New research reveals that microplastics can penetrate the brain through the nasal passages, prompting urgent questions about their impact on human health and the environment.
Study: Microplastics in the Olfactory Bulb of the Human Brain. Image Credit: MattL_Images / Shutterstock
In a recent study published in the JAMA Network Open, a group of researchers investigated the presence and characteristics of microplastics (MP) in the human olfactory bulb (OB), providing insight into potential pathways for microplastic translocation to the brain.
Background
MP pollution is a growing environmental concern, with MPs found in various human organs, including the lungs, placenta, intestines, semen, liver, and bloodstream. Although the blood-brain barrier (BBB) typically limits MP access to the brain, studies suggest that MPs can impair the BBB and lead to neurotoxic effects. The olfactory pathway, where neurons transmit sensory information to the brain, is another potential route for MPs to reach brain tissue. Further research is essential to understand how MPs reach the brain and their possible long-term impacts on neurological health.
About the study
Between February 2023 and May 2024, bilateral OBs were collected from 15 adult individuals during routine coroner autopsies. The individuals were long-term residents of São Paulo with no prior neurosurgical interventions. Information about their occupations and underlying diseases was gathered through questionnaires, and autopsy reports were reviewed. The study was conducted in compliance with the Helsinki Declaration and was approved by the ethical board of the São Paulo University Medical School. Written informed consent was obtained from the next of kin of the deceased individuals. Additionally, two OB samples from stillbirths at seven months gestation were collected as negative controls.
A plastic-free approach was implemented throughout the study to ensure data integrity, with procedures to avoid contamination. Solutions were prefiltered, and all equipment was carefully cleaned to prevent the introduction of external particles. The samples were processed in a laminar flow cabinet with restricted access to prevent atmospheric contamination. MPs were assessed in two ways: through cryo-cuts for spatial context and digestion for more accurate quantification.
Single-point measurements were performed on the samples using micro-Fourier transform infrared (μFTIR) spectroscopy. Spectra were compared to established MP libraries, and particle sizes were analyzed through microphotographs. Statistical analyses were completed in April 2024 using SPSS Statistics software.
Study results
The median age of the 15 deceased individuals was 69.5 years, ranging from 33 to 100 years, with 12 males and 3 females. Among the group, two individuals had evidence of previous ischemic cerebral infarctions (Stroke from blocked blood flow to the brain), and one had a subarachnoid hematoma (Bleeding in the space around the brain) caused by a ruptured aneurysm of the middle cerebral artery. No other cerebral histological abnormalities were noted. The mean mass of the OBs was 0.187 grams, ranging between 0.100 and 0.273 grams.
Sixteen synthetic polymer particles and fibers were identified in the OBs of 8 out of the 15 individuals, with each OB containing between 1 and 4 MPs. Of these, 75% were particles, of which 83.4% were fragments and 16.6% were spheres, while 25% were fibers, all of which had a length-to-width ratio greater than 3. The mean particle length was 12.1 micrometers, ranging from 5.5 to 26.4 micrometers, with a mean width of 8.9 micrometers. The fibers had a mean length of 21.4 micrometers and a mean width of 3.8 micrometers.
In the procedural blank filters, two silica beads, two cotton fibers, and one silicate fragment were found, but no polymeric materials were present in either the procedural blanks or negative control filters. Among the two OB samples collected from stillborn individuals, one was analyzed and showed no presence of MPs, while the other had insufficient material for analysis.
Polypropylene was the most commonly detected polymer, accounting for 43.8% of the total identified MPs. Other detected polymers included nylon, polyamide, and polyethylene vinyl acetate at 12.5%, with perlon polyamide, polyethylene, and wool-polypropylene each making up 6.3%. Analysis of the microplastics indicated signs of weathering, as the μFTIR spectra revealed attenuated or missing peaks compared to pristine samples, suggesting degradation over time.
Microphotographs and μFTIR point-spectra confirmed the presence of different types of MPs in the OBs. The particles and fibers' chemical composition and morphological characteristics were consistent with common environmental microplastics.
Conclusions
This study is the first to identify and characterize MPs in the human brain using μFTIR, allowing detailed analysis of their morphology and polymeric composition. MPs were predominantly found as particles in the OB in 8 of 15 individuals. The anatomy of the cribriform plate in the nasal passages may act as a gateway for these particles to enter the brain. Given the widespread presence of MPs in the air, particularly in indoor environments, and their link to neurological effects, the olfactory pathway is an important potential route for exogenous particles to reach the brain.