The Smallest of Pollutants Are Linked to Outsize Health Risks
Can steering clear of particles from traffic fumes protect the heart?

By Adam Voiland
February 27, 2008

Sitting in traffic triples a person's short-term heart-attack risk.
Living in a city with heavy air pollution such as Los Angeles is as
risky for the heart as being a former smoker. And having a house near a
highway ups the risk of hardened arteries by some 60 percent. In each
case, tiny "ultrafine" particles in the air may be a key culprit.

While air pollution comes in many forms, scientists are increasingly
concerned about its most minute constituents—virus-size particles
produced by combustion. These ultrafines, which measure no more than 0.1
micrometer in diameter, are ubiquitous near roadways and are emerging as
one of the most dangerous components of air pollution, which kills an
estimated 60,000-plus Americans a year. That's more than the number
killed annually by automobile accidents.

The tiny particles are worrisome for several reasons. For one, they tend
to be rich in potentially toxic organic compounds and other reactive
chemicals. Their size, moreover, allows them to travel deep into the
lungs, lodge there for long periods, and stress the body in a variety of
ways, researchers theorize. They may even slip into the bloodstream,
where they can do further damage. In comparison, so-called fine
particulates, which can be up to 25 times wider than ultrafines, are
snared more easily by protective hairlike structures in the nose and
throat. Not that fine particulates are benign: Last year, a study of
older women in the /New England Journal of Medicine/ linked a
10-microgram-per-cubic-meter increase in fine particulate
pollution—approximately the difference between Pittsburgh and cleaner
Anchorage—to a 76 percent increase in the cardiovascular death rate.

More recent data seem to confirm researchers' suspicions that smaller
particles are even worse. With Environmental Protection Agency funding,
a team co-led by Jesus Araujo, an environmental cardiologist at UCLA,
zoomed in on the ultrafines and found that mice exposed to those
particles developed more atherosclerotic plaque than mice breathing fine
particulates only—and did so faster. "Much, much faster," says Araujo.
In addition, HDL, or good cholesterol, didn't work as well in
ultrafine-exposed animals, Araujo's team will report in the March 14
/Circulation Research/. Other recent experiments have found troubling
cardiovascular changes in human volunteers following exposure to ultrafines.

Such findings are bad news for people with heavy exposure to traffic.
Diesel vehicles are particularly potent sources of both fine and
ultrafine particles, and their fumes, recent studies show, have adverse
effects on the heart. European researchers found, for example, that
exercising men who inhaled fresh diesel fumes at levels that can occur
near major roads experienced rapid reduction in blood flow to the heart
and a one-third drop in a protective protein that prevents dangerous
clotting. "The effect was about the same as what we see with secondhand
smoke," explains Nicholas Mills, the University of Edinburgh
cardiologist who led the research.

*At risk. *The elderly, young children, and those with pulmonary and
cardiovascular problems are most at risk from particulate air pollution.
However, particles affect everybody. Recent Taiwanese research shows,
for example, that inflammation, oxidative stress, and other
cardiovascular warning signs are detectable among urban teens breathing
polluted air as well.

While fine particulate matter and certain smog-generating emissions are
regulated, ultrafine particles are not. "There's no doubt particulate
matter is the elephant in the room," says Dan Costa, the director of the
Environmental Protection Agency's air research program. Since 1997, the
agency has been cracking down on fine particulates, and their levels
have generally been falling nationwide. A new rule, phased in last year,
requires trucks to use cleaner-burning diesel fuel and should help
reduce both fines and ultrafines. But it may be a decade, Costa says,
before scientists amass enough evidence on ultrafines to justify
directly limiting them.

A third to a half of ultrafine exposure comes from driving. "If you have
otherwise healthy habits and don't smoke, driving to work is probably
the most unhealthy part of your day," says Scott Fruin, an environmental
scientist at the University of Southern California. The tiny particles
can also slip into homes, especially those near busy roads. Cooking with
a poorly ventilated stove can be another source of exposure to
ultrafines, he says. Some fireplaces also generate particulates.
However, so-called HEPA filters can help clear indoor air of
particulates, including ultrafines.

*Avoiding exposure.* Exercising near traffic increases one's exposure,
since heavy breathing draws particles deep into the body. Murray
Mittleman, a cardiologist at Harvard University, suggests that
people—especially those with heart conditions—try to exercise away from
major roadways. Masks probably won't have much of an effect on the tiny
ultrafines, says Fruin, but might stop larger particles. (Some U.S.
Olympians, in fact, have been advised to wear face masks in heavily
polluted Beijing.) Two government websites, airnow.gov
<http://www.airnow.gov> and epa.gov/airtrends
<http://www.epa.gov/airtrends>  can help people plan outdoor activities.

Still, there's no reason to live in complete fear of particulates; the
risk for any individual remains quite small. That tripling of heart
attack risk due to traffic exposure, for example, sounds frightening but
is similar to the increased short-term risk posed by exercise or even
sexual activity, says Robert Brook, a University of Michigan
cardiologist. "The absolute risk—meaning the risk you have every single
time you are exposed to air pollution, exercise, or have intercourse—is
still very, very low," he says. "But when you multiply that by the tens
of millions of people being exposed to polluted air all of the time, you
end up getting large numbers of people who are affected."

Araujo, for one, isn't taking any chances. He used to bike frequently in
heavy traffic. However, after seeing what happened to his mice, he says:
"You won't find me stuck behind bus tailpipes anymore."

(US News and World Report)