Mounting evidence suggests the health risks of diesel exhaust extend beyond respiratory ailments, with a new Finnish study highlighting potential impacts on brain function. Researchers at the University of Eastern Finland have identified a link between particles from older diesel engines and disruptions to microglia, the brain’s immune cells, raising concerns about neurodegenerative diseases. The study, published as concerns over air quality continue to grow globally, differentiates between the toxicity of particles emitted by older versus newer diesel engines and their potential impact on neurological health.
A new Finnish study raises concerns about the impact of older diesel engines on brain health. Researchers are investigating the connection between vehicle pollution and the brain’s immune cells, known as microglia.
For years, the health effects of vehicle pollution have been largely associated with respiratory issues. However, emerging research suggests that the impact may extend to the brain. In 2019, vehicles accounted for 16% of all greenhouse gas emissions in France, contributing to over 40,000 deaths annually – a figure traditionally linked to heart and lung disease. Now, scientists are expanding their focus to understand the potential neurological consequences of air pollution. This is particularly important as neurodegenerative diseases are a growing public health concern.
Researchers at the University of Eastern Finland have identified a potential link between particles from older diesel engines and disruptions in the function of the brain’s immune cells. The study suggests these particles may trigger mechanisms similar to those seen in neurodegenerative diseases.
Diesel Pollution: A Threat to the Brain?
Not all diesel exhaust is created equal. The particles released during the combustion of fossil fuels vary in toxicity depending on the engine technology and vehicle age. The researchers focused on particles known as A20 and A0, which are commonly emitted by older diesel engines lacking modern filtration systems.
Without a diesel particulate filter, these engines release high levels of A20 and A0 particles. According to the study authors, “These diesel particles are rich in black carbon and polycyclic aromatic hydrocarbons (PAHs),” both of which are considered highly toxic components of exhaust fumes with documented genotoxic potential.
In contrast, the researchers also examined newer engines compliant with the Euro 6 standard. These engines are equipped with particulate filters and use higher-quality fuel, emitting particles designated E6, which are considered much “cleaner.” E6 particles contain neither black carbon nor PAHs, and their pollutant concentration is described as very low.
While all diesel models manufactured since 2018 are expected to meet the Euro 6d-Temp standard, researchers are particularly concerned about emissions from older engines. They directly tested the impact of these emissions on a key component of the nervous system: microglia.
Older Diesels, Microglia, and Brain Disease
Microglia act as the brain’s resident immune cells, providing protection and clearing waste. Dr. Sohvi Ohtonen, the study’s lead author, explains their role: “Microglia play a crucial role as the brain’s first line of immune defense, and pollutants threaten their proper functioning.”
In their experiments, the researchers exposed microglia to particles from older engines (A20, A0) and to E6 particles from modern engines. They found that exposure to the older particles caused significant changes in gene expression, reduced activity of lysosomes and phagocytosis – processes essential for clearing cellular debris – and activated cellular stress pathways like ferroptosis and pyroptosis. These findings suggest a potential pathway by which air pollution could contribute to neurological damage.
According to the research team, these disruptions interfere with waste removal and maintaining brain balance, significantly increasing the risk of chronic neuroinflammation and, consequently, neurodegenerative diseases. E6 particles, however, had “virtually no impact” on these cells under the study conditions. The researchers caution that prolonged exposure to diesel pollution, even from newer models, could still increase the risk of brain diseases, and suggest reducing aromatic compounds and black carbon in fuels could limit toxicity. Further research is needed to compare different engine and fuel technologies.
Which Vehicles Are Most Concerning?
The vehicles of greatest concern are those equipped with older diesel engines, “often lacking modern filtration systems,” where A20 and A0 particles – rich in black carbon and PAHs – are formed. Conversely, models compliant with the Euro 6 standard, with particulate filters, primarily emit E6 particles with a much lower toxic component load. Vehicle owners can determine their car’s classification by checking the vehicle registration document (carte grise). The “V.9” section should indicate “EURO 6,” “EURO 6b,” or “EURO 6d-TEMP” if the vehicle meets these standards.
This technological difference aligns with broader findings: air pollution, particularly fine and ultrafine particles linked to road traffic, doesn’t just affect the lungs. Large-scale studies have shown an increased risk of dementia with higher levels of PM2.5 particulate matter, nitrogen dioxide, and soot, correlating with long-term brain inflammation. The study’s findings reinforce the growing body of evidence linking air quality to neurological health.
Older diesels without filtration systems stand out in this context, emitting the particles most heavily laden with black carbon and PAHs – those that microglia appear to be most vulnerable to.
