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Lanthanide emissions to the environment increase as a result of the growing industrial applications of these elements. However, robust data to evaluate the environmental fate of lanthanides are scarce. This article describes the accumulation and elimination of lanthanum (La) by common duckweed (Lemna minor L.). Speciation modeling was performed to assure that solubility products were not exceeded. It also showed that La was predominantly associated with ethylenediaminetetraacetic acid (EDTA). Lanthanum concentrations in plants and medium and the amounts sorbed to glass vessels were quantified by using the radioisotope 140La. The amount of La adsorbed on the glass reached values of 25% of the total La present. A model was formulated to describe La uptake in exponentially growing duckweed in the presence of an adsorptive surface. Growth-induced dilution appeared more efficient in lowering plant La concentrations than actual elimination. An elimination study revealed two compartments, of which the smallest eliminated 50 times faster than the bigger compartment, which eliminated mainly by growth dilution. The average bioconcentration factor was 2,000 L/kg fresh weight and 30,000 L/kg dry weight, comparable with those of other higher plants. At the applied concentration of 10 nM, no effects were observed on duckweed growth. However, the high bioconcentration factor warrants monitoring of lanthanide emissions.