Bioacessibilidade de arsênio em amostras de solo em região de mineração de ouro

• Autor(a) principal: Daphne Chiara Antônio
• Data de Publicação: 2017
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Institucional da UFMG
• Texto Completo: http://hdl.handle.net/1843/32350
• topic: Arsenic fixation in soil; Gastric bioaccessibility; Nanostructured iron oxy- hydroxides; Health-risk assessment; Quantitative mineralogy; Engenharia de minas; Tecnologia mineral; Bioacessibilidade; Arsênio; Avaliação de riscos de saúde

High levels of arsenic (As) (up to approx. 6354 mg kg-1) associated with a geologic anomaly are found in soil samples collected in a gold mining region in Minas Gerais state, Brazil. The samples were collected and prepared for different analyses: chemical analyses, energy dispersive X-ray fluorescence (EDXRF), Mineral liberation analysis (MLA), Scanning and Transmission electron microscopy (SEM and TEM) and micro Raman spectroscopy. Bioaccessibility tests were carried out in order to evaluate risk assessment. The results indicated that silicates (quartz and muscovite) are the main mineral constituents; iron (hydr)oxides (goethite and hematite) and gibbsite are also identified in some samples. Among the minor elements, only As showed concentrations significantly higher (median of 748.0 mg kg-1) than the National guideline values established for As concentration in soils. According the chemical analysis, an As-enrichment in the coarse fractions is associated to Fe-enrichment. Nevertheless, bioaccessible fraction was very low. The mean bioaccessible As is 7.0 mg kg-1, with a median value of 4.4 mg kg-1; percent As bioaccessible has a mean value of 1.3% and a median of 0.7%. Quantitative, single particle identification of As-bearing phases showed that arsenic is mainly found in iron (hydr)oxides–phyllosilicates mixture. Few arsenopyrite (e.g. 7 out of approx. 74,000 particles) and scorodite particles (e,g, 9 out of approx. 74,000) were identified. Arsenic was shown to be trapped in oriented aggregates of crystalline Fe-(hydr)oxides nanoparticles. The unambiguously and precise identification of As association with crystalline nanoparticles of Fe-(hydr)oxides supports the low As bioaccessibility reported here. Furthermore, the intergrowth of the Fe-(hydr)oxides with the phyllosilicates adds additional constraint to arsenic release/mobilization in the environment, thus minimizing the health risks.