The Hidden Dangers in the Rain: Human Health Risk Assessment of Fluoride and Nitrate in Rainwater from a Medium-Sized Industrial City

Rainwater is a vital water source with multiple applications, including domestic use. However, it also plays a crucial role in removing pollutants from the atmosphere, which can pose risks to ecosystems and human health. This study is aimed at assessing the levels of fluoride (F⁻) and nitrate (NO₃⁻) ions in rainwater from different areas (industrial, urban, and rural/control) in the industrial city of Rio Grande, Brazil. Additionally, a Human Health Risk Assessment (HHRA) was conducted to investigate the non-carcinogenic risk associated with exposure to these ions in the rainwater samples. A total of 95 rainwater samples were collected and analyzed to evaluate spatial variations and potential contamination sources of fluoride and nitrate. The industrial area exhibited significantly higher concentrations of fluoride compared to the urban and control areas, emphasizing the influence of local industrial emissions. Furthermore, the distribution of fluoride and nitrate concentrations across different precipitation events in the study period demonstrated their relatively consistent levels throughout the year, with a notable increase in nitrate concentrations during the winter season. Importantly, our study is the first to identify and report non-carcinogenic risks to human health from exposure to fluoride concentrations in rainwater, with the industrial area being the most affected. Approximately half of the investigated samples, mainly from the industrial and urban areas, showed non-carcinogenic risk associated with fluoride contamination. However, the observed levels of nitrate did not pose non-carcinogenic risks in all samples. These findings highlight the potential health hazards posed by fluoride in rainwater, particularly in areas influenced by industrial activities and urban zones near industrial complexes. The findings highlight the hidden dangers present in rainwater and underscore the significance of monitoring and managing atmospheric pollution to safeguard both ecosystems and human well-being.