Why in News?

A new study conducted over Kolkata has revealed that the toxicity of PM2.5 air pollutants significantly increases after a certain concentration threshold is crossed, highlighting a sharper health hazard linked to rising pollution levels in Indian cities.

What’s in Today’s Article?

• About the Study
• Key Findings of the Study
• Why Toxicity Rises Sharply Beyond a Threshold
• Current Air Quality Standards: Concentration-Based
• Need for Toxicity-Based Air Quality Standards

About the Study

• Title: Contrasting features of winter-time PM2.5 pollution and PM2.5-toxicity based on oxidative potential: A long-term (2016–2023) study over Kolkata megacity at eastern Indo-Gangetic Plain
• Published in: Science of the Total Environment, December 2024
• Significance
  • First-of-its-Kind in India: This is the first study to assess how PM2.5 toxicity varies with concentration levels in an Indian city.
  • Public Health Implications: The findings call for urgent pollution control measures, especially in winter when PM2.5 levels peak.
  • Policy Insight: Could guide threshold-based interventions and health advisories in Indian cities facing high air pollution.

Key Findings of the Study

• Threshold Level Identified: The study found that PM2.5 toxicity sharply increases once the concentration exceeds 70 µg/m³.
• Peak Toxicity Range: The toxicity continues to rise until the concentration hits 130 µg/m³, after which it stabilises.
• No Safe Limit: Even at concentrations below 70 µg/m³, PM2.5 poses health risks, though less severe compared to higher levels.
• Variation Expected: Thresholds for a sharp rise in toxicity are likely to differ across cities.
  • This is because pollution sources vary — for example, vehicular emissions might dominate in one city, while biomass burning could be a bigger factor in another.

Why Toxicity Rises Sharply Beyond a Threshold

• At lower PM2.5 concentrations, the human body can manage the adverse effects of pollutants more effectively.
• However, beyond a certain threshold (~70 µg/m³ for Kolkata), the body’s natural defence mechanisms become overwhelmed, leading to significantly greater cellular damage, especially in the respiratory system.
• Role of Reactive Oxygen Species (ROS)
  • Immune Response: When pollutants are inhaled, the immune system releases ROS to combat foreign particles.
  • Double-Edged Sword: ROS can also harm healthy cells in the body.
  • Antioxidants as Defenders: To counteract ROS, the body generates antioxidants, which neutralize ROS and protect cells.
  • Oxidative Stress: When pollutant levels are high, ROS production exceeds the body’s antioxidant capacity, leading to oxidative stress, which damages internal cells.
• Understanding Oxidative Stress and PM2.5
  • The sharp rise in oxidative stress at PM2.5 levels beyond 70 µg/m³ is mainly due to chemical components from biomass or solid waste burning.
  • Vehicular emissions also contribute, but to a lesser extent compared to biomass burning.
• Need for Oxidative Stress-Based Standards
  • While India has set air quality standards for PM2.5 and PM10, there are no benchmarks for toxicity or oxidative stress.
  • This study aims to establish toxicity-based threshold values, helping cities adopt more health-focused pollution control policies.

Current Air Quality Standards: Concentration-Based

• In India, air quality standards for PM2.5 are based only on concentration levels, not on how toxic the air is.
• Safe Limits
  • Annual average: 40 µg/m³
  • Daily average: 60 µg/m³
• Limitations of Concentration-Based Standards
  • Health risks depend not just on how much PM2.5 is present, but also on its chemical composition and toxicity.
  • The same concentration may be more harmful in one city than another, depending on the pollutant source (e.g., biomass burning vs. vehicular emissions).
• Why Toxicity Matters More
  • In Kolkata, PM2.5 levels of 50–60 µg/m³ may not be significantly more harmful than 30–40 µg/m³.
  • But toxicity spikes sharply after 70 µg/m³, indicating a real health emergency.

Need for Toxicity-Based Air Quality Standards

• This study strengthens the case for incorporating toxicity thresholds into air quality norms.
• City-specific thresholds should be developed, reflecting local pollutant profiles.
• Such standards could help trigger early warnings or emergency actions when toxicity crosses a critical level, even if concentrations seem “moderate.”