Bioacessiblidade no sistema digestivo/respiratório, determinação das fases e fontes de arsênio em partículas finas superficiais

Abstract

Arsenic exposure and the consequent risks to human health, represents a common concern for populations living near gold mining operations producing arsenic-bearing wastes. This is the case of arsenic-rich gold mining districts in the State of Minas Gerais, Brazil. Arsenic bioaccessibility (BAC) in fine surface dust (FSD, particle size ≤10 µm) and surface dust samples (particle size ≤250 µm) collected from a gold mining district was used as a tool to determine the portion of arsenic that would be available via simulated lung and gastrointestinal (G.I) fluids. BAC was considered low for both tests (lung 2.7 ± 1%, n = 5 and G.I 3.4 ± 2%, n = 14 for residential surface dust samples). An analytical procedure was developed to further identify arsenic-bearing phases found in FSD samples and analyze the main components that regulate arsenic solubility. Up to five different arsenic-bearing phases were identified among a total of 35 minerals surveyed by scanning electron microscopy-based automated image analysis (Mineral Liberation Analyzer - MLA). Arsenic-bearing Fe oxy-hydroxides and mixed phases comprised the main arsenic phases encountered in FSD samples, thus likely being responsible for regulating arsenic bioaccessibility. Transmission electron microscopy showed that the mixed phases comprised a mix of oriented nanostructure aggregates formed by hematite and goethite entangled with phyllosilicates. The main As-bearing phases identified in FSD samples are similar to those reported in soil samples in the same region. The predominant arsenicbearing phase encountered in the ore was arsenopyrite, mostly in large particles (>10 µm in size), and therefore unlikely to be found in residential dust. Arsenic intake from both inhalation and ingestion were minimal when compared to total arsenic intake (considering food and water ingestion), which itself was <7% of the value established by the Food and Agriculture Organization of the United Nations Benchmark Dose Lower Confidence Limit (BMDL0.5) of 3.0µg per kg−1 body weight per day. These findings are relevant and clarify that the exposure from inhalation or ingestion of dust-related arsenic derived from the studied mining operation is likely to be minimal.