FASTOSH: a new program to elucidate lead speciation in contaminated soils

Gautier Landrot^a and S. Khaokaew^b

^aSynchrotron SOLEIL, L’Orme des Merisiers, Saint-Aubin, BP 48 91192, Gif-sur-Yvette, France

^bDepartment of Soil Sciences, Kasetsart University, 50 Ngam Wong Wan Road, Lat Yao Chatuckak, Bangkok, Thailand

gautier.landrot@synchrotron-soleil.fr

FASTOSH is a new standalone program to process X-ray Absorption Fine Structure (XAFS) spectroscopy data. It should be particularly useful for geochemical and environmental applications where the XAFS technique is employed. Imported functions from Larch allow normalizing XAFS spectra and conveniently background-subtracting EXAFS scans collected with a step-by-step or rapid continuous acquisition mode. The code enables beam line users to follow in real-time the progress of their acquisition by automatically displaying in 2 or 3D the XANES or EXAFS spectra collected including the merge and progressive improvement of its signal-to-noise ratio. It also proposes an interactive background-subtraction tool for Multi-Channel Analyzer (MCA) patterns collected by multi-pixel fluorescence detectors. This can help minimize, in the XAFS spectrum extracted from MCA patterns, distortions due to acquisition artefacts such as diffraction phenomenon arising from well-crystalline solid or frozen liquid samples. Additionally, the code features auto-deglitching options, and a PCA/Target Transformation module that can instantaneously process a large library of XAFS spectra. It also proposes a tool to post-treat data processed by the MCR-ALS Matlab Toolbox of Jaumot et al. This enables to calculate an amplitude correction factor that allows comparing the EXAFS spectra of the extracted pure phases with those corresponding to references [4]. This study showcases the functionalities of FASTOSH. It also demonstrates how a combination of Target Transformation and MCR-ALS approaches can be helpful in identifying the chemical forms of lead (Pb) present in polluted soils.