Microplastics in the Olfactory Bulb of the Human Brain
September 16, 2024 | JAMA Network
READ AND DOWNLOAD THE REPORT >>
Introduction
The ubiquity of microplastic (MP) pollution has become a pervasive environmental concern,1 raising questions about its occurrence within the human body and its harmful effects.2 While MPs have been detected in various organs of the human body, such as the lungs,3,4 large and small intestines,5 liver,6 placenta,7,8 semen,9 and bloodstream,10 to our knowledge, there have been no published studies to date reporting their presence in the human brain.
The presence of the blood-brain barrier (BBB) is likely an important limiting factor for the access of MPs to the human brain via hematogenous translocation. Despite this, some animal studies have shown that MPs can impair the BBB and reach the brain via oral ingestion, leading to neurotoxic effects.11-13 Another potential entry site for micro- and nanoplastics (MNPs) in the human brain is the olfactory pathway.14 This pathway involves olfactory neurons in the nasal that transmit information about odors to the central olfactory system of the brain. Olfactory axons pass through the cribriform plate (CP) of the ethmoid bone and reach the olfactory bulbs (OB), which are connected to the limbic system of the brain.
There are different levels of evidence suggesting that the olfactory pathway might allow the translocation of exogenous particles to the brain. Environmental black carbon particles have been detected in various human brain regions, with one of the highest concentrations found in the OB, measuring 420.8 particles/mm3.15 Rarely, the 15- to 30-μm–sized ameboid form of Naegleria fowleri penetrates the brain via the nose, causing amebic meningoencephalitis.16 Affected individuals typically present with the disease after contact with contaminated freshwater bodies or after rinsing the nose with nonsterile tap water.17 Furthermore, the permeability of this barrier has been evoked as a possible quicker and safer drug delivery route to the brain,18,19 as well as access to cerebrospinal fluid through nasal lymphatic vessels.20
In this study, given the ubiquitous presence of MPs in the air21 and their previous identification in the human nasal cavity,22,23 we hypothesized that the smallest-size fraction of MPs could reach the OB. Therefore, we conducted an investigation into the presence of MPs within human OB obtained from 15 deceased individuals during coroner autopsies. We identified and analyzed various characteristics of the MPs, including their size, morphology, color, and polymeric composition.
