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Air on Delhi roads contain cancer-causing chemicals, shows study

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New Delhi
10 May 2018

Delhi, the city once famous for the charm of the Red Fort and the elegance of Qutub Minar, is today infamous for its pollution crisis. Ranked one of the most polluted cities in the world, the air in the city is taking a toll on its residents’ health. With over 10 million vehicles registered in Delhi, it is not surprising that the air is turning toxic. But how bad is the air really in the roads of Delhi? What are some of the hazardous pollutants in the air that Delhiites breathe? A new study by researchers at the Indian Institute of Technology Delhi and the Indian Institute of Technology Kanpur has an answer. And, it's not good news.

The main culprits in Delhi’s undoing are the aerosols—a mixture of tiny solid and liquid particles suspended in air that adversely affect our health. Also called particulate matter, they can easily enter into our lungs and transfer to the bloodstream. About 2.5 million deaths are attributed to these tiny particles in India. Commonly measured particulate matter include PM1.0 (particulate matter with a diameter less than or equal to 1 micrometre), PM2.5 (particulate matter with a diameter less than or equal to 2.5 micrometres) and PM10 (particulate matter with a diameter less than or equal to 10 micrometres).

In this study, published in the Journal of Environmental Science and Pollution Research, the researchers measured the levels of PM1.0 and its chemical composition from two roadside sites in Delhi. PM1.0 is emitted from burning fuels and is usually found in the vehicular exhaust. The air samples were collected three days a week over five months during November 2009 and March 2010. The risk to human health through inhalation was assessed based on the concentration of trace elements. They also calculated the excess cancer risk (ECR) of PM1.0. ECR is the probability of developing cancer due to exposure to a particular cancer-causing element over a lifetime.

The results showed that the values of ECR at the study sites far exceed the acceptable levels—a significant concern for the residents of Delhi. “An increased lung cancer mortality may occur among population residing close to the roadside in Delhi due to inhalation of particulate-bound trace elements”, warn the authors.  The ECRs of chromium and nickel, found in the air sampled at these sites, were near the tolerable limit for adults but significantly higher than the safe limit for children.

The total ECR values for adults and children were estimated to be four to five times higher for road sites than those for elevated sites. So, if you are living in a high-rise building, you may not be inhaling as many toxins as compared to your ground-level neighbours. The overall health risks, other than cancer, were twice as much for children than that for adults.  The researchers also attempted to identify the source of these particulate matters. While fuel and oil combustion accounted for the presence of a majority of chemical compounds, road dust and brake/tire wear of vehicles were also identified as a source for few elements.

An interesting finding of the study is that the concentration of particulate matter was always higher during the night than the day. The authors attribute this observation to the emissions from heavy-duty diesel trucks that are allowed inside the city only at night. Also, the PM concentrations were maximum in December and minimum in March during the study period since the winter atmosphere instigates the formation of fog and secondary aerosols (particulates formed due to atmospheric reactions). This phenomenon, coupled with low temperatures at ground level, confines these particles to the ground, the study elaborates.

The study also considers some of the neglected sources of air pollution like biomass burning that accounts for 44% of the cancer risk. As the authors point out, these aerosols are one of the most significant threats to public health in Delhi and need immediate attention from authorities.