Is there a link between traffic-related air pollution and neurodevelopmental disorders? Researchers at the University of California, Davis have just released a study — based on rodent models — that corroborates previous epidemiological evidence showing the effects of traffic-related pollution on the brain. Their findings are scary and should make anyone who isn’t driving an electric vehicle inspired to get right out there and buy one.
As far back as 2012, CleanTechnica started reporting on the public health implications of exposure to traffic-related air pollution during pregnancy and during the first year of life and the risk of autism. Researchers had been chronicling connections between proximity to busy roadways and neurodevelopmental disorders such as autism. Autism spectrum disorder (ASD) and attention deficit and hyperactivity disorder (ADHD) are the 2 most common neurodevelopmental disorders observed in childhood.
Pre-clinical data based on real-time exposures to traffic-related air pollution, however, was really hard to locate until the new UC Davis study.
Understanding Traffic-Related Air Pollution & Epidemiology
Epidemiological studies measure the risk of illness or death in an exposed population compared to that risk in an identical, unexposed population. In the UC Davis paper published on May 27th 2020, researchers focused on epidemiological studies that link traffic-related air pollution (TRAP) to increased risk for various neurodevelopmental disorders (NDDs) .
Limited preclinical data demonstrating a causal relationship between TRAP and adverse neurodevelopmental outcomes didn’t stop the investigating team. They persisted, determining that other researchers had reported effects of concentrated ambient particles or diesel exhaust , but these indicators did not recapitulate the complexity of real-world TRAP exposures.
So the UC Davis researchers decided to assess the developmental neurotoxicity of more realistic TRAP exposures.
Neurotoxicity occurs when the exposure to toxic substances alters the normal activity of the nervous system. Such exposure can eventually disrupt or even kill neurons, which are the key cells that transmit and process signals in the brain and other parts of the nervous system.
UC Davis toxicologist Pamela Lein, senior author of the study published in Translational Psychiatry, worked with a team to investigate the impacts of traffic-related air pollution in real time. They set up a vivarium — an enclosure adapted for keeping animals under seminatural conditions for observation — near a traffic tunnel in Northern California so they could mimic, as closely as possible, the experience of humans in a rodent model.
They exposed the male and female rats during gestation and early postnatal development to TRAP and delivered to animals in real-time. Their investigation sought to illuminate NDD-relevant neuropathological outcomes at postnatal days 51–55 in TRAP-exposed animals versus control subjects exposed to filtered air. They conducted immunohistochemical analyses, which is a method for demonstrating the presence and location of proteins in tissue sections.
“This approach was a creative way to get at the question of what impacts air pollution has on the brain in the absence of confounding factors such as socioeconomic influences, diet, etc..
It’s important to know if living close to these roadways poses a significant risk to the developing human brain. If it does, scientists can warn susceptible individuals, such as pregnant women — particularly those who have already had a child diagnosed with a neurodevelopmental disorder — to take appropriate precautions to minimize risks to the health of their child’s brain.”
The UC Davis study saw subtle changes — significantly, the effects of air pollution exposures do fall within regulatory limits. Among their conclusions were:
TRAP significantly increased microglial infiltration in the CA1 hippocampus but decreased astrogliosis in the dentate gyrus.
Translation: Activation of resident microglia accompanies every known form of neurodegeneration. The hippocampus is the region of the brain that is associated primarily with memory. Astrogliosis is an abnormal increase in the number of astrocytes due to the destruction of nearby neurons from central nervous system trauma. The dentate gyrus is the first region where all sensory modalities merge together to form unique representations and memories that bind stimuli together, and, thus, it plays a critical role in learning and memory.
TRAP exposure did significantly elevate the anti-inflammatory cytokine IL-10 in females.
Translation: Cytokine with potent anti-inflammatory properties plays a central role in limiting host immune response to pathogens, thereby preventing damage to the host and maintaining normal tissue homeostasis. Dysregulation of IL-10 is associated with enhanced immunopathology in response to infection as well as increased risk for development of many autoimmune diseases.
Collectively, these data indicate that exposure to real-world levels of TRAP during gestation and early postnatal development modulate neurodevelopment, corroborating epidemiological evidence of an association between TRAP exposure and increased risk of NDDs.
Final Thoughts about Traffic-Related Air Pollution
The UC Davis synthesis suggests that air pollution exposure during critical developmental periods may increase the risk for changes in the developing brain that are associated with neurodevelopmental disorders. Also, living in close proximity to roadways increases exposure to not only TRAP but also noise and vibration, which are both associated with maternal stress, adverse neurodevelopmental outcomes, and poor cognition.
In 2017, CleanTechnica‘s own James Ayre wrote about how air quality models vastly underestimate real-world traffic-related nitrogen oxide pollution, by up to a factor of 4. In 2018, CleanTechnica‘s writer Cynthia Shahan reported how bicyclists are the least affected or exposed to air pollution on daily commutes. More at risk are the people in cars and buses. Her investigation uncovered that pedestrians, who have such a light and peaceful footprint, are even more affected.
We who own electric cars are keenly aware of the impact that carbon-free transportation has on the environment and human health, as Daryl Elliott described in a recent CleanTechnica article about autonomy. With the UC Davis data supporting a model in which TRAP exposure during critical developmental windows can bias brain growth towards NDD phenotypes, doesn’t it make sense more more people drive EVs — from zero-emission last mile deliveries to everyday around-town transportation?
After all, saving planet Earth and the environment is not a political issue — it is an ethical issue, and each of us has a challenge to help ameliorate how people living in poverty experience the brunt of climate change yet are responsible for just a fraction of global emissions. Traffic-related air pollution analyses like this UC Davis study can provide scientists with the data they need to approach legislators, with the goal to develop scientifically based regulations to protect the developing human brain.