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Objectives of this series

Pure selenium in the periodic table of my faculty

Selenium is a quite unknown element. I have learn a lot about it during my end of degree work, named "Selenium and its species analysis" for which I analysed several fishes of high human consumption. I am trying to explain myself as clear as possible for everybody, if there are still some remaining questions feel free to ask.

Depending of the support I receive I will continue this series with more or less posts.

Properties

Selenium is an element (atom) in the non-metal area within the periodic table. It has 34 protons, and his chemical properties are very similar to sulphur, because the external electronic layer is very similar.

Image source

As most elements, selenium is compounded of several isotopes, that means that their atoms have different amount of neutrons. Isotopes are usually mixed in the same proportion worldwide, and the only effective difference between them is that some of them fall liberating radiation and others are stable.

Selenium has 9 isotopes, 5 of them stable and 4 radioactive. The most abundant isotopes are 80, with 50% abundance, and 78, with 24% abundance, both are stable. Radioactivity emitted by selenium is usually minimal so it can be considered as completely safe in that aspect. The radioactive isotope 75, because it is not present in natural samples and has an adequate fall time, can be applied as marker in several medic, biologic and environmental studies [1]

Image source: [1]

Selenium is an essential element for animals, including humans. It is part of proteins, and when it is present in optimal amounts it reduces the risk of heart diseases and some types of cancer, among other benefits. In the next chapters, selenium influence in health will be further explained.

Abundance

Selenium is the 30th more abundant element in Earth´s crust[2]. However it is rarely found pure in nature. Most of selenium is present in soil, mixed in a low concentration in sulphur minerals like pyrite. That is because the similar properties of selenium and sulphur, as stated earlier.

In soil, it is usually found as selenate (SeO4-2) and selenite (SeO3-2) Which of the two species will be present mainly depends of two factors: soil acidity and airing.

In air it is present as selenium hydride (H2Se). This element is rarely found as gas. Gas emissions are caused by fossil fuel burning, specially for those fuels with high amount of sulphur, metal refining from sulphide emtal ores and volcano activity.

In next chapters

• Selenium effects to health and optimal intake
• Food with selenium
• How selenium in food is analyzed
• Selenium amount in fish
• Conclusiones

Thanks for your attention. I will be glad to explain any question about this topic.

Bibliography

[1]Fernández-Martínez, A., & Charlet, L. (2009). Selenium environmental cycling and
bioavailability: A structural chemist point of view. Reviews in Environmental Science
and Biotechnology, 8(1), 81–110. https://doi.org/10.1007/s11157-009-9145-3

[2]Jagtap, R., Maher, W., Pedrero, Z., Madrid, Y., Thiry, C., Ruttens, A., … Cámara, C. (2005).
Quantification and speciation of mercury and selenium in fish samples of high
consumption in Spain and Portugal. Biological Trace Element Research, 103(1), 17–35.
https://doi.org/017