Selenium environmental cycling and bioavailability: a structural chemist point of view

Abstract

International audienceSelenium is usually known as the ‘double-edged sword element' for its dual toxic and beneficial character to health. Since the pioneer works by Schwarz and Foltz on the relationships between selenium deficiency and liver, muscle and heart diseases, many efforts have been undertaken to better understand the role of selenium in health. At the same time, an increasing number of publications have appeared during these last years on the selenium physico–chemical interactions within the environment. Both types of research represent ongoing efforts to correctly estimate the bioavailability of selenium species for health and the environment. Redox reactions, diffusion, adsorption and precipitation processes or interactions with organic matter and biota govern the speciation and mobility of selenium in the environment. This review intends to emphasize and collect the important advances made during these last years in the mechanistic understanding of processes which govern selenium cycling and bioavailability, like adsorption at the mineral/water interface, precipitation of elemental selenium, or bioavailability of nanoscaled precipitates. The advent of powerful spectroscopic techniques, like X-ray absorption spectroscopy, has allowed the structural description of adsorption and substitution processes that selenium undergoes in a variety of minerals. These and other structural details about selenium precipitates are reviewed here, together with their relationships to the bioavailability of the element in the environment

Natural wetland emissions of methylated trace elements

“…Since no unmatched peaks occurred within 90 min in anion chromatography, other anionic species of Se, S or As were excluded as present in significant concentrations. The fraction of unidentified species is most likely explained by dissolved gaseous species or by (overall) neutral or cationic species (for example, complexes with organic matter, colloidal Se 33 , S or As 34 , or elemental Se, which is thermodynamically the most stable species in water at slightly acidic and redox neutral conditions 33 ). Although combined As-S or Se-S species have been observed in natural waters (for example, thio-arsenates in geothermal waters 35 , or DMSeS in marine waters 31 ), the absence of corresponding peaks for Se, S or As indicates that such species were not significantly present in the surface water samples.…”

“…The fact that trapped Se and S concentrations are positively correlated ( Supplementary Fig. 2), although S is volatilized to a much higher extent than Se on an absolute scale (on average up to a factor 335), might indicate that Se is volatilized by the same enzymatic system(s) as S due the chemical similarities between these elements 13,33 . For instance, thioether S-methyltransferase (EC 2.1.1.96) catalyses the methyl group transfer on DMSe and DMS with similar affinities (K m 1 and 0.4 mM, respectively) 36 .…”

Selenium mobilization in soils due to volcanic derived acid rain: An example from Mt Etna volcano, Sicily

“…The high concentrations of dissolved Al and Fe in the acid leachates indicate that some soil compounds containing Al, and to a lesser extent Fe, are unstable at low pH. In previous works, Fe oxides are recognized as the main carrier phase of Se in non-volcanic soils (Dhillon and Dhillon, 1999;Fernández-Martínez and Charlet, 2009). However, our results (Fig.…”

“…6-15 mg/kg in Hawaii compared to 0.4 mg/kg as worldwide average), but in contrast show low Se mobility (Byers et al, 1938;John et al, 1975;Nakamaru et al, 2005). This low mobility is believed to originate from adsorption on Fe and Al minerals (John et al, 1975;Nakamaru et al, 2005), which have been widely reported as potential adsorption phases for Se (Balistrieri and Chao, 1990;Dynes and Huang, 1997;Parida et al, 1997;Wijnja and Schulthess, 2000;Duc et al, 2003;Peak et al, 2006;Fernández-Martínez and Charlet, 2009). Although soils play a key role in determining the level in food and water and thereby human health, the knowledge about the processes affecting the Se mobility in volcanic soils is limited.…”

Selenium speciation and bioavailability in Dutch agricultural soils: the role of soil organic matter

“…This association is possibly due to either selenium-metal-organic matter complexation, such as Se-Fe(III)-organic matter complexes, or due to biotic formation via microbial reduction of Se and further incorporation into soil organic matter structure (Gustafsson and Johnsson, 1994;Fernández-Martínez and Charlet, 2009). Most studies indicated that the association relies more on biotic formation than on abiotic complexation (Fernández-Martínez and Charlet, 2009). …”