Oral bioaccessibility of trace metals in household dust: a review

Because household dust is a heterogeneous assortment of particles derived from a multitude of diverse sources, concentrations of toxicants, like trace metals, vary widely among sample populations. For risk assessment purposes, the bioaccessibility of a trace metal, or its degree of solubilization in the human lung or digestive environment, provides a better metric of its potential health impact than its total concentration. In this paper, the relatively little direct information that exists on the in vitro oral bioaccessibilities of metals in household dust is reviewed. Data and mechanisms from studies involving better characterized geosolids, like soil and street dust, or metal-rich components thereof, such as paints, are also extrapolated to the household setting, although use of these solids as surrogates of household dust is not recommended. The bioaccessibility of a given metal is highly variable in the household setting; for instance, reported accessibilities of Pb in fluids that mimic the human stomach range from 25 to 80%, and accessibility is usually, but not always, reduced when conditions are altered to mimic the intestine. While part of this variation reflects the inherent heterogeneity of samples arising from local to regional differences in geology, industrial emissions, and domestic (and cultural) practices, considerable variation results from the precise means by which bioaccessibility is determined in vitro. It is recommended, therefore, that the effects of physicochemical variables, and in particular, the solid to fluid ratio and the pH of the stomach phase, are studied systematically such that appropriate algorithms or corrections may be factored into measures of bioaccessibility obtained under operationally defined default conditions.