A study published in Nature Health provides the first detailed measurements of micro- and nanoplastics (MNPs) in the human brain. The finding: MNPs were detectable in all samples — with significantly higher concentrations in tissue surrounding brain tumors.

“In general, I would classify the current data as exploratory,” said Frank Winkler, head of the experimental neuro-oncology research group and managing senior physician, Department of Neurology, University Hospital Heidelberg, Heidelberg, Germany, in comments to the Science Media Center Germany — “They are suitable for generating important new research questions, but do not yet allow for conclusions regarding a causal role of micro- or nanoplastics in the development or progression of brain tumors.”

Advanced Detection Techniques

A total of 191 tissue samples were examined. These included 156 samples from 113 patients with brain or meningeal tumors and 35 samples from five deceased persons without neurological or oncologic disease. The tumor samples were taken intraoperatively under controlled conditions to minimize exogenous contamination. 

Several physical methods that detect different particle properties were used to analyze MNP:

• Laser direct infrared spectroscopy (LDIR) uses infrared light to determine the chemical composition of particles. Because different plastics absorb characteristic wavelengths, they can be identified unambiguously — and nondestructively.
• Optical photothermal infrared spectroscopy (O‑PTIR) works similarly: the sample is slightly heated by an infrared laser, which alters its optical properties depending on the material. This method also yields a specific spectrum and can even detect particles smaller than 1 µm — again without damaging the sample.
• By contrast, pyrolysis gas chromatography-mass spectrometry (Py GC/MS) is a destructive technique. The sample is heated intensely, causing the plastic components to decompose; the resulting gases are then separated and identified based on their mass. That allows identification of the polymer types present.
• Scanning electron microscopy (SEM) was also used. It provides high-resolution images of particles and information on their shape, surface structure, and topography.

A combination of the methods allows both qualitative and quantitative statements about particle size, structure, and chemical composition.

Marked Concentration Discrepancies

Results show substantial differences in MNP burden depending on tissue type. In healthy brain tissue, the average concentration was 50.3 µg/g, while the meninges of healthy individuals measured 60.9 µg/g. A particularly high burden was seen in peritumoral tissue, for example around gliomas, with an average of 129.4 µg/g. The tumor tissue itself, however, showed significantly lower levels.

“In principle, the methods for detecting MNPs are suitable. But the presented results are not plausible because the reported particles and their masses are (far) too high,” said Dieter Fischer, head of the microplastics and Raman spectroscopy working group, Analytical Department, Leibniz Institute for Polymer Research Dresden, Dresden, Germany. “MNPs are likely present in human tissue but certainly not in the quantities reported here.” He cited methodological errors and resulting misinterpretations in the identification and quantification of MNPs as possible reasons for such discrepancies.

Peritumoral Plastic Accumulation

According to the study, MNP concentration in the immediate vicinity of the tumor is more than twice as high as in healthy brain tissue. How is that possible?

The authors discuss several hypotheses. Tumor growth may compromise the blood‑brain barrier, making it easier for MNPs to enter. The researchers also suggest that rapidly proliferating tumor tissue could essentially “dilute” existing microplastic, while the less dynamic rim area accumulates them. Structural changes and inflammatory processes in the peritumoral tissue might also favor local retention. The study does not provide causal evidence. 

Surface Area Matters

Beyond concentration, the investigators also examined physical properties of the particles. This revealed a potentially relevant correlation: Larger particle surface area correlated with faster tumor growth.

This finding matters because larger surfaces can adsorb more toxic substances, such as environmental pollutants or heavy metals. Whether these interactions are biologically relevant to tumors remains unclear.

Questions About Particle Size Remain

Experts particularly criticized another result of the publication: Fischer commented, “It is not plausible that the microplastic particles ‘found’ with LDIR/O‑PTIR — which have an average diameter of 32 µm — originated from the tissue samples. Those particles were also detected in samples of healthy tissue. How would such large particles have crossed the blood‑brain barrier in healthy individuals?” he asked. 

Eleonore Fröhlich, head of the Core Facility Imaging Department, Center for Medical Research, Medical University of Graz, Graz, Austria, was similarly surprised, she said, “An average particle size of 32 µm is surprising as particles of this size can hardly reach the brain via the bloodstream. The only possible explanation would be that they originated from medical procedures performed on the brain, which would be rare. Alternatively, these particles could have formed through clumping.” 

Causation or Association?

Independent of these questions, the key issue remains whether MNPs promote tumor development or progression or whether the tumor leads to increased uptake or retention of particles.

Winkler said “In my opinion, there is currently no reliable data to support a causal link between ‘plastic [particles] leading to tumor development or progression.’ Theoretically conceivable mechanisms would include chronic inflammation, oxidative stress, or effects on the blood-brain barrier. Interactions with immune cells or changes in the microenvironment could also play a role. However, we are clearly in the realm of plausible hypotheses here, not established evidence.”

Winkler added: “Conversely, the opposite direction — that is, ‘tumor leads to increased plastic accumulation’ — seems at least as plausible to me, if not more obvious. Brain tumors, especially gliomas, are associated with a disrupted blood-brain barrier, altered vascular permeability, and pronounced remodeling processes of the extracellular matrix. These changes could promote the accumulation of exogenous particles in the tumor and its surrounding tissue. The increased cell turnover rate and the altered tissue architecture could also lead to altered accumulation.”

Impetus for New Studies

Despite many questions, the new data at least provide a basis for further neuro-oncological research — especially on the role of the blood‑brain barrier, interactions of MNPs with cellular structures, and potential inflammatory effects. Given the high global exposure to microplastics, there is good reason to pursue these details further.

This story was translated from Medscape’s German edition.