| Abstract | | Selenium (Se) is a trace element that is both an essential nutrient for humans and animals and an environmental toxicant; the boundary between the two roles is narrow and depends on its chemical form, concentration, and other environmentally influenced variables. Se is important in the metabolism of cyanobacteria and some plants, being involved in their antioxidative processes. The essentiality of Se to higher plants, however, is still under debate. Although it is harmful for plants in high concentrations, it can exert beneficial effects at low concentrations. It can increase the tolerance of plants to UV-induced oxidative stress, delay senescence, and promote the growth of ageing seedlings. Recently it has been shown that Se is able to regulate the water status of plants under conditions of drought. It is widely distributed on the Earth's surface and available for plants in at least small traces. Cultivation of plants enriched with Se could be an effective way of producing Se-rich foodstuffs which can be beneficial to health. Se is also a major contaminant in the effluents from some oil refineries, power plants, and in mine drainage water. Se has become the primary element of concern in much environmental contamination because of its bioaccumularion in food webs. Bioaccumulation of Se is leading to toxic impact and changes in communities. However, it is possible to remove it from soils and Se-contaminated agricultural drainage water using plants in a phytoremediation process.
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