| SPECIAL
REPORTS: HEALTH - BRAZIL |
|
|
|
Ozone
Pollution Linked to Lung Cancer
Mario
Osava
RIO DE JANEIRO, (Tierramérica) -
Ozone gas, which in the stratosphere
forms a protective layer against the
sun's harmful rays, at the earth's
surface becomes a pollutant that is a
threat to human health. In addition to
damage it causes the respiratory
system, there is strong evidence that
ozone is linked to lung cancer.
Scientists from Brazil, Britain,
France and Germany have proved that
intense exposure to ozone causes
genetic mutations similar to those
found in non-smoking persons who
develop lung cancer, or 10 percent of
the cases of this oncological disease
in Sao Paulo, according to the
Brazilian city's Cancer Hospital.
While tobacco is the major risk factor
for lung cancer, ”ozone should be
considered another possible cause in
urban areas,” says Carlos Menck,
coordinator of the study and professor
of microbiology at the Biomedical
Sciences Institute at Sao Paulo
University.
Confirming that relationship requires
further research, acknowledged Menck
in comments to Tierramérica.
But the progress made in identifying
genetic alterations caused by ozone
looks like yet another concern to be
added to others in the world's
metropolises suffering major air
pollution problems, like Sao Paulo
(more than 10 million inhabitants) and
Mexico City (20 million).
According to the research effort,
ozone can trigger genetic
modifications in human cells that are
exposed to it, according to
observations made of the four
”letters” or chemical bases in DNA
sequences.
Under normal circumstances, C
(cytosine) is always linked to G
(guanine), while T (thymine) goes with
A (adenine).
In the genes of cells exposed to
ozone, these pairs are switched, or
appear in a different order, similar
to the case of non-smokers who develop
lung cancer, Menck explained.
For the purposes of the study, ”we
exposed the DNA to a higher dose of
ozone than is found in a city's
polluted air,” noted Soaria Calil
Jorge, a genetics expert who worked on
the project.
But while people might inhale less of
the gas, they do so regularly and over
many years, and the ozone has a
cumulative effect, she told Tierramérica.
Simple exposure does not immediately
affect the genes because the ozone
”first enters into contact with the
cell membrane and does not always
reach the DNA,” but has a long path
to follow, explained Calil Jorge.
The study revealed the possibility
that ozone might cause alterations in
gene P53, which controls the cellular
cycle and ”induces the 'suicide' of
the altered” or cancerous cells,
preventing cell multiplication and
potentially triggering the formation
of tumours, she explained.
Mutations of this regulator gene are
common in lung cancer patients who
have never been smokers, the expert
added.
The high concentration of ozone -- a
molecule made up of three oxygen atoms
-- is a problem in cities around the
globe that have heavy traffic
congestion.
In 2002, Sao Paulo recorded 82 days in
which ozone concentrations were above
the acceptable limit of up to 160
micrograms per cubic meter of air,
says chemist María Helena Martins,
head of air quality analysis at the
state-run Environmental Technology
Company of Sao Paulo (CETESB).
Through technical standards in vehicle
manufacture, in place since 1986,
Brazil has reduced contaminating
emissions of carbon monoxide and solid
particulates.
But the ozone levels in Sao Paulo have
remained stable, ”with no tendency
to increase or decrease,” noted
Martins.
Ozone is not a direct product of
emissions but rather of chemical
reactions involving nitrogen oxides
and hydrocarbons generated from the
combustion of fossil fuels, incomplete
combustion or evaporation.
Automobiles are the leading sources of
these ”precursor” agents of ozone,
which are also emitted by gasoline
service stations and some industries.
Sunlight is essential for the chemical
reaction that unites the three oxygen
atoms, a process that takes several
hours. This sets the ozone cycle in
motion, with the concentration in the
air beginning to form at 11:00 am in
the case of Sao Paulo, diminishing in
late afternoon, but only on sunny
days, according to Martins.
The mass of polluted air extends over
the entire metropolitan region, but
winds lead to heavier concentrations
of contamination in certain areas. It
is not always the most heavily
congested roads that are most
affected, because nitrogen oxide, for
example, is a precursor to ozone, but
also destroys ozone, explained the
chemist.
Often the gas is concentrated over
”green areas”, like Sao Paulo's
Ibirapuera Park, where many residents
go for walks or practice sports in
what they believe is cleaner air.
CETESB maintains an air quality
monitoring system that indicates which
neighbourhoods have excessive levels
of air contamination.
The ozone concentrations in Sao Paulo
are particularly high beginning in
September, when the southern
hemisphere spring begins and there are
fewer rains and clouds, with a strong
sun prevailing. This situation extends
until February or March, Martins said.
Other contaminants, like carbon
monoxide, are more severe in the
southern hemisphere winter because the
lower temperatures prevent them from
being dispersed.
Research shows that sustained exposure
to ozone inflames the lungs, altering
their elasticity, and in general
irritating all membranes, thus
reducing the body's capacity to fight
off infections.
Email
this page to a Friend
|
|
|
|
|
