Assessing Short-Term Cardiovascular Effects of PM2.5 and Its Components in a Traffic Microenvironment: A Crossover Panel Study in Urban India

Traffic-related air pollution is one of the major sources of exposure in urban areas and an increasingly important contributor to anthropogenic emissions in lower and middle-income countries. Due to a rapid rise in the motor fleet owing to population growth, economic development, the expansion of metropolitan areas, and the increasing dependence on motor vehicles because of changes in land use, the concerns about the health effects of traffic-related air pollutants (TRAPs) have greatly increased. In the light of limited evidence in the Indian context, the present research work involved conducting a crossover panel study on a group of healthy adults in Delhi (security guards on a university campus; sample size ~ 40) to understand the short-term effect of PM_2.5 (particles having aerodynamic diameter less than 2.5 microns) and their chemical components on acute changes in cardiovascular health. The study improved the exposure estimates by real-time monitoring of PM_2.5 mass, its chemical components like ions and trace metals, black carbon (BC) and size-resolved particle number concentration in a traffic microenvironment instead of using ambient concentrations as a proxy to traffic exposure. The participants were administered questionnaires to gather the background data about socio-economic status, secondary exposures or prevailing health conditions and any potential confounders. The ECG holter systems were used to monitor the real-time changes in heart rate variability (HRV) parameters, which are an indicator of cardiac activity (both time-domain (SDNN- standard deviation of normal-to-normal; pNN50- percent normal-to-normal intervals > 50ms; rMSSD- root mean square of successive differences between normal heart beats) and frequency domain (HF- high frequency; LF- low frequency and LF/HF ratio) were monitored). Mixed models were used to quantify the associations between TRAPs and HRV parameters. A significant decline was observed in all the HRV indices with an increase in the pollutant concentrations. The highest decline in HRV with respect to particle size was observed for the particles with a diameter between 0.03-0.1 µm with negligible change in particles with dia. > 1µm. Similarly, amongst the PM_2.5 constituents, BC showed the highest decline in HRV, followed by nitrates and sulfates. The study emphasized the need to study exposures in specific microenvironments due to differences in the pollutant concentrations and composition with respect to ambient. It also highlighted the need to investigate the micro-physical and chemical characteristics of PM_2.5 because of their potential to have greater health impacts as compared to the total PM_2.5 concentrations.