It is known that rare earth elements (REEs) comprise a homogenous group of elements in the periodic system. They include the elements scandium (Sc), yttrium (Y) and 15 lanthanides with successive atomic numbers from 57 to 71. In fact, the term rare earth elements is misleading because these elements are not rare. The abundances of cerium (average concentration in the Earth s crust 60 mg kg-1), lanthanum (average 30 mg kg-1), and neodymium (average 28 mg kg-1) are similar to those of copper (average 55 mg kg-1), lead, tin and cobalt. Data on the biological effects of REEs are scarce and...