IIT-Bombay study links Pune-Mumbai Eway vehicle pollution to cancer, climate warming

Pune: A study by Indian Institute of Technology Bombay (IIT-B) has found concerning levels of cancer-causing pollutants from vehicles plying on Pune-Mumbai Expressway, one of the busiest routes in western India.
The research, published in Nature's ‘Clean Air' journal this month, highlighted the urgent need for stricter emission controls and a transition to cleaner fuels. The study conducted in Kamshet tunnel measured polycyclic aromatic hydrocarbons (PAHs). Polycyclic aromatic hydrocarbons are dangerous compounds released during fuel combustion that are linked to serious health risks, including cancer.
Researchers found that heavier molecules with four to six rings dominated the pollutant mix, comprising 75-89% of total the PAHs detected. These compounds are primarily associated with diesel vehicles, which made up 51% of the traffic observed. "Diesel vehicles across all categories dominated the fleet, followed by petrol vehicles at 41%, while CNG vehicles comprised just 8%," said Harish C Phuleria, IIT-B associate professor in Environmental Science and Engineering Department.
The research revealed a significant presence of older, poorly maintained and overloaded heavy-duty diesel vehicles, which accounted for 21% of the total traffic but contributed disproportionately to pollution levels.
The researchers also estimated the cancer risk and found that the calculated incremental lifetime cancer risk (ILCR) values were approximately 5 per million for adults and 2 per million for children — falling into what experts categorized as "moderate risk" territory.
"Health risk assessments showed concerning results when the team analysed the toxicity of these pollutants. Using the benzo[a]pyrene-equivalent concentration method, which estimates the cancer-causing potential of a mix of toxic compounds called PAHs, we found the average concentration was 13.5 ng/m³ at the tunnel entry and about twice at the exit," lead resercher Sohana Debbarma said.
"These levels far exceed the Indian National Ambient Air Quality Standards limit of 1 ng/m³," Debbarma said. ng/m³ stands for nanograms per cubic metre — that's one-billionth of a gram of pollutant in a cubic metre of air. Even in such small amounts, PAHs released from vehicle exhaust can pose serious health risks.
The study found that nearly all the cancer risk — about 99% — came from just seven specific PAHs that are classified as carcinogenic by the World Health Organization's cancer research agency. These harmful compounds were detected in air samples collected at the tunnel site, he said.
Beyond health risks, the study revealed how these pollutants intensified climate impacts. The researchers found a strong correlation between higher molecular weight PAHs and greater light absorption properties, significantly enhancing the climate warming effect of these emissions.
Using ultraviolet-visible spectrophotometry, researchers found a strong correlation between higher molecular weight PAHs and greater light absorption capacity.
"We discovered that higher molecular weight PAHs significantly enhance light absorption, which contributes to atmospheric warming. As molecular weight increases and volatility decreases, the light-absorbing properties of these compounds increase," Debbarma said.
Researchers from IIT Bombay led the study in collaboration with professor Pradhi Rajeev from Indian Institute of Technology Patna and professor Tarun Gupta grom Indian Institute of Technology Kanpur.