Kasra Zarei
is a science and global health writer who has published
in Scientific American, Slate, Wired, STAT, Undark,
Science, and other publications.
_____________________________________________
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 IMPACT
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 theseobservational 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.
This article is republished from ENSIA
under a Creative Commons license.
