloves. Environmental Science & Technology 2020. 54(19): p. 12164-12172. https://doi.org/10.1021/acs.est.0c03742

[3] Rauert C. et al. Blueprint for the design construction and validation of a plastic and phthalate-minimised laboratory. Journal of Hazardous Materials 2024. 468: p. 133803. https://doi.org/10.1016/j.jhazmat.2024.133803  

Prof Tamara Galloway, Professor of Ecotoxicology, University of Exeter, said:

“Microplastics are a ubiquitous consequence of modern life, present in air, water and food and it should come as no surprise to find that most people have microplastics present in their bodies. What we don’t yet know is what the implications are for human health.

“To understand more about this, Nihart and colleagues took a detailed look at how microplastics were distributed in the human brain, using postmortem samples. Their study identified tiny shards and flakes of plastic in the brains they studied, most of which were made out of polyethylene, a plastic widely used in food and drinks packaging and the most common component of plastic litter. 

“Two things stand out from this study. The first is that there was no relationship between the age of the subjects and the amount of microplastics present in the brain samples. This is important because it suggests that microplastics do not accumulate continuously in brain tissues as we age. 

“The second thing to stand out is the increase in levels of contamination over time, with a 50% increase in levels of microplastics present in the brain samples collected over the last 8 years, reflecting the increased production and use of plastics over a similar timeframe. This is significant because it suggests that if we were to reduce environmental contamination with microplastics, the levels of human exposure would also decrease, offering a strong incentive to focus on innovations that reduce exposure.

“A final note of interest is in the nature of the contamination. Polyethylene (PE) is the most widely encountered polymer in environmental plastic litter, it is used for making disposable food and drinks packaging amongst other uses and its abundance in human brain tissues reflects its abundance in wildlife samples. Perhaps of more concern is the apparent presence of other polymers including polyvinylchloride (PVC) and styrene butadiene rubber (SBD), both of which were present in smaller amounts in the samples. PVC has many uses eg. in construction and packaging, and SBD rubber is used in car tyres and other items.

“Both substances have raised concerns over their potential environment and human health effects and whilst the current study offers no evidence that they are causing harm, it does highlight the importance of understanding more about the many materials we use in daily life.”

Prof Theodore B. Henry, Professor of Environmental Toxicology from the School of Energy, Geoscience, Infrastructure and Society at Heriot-Watt University, said:

“The Nihart et al. (2025) article presents interesting initial results about contamination of human tissues by plastics, and, as with any such results, we must be careful not to speculate about the implications until independent confirmation can validate the findings. 

“Without doubt the increasing presence of plastic particles in the environment and potential negative effects on humans are a concern. 

“The difficulty in assessing the accumulation of plastic particles in internal organs because of a lack of analytical methods is addressed to some extent in this paper and this advancement is noteworthy. 

“A disadvantage of the pyrolysis-GC-MS analytical method used in the study is that because any plastic polymers present are disintegrated into small fragments in the process it is then not possible to determine the size, characteristics, or number of particles present in the original sample.  Another challenge of interpretation of these results is the difficulty in finding suitable control tissues, or tissues that have not been exposed to plastics, for which presence of polymers does not occur and the presence in the tissues can be compared (essentially all tissues had plastic polymers, which does suggest that there could be artifacts or analytical issues that are affecting the analyses that are not accounted for). 

“The reported presence of plastic particles in histological sections of tissues by polarised wave microscopy should be verified independently and could readily be done within existing banks of preserved human tissue sections held at many institutions.  Given the levels of particles that are reported in the present study it is surprising that similar particles have not been detected in other studies or examinations of the same tissues that have applied the same techniques.  The authors of this article correctly note in their conclusion that their results of detection of plastic polymers in tissues are associative and not linked to any negative health outcome.”

 

Dr Antonis Myridakis, Lecturer in Environmental Sciences, Brunel University of London, said:

“The study by Nihart et al. provides compelling evidence that microplastics (MPs) and nanoplastics (NPs) (plastic particles from 500 µm down to 1 nm) can cross the blood-brain barrier (the security filter protecting the brain from harmful entities) and accumulate in human brain tissue, particularly polyethylene, with concentrations increasing over time. The authors employ state-of -the-art and complimentary methodologies to detect, identify and quantify these particles (Py-GC-MS, SEM-EDS, ATR-FTIR), strengthening the credibility of their findings.”

 Does the press release accurately reflect the science?

“Yes, the study does support convincingly the claim that these particles are detectable in human brains. However, it is crucial to emphasise that the study does not establish causality between MPs/NPs and any negative health impacts.”

Is this good quality research? Are the conclusions backed up by solid data?

“The methodology is robust and multidisciplinary, using complementary analytical techniques to measure MPs and NPs. The data show a trend of increasing microplastic accumulation over time and higher concentrations in dementia cases. However, the sample size remains relatively small, and causation cannot be inferred at this stage.”

How does this work fit with existing evidence?

“This study aligns with recent findings that MPs/NPs are present in blood and major organs. The discovery of MPs in cerebrovascular walls and immune cells adds new insight into their potential role in neuroinflammation and warrants further investigation.”

Have the authors accounted for confounders? Are there important limitations?

“The study controls for key demographic factors (age, sex, cause of death) and finds no correlation between age and MP accumulation, suggesting environmental exposure may be increasing over time. However, it does not account for lifestyle-related factors (diet, occupation, regional pollution exposure), which could influence individual MP burdens. The inevitable use of post-mortem samples also limits the ability for functional assessments of MP toxicity in living brains.”

Real-world implications: Over-speculation or justified concern?

“The finding that MPs are accumulating in human brains is concerning, however, it is too early to draw conclusions about direct health risks. Further research is needed to determine whether MPs actively contribute to neurological disorders or if they are merely bystanders in an increasingly plastic-polluted environment.”

‘Bioaccumulation of microplastics in decedent human brains’ by Nihart et al. was published in Nature Medicine at 16:00 UK time on Monday 3rd February. 

DOI: 10.1038/s41591-024-03453-1

Declared interests:

Prof Oliver Jones “I am a Professor of Chemistry at RMIT University in Melbourne. I have no conflicts of interest to declare, but I have previously published research on microplastics in the environment. I have in the past received funds from the Environment Protection Authority Victoria and various Australian Water utilities for research into environmental pollution.”

Prof Tamara Galloway “None”

Prof Theodore B. Henry “None”

Dr Antonis Myridakis “None”