Gastric/lung bioaccessibility and identification of arsenic-bearing phases and sources of fine surface dust in a gold mining district.

Abstract

Bioaccessibility (BAC) of fine surface dust (FSD, particle size ≤10\u202fμm) and surface dust samples (particle size ≤250\u202fμm) 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\u202f±\u202f1%, n\u202f=\u202f5 and G.I 3.4\u202f±\u202f2%, n\u202f=\u202f14 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 arsenic-bearing phase encountered in the ore was arsenopyrite, mostly in large particles (>10\u202fμm 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 3.0\u202fμg per kg-1 body weight per day. These results indicated that the relative risks associated with arsenic exposure by inhalation and oral ingestion in this region are low.