As, Cd, and Pb relative bioavailability in contaminated soils: Coupling mouse bioassay with UBM assay

The robustness of in vitro bioaccessibility assays to predict oral relative bioavailability (RBA) of multiple metals in contaminated soils requires validation using additional soil samples. In this study, 11 contaminated soils from mining/smelting areas were analyzed for As-, Cd-, and Pb-RBA using a mouse bioassay and metal bioaccessibility via the UBM gastric phase assay. Metal-RBA varied considerably among soils, with As-RBA (2.5-23%, mean 12%) being generally lower than Cd-and Pb-RBA (3.4-88 and 3.3-59%, mean 42 and 28%), due to higher proportions of As in the residual fractions. Metal-RBA generally decreased with increasing metal concentrations probably due to reduced labile metal fractions. In addition, strong negative correlations were observed between total Fe with As-, Cd-, and Pb-RBA (R² = 0.46-0.77), suggesting the role of Fe in controlling metal-RBA in soils. Like RBA, metal bioaccessibility by the UBM assay also varied among samples. However, strong in vivo-in vitro correlations (IVIVCs) were observed between metal-RBA and bioaccessibility (R² = 0.52-0.81). Further, there were little differences when As-, Cd-, and Pb-IVIVCs established using soils from this study and soils pooled from literature were compared, suggesting the robustness of the UBM assay to predict metal-RBA in contaminated soils.