Data on the biological effects of REEs are scarce and contradictory. There are no
indications that REEs are essential to humans and animals. For plants, no data concerning essentiality are available either. It has been suggested that REEs may increase the yield of crop plants. However, the reported effects of application of REEs as fertilizers ranged from stimulation to no role in increasing agricultural plant production up to reduction of growth, apparently as a function of concentration, speciation and bioavailability.