The PM2.5-bound metals in the metropolitan area of Bangkok, Thailand: Temporal trends, sources, and human health challenges

Abstract

Background

Particulate matter (PM) is comprised of solid and liquid particles that vary in size and shape. Urbanization has significant effects on the concentration of PM_2.5, which is used as an indicator of urban air quality. PM_2.5, containing metal elements, has detrimental effects on both human health and ecosystems.

Methods and materials

An automated X-ray fluorescence analyzer are used to continuously measure PM_2.5-bound metal elements over four months in the dry season (October 2023 to January 2024). An XRF analyser (PX-375, Horiba Ltd., Kyoto, Japan) coupled with a continuous particulate monitor measures the elemental compositions of PM_2.5 aerosols. The mass of PM_2.5 is determined by using a beta-ray attenuation method based on radiocarbon. The PMF model and enrichment factor determine the potential sources of PM_2.5-bound metal elements. The PSCF model is used to determine the source regions of PM_2.5 in the urban area of Bangkok. Heavy metals are studied in Bangkok, Thailand, for their potential cancer, non-cancer, and ecological risks.

Results

The average concentration of PM_2.5 in January 2024 is relatively higher than in the other studied months. The PM_2.5 average concentration in October 2023 is 24.9 ± 9.7 µg/m³; in November 2023 is 23.1 ± 9.5 µg/m³; in December 2023 is 26.7 ± 9.8 µg/m³, and in January 2024 is 34.6 ± 10.3 µg/m³. During the studied months, the metal element with the highest concentration bound to PM_2.5 is S, followed by Ag, Te, Si, Pd, Cd, Hg, K, Ca, Fe, Bi, Al, Mg, and Zn. On the other hand, Cu, Co, As, Ni, V, Mn, and Ti had lower concentrations. The PMF analysis and binary ratios of metals show that vehicle emissions, industrial emissions, construction dust, coal and biomass combustion are the main sources of PM_2.5 and metal elements bound to PM_2.5. The most enriched elements (EFs > 100) are V, As, Cr, Cu, Pb, Mn, Ni, and Zn, which can be attributed to a significant anthropogenic source. During the studied months, the results of cancer and non-cancer risk assessments showed that Cd poses both carcinogenic and non-carcinogenic risks to adults and children via inhalation, dermal contact, and ingestion exposures. According to the PSCF analysis, the local emission sources in urban Bangkok are the major contributors to the PM_2.5 mass.

Conclusion

The daily mean concentrations of PM_2.5 and PM_2.5-bound metal elements in Bangkok are significantly higher than the acceptable limits specified by the World Health Organization (WHO). Therefore, it is essential to monitor PM_2.5 pollution regularly and take action to reduce the high concentrations of PM_2.5. The impact of metal elements bound to PM_2.5 on the climate of Thailand will be determined through future research studies that use long-term datasets from this region.