United States animal species selection

Qelenium in concentrations of 4 ppm or more in the diet is toxic to animals. Certain soils in the western plains of the United States were found in the 1930 s to produce vegetation, including wheat, that was toxic to animals because of the selenium content of the crops. Certain species of plants were discovered by Death and others (1) that selectively accumulated selenium reaching a selenium content as high as 0.9% of the dry weight of the plant. These accumulator plants are exceedingly poisonous to livestock. 

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