Arsenic is often released during microbial-reductive Fe (hydr)oxides interaction between water and soil/sediment under anaerobic conditions. However, the biogeochemistry of As in high As soil exposed to aerobic conditions has been rarely explored. The current study examined the depth profiles of As in geologically derived subsoil cores from Hong Kong, and investigated As mobilization in incubation experiments, As plant availability, and human bioaccessibility from the excavated soil in surface environments. The results indicated significant heterogeneity with high As in three soil layers reaching 505 mg/kg at 5 m depth, 404 mg/kg at 15 m depth, and 1510 mg/kg at 27-32 m depth, but with only &lt;0.1-11.5 μg/L As in the collected porewater samples. The main species was arsenate (As(V), &gt;92%) adsorbed on Fe (hydr)oxides or in the form of scorodite based on the X-ray absorption (XAS) analysis, with only 0.5±0.4% of As in exchangeable fraction determined by the sequential extraction procedure. The As(V) species and its stable adsorption structure on abundant Fe (hydr)oxides demonstrate that very little amount (0.14-0.48 mg/kg) of As desorbed from the soil in the aerobic incubation experiments, where indigenous microbe partly (59±18%) contribute to the As release. Furthermore, no As toxicity in the soil was observed for the ryegrass growth, and the As bioaccessibility was 0-27% of the total As using simplified bioaccessibility extraction test (SBET) analysis. Although the bioaccessibility was not as high as the previous published data, children and workers should avoid incidental contact of the excavated soil because of relatively high As in the digestive solution (0-268 μg/L with medium value at 30.0 μg/L).<br/>

Arsenic in geogenic soil from Hong Kong: Speciation, mobilization, and bioaccessibility

253rd National Meeting (2017)

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