Comparison of in vitro models in a mice model and investigation of the changes in Pb speciation during Pb bioavailability assessments

Abstract

In this study, the predominant Pb minerals prior to and after Pb relative bioavailability (Pb-RBA) and Pb bioaccessibility (Pb-BAc) tests were identified using SEM (scanning electron microscopy), XANES (X-ray absorption near edge structure) and XRD (X-ray diffraction). The correlations between in vitro Pb-BAc (using the UBM (Unified BARGE Method) and RBALP (Relative BioAccessibility Leaching Procedure) models) and in vivo Pb-RBA (using endpoints of kidney and liver in an mice model) were determined. The results demonstrated that both RBALP and UBM (gastric phase) reliably indicate Pb-RBA (Pb-RBA). However, raising the solid:liquid ratio of the gastric phase of UBM is necessary to determine Pb-BAc if the soils contain total Pb >10,000 mg/kg. The comparison of Pb minerals prior to and after in vitro extractions demonstrated that the relatively soluble forms of Pb (PbSO₄, PbO₂ and MgO Pb) start to dissolve than other forms of Pb minerals, suggesting there was no difference in Pb²⁺ release between chemical-based (RBALP) and physiologically-based (UBM) models. The identification of the Pb minerals of Pb₅(PO₄)₃Cl and organically-complexed Pb in mice excreta demonstrated that a portion of Pb²⁺ combined with food and humic acid to generate organically-complexed Pb in mice excreta, and that Pb₅(PO₄)₃Cl is not bioavailable.

Keywords: Bioaccessibility; Bioavailability; In vitro; In vivo; Pb speciation; Soil.