Geochemistry and occurrence of selenium: An overview

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Abstract

Selenium (Se) is both beneficial and toxic to animals, plants, and humans. Consequently, it is imperative to know its concentration in the environment and to understand the processes controlling its distribution. Determinations of Se concentrations in a variety of materials indicate that Se is widely distributed throughout the environment. The processes responsible for its distribution include volcanic activity, the burning of fossil fuels, the weathering of rocks and soils, groundwater transport, precipitation of minerals, adsorption, chemical or bacterial reduction and oxidation, and metabolic uptake and release by plants and animals. The importance of a particular process in controlling the distribution of Se is intimately linked to the speciation of Se, which is controlled by the pH and redox conditions of the environment. Selenium can exist as selenide (Se2−), elemental Se (Se0), selenite (SeO2−3), and selenate (SeO2−4). Each oxidation state exhibits different chemical behavior. Selenide and elemental Se occur in acidic, reducing, and organic-rich environments. Metal selenides, Se-sulfides, and elemental Se are insoluble, and therefore biologically unavailable. For the pH and redox conditions of most soil and aquatic environments, SeO2−3 and SeO2−4; should be the dominant forms of Se. Selenite is immobilized by adsorption onto particles, particularly Fe oxyhydroxides. Selenate is highly mobile and biologically available because of the solubility of its salts and its weak adsorption by particles. Microbial action can change the speciation of Se through oxidation or reduction, or through the formation of organic Se compounds.

Additional publication details

Publication type Book chapter
Publication Subtype Book Chapter
Title Geochemistry and occurrence of selenium: An overview
DOI 10.2136/sssaspecpub23.c1
Year Published 1989
Language English
Publisher ACSESS
Contributing office(s) Crustal Geophysics and Geochemistry Science Center
Description 13 p.
Larger Work Type Book
Larger Work Subtype Monograph
Larger Work Title Selenium in agriculture and the environment
First page 1
Last page 13