Penetrating evidence

Air pollution causes genetic damage among Kolkata residents

Published: Sunday 15 September 2002

For those immune to the known dangers of vehicular pollution, a new study comes up with a shocker. The study paints an even more scary picture of the losing battle fought by the lung's defence mechanism against air pollution. Genetic disruption and neurobehavioural problems are also part of the package. The study shows that whether on road or at home, there is no respite from the clutches of toxic fumes, especially of vehicular emissions. "Indicting any particular pollutant means targe-ting respirable suspended particulate matter," the study states.

Researchers from Kolkata-based Chittaranjan National Cancer Institute (cnci) and Calcutta University conducted the study over a period of six years. Among others, the research team included Twisha Lahiri, Senjuti Roy, Chandreyi Basu, Manas Ranjan Ray and Pulak Lahiri. The researchers compared the health problems of 1,310 urban residents with that of 200 rural residents. Almost three-fourths of the people in the city were found to have some form of respiratory problem, and about half of them had damaged lungs. In comparison, less than half the rural residents had respiratory problems. Oral cavity cells are the first to suffer from the menace of air pollution. The researchers discovered that these cells were extensively damaged in the study subjects. Their chromosomes had micronuclei, indicating genetic disruption. The rate of this process in the urban population was found to be twice that of the rural population.

To find out the worst affected lot among the urban residents, the researchers divided them into three subgroups: those who are highly exposed to vehicular emissions, like traffic policemen, drivers, garage workers and hawkers; those who are highly exposed to combustion fumes, like firefighters, asphalt workers, factory workers and canteen workers; and those who are relatively less exposed to both vehicular and combustion fumes, like office workers, housewives, maids and students.

At least 79 per cent of the hawkers, who spend a very large amount of time outdoors and were therefore regularly exposed to vehicular exhaust, were found to have the most damaged lungs amongst the three subgroups. Next were the garage workers, who are also exposed to high levels of vehicular exhaust. Sixty per cent of them had damaged lungs. However, most of the students were found to be healthy, with only 18 per cent of them having impaired lungs. Though smoking was found to aggravate problems in general, the number of hawkers with damaged lungs who smoked and who did not was almost equal. (See Graph)

Upon delving deeper into what was happening inside the lungs and other body parts, the researchers found that outward symptoms like respiratory problems were just the tip of the iceberg. When they studied the alveolar macrophages (am) -- cells generated to destroy harmful substances intruding the respiratory system -- they found that am numbers in the sputum of urban citizens was almost seven times higher than that of people in the rural areas.

This is just the beginning of the saga. The am of urban residents were found to be larger in size as well. The researchers attributed this to an abortive attempt to absorb extremely high levels of pollutants. Many of these cells, which usually contain one nucleus, were also found to have two or more nuclei. This phenomenon is indicative of chronic lung diseases like tuberculosis and pneumonia. But strangely, the subjects did not show clinical symptoms of these. In many cases, mainly among those exposed to high vehicular emissions, the cells were even found to be structurally deformed.

Deep impacts
The researchers' quest did not stop at mathematical calculations of the cell numbers. They comprehensively studied the indicators of normal cell functioning. They found that here also all was not well. Rather, far from it. The urban population was found to have 178 per cent more iron deposits in am over its rural counterparts, pointing towards a possible damage of red blood cells that carry oxygen to the different body parts from the lungs. For this also, the worst affected were those exposed to vehicular emissions -- they had 43 per cent of iron-laden am compared to 37 per cent of those exposed to combustion fumes.

Acid phosphatase (acp), a type of enzyme that helps the am digest foreign substances, was found to be 11 times higher among the urbanites as compared to the rural residents. Again, those exposed to vehicular emissions showed highest levels of this enzyme. Although this finding seems to follow from the fact that exposure to pollution causes greater secretion of this enzyme, the scientists found a rider -- a number of am cells were already seen to be disintegrated.

Elastase, an enzyme that damages connective tissues, was found to be almost 12 times higher in the am of the urban group than the rural one, and again highest in the group exposed to vehicular pollution. Under normal circumstances, production of this enzyme by am is negligible. However, air pollutants stimulate production and release of elastase by am. (See Image)

The study also indicated changes in the life cycle of am. While the death of the cells is largely regulated by genes (a process called apoptosis), certain environmental factors also influence the happening. It was found that traffic-related air pollution catalysed apoptosis of am. Moreover, this process was thrice as fast in urban areas compared to rural areas.

According to the researchers, such findings show that the body's natural resistance crashes like a house of cards when faced by air pollution, particularly toxic vehicular fumes. "Although the defence mechanism of the lungs is activated when exposed to high levels of air pollution, it only serves to compound the problems, even leading to genetic disruption," says Twisha Lahiri. The study recounts a gloomy story about intense suffering and slow death, and this is not just Kolkata's story.

Subscribe to Daily Newsletter :

Comments are moderated and will be published only after the site moderator’s approval. Please use a genuine email ID and provide your name. Selected comments may also be used in the ‘Letters’ section of the Down To Earth print edition.