Selenium Phytoaccumulation by Sunflower Plants under Hydroponic Conditions

Selenium is an essential trace element for many organisms, including humans, but it is bioaccumulative and toxic at higher than homeostatic levels. Both selenium deficiency and toxicity are problems around the world. Mines, coal-fired power plants, oil refineries, and agriculture are important examples of anthropogenic sources, generating contaminated waters, and wastewaters. For reasons of human health and ecotoxicity, selenium concentration has to be controlled in drinking-water and in wastewater, as it is a potential pollutant of water bodies. In this regard, in the present study, the ability of sunflower (Helianthus annuus L.) to tolerate and accumulate selenium was assessed in hydroponic culture as a model of rhizofiltration system. Selenium content and the chlorophyll parameters of sunflower plant treated using different concentrations of selenium in two forms of sodium selenite and sodium selenate were measured to clarify (1) the response of sunflower to selenium tolerance capacity and (2) the relationship between selenium, chlorophyll fluorescence parameters, and photosynthetic pigments contents. The results showed that selenium content in sunflower plants significantly increased by increasing added selenium levels. Furthermore, Chl a and b were not impaired after 3 weeks from selenium exposure up to 3 mg L-1 for both selenite and selenate. Moreover, sunflower plants have a high selenium tolerance capacity for hydroponic clean-up. Translocation of selenate from sunflower roots to shoots was easier comparing with selenite in concept of phytoremediation processes.