Short-term exposure to pollution kills over 2,800 in Chennai, 2,100 in Bengaluru, and 1,500 in Hyderabad: Study

Researchers found that 7.2 percent—equivalent to 33,627 deaths—of all fatalities across 10 Indian cities annually could be attributed to short-term PM 2.5 exposure.

BySumit Jha

Published Jul 05, 2024 | 1:00 PM Updated Jul 05, 2024 | 1:00 PM

Cubbon Park in Bengaluru.

The ‘Pensioners’ Paradise’ moniker is becoming an insult to the fast-changing Bengaluru, where 2,102 people have died of atmospheric pollution.

A study published in The Lancet put Bengaluru’s pollution-related death behind Chennai’s 2,870 fatalities. A total of 1,597 people in Hyderabad, too, succumbed to pollution.

The study, conducted between 2008 and 2019, underscored the need to redefine India’s current standards of good air quality to better align with scientific findings.

Researchers found that 7.2 percent—equivalent to 33,627 deaths—of all yearly fatalities across 10 Indian cities could be attributed to short-term Particulate Matter (PM) 2.5 exposure, exceeding the World Health Organization (WHO) guideline of 15 micrograms per cubic metre.

The national standard for fine particulate matter, PM 2.5, over 24 hours is 60 micrograms per cubic metre.

PM 2.5 consists of highly toxic ultrafine particles with a diameter of 2.5 microns, significantly smaller than a strand of human hair.

In terms of proportion, Chennai reported 4.9 percent of deaths, Bengaluru 4.8 percent and Hyderabad 5.6 percent. Delhi reported the highest at 11.5 percent.

Related: Over 7% of daily deaths in 10 Indian cities linked to PM2.5 pollution

Death by air

The North Indian region is considered to have high pollution levels. However, the southern states, which generally have pollution levels below the national average, also witness significant fatalities.

“We see that cities such as Bengaluru and Shimla, which have relatively lower levels of air pollution, showed stronger effects,” the study said. “This is likely due to the sharp increase in risk at lower levels of exposure which plateaus at higher levels which are unlikely to be experienced in these cities.”

“We observed a significant number of deaths even in cities like Chennai, Bengaluru, Hyderabad, and Pune which are generally considered to have good to moderate air quality under our current AQ (air quality) standards. Risk is non-linear, our policies are not,” Bhargav Krishna, Fellow at the Sustainable Futures Collaborative and a lead author on the study, said on X.

“Increases in risk were most rapid at low to moderate concentrations, especially below the current Indian standard, with the risk increase slowing down at higher concentrations of air pollution indicating a need to review the current standards,” he said.

“Short-term PM2.5 exposure was associated with a high risk of death in India, even at concentrations well below the current Indian PM2.5 standard. These associations were stronger for locally generated air pollutants quantified through causal modelling methods than conventional time-series analysis, further supporting a plausible causal link,” the study concluded.

Related: Bengaluru tops list of most polluted South Indian cities in terms of PM 2.5

The study

The authors utilised PM 2.5 exposure data from 10 cities and correlated it with daily mortality counts between 2008 and 2019.

They said it is the first multi-city study in India to evaluate the relationship between short-term air pollution exposure and mortality, encompassing cities with varying air pollution concentrations, including those meeting national standards.

During the study period, they found that 7.2 percent of all deaths, totalling 33,000 annually across these cities, could be attributed to short-term PM 2.5 exposure exceeding the WHO guideline of 15 micrograms per cubic metre.

Integrating data from monitors, satellites, and other sources, the study examined over 3.6 million deaths over 11 years. The more complex causal modelling revealed a greater risk of death than earlier basic approaches had indicated.

The causal modelling estimated a 3.57 percent increase in the risk of death for every 10 micrograms per cubic metre rises in PM 2.5 over two days, compared to a 1.42 percent increase by simpler methods.

The study assessed the link between short-term pollution exposure and mortality across cities spanning diverse agro-climatological zones.

The authors said the current Indian government standard for PM 2.5 of 60 µg/m³ (micrograms per cubic metre of air) is “substantially higher” than what should be considered a measure of ‘safe’ air quality. In contrast, the WHO’s 24-hour standard is 15 µg/m³.”

Also Read: Pollution threatens crucial haven for migratory birds

Increase in deaths

“Each 10 μg/m3 increment in PM2.5 was associated with a 1.42 percent increase in daily deaths. This number almost doubled to 3.57 percent when we used a causal instrumental variable model that isolates the effect of local air pollution,” Krishna further said.

He emphasized that this work underscored the need to redefine our current standards of what constitutes good air quality to better align with scientific findings. Addressing air quality issues required moving beyond simplistic categorisations of ‘clean’ versus ‘non-attainment’ cities.

Krishna further highlighted the importance of focusing on dispersed local sources of pollution and combustion emissions, noting a necessary shift from the current dust-centric strategies to tackling the most harmful pollutants in urban environments.

Beyond well-known high-pollution cities like Delhi and Varanasi, the study also examined cities typically perceived as having clean air, such as Shimla in the Himalayas and coastal metropolises like Chennai and Mumbai.

“We are observing significant risks and high numbers of deaths even in cities with moderate air pollution levels. For example, Mumbai, despite having about a third of Delhi’s annual PM2.5 levels and being a coastal city, still records over 5,000 air pollution-related deaths annually,” Krishna said.

Also Read: Residential buildings are a source of microplastic pollution, says IIT-Madras

Wanted: Urgent attention

“Similarly, cities like Hyderabad, Kolkata, Bengaluru, Chennai, Ahmedabad, and Pune, all with PM2.5 levels below current Indian standards, still experience substantial annual mortality due to air pollution,” Krishna further said.

“This calls for urgent attention not only to cities with high seasonal pollution spikes but also to those considered relatively clean but still burdened with significant health impacts,” he added.

The study also noted stronger pollution effects in less polluted areas like Shimla and Bengaluru compared to heavily polluted areas like Delhi, likely due to a supralinear exposure-response curve.

Similar findings have been reported in other studies in the region and Europe, highlighting a sharp risk increase at lower exposure levels that plateaus at higher concentrations.”

Dr Vivek Anand Padegal, Director – Pulmonology, Fortis Hospital, Bannerghatta Road, Bangalore

Bengaluru-based Pulmonologist Dr Vivek Anand Padegal said air pollution poses a significant health threat in Bengaluru contributing to a high number of deaths.

“Fine particulate matter (PM2.5), a major pollutant, infiltrates deep into lungs, triggering respiratory illnesses like chronic obstructive pulmonary disease (COPD) and asthma,” Dr Padega, Director (Pulmonology) of the Foris Hospital on Bennerghatta Road, explained.

“This can worsen existing conditions like heart disease and diabetes, and increase susceptibility to infections. Long-term exposure even raises cancer risks. These effects disproportionately impact vulnerable populations — children, the elderly, and those with pre-existing health issues,” he elaborated.

“Pregnant women exposed to air pollution are at higher risk of low birth weight, premature delivery, and birth defects in their babies,” he added.

(Edited by Majnu Babu)

(South First is now on WhatsApp and Telegram)