Analysis of heavy metals in PM2.5 and PM1 aerosols from rural and semiurban environments in India
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Heavy Metal Concentrations in PM2.5 and PM1 Aerosols: Rural and Semiurban India
PM2.5 and PM1 Levels and Exceedance of Standards
Studies across various regions in India consistently report that PM2.5 concentrations in both rural and semiurban environments often exceed the limits set by the World Health Organization (WHO) and the National Ambient Air Quality Standards (NAAQS) of India. For example, annual mean PM2.5 concentrations in Agra were found to be 104.9 µg/m³ in urban areas and 91.1 µg/m³ in rural areas, both well above recommended standards Kulshrestha2009Sah2022. Similar exceedances were observed in other cities such as Warangal and Dhanbad, with average PM2.5 values ranging from 41.58 to 129.73 µg/m³ Selvetikar2023Kumari2021.
Heavy Metal Composition in PM2.5 and PM1
The most commonly detected heavy metals in PM2.5 and PM1 aerosols include lead (Pb), zinc (Zn), nickel (Ni), iron (Fe), manganese (Mn), chromium (Cr), copper (Cu), cadmium (Cd), and arsenic (As) Kulshrestha2009Lal2024Sah2022+3 MORE. Among these, Zn and Fe are often present in the highest concentrations, followed by Cu, Ni, and Cd . In some locations, Pb and Zn concentrations in PM2.5 have reached as high as ~2000 ppm and 3700 ppm, respectively, indicating significant heavy metal pollution .
Sources of Heavy Metals in PM2.5 and PM1
Principal component analysis and enrichment factor studies reveal that the primary sources of heavy metals in PM2.5 and PM1 are anthropogenic. These include vehicular emissions, resuspension of road and soil dust, solid waste incineration, industrial emissions, construction activities, and biomass burning Kulshrestha2009Sah2022Mehra2020+2 MORE. In rural areas, wind-blown dust carrying industrial emissions and construction activities also contribute significantly . Cluster and trajectory analyses further show that air masses from western and north-western India can transport heavy metals to other regions .
Seasonal and Temporal Variations
Heavy metal concentrations in PM2.5 and PM1 show clear seasonal patterns. The highest concentrations are typically observed in winter, likely due to lower atmospheric dispersion and increased emissions, while the lowest concentrations occur during the monsoon season, when rainfall helps remove particulates from the air Kulshrestha2009Sah2022. Weekday concentrations are generally higher than weekend levels, reflecting the impact of human activities such as traffic and industry .
Health Risks Associated with Heavy Metals in PM2.5 and PM1
Health risk assessments indicate that both carcinogenic and non-carcinogenic risks from heavy metals in PM2.5 are a concern, especially for children. The carcinogenic risks of Cd for children and As, Cr, and Ni for both children and adults were found to be above safe thresholds in some studies . Non-carcinogenic risks also exceeded safe levels for both age groups in certain locations . However, in other regions, the risks were found to be negligible Selvetikar2023Kumari2021. Ingestion was identified as the primary exposure pathway, followed by dermal contact and inhalation .
Regional Differences and Policy Implications
The composition and risk profile of heavy metals in PM2.5 and PM1 can vary significantly between different ecological regions of India. A heavy metal exposure index (HEI) has been proposed to help differentiate toxic PM2.5 and guide public health policy . The findings highlight the need for targeted mitigation strategies, especially in areas with high anthropogenic emissions and during seasons with elevated pollution levels Kulshrestha2009Lal2024Sah2022+3 MORE.
Conclusion
Heavy metals in PM2.5 and PM1 aerosols pose a significant environmental and health challenge in both rural and semiurban areas of India. The main sources are anthropogenic, with concentrations often exceeding national and international standards. Seasonal and regional variations are pronounced, and health risks, particularly for children, can be substantial. These insights underscore the importance of continuous monitoring and the implementation of effective air quality management policies.
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