Mobilization of redox-sensitive trace elements during water-rock interaction in presence of siderophores: Effects of solution pH, oxygen fugacity and weathering state

Siderophores are important biogenic chelators produced by plants, microbes and fungi, which promote the (bio-)availability of iron and other highly-charged cations in the natural environment. The hydroxamate siderophore desferrioxamine B (DFO-B) enhances the mobilization of certain trace elements that hydrolyze easily and hence are traditionally assumed as being ‘immobile’ during water-rock interaction. Leaching of different rock material with DFO-B under ambient conditions, for example, facilitates the formation of a very pronounced positive Ce anomaly in bulk-normalized patterns and fractionates the Th-U element pair, which we tentatively attributed to an oxidation of Ce(III) to Ce(IV) and U(IV) to U(VI). We here reports results of an investigation into the effects of solution pH, fO₂ and weathering state of different rocks on the mobilization of redox-sensitive trace elements and their isotopes during water-rock interaction in presence of DFO-B. The impact of natural organic ligands on redox-sensitive elements may be largely underestimated. Siderophores are omnipresent today and may also have been present in the geological past. Our preliminary results indicate that the impact of solution pH on fractionation of redox-sensitive trace elements is rather small, but that fractionation is strongly controlled by oxygen fugacity and by the weathering state of the studied rock. Siderophores have the potential to significantly catalyze the oxidation of these elements even under strongly hypoxic conditions.