Wildfire smoke can damage the brain long after flames are out

A growing body of international research suggests pollution from wildfire smoke can produce cognitive deficits, post-traumatic stress and may even increase the risk of dementia, Alzheimer's and Parkinson's disease.

Until recently, the effects of wildfires have been studied on patients' lungs, hearts and blood. But several researchers have started looking into how fine particulate matter from wildfire smoke can enter the body and travel to the brain.

Kent Pinkerton, pediatrics professor at the University of California, Davis, said the nose is typically a good filter and keeps a number of inhaled particles out of the lungs. But there is concern that during wildfires, tiny particles of soot and other chemicals in smoke have the ability to enter the cells and nerves of the nose, both of which scientists have shown have a direct connection to the brain.

Cells and nerves connecting the nose-brain passage, Pinkerton said, can get inflamed and damaged by wildfire smoke.

"Some particles from wildfire smoke have been shown to be able to cross the blood-brain barrier and cause inflammation of the brain," he said in a recent interview.

This year has been one of the worst for wildfires in Canada with nearly 137,000 square kilometres of land scorched. Currently, there are out-of-control wildfires blazing in the Northwest Territories and British Columbia, forcing thousands of people from their homes. Wildfire smoke is not only composed of vegetation from trees and other plants that are burned but also everyday products that are caught in the flames, including metals from vehicles and homes, plastic, and clothes.

Ray Dorsey, neurology professor at the University of Rochester, New York, said some of the particulate matter from wildfire smoke is small enough that it can travel into the smell centres of the brain.

"Hitchhiking on these tiny particulate matter are pieces that are toxic metals — lead from leaded gasoline, iron from brake pads and platinum from catalytic converters," he said in an interview.

Brains of people with Parkinson's and Alzheimer's show higher concentrations of heavy metal, Dorsey said. Damage to the smell centres of the brain is found almost universally in patients with these two diseases, he said.

"It may be that this particulate matter entering into our nose," he said, "and the gateway to our brain, which is normally protected by a blood-brain barrier, is getting exploited by the front door."

He pointed to a July 2018 study published in the journal Environmental Research in which a group of international researchers found that people exposed to air pollution in Mexico City showed Alzheimer's and Parkinson's signatures in their brains.

"Exposure to air pollutants plays a major role in the development and-or acceleration of Alzheimer's disease," said the study, called "Hallmarks of Alzheimer's disease are evolving relentlessly in Metropolitan Mexico City infants, children and young adults."

Dorsey said he's seen recent reports suggesting air pollution from wildfires has a denser or higher concentration of particulate matter than air pollution from vehicle traffic.

"In short, whether you are a newborn baby or an older adult with Alzheimer's disease, air pollution is likely harmful to your brain," he said.

A study published in January in the journal PLOS Climate found that people exposed to smoke from the 2018 Camp fire — the deadliest and most destructive wildfire in California's history — had "significantly" greater chronic symptoms of post-traumatic stress disorder, anxiety and depression than those who were not exposed to the fire.

"Studying cognitive abilities is important because they are core to all daily life functioning and can be key to understanding individual needs as they rebuild and rehabilitate in disaster-affected communities," said the study.

Exposure to wildfires also caused a decrease in cognitive performance, which is the ability to suppress distractions and focus on the task at hand, said Jyoti Mishra, lead author of the California fire study and associate professor of psychiatry at the University of California, San Diego.

The study began six months after the wildfire and the smoke had subsided. The particulates could have entered the lungs at the height of the wildfires and affected the brain in a chronic way, she said.

"We don't know that exact link as to how the particulates can affect the brain systems over the long term but what we found in a series of studies was that there was definitely prevalence of climate trauma."

There's "lots of complex interactions" when a person suffers from loss of property, family and injury, she said. Wildfires can set off emotional responses that are usually associated with post-traumatic stress disorder. The particulate matter from wildfire smoke causes the body to react in the same way as when there is an inflammation, she said.

"We see the final outcome, we see that there's cognitive deficits, there are brain changes, there are psychiatric symptoms, but how do you get from wildfire smoke to that kind of an end point?" Mishra said. "Those intermediate complexities and mechanisms are not well understood."

This report by The Canadian Press was first published Aug. 23, 2023.