Nature Medicine: Bioaccumulation of microplastics in decedent human brains

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https://doi.org/10.1038/s41591-024-03453-1

Brief Communication | Open access | Published: 03 February 2025
Bioaccumulation of microplastics in decedent human brains

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Nature Medicine (2025)Cite this article

Abstract
Rising global concentrations of environmental microplastics and nanoplastics (MNPs) drive concerns for human exposure and health outcomes. Complementary methods for the robust detection of tissue MNPs, including pyrolysis gas chromatography–mass spectrometry, attenuated total reflectance–Fourier transform infrared spectroscopy and electron microscopy with energy-dispersive spectroscopy, confirm the presence of MNPs in human kidney, liver and brain. MNPs in these organs primarily consist of polyethylene, with lesser but significant concentrations of other polymers. 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. Plastic concentrations in these decedent tissues were not influenced by age, sex, race/ethnicity or cause of death; the time of death (2016 versus 2024) was a significant factor, with increasing MNP concentrations over time in both liver and brain samples (P = 0.01). Finally, even greater accumulation of MNPs was observed in a cohort of decedent brains with documented dementia diagnosis, with notable deposition in cerebrovascular walls and immune cells. These results highlight a critical need to better understand the routes of exposure, uptake and clearance pathways and potential health consequences of plastics in human tissues, particularly in the brain.

Main
Environmental concentrations of anthropogenic microplastic and nanoplastic (MNP), polymer-based particulates ranging from 500 µm in diameter down to 1 nm, have increased exponentially over the past half century1,2. The extent to which MNPs cause human harm or toxicity is unclear, although recent studies associated MNP presence in carotid atheromas with increased inflammation and risk of future adverse cardiovascular events3,4. In controlled cell culture and animal exposure studies, MNPs exacerbate disease or drive toxic outcomes, but at concentrations with unclear relevance to human exposures and body burdens5,6. The mantra of the field of toxicology—‘dose makes the poison’ (Paracelsus)—renders such discoveries as easily anticipated; what is not clearly understood is the tissue distribution and internal dose of MNPs in humans, which confounds our ability to interpret the controlled exposure study results.

So far, visual microscopic spectroscopy methods have identified particulates in organs, such as the lungs, intestine7 and placenta8. These methods are often limited to larger (>5 µm) particulates; thus, smaller nanoplastics are unintentionally excluded. As a new approach, pyrolysis gas chromatography–mass spectrometry (Py-GC/MS) has been applied to blood9, placentas10 and recently major blood vessels3,4 in a manner that appears more cumulative, quantitative and less biased when coupled with orthogonal methods. Py-GC/MS data between labs has been comparable, providing confidence in this method for human tissue analysis3,9,10. Here we applied Py-GC/MS in concert with visualization methods to assess the relative distribution of MNPs in major organ systems from human decedent livers, kidneys and brains.

Results and discussion
We obtained de-identified, postmortem human liver (right central parenchyma), kidney (wedge piece containing cortex and medulla) and brain (frontal cortex) samples, retrospectively from 2016 and 2024 autopsy specimens (Supplementary Table 1), in cooperation with and approval from the University of New Mexico (UNM) Office of the Medical Investigator (OMI) in Albuquerque, New Mexico (NM), under the guidance of a trained forensic pathologist (D.F.G.) who selected consistent regions from all organs. Py-GC/MS measurements of MNP concentrations in decedent liver and kidney specimens were similar, with the median value of total plastics at 433 and 404 µg g−1, respectively, from 2024 samples (Fig. 1a and Supplementary Table 1). These were higher than previously published data for human placentas (median = 63.4 µg g−1)10 and testes (median = 299 µg g−1)11. Brain samples, all derived from the frontal cortex, exhibited substantially higher concentrations of MNPs than liver or kidney (two-way analysis of variance (ANOVA), P 

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1. Probably nothing important

❝…brain samples from dementia cases exhibited even greater MNP presence. These data are associative and do not establish a causal role for such particles affecting health. …❞