[Selenium in human environment]

Selenium belongs to the group of elements which may be regarded as useful only in a very narrow range, while in excess doses they exert a harmful action. The content of the element in soil is usually from 0.1 to 2 mg/kg, with the Scandinavian soils have a low level of selenium, not exceeding 0.3 mg/kg. The highest level, exceeding 3000 mg/kg was noted in Northern Ireland. Selenium content in soil over 500 mg/kg produces chronic selenium intoxication in domestic animals. Selenium accumulation by plants is a selective process and depends on the chemical state of the element in soil and pH of soil. It is considered that the daily requirement for selenium is 50-300 mcg for adults, while the toxic dose is regarded as 5 mg daily. The toxic effects of selenium in the environment include inflammatory processes of the extremities in herbivorous animals (the so called Degnal disease in India and the Alkali disease in Great Britain). Selenium deficiency in the environment leads to the so called white muscle disease in these animals in Great Britain. Selenium is considered also to protect the organism in case of poisoning with lead, mercury or cadmium.