Determinação sequencial de Cd, Cu, Mn e Pb utilizando análise de suspensão por FS-F AAS e avaliação da concentração de Hg em amostras de poeira urbana coletadas em Santo Amaro, Bahia, Brasil.

Abstract

This master’s dissertation addresses the development, analytical performance characteristics, and application of analytical methods for the determination of trace metals in urban dust samples, with a focus on the environmental assessment of the urban area of Santo Amaro, Bahia, Brazil. The work was divided into two complementary parts, involving distinct analytical approaches and environmental and human health risk applications. In the first part, an analytical method was developed and optimized for the sequential determination of Cd, Cu, Mn, and Pb in urban dust using sample preparation in the form of slurry and detection by flame atomic absorption spectrometry (F AAS) in fast sequential mode (FS). The study of sample mass indicated that the range between 10 and 75 mg provided the most suitable condition for the suspension preparation procedure, thus, a mass of 50 mg was selected, ensuring a good signal-to-noise ratio while maintaining analytical linearity. Fractional factorial design and Doehlert design were employed to optimize the experimental conditions, including the evaluation of the acidic medium, sonication time, and the use of a surfactant (Triton X-100). Experimental optimization indicated that the use of 1.25 mol L-1 HNO3, without surfactant addition, and a sonication time of 30 min resulted in the best analytical performance. The analytical method presented limits of quantification (LoQ) ranging from 3.03 to 81.6 mg kg-1. Accuracy was confirmed by the chemical analysis of certified reference materials (CRM) of fly ash (BCR 176R) and road dust (BCR 723), with agreement values ranging from 88.0 (± 0.6) to 91.8 (± 0.1)%. Precision was expressed as relative standard deviation (%RSD), with values below 5% (n = 3). The methodology enabled the analysis of urban dust with reduced reagent consumption and simplified sample preparation, supporting its applicability in environmental studies. In the second part, the direct determination of Hg was applied to 21 urban dust samples collected in the municipality of Santo Amaro, Bahia, using thermal decomposition and detection by atomic absorption spectrometry (AAS). The limits of detection (LoD) and quantification (LoQ) obtained were 0.08 ng g-1 and 0.25 ng g-1, respectively. Method accuracy was confirmed by the chemical analysis of a CRM for trace elements in multi-nutrient fertilizer (NIST 695), with an agreement of 106.3 (± 5.2)%. The %RSD value was below 5%. The analytical method allowed the quantification of Hg over a wide concentration range, revealing a heterogeneous spatial distribution, as well as good accuracy and precision. Hg concentrations ranged from 15.8 (± 0.3) ng g-1 to 1198 (± 29) ng g-1, with a mean of 54.9 (± 32.6) ng g-1 and a median of 46.1 ng g-1, after application of the Shapiro–Wilk (SW–W) normality test. The highest concentrations were observed in areas with greater urbanization, intense vehicular traffic, and proximity to industrial sites. Environmental interpretation was performed using the enrichment factor (EF), geoaccumulation index (Igeo), and ecological risk indices (Er), calculated based on a regional geochemical background specific to the state of Bahia. The results indicated significant enrichment and elevated ecological risk at localized points, with a very high potential ecological risk for the study area, considering the specific sampling period and the prevailing climatic conditions at that time. The sustainability of the analytical methods for the sequential determination of Cd, Cu, Mn, and Pb using suspension preparation and for the direct determination of Hg was evaluated using the AGREE (Analytical Greenness Metric) index, yielding scores of 0.78 and 0.86, respectively, indicating high adherence to the principles of Green Analytical Chemistry. Overall, the results demonstrate that the applied analytical methods are feasible, reliable, and suitable for the environmental monitoring of trace metals in urban dust.