Adsorption of Eu(III) onto roots of water hyacinth

The water hyacinth (Eichhornia crassipes) has drawn attention as a plant capable of removing pollutants, including toxic metals, from water. We are interested in the capacity of the water hyacinth to remediate aquatic environments that have been contaminated with the lanthanide metal, europium (Eu(III)). Using scanning electron microscopy (SEM) we have been able to determine that Eu(III) is adsorbed onto the surface of the roots from water and that the highest concentration of Eu(III) is on the root hairs. X-ray absorption spectroscopy (XAS) techniques were used to speciate the Eu(III) adsorbed onto the surface of the roots. The XAS data for Eu-contaminated water hyacinth roots provides evidence of a Eu-oxygen environment and establishes that Eu(III) is coordinated to 10-11 oxygen atoms at a distance of 2.44 Å. This likely involves binding of Eu(III) to the root via carboxylate groups and hydration of Eu(III) at the root surface.