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Fig. S1 An association plot showing the relationship between energies used for selecting pixel populations.

Fig. S2 Results of fluorescence-XANES imaging in roots of wheat, demonstrating the background noise generally excluded from all analyses.

Fig. S3 Damage to a wheat root scanned three times with fluorescence-XANES imaging at different velocities.

Fig. S4 Light micrographs of wheat roots following the collection of a XANES stack for 7 h.

Fig. S5 The derivative of normalized XANES spectra for roots of wheat exposed to As(V).

Fig. S6 Normalized XANES spectra showing photooxidation in a preliminary scan for an uncomplexed As(III) standard.

Fig. S7 Accumulation of As within Fe plaque.

Table S1 Concentrations of As in bulk root and shoot tissues exposed to As(V) or As(III)

Notes S1 Characterizing the effect of As on plant growth.