Chennai: If you ride through the busy stretches of Sardar Patel Road, 100 Feet Road, and Manali Industrial Area, you may be exposed to greater pollution than other parts of the city. A recent study has found high levels of polycyclic aromatic hydrocarbons (PAHs), toxic pollutants linked to cancer, in these areas.
These PAHs, which primarily result from vehicle emissions, construction activities, and waste burning in urban areas, were found in high concentrations bound to PM10, PM2.5, resuspended road dust, and gaseous emissions.
The study by IIT Madras and Helmholtz Centre for Environmental Research, Leipzig, Germany, was conducted in the city at eight locations with high pollution levels. Other locations that were part of the study were Velachery Main Road, Taramani Link Road, Velachery-Tambaram Main Road, Natco Colony Street (Thiruvanmiyur), and Alandur Bus Depot.
“Urban commuters are most likely to get significantly exposed to tailpipe emissions. Diesel particulates (soot) are the major source of PAHs bound to particulate matter (PM) in urban roads. PAHs in PM and resuspended road dust also pose a significant health risk, especially for two-wheeler riders,” said Dheeraj Alshetty, the study’s corresponding author.
The authors said prolonged exposure to PAHs puts both adults and children at risk of developing cancer. On 100 Feet Road, where heavy vehicles and construction activities contribute to the crisis, the PAH levels in PM10 peaked at 17ng/m³.
In Manali industrial area, PAH levels in PM2.5 were highest at 9ng/m³ due to petroleum refineries. Road dust PAH levels were 50 times lower than PM10 but peaked at Sardar Patel Road (3ng/mg), Velachery-Tambaram Road (2.3ng/mg), and Alandur bus depot (2.1ng/mg) due to slow-moving traffic.
“Since the air quality is good in Chennai compared to cities such as Delhi, it does not reflect the worst conditions of PAH. But it could still be high near dumpsites or industrial areas,” said Prof S M Shiva Nagendra, IIT Madras.
Dominant pollutants found in the city include coronene (petroleum refining), pyrene (gasoline combustion, cigarette smoke), indeno (fuel combustion, tobacco), and benzo ghi perylene (incomplete waste incineration, asphalt production, and oil refining).
“PM2.5 itself is not an inert dust but is classified as a carcinogen. However, the carcinogenic process is a complex one. It depends on the body’s ability to metabolise the toxic PAH chemicals. There can be many factors such as age, gender, nutrition intake, genetic makeup, and the body’s ability to repair the DNA. There are studies linking PAH with cancer, but the causal evidence is still lacking,” said Prof S Sankar, Head of Department of Environmental Health Engineering, Sri Ramachandra Institute of Higher Education and Research.
The researchers concluded that strict controls on road dust, region-specific air quality guidelines, and regulations to curb vehicular emissions will reduce PAH concentrations.