Siderophore-Promoted Mobilization of Chromium From Hydroxide Minerals.

Biomolecules have a significant impact on the fate and transport of contaminant metalsin soils and natural waters. Siderophores, biogenic chelating agents with high affinities for iron that are exuded by microbes and plants, may form strong complexes with contaminants metals. Additionally, previous work has shown siderophores may promote the dissolution or increase the mobility of contaminants that exist environmentally as hard metal ions, such as Co(III), U(IV), or Pu(IV). Although Cr(III) complexes with siderophores have been know for almost 40 years, few studies have explored interactions of siderophores with Cr-bearing minerals. To better understand the possible effects of siderophores on chromium mobility, we conducted a series of dissolution experiments to quantify the dissolution rate of Cr(OH)₃ in the presence of hydroxamate, catecholate, and α-hydroxycarboxylate siderophores over a range of environmentally relevant pH values. At acidic pH, siderophore promoted dissolution rates are similar to proton-promoted rates, with little evidence for the formation of Cr(III)-siderophore complexes. At alkaline pH, siderophores promote dissolution at rate similar to that of iron hydroxides.The results suggest that, although siderophores may interact strongly with Cr(III) and promote dissolution of Cr(OH)₃ under certain conditions,  the impact of siderophores on Cr mobility in the environment may be kinetically hindered.