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Short-term PM2.5 exposure is deadly too — new study finds strong links to mortality in Delhi

Researchers says Delhi's Graded Response Action Plan to combat pollution is futile. Also says reducing exposure could have 'averted' over 17,000 deaths.

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New Delhi: Researchers have found a strong association between short-term exposure to PM2.5 (particles that have a diameter less than 2.5 micrometres) and mortality in Delhi, where acceptable levels of PM2.5 are routinely crossed, causing intense air pollution through the winter season.

They also noted that the city’s Graded Response Action Plan, designed to curb pollution levels, was not effective, with more ambitious, long-term goals to cut emissions required to bring about significant health benefits.

The study — the result of a collaboration between Harvard University, Population Foundation of India, and the Delhi-based Centre for Chronic Disease Control — is the first of its kind to look into over 7 lakh deaths not caused by accidents between 2010 and 2016 to arrive at its conclusion.

Researchers said it “presents a strong case for the harmful effects of short-term PM2.5 exposures”. The study was published earlier this month in the peer-reviewed journal, Environmental Epidemiology.

“Essentially what we’re trying to do with this study is assess whether changes in PM2.5 levels over 24 hours can affect the number of deaths that occur every day. We found that with every 25 μg/m3 increase over 24 hours, mortality increases by 0.8 per cent,” Dr Bhargav Krishna, lead author of the study told ThePrint.

Delhi’s PM2.5 levels exceeded 130 µg/m3 in 2016 — over 10 times the recommended World Health Organization (WHO)’s levels — and have been on the rise since.

“Overall, we observed a 0.8% increase in non-accidental mortality with every 25 μg/m3 (micrograms per cubic metre) increase in exposure,” the paper noted, adding that people above the age of 60 are disproportionately affected and “reducing exposures significantly below current levels would substantially decrease the mortality burden associated with PM2.5”.

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Over 17,000 ‘air pollution’ deaths could have been averted

The WHO draws the line of acceptable PM2.5 levels at a mean of 10 μg/m3 annually and 25 μg/m3 in 24 hours. PM2.5 particles are considered dangerous for health because they can penetrate the lungs and enter the bloodstream, causing a higher risk of developing cardiovascular, respiratory diseases, and lung cancer. This risk is aggravated by chronic exposure.

The researchers note that in Delhi, annual average exposures “exceeded 130 µg/m3 in 2016, having grown steadily over the 7 years between 2010 and 2016, with large spatial and temporal variations.”

“Seasonal factors, high emissions related to fireworks combustion during religious events and periodic crop-stubble burning also contribute to extremes of PM2.5 in the winter which can sometimes breach 1,000 µg/m3 in the very short term,” they added.

For accurate representations of daily average PM2.5 levels across six years, the researchers used a “machine learning-based predictive model” that used various sources of data, like ground monitors, satellite observations, meteorology, land-use variables and emissions inventories.

“Reducing the exposure from the median of 91.1 µg/m3 to the WHO guideline level of 10 µg/m3 would have potentially averted 17,526 deaths (approximately 7 deaths a day) among the entire study population, with the vast majority of averted mortality observed among the elderly population, and largely among men,” the paper said.

Need ‘ambitious long-term targets’

In a note to policymakers and the media, the researchers said the city’s Graded Response Action Plan, which seeks to reduce pollution levels during their peak in the winter season is futile. Reducing PM2.5 levels after they have crossed 125 μg/m3 levels “confer only marginal benefits for mortality”.

They also said the National Clean Air Programme’s target to reduce emissions by 30 per cent wouldn’t lead to significant health benefits and “must be revised to meet more ambitious long-term targets.”

“Overall, reductions in high seasonal exposures must be coupled with systemic actions to reduce baseline exposure levels throughout the year to ensure that WHO guidelines for safe exposure are met and the health of the populace is adequately protected,” they recommend.

(This report has been updated to include a quote from Dr Bhargav Krishna, lead author of the study)

(Edited by Paramita Ghosh)

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