ABSTRACT
The major route of selenium exposure in humans is through diet. High dietary intakes of selenium have caused toxicity in humans after consuming selenium-rich food grown in seleniferous areas. Selenium status in a population varies widely and tends to reflect selenium levels in the soils and the produce of the region. Environmental contamination from the release of selenium from agriculture and industrial activities has caused diseases and death for wildlife and aquatic animals. Selenium toxicity in humans is rare. However, when it occurs, the clinical symptoms are similar to those of animals. Hair loss and nail deformity are common symptoms 30of chronic selenium exposure in humans. Selenium levels in hair and toenails are widely used to assess a long-term selenium status and exposure in humans, whereas levels in blood and urine are used for assessing a short-term selenium status. The enzyme activity of GSHPx, a selenoenzyme, is also widely used for assessing selenium status and exposure. However, GSHPx is sensitive only for detecting selenium deficiency and not overexposure. Other selenoproteins, such as selenoprotein P, may also be useful biomarkers for assessing selenium exposure in humans. In animals, selenium toxicity (selenosis) is well documented, in particular in the livestock grazing in seleniferous areas. The severity of this selenosis depends on the selenium compounds, route of administration, and the nutritional and health status of the animals. The symptoms of chronic selenosis in animals include rough coat, loss of fur, and lameness. In severe cases of acute selenosis, the symptoms are characterized by loss of appetite, hoof damage, abnormal movement, respiratory failure, and blindness; death may follow. Even though the effects of selenium toxicity are well documented, the mechanisms of action are not fully understood. There is a need for further research in this area, and in particular the elucidation of specific molecular and genetic biomarkers of selenoproteins for exposure and biological response. Research on the identification and characterization of selenium metabolites and pathways would also be useful in order to understand their toxicity and detoxification process.
