Trace Metal Concentrations in Rainwater, Sources, and Health Risks: A Case Study of Hanoi, Vietnam
Abstract
Atmospheric wet deposition, where pollutants, including metals, are washed from the atmosphere by rain, is a significant concern, particularly in urban and industrial areas, given the risks to human and ecosystem health. This study investigated the concentrations, sources, and potential health risk of 10 metals in 102 rainwater samples collected in Hanoi city during the period 2023–2025. The results showed that zinc-(Zn) was the most abundant metal, followed by iron-(Fe), manganese-(Mn), nickel-(Ni), copper-(Cu), lead-(Pb), chromium-(Cr), arsenic-(As), cadmium-(Cd), and mercury-(Hg). Although the mean values of these 10 metals were within the limits of the Vietnam technical regulation for drinking water, the maximal values of Fe, Mn and Pb were higher than the permissible values. Single-factor pollution index (Pi), and Nemerow pollution index (PN) showed a low pollution level of rainwater. Both the hazard index (HI) and the total carcinogenic risk demonstrated low potential health risks. Enrichment factor (EF) values revealed strong anthropogenic impacts on three metals (Hg, Cd, and Zn), whereas the remaining metals were from both natural and anthropogenic sources. Increasing population, urbanization, and industrial production, with the combustion of fossil fuel, domestic and agricultural waste, and urban construction, are probably major sources. Our results provide scientific evidence for policy-makers in environmental and ecosystem protection and provide data for the estimation of metal loads from wet deposition at regional and global scales. 10 rainwater metal concentrations were measured in Hanoi city in 2023–2025. Concentrations decreased in the order: Zn > Fe > Mn > Ni > Cu > Pb ~ Cr > As > Cd > Hg. Maximal values of Fe, Mn and Pb exceeded the limits for drinking water. Pi and PN indices revealed low pollution levels, whereas HI and total CR demonstrated low potential health risks. Hg, Cd, and Zn originated from anthropogenic activities, whereas the remaining metals were from both natural and anthropogenic sources. 10 rainwater metal concentrations were measured in Hanoi city in 2023–2025. Concentrations decreased in the order: Zn > Fe > Mn > Ni > Cu > Pb ~ Cr > As > Cd > Hg. Maximal values of Fe, Mn and Pb exceeded the limits for drinking water. Pi and PN indices revealed low pollution levels, whereas HI and total CR demonstrated low potential health risks. Hg, Cd, and Zn originated from anthropogenic activities, whereas the remaining metals were from both natural and anthropogenic sources.