Characterisation of varyingly soluble Pb-rich particles in soil using Differential Individual Particle Analysis (DIPA) and Computer Controlled Scanning Electron microscopy (CCSEM)

Jane Entwistle, Andrew Hunt

Research output: Contribution to conferencePaperpeer-review

Abstract

Computer Controlled Scanning Electron Microscopy (CCSEM), coupled with energy dispersive X-ray spectroscopy, has been widely used to characterise particulate matter in a range of environmental media. Bioaccessibility protocols, by their very nature, generate ‘bulk’ or aggregate bioaccessibility data. To better understand the particle phases that constitute the sample and the variability in particle solubility, an approach based on CCSEM and subsequent differential response of representative particles following chemical treatment was undertaken. Soils, collected from Mitrovica, Kosovo, were selected to cover a range of total Pb concentrations and a range of oral bioaccessibilities (Boisa et al., 2013). Soil aliquots were deposited from a deionised water suspension onto 25mm diameter, 0.4µm pore size, polycarbonate membrane filters. The particulate material on the filter was evaporatively coated with carbon before it was submitted for CCSEM. Automated particle detection in the SEM was accomplished using a high backscatter electron image (BEI) threshold. A particle detection threshold was set using an imaging standard (fine particulate TiO2) such that only particles with an average atomic number >TiO2 would be detected during automated analysis. The aim of the CCSEM, and subsequent particle classification, was to identify homogenous groups of ‘like’ particles in the sample as a basis on which to focus the Differential Individual Particle Analysis (DIPA) protocol. DIPA (Hunt and Johnson, 2011) involves the collection of particle-by-particle information (element and morphological) on the particles in their original form, followed by removal from the SEM for chemical treatment of the sample in situ (in this case with 0.4 M glycine, adjusted to pH 1.5, at 37◦C for 2 hours, to mimic oral bioaccessibility; USEPA, 2007), particle relocation and subsequent analysis of differential changes. Our post chemical treatment observations indicated Pb to be present in a range of complex phases, some more resistant to dissolution than others, but we were unable to discern the exact nature of these phases (if crystalline, or as surface coatings), due to limitations in the image resolution. CCSEM, especially when allied to DIPA, provides detailed information on particles in environmental media which can help support environmental interpretations based on chemical extraction data to better inform intervention decisions.
Original languageEnglish
Publication statusPublished - Jul 2014
Event30th SEGH Conference - Newcastle upon Tyne
Duration: 1 Jul 2014 → …
http://www.segh.net/events/segh-conference/

Conference

Conference30th SEGH Conference
Period1/07/14 → …
Internet address

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