What drives bioaccessibility? A mulit-technique approach to investigate the Pb-phases which control the overall solubility of Pb in topsoils and metalifferous wastes

Evidence for the impact of even low-level environmental Pb exposure on human health, cognition and behaviour is well documented. Highly contaminated soils pose a particular risk, however not all forms of ingested Pb are solubilised in the gastrointestinal (GI) tract. Oral bioaccessibility protocols seek to model extraction during the passage through the human GI system and the solid phase partitioning/mineralogical form of the contaminant has a large influence on its bioaccessibility. Here we report on a study to evaluate which Pb phases control the overall Pb solubility in samples from Mitrovica, northern Kosovo. The Pb mineral phases were determined by X-ray diffraction, and Computer Controlled Scanning Electron Microscopy (CCSEM), coupled with energy dispersive X-ray spectroscopy (EDS), was utilized to identify specific Pb-particle associations (phases) in the samples (with approximately 4,000 particles analyzed per sample). Lead solubility was investigated at the bulk sample level by the Unified BARGE method (UBM), and by chemometric analysis of sequential extraction data (CISED). At the individual particle level, Pb solubility was investigated by Differential Individual Particle Analysis (DIPA). DIPA involves the collection of particle-by-particle information (elemental and morphological) on the particles in their original form, followed by removal from the SEM for chemical treatment of the sample in situ, followed by particle relocation and subsequent analysis of differential changes. The samples investigated had Pb levels ranging from 54 – 47,260 mg/kg, and in vitro oral Pb bioaccessibilities of between 1.2 and 92%. Initial results indicate Pb-particle classes that vary in form (morphology/habit), composition (separate phase vs. homogenous composition), amount of Pb present & acid solubility. Across the suite of samples Pb-particles with Fe associations were less soluble than Pb-particles with Ca associations. Other Pb-particle associations that are sample specific (e.g. Mn associations) were also found to be important in controlling Pb solubility.