Bioaccumulation of microplastics in decedent human brains

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 (Py-GC/MS), attenuated total reflectance–Fourier transform infrared spectroscopy (ATR-FTIR), 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 liver or kidney, and electron microscopy verified the nature of the isolated brain MNPs, which present largely as nanoscale shard-like fragments. Plastic concentrations 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.

Tissue concentrations across organs

Postmortem human liver, kidney, and brain samples were obtained from autopsy specimens collected in 2016 and 2024 at the University of New Mexico (UNM) Office of the Medical Investigator (OMI). Tissue regions were consistently selected by a trained forensic pathologist: right central parenchyma for liver, cortex-and-medulla wedge for kidney, and frontal cortex for brain.

Py-GC/MS measurements revealed that liver and kidney had similar median MNP concentrations: 433 μg g⁻¹ and 404 μg g⁻¹, respectively, from 2024 samples. These values are already higher than previously published data for human placentas (median 63.4 μg g⁻¹)¹⁰Garcia MA et al. (2024) Quantitation and identification of microplastics accumulation in human placental specimens using Py-GC/MS. Toxicol Sci 199:81–88. Open → and testes (median 299 μg g⁻¹).¹¹Hu C et al. (2024) Microplastic presence in dog and human testis and its potential association with sperm count. Toxicol Sci 200:235–240. Open →

Brain accumulates far more plastic than other organs

Brain samples exhibited substantially higher concentrations of MNPs than liver or kidney (two-way ANOVA, P < 0.0001). The median brain MNP concentration was 3,345 μg g⁻¹ in 2016 samples and 4,917 μg g⁻¹ in 2024 samples — roughly 7 to 30 times the concentrations found in liver and kidney.

The proportion of polyethylene in the brain (75% on average) was greater relative to other polymers and compared to PE in liver and kidney (P < 0.0001). The specific polymers that increased from 2016 to 2024 in liver and brain were PE, polypropylene (PP), polyvinyl chloride (PVC), and styrene-butadiene rubber (SBR). PE predominance was confirmed independently with ATR-FTIR spectroscopic analysis from five brain samples.

Five brain samples from 2016 (highlighted in orange in Fig. 1a) were analyzed independently by colleagues at Oklahoma State University using Py-GC/MS, and those values were consistent with UNM findings (P = 0.49 for a Student's t test), providing cross-laboratory validation.

Increasing concentrations over time

Liver and brain samples from 2024 had significantly higher concentrations of MNPs than 2016 samples, consistent with the exponentially increasing environmental concentrations of MNPs over the past half century.^1,2Thompson RC et al. (2004) Lost at sea: where is all the plastic? Science 304:838; Stubbins A et al. (2021) Plastics in the Earth system. Science 373:51–55. The total mass concentration of plastics in the brains analyzed increased by approximately 50% in the past 8 years.

To expand these findings further, the researchers obtained brain tissue from earlier time frames (1997–2013) from repositories on the East Coast of the United States, including the Duke Kathleen Price Bryan Brain Bank, the Harvard Brain Tissue Resource Center, and the NICHD Brain and Tissue Bank at the University of Maryland. Py-GC/MS analysis revealed lower overall MNP concentrations in these earlier East Coast samples (median 1,254 μg g⁻¹), and a simple linear regression including all normal brain data revealed significantly increasing trends for total plastics, PE, PP, PVC, and SBR.

Even greater accumulation in dementia patients

To extend findings to a specific neurological condition, Py-GC/MS was conducted on 12 dementia cases collected at the NM OMI, including Alzheimer's disease (n = 6), vascular dementia (n = 3), and other dementias (n = 3), from specimens dated 2019–2024.

The association between dementia and extremely high MNP concentrations raises urgent questions about whether plastic accumulation contributes to neurodegeneration, or whether neurodegenerative processes simply allow more plastic to accumulate. More complex study designs and much larger cohorts will be needed to disentangle these possibilities.

Visualizing nanoplastics in the brain

Using scanning electron microscopy (SEM) and polarization wave microscopy, the researchers identified refractory inclusions in all organs. In the liver, inclusions were dispersed and aggregated within acellular regions consistent with lipid droplets, with rod-shaped particles in the 1–5 μm range. In the kidney, inclusions were elevated in glomeruli and along tubules. SEM with energy-dispersive spectroscopy (EDS) confirmed that observed particles were principally composed of carbon — not mineral or metallic.

In brain tissues, however, larger (1–5 μm) inclusions were not seen. Instead, smaller particulates (<1 μm) were noted in the brain parenchyma. Transmission electron microscopy (TEM) of resuspended brain pellets revealed largely 100–200 nm long shards or flakes — nanoscale fragments far below the resolution of standard light microscopy.

The mechanism by which nanoplastics are delivered to and taken up by the brain is unknown. Insights from Daphnia magna suggest clathrin-dependent endocytosis and macropinocytosis may underlie nanoplastic translocation within the intestine.¹³Das A et al. (2024) Confocal surface-enhanced Raman imaging of the intestinal barrier crossing behavior of model nanoplastics in Daphnia magna. Environ Sci Technol 58:11615–11624. Open → The authors posit that a similar uptake may occur during human ingestion of lipids, which could facilitate selective transfer into the lipid-rich brain.

Methods and quality controls

Py-GC/MS is an informative and reliable method for determining plastic concentrations in tissue samples.^3,4,9,10Multiple validation studies: Liu S et al. (2024), Marfella R et al. (2024), Leslie HA et al. (2022), Garcia MA et al. (2024). Py-GC/MS data between labs has been comparable. Tissue samples (~500 mg) were digested with 10% KOH for at least 3 days at 40°C, then ultracentrifuged at 100,000 g for 4 hours to generate a pellet enriched in solid polymer-based materials. A 1–2 mg portion was analyzed by single-shot Py-GC/MS against a standard panel of 12 polymers.

The study included extensive quality controls: Py-GC/MS assessment of KOH and formalin storage control “blanks,” plus polymer composition measurements of all plastic tubes and pipette tips used in sample processing. Both analytical labs (UNM and OSU) observed approximately 25% within-sample coefficient of variation, which does not alter the conclusions given the magnitude of the observed effects.

A potential concern is that 2016 samples were stored for 84–96 months versus only 2–4 months for 2024 samples. However, the 2024 samples exhibited greater polymer concentrations despite shorter storage — ruling out contamination from plastic storage vessels as a confounding factor.

Regarding potential overestimation, the KOH digestion reduced liver and kidney mass by 99.4%, while brain samples were reduced by 91.8%. The resultant pellets still contained unknown residual biomatrix that could present challenges for mass spectral interference. However, the researchers note several factors that may lead to underestimation: advanced oxidative degradation of MNPs causing shorter carbon chains in chromatograms, and incomplete nanoplastic recovery from ultracentrifugation given the extremely small (<200 nm) particle sizes observed.

Conclusions

The present data suggest a trend of increasing MNP concentrations in the brain and liver. The majority of MNPs found in tissues consist of polyethylene and appear to be nanoplastic shards or flakes. MNP concentrations in normal decedent brain samples were 7–30 times greater than the concentrations seen in livers or kidneys, and 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. For this, refinements to the analytical techniques, more complex study designs, and much larger cohorts are needed. Given the exponentially rising environmental presence of MNPs,^19–21Wang CH et al. (2021) Environmental source, fate, and toxicity of microplastics; Geyer R et al. (2017) Production, use, and fate of all plastics ever made; Landrigan PJ et al. (2023) The Minderoo-Monaco Commission on plastics and human health. these data compel a much larger effort to understand whether MNPs have a role in neurological disorders or other human health effects.

This article is an enhanced web presentation of the original open-access paper published in Nature Medicine under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0). All text, data, and figures are from the original publication by Nihart, Garcia, El Hayek et al. (2025). © The Author(s) 2025, corrected publication 2025. Presented by DetoxBio for educational purposes. No adaptations have been made to the original content.