Selenium (Se) is an essential micronutrient for humans and animals, with a narrow range between its nutrient requirement and its toxicity (Rayman 2000). Selenium consumption for humans is supplied mainly by the food chain. In soil, Se exists mainly in four valence states: 2−, 0, 4+, and 6+). Selenate https://www.w3.org/1998/Math/MathML"> ( SeO 4 2 − ) https://s3-euw1-ap-pe-df-pch-content-public-u.s3.eu-west-1.amazonaws.com/9780429423482/fb4dd114-ce13-4e5c-aae2-028ecb69317b/content/eq3.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/> and selenite https://www.w3.org/1998/Math/MathML"> ( SeO 3 2 − ) https://s3-euw1-ap-pe-df-pch-content-public-u.s3.eu-west-1.amazonaws.com/9780429423482/fb4dd114-ce13-4e5c-aae2-028ecb69317b/content/eq4.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/> are highly soluble and Se4+is mainly adsorbed to charged surfaces of clay minerals, whereas elemental Se (Se0) and selenide (Se2−) are poorly mobile, and are represented as stable and insoluble forms (Hartikainen 2005).