Context: A study has found that the toxicity of air pollution changes with the concentration levels of PM2.5 in Indian cities, bringing attention to a critical gap in current air quality standards.
Relevance of the Topic: Prelims: PM2.5, Air Quality Index (AQI), Reactive Oxygen Species (ROS), Oxidative Stress, Pollution Sources.
What is PM2.5?
- PM2.5 refers to fine particulate matter with a diameter of less than 2.5 micrometres, small enough to penetrate deep into the lungs and bloodstream.
- It originates from sources- biomass and solid waste burning, vehicular emissions, industrial activities, construction dust etc.
- Due to its size and chemical composition, PM2.5 is associated with respiratory, cardiovascular, and neurological disorders.
- A recent study by Indian researchers has highlighted how toxicity of air pollution changes with concentration levels of PM 2.5 in Indian cities.
Key Highlights of the Study:
The study- “Contrasting features of winter-time PM2.5 pollution and PM2.5-toxicity based on oxidative potential” (2016-2023), conducted in Kolkata, found the following:
- Pollution is damaging even at lower concentrations, but itsability to cause damage to cells increases sharply after the concentration level crosses a certain threshold value.
- When PM2.5 concentration level exceeds about 70 µg/m³, its potential to create oxidative stress in the body increases steeply, and continues to rise until the concentration reaches about 130 µg/m³.
- Toxicity stabilises after that, and further increase in concentration do not lead to an appreciable rise in damage potential.
- The threshold level is expected to vary from city to city. E.g., This threshold value is about 70 micrograms per cubic metre (µg/m³) for Kolkata.
- Threshold level of toxicity varies due to differences in the composition of air pollutants. E.g., pollutants from biomass and solid waste burning contribute more significantly to toxicity than those from vehicular emissions.
Why does toxicity increase after a point?
At lower concentrations the body can manage pollutant effects, but beyond a threshold the defences of the body are overwhelmed.
- When pollutants are inhaled, the body’s immune system fights back through the release of Reactive Oxygen Species (ROS), which are chemicals used by immune cells to neutralise foreign substances. When larger concentrations of pollutants are inhaled, greater amounts of ROS are released.
- The problem is ROS is damaging for the body’s cells as well. Therefore, as a natural counter-defence mechanism, the body produces another set of chemicals called antioxidants, that protect the cells against ROS.
- However, antioxidants are present in small quantities, and take time to build up. So, while they are able to effectively deal with smaller amounts of ROS, they are helpless when ROS is produced in large amounts. This leads to an imbalance in the body, a situation called oxidative stress, which leaves the internal cells prone to damage from excess ROS.
Current Air Quality Standards:
- Air quality standards are framed in terms of their concentration, not toxicity. E.g., in India, a PM2.5 concentration level of 40 µg/m³ averaged over a year is considered safe. On a daily basis, a concentration of 60 µg/m³ is considered safe.
- However, the harmful impacts of air pollution on human health depend not just on concentration, but also on toxicity, which takes into account factors like chemical composition of pollutants.
Way Forward
The study underlines a crucial gap in how we currently assess and respond to air pollution. It calls for a nuanced, city-specific and health-focused approach to pollution control.
- Incorporate toxicity into AQI systems: AQI should reflect not only PM2.5 concentration but also its oxidative potential, giving a more accurate picture of health risks.
- Develop city-specific toxicity thresholds: Since pollutant composition varies by location, region-specific toxicity thresholds must be established for effective local interventions.
- Revise Air Quality Standards: National standards must evolve to include toxicity measures.