ABSTRACT
Before the middle of this century, the public perception of selenium was similar to the present-day view of arsenic. That is, selenium was regarded as highly toxic (Moxon and Rhian, 1943) and carcinogenic (Nelson et ah, 1943). The first report to note any nutritional benefit from selenium described the prevention of liver necrosis in rats when selenium was included in the diet (Schwarz and Foltz, 1957). Since then, many beneficial aspects of selenium to animal metabolism have been catalogued, among them improved animal husbandry (Ullrey, 1978), and a negative correlation has been found for some forms of cancer in humans (Jansson, 1980). Selenium appears nowadays as a supplement in many vitamin preparations. The late recognition of the importance of selenium in metabolism arises from its low abundance and the narrow range of concentration between beneficial and toxic effects. Selenium is ranked 69th in abundance in the earth’s crust, with an average concentration of 0.09 mg/kg, and 29th in seawater at 0.004 mg/kg (Weast, 1969). Concentrations of the order of hundreds of milli grams per kilogram have however been found in some shales and accumulator plants (Mayland et al., 1989). Toxic effects in animals become apparent with diets containing above 5 to 15 mg/kg Se and deficiencies with diets containing below 0.05 to 0.10 mg/kg.
