Define briefly about the Selenium?
The element selenium was discovered in 1817 in association with the element sulphur. However, selenium as an essential nutrient remained unrecognized for many years, although selenium toxicity in horses and cattle, "blind staggers" and "alkali disease" was known since the 1930s. The first description of the dietary selenium deficiency in isolated populations in the People's Republic of China, was made in 1979. The disease known as Keshan disease, named for the country where it was first recognized, was characterized by cardiomyopathy affecting primarily children and young women. The disease was often fatal. The second selenium deficiency disease Kashin-Beck disease was reported in 1980. It was prevalent in China and Sino-Soviet border. Both the diseases were caused primarily due to selenium deficiency in the soil.
Selenium is a non metallic element and exists in several oxidation states which include Se2+, Se4+ and Se6+. The chemistry of selenium is similar to that of sulphur. Selenium replaces sulphur to form organic compounds such as selenocysteine and selenomethionine. Total selenium content of the body varies from 3-15 mg depending on the dietary intake. Approximately 30% of tissue selenium is contained in the liver, 15% in kidney, 30% in muscle and 10% in blood plasma. Much of tissue selenium is found in proteins as selenoanalogues of sulphur amino acids; other metabolically active forms include selenotrisulphides and other acid-labile selenium compounds.