Microplastic particles were discovered in the human olfactory bulb for the first time, according to a case series.
The study, published in JAMA Network Open, identified synthetic polymer particles and fibers in the olfactory bulbs of 8 out of 15 deceased individuals. Investigators analyzed tissue samples from routine autopsies in São Paulo, Brazil, and, using micro-Fourier transform infrared (μFTIR) spectroscopy, detected 16 microplastic particles and fibers across the eight positive samples.
Key findings:
Microplastics were present in 53% of olfactory bulb samples.
75% of detected microplastics were particles, and 25% were fibers.
Particle sizes ranged from 5.5 μm to 26.4 μm in length and 3.0 μm to 25.4 μm in width.
The mean fiber length was 21.4 μm (range 19.0-24.5 μm) with a mean width of 3.8 μm (range 3.0-6.0 μm).
Polypropylene was the most common polymer type (43.8%).
Other polymers detected included polyamide (12.5%), nylon (12.5%), polyethylene vinyl acetate (12.5%), polyethylene (6.3%), perlon polyamide (6.3%), and wool-polypropylene (6.3%).
The number of microplastics per olfactory bulb ranged from 1 to 4.
The study participants had a median age of 69.5 years (range, 33-100 years) and included 12 males and 3 females. All participants had resided in São Paulo for > 5 years. Exclusion criteria included previous neurosurgical interventions. The mean mass of the olfactory bulb samples was 0.187 g (SD, 0.050 g), with a range of 0.100 to 0.273 g.
Methods:
Researchers used two approaches to detect microplastics:
Direct tissue examination: The left olfactory bulb was cryo-sectioned at 10 μm thickness and analyzed via μFTIR spectroscopy.
Digested tissue filtration: The right olfactory bulb was enzymatically digested using Corolase 7089 (20 UHb/mL), filtered through 0.45-μm pore size silver membrane filters, and the resulting particles were analyzed via μFTIR spectroscopy.
Procedural blank filters and negative controls were used to control for contamination. No polymeric materials were found in the procedural blank or negative control filters, supporting the validity of the findings.
Potential Entry Pathways:
The study authors suggested that the cribriform plate of the ethmoid bone may serve as a gateway for microplastics to enter the brain via nasal passages. The cribriform plate contains small foramina (<1 mm diameter) through which olfactory neurons pass from the nasal mucosa to the olfactory bulb.
In addition, the researchers analyzed the olfactory bulb of one stillborn at seven months' gestation, which showed no microplastics, confirming the negative control.
Study Limitations:
The study was limited by its inability to detect nanoplastics due to technical constraints. While the olfactory pathway appeared to be a likely route for microplastic exposure, other potential entry mechanisms, such as systemic circulation or the respiratory pathway via the trigeminal nerve, could not be excluded. The challenge of avoiding contamination during microplastic analysis was noted, although the study’s rigorous controls suggested that contamination was not an issue in these results.
Broader Context:
The findings built on previous studies that identified microplastics in human tissues such as the lungs, intestines, placenta, and bloodstream. The detection of microplastics in the olfactory bulb raised new concerns about their potential to bypass the blood-brain barrier and cause neurotoxic effects. The study authors called for further research to explore the long-term health implications of microplastic exposure in brain tissues.