Selenium cycle

Hypothetical problem for chemists consider the global cycle of selenium which has many chemical similarities to sulfur. Construct a box diagram for the global selenium cycle based on known similarities and differences of Se and S. 

Flueck, W.T. and J.M. Smith-Flueck. 1990. Selenium deficiency in deer the effect of a declining selenium cycle Trans. 19th Inter. Union Game Biol., Trondheim, Norway 1989 292-309. 

Zawislanski PT, McGrath AE (1998) Selenium cycling in estuarine wetlands overview and new results from the San Francisco Bay. In Environmental Chemistry of Selenium. Frankenberger Jr. WT, Engberg RA (eds), Marcel Dekker, New York, p 223-242... 

Schindler, J.E., D.J. Williams, and A.P. Zimmerman. 1976. Investigation of extracellular electron transport by humic acids. In J.O. Nriagu, ed., Environmental Biogeochemistry, Vol. 1. Carbon, Nitrogen, Phosphorus, Sulfur, and Selenium Cycles, pp. 109-115, Ann Arbor Science Ann Arbor. 

Nissenbaum A. and Kaplan I. R. (1976) Sulfur and carbon isotopic evidence for biogeochemical processes in the Dead Sea ecosystem. In Environmental Biogeochemistry Carbon, Nitrogen, Phosphorus, Sulfur and Selenium Cycles (ed. J. O. Nriagu). Ann Arbor Sci. Publ, Ann Arbor, vol. 1, pp. 309-325. 

Typical concentrations of selenium in seawater are —0.1-0.2 p,g (Table 9) with an estimated mean residence time of 70 yr in the mixed layer and 1,100 yr in the deep ocean. The oceans are, therefore, an important sink for selenium (Haygarth, 1994 Jacobs, 1989). Biogenic volatilization of selenium from seawater to the atmosphere is estimated to be 5,000-8,0001 yr. Amouroux et al. (2001) have demonstrated that biotransformation of dissolved selenium in seawater by blooms of phytoplankton in the spring is a major pathway for the emission of gaseous selenium to the atmosphere. Hence, oceans are an important part of the selenium cycle. 

A biogeochemical cycle results from the integration of several biological, chemical and, in many cases, physical processes. In this section, we discuss the nitrogen cycle to illustrate the ways in which organisms cooperate to effect the cyclic turnover of an element, and the selenium cycle to demonstrate the interaction between the biosphere and geosphere. 

Biological reactions involved in the selenium cycle (Silverman and Ehrlich, 1964 Shrift, 1964, 1973 Martin, 1973)... 

It has been suggested that a biological cycle exists for selenium (Shrift 1964), but certain components of the cycle remain uncharacterized. The biological transformation of selenide to elemental selenium has not been well described in the literature (see Maier et al. 1988). Further research on the biological selenium cycle might help to identify "hot spots" of selenium in the environment. For example, further investigation of parameters that influence the tendency of selenium to move from one medium to another (e.g., from soil to water) would improve fate and transport modeling efforts. 

Chapter 8.22). Dietary studies showed that molybdenum was an essential element for the normal growth and health of humans, animals, plants, and microorganisms. The first confirmation of the presence of molybdenum within an enzyme came in 1953 when dietary studies and atomic spectroscopy revealed its presence in hepatic and lactic xanthine oxidase." Since then, extensive investigations have shown that molybdenum is an integral component of the active site of a large number (>40) of enzymes that catalyze important reactions in the carbon, nitrogen, sulfur, and selenium cycles of the biosphere. " ... 

Masscheleyn, P. H. and W. H. Patrick, Jr. 1993. Biogeochemical processes affecting selenium cycling in wetlands. Environ. Toxicol. Chem. 12 2235-2243. 

Winkel LHE, Vriens B, Jones GD, Schneider LS, PUon-Smits E, Banuelos GS (2015) Selenium cycling across soU-plant-atmosphere interfaces a critical review. Nutrients 7 4199-4239. doi 10.3390/nu7064199... 

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