Arsenic microdistribution and speciation in toenail clippings of children living in a historic gold mining area

Abstract

Arsenic is naturally associated with gold mineralisation and elevated in some soils and mine waste around historical gold mining activity in Victoria, Australia. To explore uptake, arsenic concentrations in children's toenail clippings and household soils were measured, and the microdistribution and speciation of arsenic in situ in toenail clipping thin sections investigated using synchrotron-based X-ray microprobe techniques. The ability to differentiate exogenous arsenic was explored by investigating surface contamination on cleaned clippings using depth profiling, and direct diffusion of arsenic into incubated clippings. Total arsenic concentrations ranged from 0.15 to 2.1 microg/g (n=29) in clipping samples and from 3.3 to 130 microg/g (n=22) in household soils, with significant correlation between transformed arsenic concentrations (Pearson's r=0.42, P=0.023) when household soil was treated as independent. In clipping thin sections (n=2), X-ray fluorescence (XRF) mapping showed discrete layering of arsenic consistent with nail structure, and irregular arsenic incorporation along the nail growth axis. Arsenic concentrations were heterogeneous at 10x10 microm microprobe spot locations investigated (<0.1 to 13.3 microg/g). X-ray absorption near-edge structure (XANES) spectra suggested the presence of two distinct arsenic species: a lower oxidation state species, possibly with mixed sulphur and methyl coordination (denoted As(approximately III)(-S, -CH3)); and a higher oxidation state species (denoted As(approximately V)(-O)). Depth profiling suggested that surface contamination was unlikely (n=4), and XRF and XANES analyses of thin sections of clippings incubated in dry or wet mine waste, or untreated, suggested direct diffusion of arsenic occurred under moist conditions. These findings suggest that arsenic in soil contributes to some systemic absorption associated with periodic exposures among children resident in areas of historic gold mining activity in Victoria, Australia. Future studies are required to ascertain if adverse health effects are associated with current levels of arsenic uptake.