Toxicity assay of lanthanum and cerium in solutions and soil.

Lanthanum (La) and cerium (Ce) are one of the most abundant rare earth elements (REEs). In spite of quite extensive studying of the effects of these lanthanides on biota, some contradictions remain in the results. Also little is known about the effect of lanthanum and cerium on plant cells and their mitotic cycle, especially in soils. In this study, the effects of La and Ce in solutions and soil samples on root growth, mitotic index (MI) and frequency of aberrant cells (FAC) were assayed using one of the most convenient objects for testing of cytotoxicity - onion Allium cepa L. Bulbs were germinated on media containing La and Ce in concentrations 0-200 mg/l and 0-50 mg/l respectively for solutions and 0-200 mg/kg for soil samples. After 5 days of germination in solutions, a significant decrease in root elongation and MI in apical meristem cells are shown. We have also observed an increase in the number of cells with aberrations at 50 mg/l La and Ce concentration. The number of observed stickiness and disturbed metaphase has increased significantly. Soil samples turned out to be less toxic compared to the solutions probably due to the decreased availability of REEs. In spite of this, significant cytotoxicity of soil samples containing the highest concentration of La and Ce (200 mg/kg) is observed. The latter may indicate the importance of considering the cytotoxicity of soils containing high lanthanides concentrations - in extraction and production areas and actively fertilized fields.