Chromium (Cr) is one of the most and important trace metals which can be present in two oxidation states: toxic Cr (Ⅵ) and non-toxic Cr (Ⅲ).Cr (Ⅲ) is an important microelement for plant and animal nutrition and essential for the maintenance of glucose as well as for the lipid and protein metabolism.With regard to human health, Cr (Ⅲ) is a required nutrient, with 50-200 μg per day recommended for adults.