Author: Lindsey Konkel / Source: Science News for Students
The year was 1952. The setting: London, England.
“On December 8, cool air from across the English Channel settled over the Thames River valley and did not move. London’s 8 million residents did what they had been doing for centuries: They huddled indoors and warmed themselves by their coal stoves. Smoke ran like tap water from a million chimneys. In the motionless air, the hot vapors chilled and, instead of rising, settled back to the ground. The smoke became so thick that visibility dropped to near zero.”— Devra Davis, When Smoke Ran Like Water, Basic Books 2002
That super-thick fog of pollution, 65 years ago, turned the air into a toxic soup that lasted five long days. Local reporters would call it the Great Smog. Inhaling the blackened air sent 150,000 people to the hospital with breathing problems. In all, some 4,000 would die. This disaster provided some of the strongest, early evidence that urban air could prove deadly.
It evolved owing to an unfortunate combination of bad weather and especially heavy pollution. Yet even today, air pollution sickens and kills people. Lots of people. A 2016 study reported that breathing dirty air is now the fourth-leading cause of deaths worldwide.
Air pollution tends to pose the biggest risk to the very old, to the very young and to people already suffering from some chronic ailments. What types? Asthma (a breathing disorder) and heart disease are two major conditions that put people at risk.
But scientists are learning that air pollution can pose serious risks to anyone. You don’t have to be old or sick. You don’t have to suck in horrible fumes or air so full of pollutants that you can see and taste them.
Indeed, emerging data show that even pollutants too small to see with the naked eye can harm healthy children and teens. That pollution can alter how their brains function. It can make it hard for kids to concentrate. It also can throw out of whack hormones — chemical messengers that direct the body’s activities. In short, it can seriously damage young minds and bodies.
Polluting the brain
Lilian Calderón-Garcidueñas works at the University of Montana in Missoula. As a pathologist, she’s a doctor who looks at the body’s tissues to diagnose disease. She looks for disease caused by pollutant particles that are small — often way too tiny to see. Scientists call these tiny specks particulates. They come from many sources. Power plants, factories, homes and cars — all spew particulates. So can forest fires.
Once inhaled, these particles can move deep into the lungs. The oxygen you breathe passes from the lungs through a thin membrane. From there it enters the blood. Many particulates are small enough to cross that membrane into the blood, too. They’re known as nanoparticulates. They can trigger inflammation wherever they travel. And the blood can carry them everywhere, even to the brain.
Some particulates may enter the brain more directly. If breathed in through the nose, they can contact nerves that bring scent signals to the brain through a structure known as the olfactory bulb. Just as the pollutants’ small size allows them to slip into blood through lung membranes, nanoparticles’ size lets them enter that bulb’s nerve cells. And from there, those inflammatory pollutants can climb into the brain.
Inflammation can be a good thing. The body uses it to kill off damaged cells and harmful germs. But inflammation in the brain is dangerous. It can destroy sensitive cells, causing memory problems.
Digging into the brain
Mexico City, where Calderón-Garcidueñas does her research, is home to nearly 9 million people. Every day, they get around using some 3.5 million cars. And the cars’ exhaust pollutes the air. “High-traffic roads are a very important source of particulate [pollution],” notes Calderón-Garcidueñas.
Research has shown that older adults who live in areas with lots of traffic-related air pollution are more likely to suffer Alzheimer’s disease than are people at cleaner sites. Alzheimer’s causes a type of brain damage that results in memory loss and other problems with thinking, language and behavior.
Alzheimer’s symptoms usually show up in old age. Yet researchers believe the disease may start years — even decades — earlier. Calderon-Garcidueñas wants to know just how early. The answer, she says, might one day help researchers prevent some cases of this memory-robbing disease.
Some elderly dogs can develop brain abnormalities seen in people with Alzheimer’s disease. Waxy clumps of protein, called plaques (PLAKS), may start to litter their brains. But 15 years ago, Calderon-Garcidueñas reported finding these same plaques in the brains of 11-month-old pups! The dogs had been living outdoors, exposed to Mexico City’s heavy air pollution.
At the time, she told Science News, this is “definitely worrisome.” Even more concerning was her finding of the same type of plaques in the brains of seemingly healthy Mexico City children. The plaques hadn’t caused symptoms. She was only able to find those plaques because of autopsies done on kids who had died in car crashes or other accidents.
But not all children had them. Those living in distant suburbs, breathing cleaner air, had no brain plaques. Air pollution seemed to explain these brain lesions.
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