Siderophores, NTA, and Citrate: Potential Soil Amendments to Enhance Heavy Metal Mobility in Phytoremediation

Phytoremediation of heavy metal-contaminated sites is often limited by the low bioavailability of the contaminants. Complexing agents can help to improve this technique by enhancing heavy metal solubility. We investigated the effect of three organic chelating agents, that is, the siderophore desferrioxamine B (DFOB), nitrilotriacetate (NTA), and citrate on binding of Cu, Zn, and Cd by either Namontmorillonite, kaolinite, or goethite. The different effects of the complexing agents on metal sorption can mainly be explained by the differences in stability constants and surface charge characteristics. In the presence of clay minerals, NTA was the most efficient ligand with respect to mobilization of heavy metals. In goethite suspensions, the effect of DFOB was more pronounced. In all systems, Cu proved to be the most affected element by the presence of the ligands. In batch experiments with heavy metal-contaminated soils from field sites, NTA was the most efficient metal mobilizer.