Kasra
Zarei is a freelance writer covering science, health and
the environment = twitter.com/KasraZarei. This article originally
appeared in www.ensia.com
When
it comes to the health impacts of air pollution, most people
think of lung and heart issues. However, a growing body of
research suggests our brains could be at risk as well.
The
brain starts developing weeks after conception, and like the
rest of the body, continues to change throughout the rest
of life, facing the threat of many environmental hazards —
whether old, new, unknown or unregulated. For instance, the
effects of lead and mercury on the brain have been known for
decades and still present a large global health problem. Many
pesticides are neurotoxic, and yet remain available for use.
Recent evidence suggests that fluoride, a compound used in
public water supplies to reduce tooth decay, may also be neurotoxic.
But
even the air humans breathe is associated with an increase
in the risk of many brain-related conditions — whether
people are exposed as children or as adults. Although U.S.
air pollution levels have come down in the past few decades,
it’s been well-established how environmental contaminants
and air pollution are linked to chronic medical conditions
like asthma, chronic obstructive pulmonary disease (COPD)
and heart disease. And air pollution kills millions of people
every year. Like other organs, the brain is not immune to
environmental contaminants, and there is increasingly compelling
evidence that air pollution is linked with conditions including
autism spectrum disorders, dementia and lower cognition.
“You
only have one chance to develop a brain — you can’t
go back and do it over or get a transplant,” says Philippe
Grandjean, professor of environmental medicine at the University
of Southern Denmark and an adjunct professor of environmental
health at the Harvard T.H. Chan School of Public Health.
While neurodevelopmental and neurodegenerative disorders have
their own unique features, many share a lot of the same underlying
brain tissue changes — and air pollution may exacerbate
them.
“The
risk of air pollution on the brain is a much broader risk
factor than we’ve given it credit for,” says Deborah
Cory-Slechta, professor of environmental medicine at the University
of Rochester Medical Center.
A
LIFELONG IMPACYT
Air
pollution can include a cocktail of things, from industrial
emissions to heavy metals to pesticides to particulate matter
and other airborne contaminants that can harm the human body,
including, it seems more and more likely, the brain. Besides
studying the brain-related health risks of individual contaminants
in air pollution, scientists have studied how levels of particles
that are 10 micrometers or smaller (PM10) and particles that
are 2.5 micrometers or smaller (PM2.5) are associated with
brain-related conditions.
Growing
evidence suggests that air pollution may more deeply affect
long-term human health, behavior and functioning than originally
thought. Experts say this motivates the need for science-driven
regulations and policies to minimize exposure.
“We’re
not just trying to prevent brain disease, we’re trying
to protect optimal brain development to support the highest
possible functioning level and quality of life in the interest
of the next generation and society.” –Philippe
Grandjean
Experts
say that exposure to air pollution can potentially lead to
brain inflammation. Inflammation is the body’s natural,
protective response to fight harmful contaminants; however,
too much inflammation may lead to brain-related impairments
and disease. Besides inflammation, accumulation of magnetite
particles and amyloid plaques (an Alzheimer’s-associated
protein) have been observed in the brains of humans and animals
exposed to air pollution.
Brain
damage, whether in children or adults, can have a lifelong
impact.
“The
main concern is really that even minor dysfunction of the
brain can have dramatic consequences,” Grandjean says.
“You can live a normal life with decreased liver function,
and you can donate a kidney for transplantation, and it won’t
affect your health. But for the brain, every IQ point is important.”
While
IQ is not a comprehensive measure of brain or social functioning,
it has provided a good sense of whether contaminants may be
damaging the brain, and losing IQ points can potentially impact
one’s quality of life, education and income.
“In
regard to the brain, we need to prevent even the smallest
adverse effects,” Grandjean says. “We’re
not just trying to prevent brain disease, we’re trying
to protect optimal brain development to support the highest
possible functioning level and quality of life in the interest
of the next generation and society.”
Some
skeptics are quick to point out that the large number of human
studies that have been published are observational, which
they dismiss because a causal link between air pollution and
adverse brain health hasn’t been demonstrated.
“If
we let everything run on the free market and intervene when
people develop signs and symptoms, we’ve missed the
window of opportunity. If we took this science seriously,
we could dramatically reduce exposure to hazardous chemicals.”
–Bruce Lanphear
But,
says Bruce Lanphear, professor of health sciences at Simon
Fraser University, that line of thinking is incomplete. He
points out that observational studies contributed to the conclusion
that smoking causes lung cancer. “We do make inferences
both from observational studies and parallel studies done
in the lab,” he says. “When people dismiss hese
observational studies, they do so at the peril of public health.”
Furthermore,
many animal studies have shown that air pollution negatively
impacts animal brains. Although animal studies don’t
necessarily mean the same findings translate to human beings,
they are still controlled studies that provide strong, detailed
evidence that air pollution negatively affects the brain.
WHAT
TO DO?
In
the battle to protect human health from air pollution, there
has been some recent encouraging news. The Covid-19 pandemic
and related lockdowns have caused dramatic reductions in global
air pollution. California recently passed legislation to require
all cars sold in the state to be electric by 2035; currently,
transportation is the biggest source of emissions in the state,
and in announcing the legislation, the state’s governor,
Gavin Newsom, said, “For too many decades, we have allowed
cars to pollute the air that our children and families breathe.”
The move may gradually impact the automobile industry and
motivate other states to pass similar legislation. Furthermore,
researchers have estimated that the Regional Greenhouse Gas
Initiative, a cooperative effort involving a growing number
of northeastern and mid-Atlantic states to reduce greenhouse
gas emissions, has prevented hundreds of cases of childhood
illnesses (including autism) and saved hundreds of millions
of dollars in costs.
Given
these recent events, “you can see that we can accelerate
the progress quite a bit,” Lanphear says. “But
even if we do the science, testify in front of Congress and
serve on advisory boards — that is not sufficient [for
change]. It’s not until the public gets involved.”
“We
wait until the impairments are so obvious — but this
is all structural, and it can be changed.” –Irva
Hertz-Picciotto
For
members of the public, actionable steps can take many forms,
experts say, including limiting their own contributions to
pollution, publicly voicing their concerns (as was the case
in the Flint water crisis), supporting tighter regulation
of known environmental hazards, challenging people who are
skeptical of science, and supporting candidates for elected
office who will protect the environment and human health.
But,
says Irva Hertz-Picciotto, director of the UC Davis Environmental
Health Sciences Center, “the burden shouldn’t
be on everyone for every product we buy and eat. Too much
happens after the fact. We wait until the impairments are
so obvious — but this is all structural, and it can
be changed.”
For
scientists and public health experts, prevention makes the
most sense.
“If
we let everything run on the free market and intervene when
people develop signs and symptoms, we’ve missed the
window of opportunity,” Lanphear says. “If we
took this science seriously, we could dramatically reduce
exposure to hazardous chemicals.”
Hertz-Picciotto
notes there are moneyed interests in maintaining the uses
of certain chemicals, and that some pollutants that need to
be regulated are already known, but protections that have
been in place are in some ways being systematically dismantled.
According to academic experts and non-governmental organizations,
there are many chemicals that need regulatory oversight, as
well as a growing trend in recent years of increased rollbacks
of environmental legislation that will allow more pollution
and a decrease in prosecutions of pollution-related violations
of existing laws.
Meanwhile,
some contaminants remain unregulated. For instance, unlike
PM10 and PM2.5, ultrafine particles (that are 100 nanometers
or less in diameter), including those generated from diesel
exhaust, are unregulated everywhere despite having a relatively
large surface area and ability to carry contaminants. Furthermore,
most experts believe the ultrafine components of pollution
carry the most adverse effects.
“They
get to the bottom of your lungs and can go directly to the
bloodstream,” Cory-Slechta says. “You can breathe
them through your nose and they can go directly to your brain.”
With
U.S. Environmental Protection Agency regulations, there have
been reductions in PM10 and PM2.5 levels, but no organizations
monitor ultrafine particles, let alone regulate them.
“In
the nano-range, there’s a whole realm of effects of
what’s happening biologically, including for nano-plastics
— the normal defense systems in the brain and body don’t
really pick them up,” Cory-Slechta says.
The
effects of ultrafine particles on the brain are not all known
yet, and there are likely more neurotoxic pollutants in the
world that scientists are yet to discover. These risks are
causes for concern — because each human only has one
chance to develop a brain.
