What are leaf blowers doing to the brains of Mexican children?

 Studies show leaf blowers pose unexpected health hazards, especially for Mexico

By John Pint

Mexican kids: what is in the air they’re breathing and what is their future? Photo: John Pint

EN ESPAÑOL

A recent analysis by the Icahn School of Medicine at Mount Sinai Hospital in New York City indicates that the air and noise pollution from gas leaf blowers (GLBs) seriously impact respiratory health and are also associated with problems like cancer, heart disease and dementia—and that children, in particular, are highly susceptible to these hazards.

A separate study shows how extremely tiny particles of metal from small gas engines can be carried directly to the brain via the olfactory nerve, producing the features of autism, attention-deficit disorder, and schizophrenia.

These studies suppose seasonal use of GLBs to blow leaves off paths, not the heavy and frequent use now in vogue throughout Mexico.

The toxic cloud from a leaf blower can remain in the air for hours or even days.

The Mount Sinai scientists point out that GLB combustion engines are of extremely low efficiency; 30% of the gas and oil they use is unburned and released directly to the atmosphere. They cite the estimate of the California Air Resources board that operation of a GLB for one hour releases emissions equivalent to driving a car for 15 hours or 1,100 miles.

The GLB emissions include carbon monoxide, formaldehyde, benzene, and extremely small fragments of metal (less than 50 nanometers) from the combustion chamber. When these are mixed with particulate matter blown off the ground, the result is a toxic cloud which can remain suspended in the air for up to 5 hours.

Fine particles lifted off the ground and into the air may include mold, pesticides, pollen and heavy metals as well as the excrement of birds, bats, dogs and cats.

To this must be added a noise level of more than 100 decibels, the equivalent to a jackhammer or a jet taking off, a level that eventually leads to irreparable hearing loss. Not only that, points out Mt. Sinai's Dr. Sarah Evans, chronic noise exposure has been shown to increase your risk of cardiovascular disease, anxiety and depression, and impaired focus and cognition.

When the leaf blower appeared on the market in the 1980s, some Mexicans saw it as an easy way to carry on an old custom of washing the street outside one’s door early each morning, 

That tradition has deep, preHispanic roots. It is said that the city of Tenochtitlán had a team of a thousand men to sweep and wash its streets every single day. This preoccupation with the look of the ground outside your door is still around today,  but some people have replaced brooms, buckets and water with a machine that seems to do the job quicker, without realizing that this same device throws extremely tiny particles into the air, particles 30 percent smaller than the width of a human hair.

Tenochtitlán as Diego River imagined it. A thousand workers cleaned the streets every day

The fine particles remain airborne for long periods of time, infiltrating buildings. What these microscopic specks do to you, once they reach your nose is something that has become of great concern to researchers. 

In the second study—included in the Proceedings of the National Academy of Sciences—neurotoxicologist Deborah Cory-Slechta at the University of Rochester in New York. states that these tiny particles can go up the nose and be carried straight to the brain via the olfactory nerve, bypassing the blood-brain barrier.

Unfortunately, these nanofragments don't travel alone.

On their surfaces the particles carry contaminants, from dioxins and other chemical compounds, to metals such as iron and lead. “Particulate matter may be acting as a vector,” says Masashi Kitazawa, a molecular neurotoxicologist at the University of California, Irvine. “It might be a number of chemicals that get into the brain and act in different ways to cause damage. Ultrafine particles are like little Trojan horses. Pretty much every metal known to humans is on these." 

Tiny particles of metal from leaf blowers enter the brain via the olfactory nerve. Image after Wang et al. 

Metal-toting particles that reach the brain can directly damage neurons, says Cory-Slechta. “Both the particles themselves and their toxic hitchhikers can also cause widespread harm by dysregulating the activation of microglia, the immune cells in the brain. Microglia may mistake the intruders for pathogens, releasing chemicals to try to kill them. Those chemicals can accumulate and trigger inflammation. And chronic inflammation in the brain has been implicated in neurodegeneration.”

In January 2010, Cory-Slechta received a surprising request from some University of Rochester environmental medicine colleagues. Typically, the group researched the effects of air pollution on the lungs and hearts of adult animals. But they had just exposed a group of newborn mice and asked Cory-Slechta’s team to look at the brains.

At first she didn’t think much of the request. Cory-Slechta was much more concerned about deadly lead exposure in children, her research focus at the time. “I didn’t think of air pollution as a big problem for the brain,” she says. Then she examined the animals’ tissue. “It was eye-opening. I couldn’t find a brain region that didn't have some kind of inflammation.”

Her team followed up with their own studies. In addition to inflammation, they saw classic behavioral and biochemical features of autism, attention-deficit disorder, and schizophrenia in mice exposed to pollutants during the first days after birth. 

Continuity: The plaza of Teuchitlán is swept with a kind of broom that has been used in Mexico for centuries.

Based on MRI scans, cognitive tests, and measures of inflammatory markers in the blood, the team identified neuroinflammation, brain structure changes, cognitive deficits, and Alzheimer’s-like pathologies in apparently healthy children living in Mexico City, compared with a group of similar children in a less polluted city. The findings, according to the authors, suggested that dirty air may spur brain disease at far younger ages than previously suspected.

If you don’t live in Mexico City, you can still experience plenty of the bad effects of air pollution simply by opening the window wide when your neighbor turns on his leaf blower.

"No leaf blower for me!" says Valentina Ramírez of Guadalajara