Plants seleniferous

Indicator plants generally have an offensive odor, which varies with the selenium concentration. Other vegetable matter grown on seleniferous soils may have a sufficiently high selenium content to be toxic when ingested by animals or humans. Apart from appearance in these seleniferous plants, selenium has been considered as a variable contaminant. Selenium is a necessary micronutrient in living organisms, needed by humans as well as animals (see Mineral NUTHiENTs). 

In livestock, selenium has been found to be the cause of blind staggers and alkali disease. Blind staggers occurs as a result of acute ingestion of seleniferous plants and is characterized by impaired vision, depressed appetite, a tendency to wander in circles, paralysis, and death from respiratory failure. A more chronic syndrome described in horses and livestock is alkali disease, which also is associated with consumption of grains or plants containing selenium. The disease is characterized by lack of vitality, loss of appetite, emaciation, deformed hoofs, loss of hair, erosion of the joints of long bones, anemia, cirrhosis, and cardiac atrophy ... 

Crookesite. In 1866 Baron Nils Adolf Erik Nordenskiold found among the collections at the Royal Museum in Sweden a rare mineral from Skrikerum, which C. G. Mosander had regarded as a copper selenide. When Baron Nordenskiold analyzed it, he found it to be a selenide of copper, silver, and thallium. Because it was the first mineral of which the recently discovered element thallium was shown to be an essential constituent, he named it crookesite in honor of Sir William Crookes, the discoverer of thallium (31). Although crookesite is very rare, selenium and thallium are often found associated in nature, and both of these elements, so different in chemical properties, were originally discovered in the same source, namely the slime in the lead chambers of sulfuric acid plants using seleniferous and thalliferous pyrite. 

The selenium content of a plant is dependent on the plant species and on whether it is grown in seleniferous or non-seleniferous soil. Generally, Se content in plants increases with the level of Se available and decreases with the sulphur supply. Se concen-... 

Although Se is not known to be required for the growth of plants, most assimilate it when grown on seleniferous soils, or in Se-containing... 

As Se is one of the few elements absorbed by plants in sufficient amounts that can be toxic to livestock, soils containing more than 0.5 mg Se kg are considered as seleniferous because the forages produced on such soils absorb Se more than the maximum permissible level suitable for animal consumption. Se binding onto soils and sediments depends upon the pH, Eh, Se species, competing anions, hydrous oxides of iron, and the type of clay minerals. Se in contaminated soils and water exists mainly as water-soluble selenate (SeO ) and selenite (SeOf ). 

Selenium is an essential element but is toxic when excessive quantities are ingested. Exposure of horses is usually through consumption of seleniferous (accumulator or indicator) plants (e.g.. Astragalus spp.). Exposure to high quantities of selenium over a short time causes diarrhea (which is often foul smelling and contains air bubbles), neurological and cardiovascular effects, and respiratory difficulty. Death in these horses is due to respiratory failure. Chronic exposure to low levels of excessive selenium is characterized by hoof abnormalities at the coronary bands and by discoloration and loss of hair. The hoof deformities are painful and cause lameness. 

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