Common levels of traffic pollution impair human brain function.

I believe that we should replace nearly all car traffic with mass transit (free at the point of service), better pedestrian and cycling infrastructure, and a smattering of electric personal vehicles as needed for people with disabilities or ailments that make the former options unworkable. There are plenty of reasons for this, not least of which is giving people back the time that’s currently spent on commuting, but the biggest one is probably air pollution. I mention environmental racism fairly often, and traffic pollution is one of the ways in which it manifests. A great many major highways in the United States were deliberately built through the middle of black neighborhoods, not only fragmenting them, but also poisoning their air. New research now adds to our understanding of that poison and its effects on our brains:

A new study by researchers at the University of British Columbia and the University of Victoria has shown that common levels of traffic pollution can impair human brain function in only a matter of hours.

The peer-reviewed findings, published in the journal Environmental Health, show that just two hours of exposure to diesel exhaust causes a decrease in the brain’s functional connectivity – a measure of how different areas of the brain interact and communicate with each other. The study provides the first evidence in humans, from a controlled experiment, of altered brain network connectivity induced by air pollution.

“For many decades, scientists thought the brain may be protected from the harmful effects of air pollution,” said senior study author Dr. Chris Carlsten, professor and head of respiratory medicine and the Canada Research Chair in occupational and environmental lung disease at UBC. “This study, which is the first of its kind in the world, provides fresh evidence supporting a connection between air pollution and cognition.”

For the study, the researchers briefly exposed 25 healthy adults to diesel exhaust and filtered air at different times in a laboratory setting. Brain activity was measured before and after each exposure using functional magnetic resonance imaging (fMRI).

The researchers analyzed changes in the brain’s default mode network (DMN), a set of inter-connected brain regions that play an important role in memory and internal thought. The fMRI revealed that participants had decreased functional connectivity in widespread regions of the DMN after exposure to diesel exhaust, compared to filtered air.

“We know that altered functional connectivity in the DMN has been associated with reduced cognitive performance and symptoms of depression, so it’s concerning to see traffic pollution interrupting these same networks,” said Dr. Jodie Gawryluk, a psychology professor at the University of Victoria and the study’s first author. “While more research is needed to fully understand the functional impacts of these changes, it’s possible that they may impair people’s thinking or ability to work.”

I think it’s important to note here that what was tested here isn’t “traffic pollution”. In many ways it’s probably less damaging than what’s encountered in the wild, so to speak, because a huge chunk of that pollution comes not from the exhaust, but from the tires of the cars:

Almost 2,000 times more particle pollution is produced by tyre wear than is pumped out of the exhausts of modern cars, tests have shown.

The tyre particles pollute air, water and soil and contain a wide range of toxic organic compounds, including known carcinogens, the analysts say, suggesting tyre pollution could rapidly become a major issue for regulators.

Air pollution causes millions of early deaths a year globally. The requirement for better filters has meant particle emissions from tailpipes in developed countries are now much lower in new cars, with those in Europe far below the legal limit. However, the increasing weight of cars means more particles are being thrown off by tyres as they wear on the road.

The tests also revealed that tyres produce more than 1tn ultrafine particles for each kilometre driven, meaning particles smaller than 23 nanometres. These are also emitted from exhausts and are of special concern to health, as their size means they can enter organs via the bloodstream. Particles below 23nm are hard to measure and are not currently regulated in either the EU or US.

“Tyres are rapidly eclipsing the tailpipe as a major source of emissions from vehicles,” said Nick Molden, at Emissions Analytics, the leading independent emissions testing company that did the research. “Tailpipes are now so clean for pollutants that, if you were starting out afresh, you wouldn’t even bother regulating them.”

Exhaust is getting cleaner, and that’s good, but even if we were to eliminate it altogether, by swapping to all-electric vehicles, I don’t think it would improve health as much as the first study, by itself, might imply. I’m also irked by the authors “steps to protect yourself”, because they seem to assume an array of options that simply are not available to everyone:

Dr. Carlsten speculated that the effects could be long-lasting where exposure is continuous. He said that people should be mindful of the air they’re breathing and take appropriate steps to minimize their exposure to potentially harmful air pollutants like car exhaust.

“People may want to think twice the next time they’re stuck in traffic with the windows rolled down,” said Dr. Carlsten. “It’s important to ensure that your car’s air filter is in good working order, and if you’re walking or biking down a busy street, consider diverting to a less busy route.”

When I was commuting across Boston and Cambridge, by bike, by foot, or by bus, I didn’t really have any “low-exposure” options. I suppose it’s good advice to keep your windows up in traffic, but really none of these solutions seem particularly meaningful to me. What about people who live right by a highway, as I used to? What about people who work in cities? I suppose everyone could start wearing respirators everywhere. I feel like it’d be unpleasant, but I have been wanting our cyberpunk dystopia to better fit the genre’s aesthetic.

No, we need societal solutions, not individual ones. We need to stop making so much air pollution, and fortunately we do know how to do that. It means more mass transit, as I said, but it also means far less pressure to travel in the first place. Changing to more of a steady-state economy, and ending greed-driven overproduction would go a long way toward reducing the amount of shipping and commuting required to keep things running. Beyond that, working from home should be allowed by default, where doing so is possible. This path won’t entirely eliminate air pollution, but it would make a huge difference for many millions of people, while also improving quality of life in other ways.

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  1. antaresrichard says

    All through my childhood and into my young adult years, I grew up in an urban environment, alongside a busy, six lane street, and right next door to a gasoline station. I can only wonder, and that very poorly no doubt.

  2. says

    I’ve had a fair amount of exposure myself.

    I think it’s fair to assume that this effect, while measurable, isn’t huge. It’s not like rural areas have mysteriously quick thinkers.

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