Selenium in soil, plant, and animal systems

Selenium is a paradox because the essentiality of Se to animals ends at about 0.1 ppm, while toxicity may begin at < 1 ppm diet. Seen from the point of view of animal nutrition, selenium may occur in either toxic or deficient concentrations in fodder crops in different areas of the world. Highly seleniferous soils are the sources of potential Se intoxication for animals, while selenium‐deficient soils cause deficiency disorders in cattle. Though Se has not been proved essential for plants, its essentiality for animal nutrition is well known. This is the prime reason that makes Se studies in soil‐plant‐animal systems assume greater importance. Since the study is of practical significance, efforts have been made by the scientists all over the world to study the sources of selenium in soils, their movement and absorption by plants, and finally the health consequences in animals. A significant amount of literature on reducing the Se toxicity in animals was gathered in the past, but a keen perusal indicates that a lot of work still needs to be done with respect to Se in soil‐plant‐animal systems and its environmental impact.