Determination of mercury in urban dust: direct sample analysis and establishment of a geochemical baseline

• The study enabled the direct solid analysis of Hg in urban dust samples. • Hg levels in urban dust ranged from 14.8 to 488 ng g⁻¹ in Bahia State, Brazil. • A regional geochemical baseline for Hg was established, correlating Hg and Mn levels. • Enrichment factors indicated anthropogenic Hg sources in urban areas. • The research offered a tool for environmental diagnosis. Airborne particulate matter, particularly urban dust, poses health and environmental risks by gathering toxic elements. Among these, mercury (Hg) is notable for its persistence, mobility, and tendency to bioaccumulate, with human-made emissions amplifying its harmful impacts on people and ecosystems. This study examined Hg levels in urban dust samples collected from 11 cities in Bahia, Brazil, using direct solid analysis. Quantification was carried out with an external calibration curve based on certified reference material (CRM BCR 176R). The detection and quantification limits were 0.2 ng g⁻¹ and 0.8 ng g⁻¹, respectively. Method accuracy was validated using CRM NIST 695, which yielded a recovery of 96.5 ± 3.3%. Precision, expressed as the relative standard deviation, was better than 3.1% (n = 4). Hg concentrations ranged from 14.8 ± 0.5 ng g⁻¹ to 488 ± 2 ng g⁻¹, with the highest levels observed in Salvador. The average concentration was 236 ± 149 ng g⁻¹, and the median was 262 ng g⁻¹. A geochemical baseline for Hg was established through linear regression with Mn concentrations, supporting the calculation of the enrichment factor (EF) and the geoaccumulation index (Igeo). EF values indicated Hg enrichment in Salvador, Jaguaquara, Camaçari, and Mata de São João. The Igeo revealed Hg contamination in Salvador, Jaguaquara, Camaçari, Mata de São João, Dias D’Ávila, and Caetité. These results highlight human-made mercury contributions, mainly linked to vehicular traffic and urban growth in these areas, and emphasize the need for continuous environmental monitoring and effective air quality management in cities.