New Study: Toxicity of PM2.5 in Kolkata Shows Sudden Surge Beyond 70 µg/m³

The findings are both alarming and informative. The study demonstrated a non-linear relationship between PM2.5 concentration and its oxidative toxicity.

In a recent and significant scientific breakthrough, researchers from the Bose Institute, an autonomous body under the Department of Science and Technology, Government of India, have uncovered critical insights into the behavior of PM2.5 toxicity in Kolkata's atmosphere. The findings emphasize the urgent need to reassess and tighten air pollution mitigation strategies, particularly concerning ultrafine particulate matter that poses grave health hazards to the population.

Understanding PM2.5 and Its Health Impact

PM2.5, or particulate matter with a diameter of 2.5 micrometers or less, is considered one of the most harmful air pollutants due to its ability to penetrate deep into the lungs and even enter the bloodstream. Prolonged exposure to PM2.5 has been linked to severe health outcomes, including respiratory and cardiovascular diseases, neurological disorders, and premature mortality. It is a primary parameter for measuring air quality and is at the center of national and global efforts to combat air pollution.

Toxicity Spike at 70 µg/m³: A Game-Changing Discovery

The team led by Prof. Abhijit Chatterjee, along with former Ph.D. scholars Dr. Abhinandan Ghosh and Dr. Monami Dutta, conducted an in-depth analysis of the oxidative potential (OP) of PM2.5—a metric used to assess the particles’ capability to generate reactive oxygen species (ROS) once inhaled into the human lungs. ROS are known to cause oxidative stress, damaging cells and weakening natural antioxidant defenses.

The findings are both alarming and informative. The study demonstrated a non-linear relationship between PM2.5 concentration and its oxidative toxicity. Up to a threshold of around 70 µg/m³, the OP or toxicity of PM2.5 remains relatively stable. However, beyond this point, the toxicity experiences a sudden and sharp increase, peaking near 130 µg/m³. Interestingly, further increases in PM2.5 beyond 130 µg/m³ do not significantly elevate toxicity levels, indicating a plateau.

This sharp rise at 70 µg/m³ suggests a critical toxicity threshold—a tipping point where health risks escalate dramatically. Recognizing this, the researchers have proposed the establishment of a “toxicity standard” for PM2.5 in Kolkata, setting the threshold at 70 µg/m³. This serves as a new benchmark for policy-makers and public health authorities.

Role of Biomass and Waste Burning

In addition to establishing this toxicity threshold, the study delves into the sources of PM2.5 pollution using a sophisticated source-receptor model—Positive Matrix Factorization (PMF). This model allowed the team to conduct a source apportionment analysis, revealing that biomass and solid waste burning is the dominant contributor to the highly toxic fraction of PM2.5 in Kolkata.

While other sources—such as vehicular emissions, road dust, industrial discharges, and construction-related dust—have been relatively well-controlled under existing pollution control frameworks, biomass and waste burning continues to evade strict regulation. This source is not only persistent but also disproportionately responsible for the increase in oxidative potential of the aerosols.

Policy Context: The National Clean Air Programme (NCAP)

Launched in 2019, the National Clean Air Programme (NCAP) by the Ministry of Environment, Forest and Climate Change (MoEFCC) set ambitious goals to reduce PM concentrations by 40% by 2026, relative to 2017 levels. The plan includes 131 non-attainment cities—urban areas that do not meet the National Ambient Air Quality Standards (NAAQS).

Kolkata, being one of these non-attainment cities, has been under close observation. The Bose Institute has been appointed as the Nodal Institute for guiding and implementing air pollution mitigation strategies in the city and acting as a national knowledge partner under the NCAP.

While progress has been made, especially in curbing emissions from transportation and construction, the unchecked rise of emissions from open burning of biomass and waste materials continues to jeopardize public health and the success of NCAP in Kolkata.

Local Impact and Policy Response

The study's publication in the prestigious journal Science of The Total Environment has already made waves in the policy landscape. Local urban bodies in Kolkata have begun to tighten enforcement and surveillance over open burning practices. This shift in strategy has started to yield visible results. During the winter months of 2024–2025, traditionally a period of poor air quality, Kolkata recorded noticeable improvements in PM2.5 levels and corresponding OP values.

The study serves as a wake-up call for urban planners, environmental agencies, and public health officials. It underscores the importance of not just reducing PM2.5 levels but also understanding and managing the toxicity associated with these pollutants.

Conclusion: The Road Ahead

As Kolkata and other Indian cities continue their battle against urban air pollution, this groundbreaking study from the Bose Institute offers both a scientific roadmap and a policy directive. Setting a toxicity standard for PM2.5 at 70 µg/m³ could become a pivotal guideline in future environmental legislation and public health policy.

To truly protect citizens from the hidden dangers of particulate matter, strategies must go beyond surface-level reductions and address the underlying chemical and biological threats posed by ultrafine particles—especially from persistent sources like biomass and waste burning.

This research not only advances our scientific understanding but also paves the way for transformative changes in India’s air quality governance.