Hormetic dose responses induced by lanthanum in plants.

Rare earth elements (REEs) have recently received particular attention due to their accumulation in the environment. Such heightened recognition prompted our evaluation of the possible occurrence of La-induced plant hormesis in the peer-reviewed literature. This study revealed 703 La-induced hormetic concentration/dose responses in plants, which were quantitatively and qualitatively assessed. The maximum (MAX) biological response to low La concentrations/doses is commonly below 150% of control response, with a geometric mean of 142% at 56 μM (geometric mean). The geometric mean concentration of the no-observed-adverse-effect-level (NOAEL) was 249 μM. The MAX:NOAEL distance was commonly below 5-fold, with a geometric mean of 4.5-fold. Hormetic concentration/dose responses varied as per the growth substrate pH, number of concentrations/doses below the NOAEL, and time window. These results provide a unique insight into the effects of low doses of La on plant growth, as well as offer means for improving experimental designs to assess low dose effects.