Ozone Linked to Lung Cancer
By Mario Osava*
A scientific team led by Brazil is investigating the effects of a gas emitted by vehicles, revealing a potential new nightmare for mega-cities.
RIO DE JANEIRO - Ozone gas, which in the stratosphere forms a protective layer against the sun's harmful rays, on 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 as another possible cause in urban areas," Carlos Menck, coordinator of the study and professor of microbiology at the Biomedical Sciences Institute at Sao Paulo University, told Tierramérica.
Confirming that relationship requires further research, acknowledges Menck. 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 air pollution, as do 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 the gas, 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 cases 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 said in a conversation with 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 tumors, she explained.
Mutations of this regulator-gene are common in lung cancer patients who are not 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 suffer heavy traffic congestion.
In 2002, Sao Paulo recorded 82 days in which ozone concentrations were above the acceptable limits, of up to 160 micrograms per cubic meter of air, says chemist María Helena Martins, head of air quality analysis at the state-run Company for Environmental Technology 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 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 in a process that takes several hours. This sets the ozone cycle, 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 "clean" air.
CETESB maintains an air quality monitoring system that indicates which neighborhoods 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.
* Mario Osava is an IPS correspondent