Uranium LIII-edge XANES data of monomeric U(VI) containing biomass, collected under (a) microbeam (3 µm × 2 µm) and (b) large beam (500 µm × 500 µm) conditions at the microXAS beamline. A significant change is observed between the first scan (dotted line) and subsequent scans (solid line) of the biomass monomeric U(IV) system under microbeam conditions, likely due to U(IV) oxidation by the microbeam. The subsequent scans show a slight shift in white-line energy and a flattening in the post-edge region centred around 17.19 keV, changes indicated with arrows in the figure. These features are present in the HFO + U(VI) system (dashed line), which is included for reference. The changes are not seen under large beam (500 µm × 500 µm) conditions where the initial scan (dotted line) is occluded by the later scans (solid line) due to perfect overlap (b).