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Benzene the killer
Highlights
Benzene the Killer, Clouds of Pollution, Sweet Smelling Gas, Centre for Science and Environment. Clouds of pollution are hovering over the city. In addition to the usual pollutants, the city has seen an alarming rise in the level of benzene. Benzene, a sweet smelling gas, is not harmful only if it is kept under permissible limits.
Clouds of pollution are hovering over the city. In addition to the usual pollutants, the city has seen an alarming rise in the level of benzene. Benzene, a sweet smelling gas, is not harmful only if it is kept under permissible limits. However, findings of studies done by the Centre for Science and Environment suggest that the level of benzene in the city has increased fivefold over a period of two years. Experts say that exposure to benzene could cause leukaemia, heart attack and tuberculosis. Currently the benzene level is around 8.4 micro grams as against admissible 5 micro grams per cubic metre in the city limits.
Greater Hyderabad is at a significant disadvantage geographically as only 8% of the city constitutes roads. One can imagine how crammed up the city is and what a concrete jungle it has become. This geographical disadvantage is also responsible for the increase in pollution levels across the city. Statistics with the road transport department suggest that there are 38 lakh vehicles in the city and that an estimated 600 new vehicles are hitting the roads every day. These are causing pollution due to vehicular exhausts that contain benzene and other pollutants.
Alarming facts were revealed following a study undertaken by the Centre for Science and Environment. Its experts say that the percentage of benzene in air has increased five times in the city, compared to the level in 2011. Currently, the benzene level is around 8.4 micro grams per cubic metre, compared to the permissible limit of 5 micro grams per cubic metre. In 2011, only 1.8 micro grams of benzene per cubic metre was present in the air. The increase in the level of benzene is attributed to many factors, but the foremost of them is increase in vehicular traffic.
Air-borne benzene comes from fuel vapourisation and evaporation and vehicular exhausts. Benzene and other aromatic compounds occur naturally in petroleum and become more concentrated when petrol is refined to produce high octane gasoline. While the benzene content in petrol must be minimised, the aromatics must also be reduced because they also contribute towards formation of benzene. A colourless liquid hydrocarbon, benzene is highly inflammable.
Benzene is also released through vapourisation. As it occurs naturally in petrol, whenever petrol evaporates benzene is released. It should be noted that around 10 lakh vehicles of the 38 lakh vehicles in the city are outdated and do not conform to any of the pollution control norms. These do contribute towards release of benzene. So are the filling stations in the city as there is always standard vapourisation of petrol and diesel owing to the climate.
"The city has seen an exponential increase in ozone and benzene (both carcinogenic) levels past the standard count. They have been on the rise since 2004, despite the new standards that have been imposed on the vehicles," said Anumita Roychowdhury, executive director, CSE.
Toxic effects
Benzene is a potent carcinogen and is blamed for leukaemia. The WHO estimates a 4 in 1 million risk of leukaemia on exposure to benzene to a concentration of 1μg/m3. Increased incidences of leukaemia (cancer of the tissues that form white blood cells) have been observed in humans occupationally exposed to benzene. Long-term inhalation can cause various disorders in the blood, including reduced numbers of red blood cells and aplastic anaemia, especially in occupational settings.
There are some short-term effects as well. According to US Environmental Protection Agency, exposure to benzene may cause drowsiness, dizziness, headaches, as well as eye, skin, and respiratory tract irritation, and, at high levels, unconsciousness.
Women may suffer from reproductive effects if they are exposed to high levels.
India has taken steps to meet the international standards of 1 per cent benzene in petrol. In Bharat Stage IV petrol, currently available in major cities, the total aromatic content has been reduced to 35 per cent and olefins—unsaturated chemical compound containing at least one carbon-to-carbon double bond and widely used in petrochemical industry—content to 18 per cent. But given the level of air-borne benzene in cities and rising levels of vehicular traffic, there is need for tighter control. The global best practices suggest that benzene content–as in the US–is now 0.62 per cent and that of aromatics 25 per cent in polluted areas.
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