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The amount of environmental plastic nano- and microparticles, which range in size from as small as 1 nanometer (one billionth of a meter) up to 500 micrometers (one millionth of a meter) in diameter, has increased exponentially over the past 50 years. However, whether they are harmful or toxic to humans is unclear. Most previous studies used visual microscopic spectroscopy methods to identify particulates in human tissues, but this is often limited to particulates larger than 5 micrometers.
Matthew Campen and colleagues used novel methods to analyse the distribution of micro- and nanoparticles in samples of liver, kidney, and brain tissues from human bodies that underwent autopsy in 2016 and 2024. A total of 52 brain specimens (28 in 2016 and 24 in 2024) were analysed. They detected these particles in all of the samples and found similar concentrations in the samples of liver and kidney tissues obtained in 2016. However, brain samples taken from that time, all derived from the frontal cortex region, contained substantially higher concentrations of plastic particles than the liver and kidney tissues.
The authors also found that liver and brain samples from 2024 had significantly higher concentrations of plastic micro- and nanoparticles than those from 2016. They then compared these findings with those of brain tissue samples from earlier time frames (1997–2013) and note that there were higher concentrations of plastic particles in the more recent tissue samples. Campen and colleagues also found a higher concentration of micro- and nanoplastic particles in 12 brains from individuals with a documented dementia diagnosis than in those without.
The authors note that the findings identify an association but do not establish a causal link between plastic particles and health effects. Likewise, they suggest that some variation in the brain samples could be due to geographic differences, as samples were retrieved from New Mexico and locations on the US east coast. More longer-term studies with larger, more-diverse populations are needed to determine micro- and nanoparticle accumulation trends and their potential health implications.
Expert Reaction
These comments have been collated by the Science Media Centre to provide a variety of expert perspectives on this issue. Feel free to use these quotes in your stories. Views expressed are the personal opinions of the experts named. They do not represent the views of the SMC or any other organisation unless specifically stated.
Oliver Jones is Professor of Chemistry at RMIT University in Melbourne, Australia
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
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