Accumulation of rare earth elements in corn after agricultural application

Using both pot and plot experiments, the dose-dependent accumulation of rare earth elements (REs) in corn (Zea mays L.) after application of an agricultural REs mixture was measured. In the pot experiment, the dose-dependent accumulation of REs in corn root and stem was observed, but it could not be detected in corn leaf under the dosage of 20 mg REs kg(-1) soil (oven-dry mass). The non-observed effect concentration (NOEC) for accumulation of REs in corn seedling with the pot experiment was 1.0 mg REs kg(-1). In the plot experiment, the dose-dependent accumulation was observed at an early stage after application of REs and the NOEC value of 32 mg REs m(-2) was obtained. At harvest, no dose-dependent accumulation of REs was observed in any part of the corn. These results can be confirmed by the fingerprinting analysis based on the differences between La to RE ratios in the REs mixture and in pot or plot soil. We observed that the plant shows no preference on individual RE and the results of fingerprinting indicated clearly the incorporation of exogenous REs in plant tissues, in a similar manner as that observed in the dose-dependent distribution of RE concentrations. The results indicated also a translocation process of REs from plant root to leaf when applied to soil or from leaf to root when applied to leaf. A homeostatic regulation mechanism for excessive uptake of REs in plants is suggested to regulate the concentrations of REs in the plant.