Tầm quan trọng sinh học của selenium chủ yếu là liên quan đến ba yếu tố: đó là một yếu tố thiết yếu trong động vật và có thể, chuyển hóa thực vật, trong nhiều khu vực địa lý, số lượng có sẵn là không đủ để đáp ứng yêu cầu động vật, trong một số lĩnh vực, hiện diện ở nồng độ cao như vậy trong đất, nước, nhà máy, tro, và bình phun rằng đó là độc hại cho động vật. Ở người và động vật, selen có thể hoặc mang lại lợi ích, trong một số trường. | CHAPTER 9 Selenium Contamination in Soil Sorption and Desorption Processes B. Pezzarossa and G. Petruzzelli BIOLOGICAL IMPORTANCE OF SELENIUM The biological importance of selenium is mainly linked to three factors it is an essential element in animal and probably vegetable metabolisms in many geographical areas the available quantity is insufficient to satisfy animal requirements in some areas it is present in such high concentrations in soil water plant ash and aerosol that it is toxic for animals. In humans and animals selenium can be either beneficial in some cases essential Underwood 1977 or toxic Yang et al. 1983 depending on its concentration. Its importance in human nutrition is now accepted. Selenium which acts as a metal co-factor of the enzyme glutathione peroxidase inducing the reduction of lipid hydroperoxides and hydrogen peroxide has been identified in human serum urine blood and scalp hair. Moreover there is experimental evidence for its anticarcinogenicity Chortyk et al. 1984 and for its effects in the neutralization of the toxicity of heavy metals Vokal-Borek 1979 . In order to prevent Se-deficiency which reduces growth productivity and reproduction dietary intake should be in the range of to mg Se kg-1 but Se toxicity may appear when dietary levels exceed 5 to 15 mg Se kg-1. Major sources of Se toxicity are inhalation or dermal contact uncontrolled self-medication and high levels of dietary intake mostly associated with people farming over seleniferous soils. Loss of hair and nails following nausea and diarrhea are common symptoms of Se toxicity Mayland 1994 . Plants do not require Se but absorb it from soil solution and recycle it to ingesting animals. Selenium is taken up by plants and incorporated into amino acids and proteins Shrift 1973 . The levels of accumulation in plants depend on the amount of available selenium the pH value salinity and CaCO3 content of the soil and on plant species. 191 2001 by CRC Press LLC 192 HEAVY METALS .
