Winter pollution in Delhi is known to be among the severest in the world however researchers have for the first time captured a new metric, called the Reactive Oxidative Potential (OP) that directly links aerosol exposure to adverse health effects.
The variation in OP in Delhi was wider than previous studies that have measured aerosol changes in Beijing, Athens, Chicago and Atlanta and was twice the levels in Bengaluru, in a study conducted in 2013.
The oxidative potential of PM is the ability of particles to burn off antioxidants and pose a potential health risk. This study, led by researchers at the Indian Institute of Technology (IIT), Kanpur; IIT Delhi, University of Illinois and Paul Scherrer Institute, Switzerland, found that the chemical exposure of PM (particulate matter) was 5 times higher in Delhi in comparison to levels in Illinois, U.S. in February 2019.
Implications for health policy
This was significant as the average PM levels in Delhi was 13 times more than that in Illinois. Therefore the operative part of particulate matter that is responsible for harming health is less than its raw concentration, a finding that could have implications for health policy. “These findings reveal substantial spatial heterogeneity in the redox properties of PM and highlight the importance of determining the PM chemical composition along with its mass concentrations for predicting the overall health impacts associated with aerosol exposure,” Sachchida Nand Tripathi, Professor, IIT Kanpur, told The Hindu .
The study appears in the peer-reviewed Environmental Science & Technology Letters.
Previous studies conducted in the Indo-Gangetic Plains have indicated that PM2.5 in Delhi is a mixture of particles emitted from various emission sources including crop burning, vehicles, industries, waste burning and construction activities. These mixtures of various chemical types like organic compounds, inorganic ions, transition metals, etc. coming from different sources are expected to be highly toxic but data on the toxicological properties of PM2.5 in the Indian subcontinent are limited.
Air pollution accounts for over 12.5% of the deaths in India. Due to calm wind conditions and lower boundary layer depth, particularly prevalent during Delhi’s winter, the hourly averaged PM2.5 mass concentrations frequently exceeds 500 µg/m3, which is over eight times the National Ambient Air Quality Standards (60 μg/m3).
The OP is measured using a commonly used method called the dithiothreitol (DTT) assay. DTT, in the presence of ambient PM, acts as an electron donor and converts oxygen to its superoxide radical. The oxidation rate of DTT during this reaction is assumed to be proportional to the amount of redox active species present in ambient PM. Recent studies, the authors note, have found a relationship of OP based on DTT assay with the adverse health effects, such as asthma, wheezing and cardiovascular disorders, as compared to PM2.5 mass concentrations.
