Selenium Lab Report

Selenium, found in group 16 of the periodic table, follows a cycle in the environment as it transfers between the biosphere, atmosphere and hydrosphere. It is also an essential element for humans and animals. It can cause both deficiencies and toxic effects if not taken in the correct quantities. This essay outlines the general features and behaviour of Se in the primary environment, its general abundance and its ability to substitute into minerals. Its Eh and pH also are important factors in determining the form which the Se takes, altering its mobility. This essay also covers the transition of selenium between mediums as it cycles through the environment. Once released through the effects of weathering or erosion, it enters the secondary environment where it interacts with plants animals and humans. Its bioavailability is important to determine the rate at which it can be removed from soils and water. This and its overall abundance in any given area can cause deficiency or toxicity.
1 Primary
1.1 Elemental state and properties Selenium has a proton number of 34 and mass number of 78.96, lying between As
In general, igneous rocks are low in selenium; volcanic igneous rocks are somewhat higher in Se content than other igneous rocks. Sedimentary rocks generally are higher in Se content than igenous rocks. Table *** shows an uneven balance of Se across the globe. Countries such as China, India and Sri Lanka have areas of Se deficiency. Selenium deficiency can also be caused by the conditions present rather than the total Se content. A number of techniques are availble to determine the bioavailability of Se in soils. The most commone is the water-soluble concentration. (Fordyce et al., 2000; Jacobs, 1989; Tan 1989). Typically, between 0.3% and 7% of the Se present is in a dissolved form and therefore bioavailble (Lollar,