MP9 Metals and Bioaccumulation
Monday, 14 November 2005: 8:00 AM - 5:30 PM in Exhibit Hall

(DIN-1117-548114) Studies of bioaccumulation of the rare earth elements in wheat using their fractionation property and X-ray absorption spectroscopy.

Ding, Shiming¹, Liang, Tao¹, ¹ Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Science, Beijing, China

ABSTRACT- The rare earth elements (REEs) comprise a group of trivalent metalic elements mainly including lanthanides (the elements from La to Lu). Fractionations among the REEs may occur in natural system due to the chemical differences from La through Lu, and this property has been widely applied to record geochemical processes. In this study, accumulation and mobility of the REEs in wheat were investigated, and the mechanisms involved were studied using the fractionation property and X-ray absorption spectroscopy (XAS). Significant fractionations of REEs were found in wheat after its exposure to exogenous mixed REEs solution composed of 14 lanthanides. Middle REE (the elements from Sm to Gd) enrichment and M-shape variation (M-type tetrad effect) were observed in roots, and fractionation between light REEs (the elements from La to Eu) and heavy REEs (the elements from Gd to Lu) and W-shape variation (W-type tetrad effect) were observed in stems and leaves. Changes of organic ligand and inorganic component levels in root solutions caused significant effects on REE accumulation and fractionation in wheat organs, but were not the reasons for the aforementioned fractionation phenomena. Further studies showed that the fractionations of REEs observed in the roots were attributed to cell wall absorption and phosphate precipitation occurred in/on the roots. This is consistent with XAS investigation that most of the La in the roots were associated with root cell walls and/or precipitated by phosphate. In addition, organic ligand-complexed REEs in the xylem zap of wheat were extracted by nanometer-sized TiO₂, and they accounted for most of the REEs in the zap, with the same fractionation features observed in the leaves. It is concluded that the accumulation of REEs in wheat were dominated by cell wall absorption and phosphate precipitation, while the complexation of organic ligands contained in the xylem vessels played great roles in mobility of the REEs from the roots to the leaves.

Key words: bioaccumulation, fractionation, rare earth elements, X-ray absorption spectroscopy