A study of Texas residents suggests that tiny
metallic bits of air pollution could account for
some cases of lung cancer.
The researchers aren't sure exactly how dangerous
the particles are, nor do they fully understand
their potential relationship to tobacco smoke.
Still, "It's disturbing that there might
be something in the environment causing the problem,"
said study author Dr. Yvonne Coyle, an associate
professor of internal medicine at the University
of Texas Southwestern Medical Center at Dallas.
"It could be these metals, and we need to
look at that further."
According to Coyle, 10 percent to 15 percent
of lung cancer cases occur among nonsmokers. One
possible explanation: Inhalation of air pollution,
especially fine particulate matter -- bits of
metal that are too small to be seen with the naked
eye but can still enter the lungs.
Mining, smelting and petroleum production all
produce this type of pollution, Coyle said, as
can motor vehicle exhaust.
But while air pollution has been directly linked
to respiratory disorders and heart disease, its
role in lung cancer is still under debate.
In the new study, Coyle and her colleagues tried
to determine if exposure to metallic bits of air
pollution was associated with higher levels of
lung cancer. To find the answer, they compared
lung cancer rates in 254 Texas counties from 1995-2000
to federal reports that companies filed when they
released pollution between 1988 and 2000.
The researchers found an "association"
between various types of lung cancer and releases
of zinc, chromium and copper. When the study results
were adjusted to take into account the effects
of factors such as gender and race, zinc was still
linked to lung cancer.
The findings of the federally funded study appear
in the September issue of the Journal of Thoracic
Oncology.
The study doesn't say how much more likely it
is for people to develop lung cancer if they're
exposed to higher levels of the pollutants.
Also, the role of smoking is unclear because
the county-by-county statistics didn't reveal
whether the individual lung cancer patients smoked.
However, Coyle said smoking levels were consistent
across the counties studied.
More research needs to be done to confirm the
results and "determine who is at the greatest
risk, given this exposure," Coyle said.
Dr. Michael Thun, head of epidemiologic research
for the American Cancer Society,
suggested that the value of the study is limited
because it didn't take into account smoking by
the lung cancer patients.
"It's clear that smoking is such a powerful
cause of lung cancer that it's very difficult
in wealthy countries to identify any separate
contributions from air pollution," Thun said.
"It's extremely hard to measure, and this
study doesn't solve that problem."
