Bioaccessibility of Metals in Dust from the Indoor Environment:  Application of a Physiologically Based Extraction Test

A physiologically based extraction test, simulating sequential digestion in the stomach and intestine, has been applied to dust samples collected from various domestic and working settings to define bioaccessible concentrations of metals (Al, Ca, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Sn, U, Zn) in the indoor environment. With the exception of Ca, Cd, and Zn in the stomach phase, mean bioaccessibilities (relative to respective total metal concentrations) were less than 50%. For a given metal, bioaccessibility in either phase was variable among samples but, in many cases, displayed an inverse dependence on total concentration. This suggests that, to a good approximation, variations in both metal contamination and accessibility in the indoor environment arise from variable proportions of metal-rich particulates of low digestibility. Compared with accessibility in the stomach, accessibility in the more alkaline, carbonate-rich intestine was either lower (Al, Ca, Cd, Mn, Ni, Sn, Pb, Zn), similar (Co, Cu, Fe) or greater (Cr, U). We attribute these observations to precipitation and/or readsorption in the intestine, stabilization by complexation, or anion-like adsorption of negatively charged, polyatomic species, respectively.