Selenium Speciation in the Environment

WUILLOUD, RODOLFO G.; BERTON, PAULA

Speciation Studies in Soil, Sediment and Environmental Samples

Science Publishers/CRC Press/Taylor & Francis Group

Año: 2013; p. 263 - 305

Selenium (Se) and its several species have been demonstrated to be essential for living organisms, including animals and humans. This element is required to obtain the biologically active selenol group (-SeH), which is a precursor of glutathione peroxidase, thioredoxin reductase and other seleno-containing enzymes involved in oxidative stress response. Even though plants represent the main source of this element for animal diets, it is not essential for them. Since confirmation of the essentiality of Se, evaluation of its nutritional status is a crucial task to establish the right doses avoiding deficiency-linked diseases and promoting good health conditions. However, Se has a narrow interval between toxicity and essentiality, which is puzzling toxicologists and alarming nutritionists and legislators. Different diseases can be caused by its deficiency, but it can be toxic from levels one order of magnitude higher than that required for good health. Thus, daily consumption of food containing less than 0.1 mg/kg of body weight will result in Se deficiency, whereas dietary levels above 1 mg/kg may lead to toxicity. Selenium occurs in the environment and biological materials under inorganic and organic chemical forms or species, so the role of analytical speciation is essential to fully understand how bioavailability and toxicity depend on its current species. As other living organisms, the human body accumulates Se: its level in human blood is around 200 ng/mL, which is many times higher concentration than that found in surface water. It is evident that Se can be accumulated in biological systems, with specific tissues as ending fate. Furthermore, Se levels in marine fish have been observed to be about 2 µg/g, which is around 50,000-fold higher concentration than that found in the surrounding environment of these animals. Most soils contain between 0.02 and 2.5 µg Se/g. The average crustal abundance of Se is 0.09 µg/g. Selenium concentrations range from 0.47 to 8.1 µg/g in coal and from 2.4 to 7.5 µg/g in fuel oil. Selenium dioxide (SeO2) is of high concern for industries due to potential emissions to atmosphere. The dioxide forms selenious acid with water or liquid media, and this acid is very irritant. Moreover, Se compounds released during coal or petroleum combustion might be a significant source of exposure. However, transformations and associations of Se introduced into the environment by these sources are strictly dependent on the physicochemical properties of Se species under which Se occurs. In this chapter, fundamental discussion regarding speciation studies of Se in environmental compartment is presented. Several aspects showing the crucial importance that Se speciation is having for different fields, such as toxicology and nutrition, are critically commented and discussed. A comprehensive summary of mostly-spread and useful state-of-the-art instrumental techniques and sample preparation methods to face the challenge raised by Se speciation analysis in environmental samples, mainly soil and water, is arbitrary organized and discussed.