Adsorption of selenium by amorphous iron oxyhydroxide and manganese dioxide

Chemical fractionation of soil boron: I. Method development

“…The examination of the fractionation scheme on a series of Ontario soils will be discussed in a following paper (Evans et al 1996). Some preliminary results on these soils have been presented previously (Hou et al 1994 Boron associated with Mn oxides (Rhoades et al 1970) was not considered in our proposed scheme because Mn oxides have a point ofnet zero proton charge less than 1.5 (Balistrieri and Chao 1990) For personal use only. Between each successive extraction, the reiidue was washed with 8 mL of water and the solution was discarded after centrifugation.…”

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

“…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

“…An oxidizing condition can firstly prevent reduction of Se to form insoluble elemental Se or selenides, or incorporation of Se into organic matter, and secondly an oxidizing condition favours mineralization of soil organic matter, releasing bioavailable organic and inorganic Se. In relation to soil mineralogy and organic matter content, the bioavailability of Se is in general decreased with an increase of clay content, organic matter content (Bisbjerg and Gissel-Nielsen, 1969;Gissel-Nielsen, 1971;Yläranta, 1983;Johnsson, 1991) and Fe-(hydr)oxide content, due to adsorption or Chapter 1 14 immobilization of Se by those soil minerals and organic matter Hamdy and Gissel-Nielsen, 1977;Balistrieri and Chao, 1990;Gustafsson and Johnsson, 1992). In any case, it can be expected that the amount of soluble selenomethionine, selenocystine and other possible bioavailable organic Se species is influenced by factors affecting soil organic matter mineralization, such as pH and soil moisture.…”

“…Previous studies have shown that uptake of Se from selenate or selenite fertilizer added to soils by plants grown under controlled conditions (pot experiments) decreased with an increase of soil organic matter content and clay content (Bisbjerg and Gissel-Nielsen, 1969;Gissel-Nielsen, 1971;Yläranta, 1983;Johnsson, 1991), which was attributed to Se fixation or immobilization by soil organic matter and clay Hamdy and Gissel-Nielsen, 1977;Gustafsson and Johnsson, 1992). The solubility and availability of Se in soils can also be lowered due to Se (mainly selenite) adsorption on Fe-(hydr)oxide surfaces Balistrieri and Chao, 1990). However, the nature of Se fixation by soil organic matter is different from that by phyllosilicate clays and Fe-(hydr)oxides (Gissel-Nielsen et al, 1984;Mikkelsen et al, 1989), and more recent studies suggested that soil organic matter has a greater fixation capacity for Se than clay and Fe-(hydr)oxide minerals (Coppin et al, 2009).…”

“…However, the nature of Se fixation by soil organic matter is different from that by phyllosilicate clays and Fe-(hydr)oxides (Gissel-Nielsen et al, 1984;Mikkelsen et al, 1989), and more recent studies suggested that soil organic matter has a greater fixation capacity for Se than clay and Fe-(hydr)oxide minerals (Coppin et al, 2009). Selenium fixation by clays and Fe-(hydr)oxides is mainly attributed to adsorption via anion exchange, forming outer-sphere complexes, or via ligand exchange, forming inner-sphere complexes (Balistrieri and Chao, 1990), whereas the mechanism of Se fixation in soil organic matter is still unclear. Selenium can be fixed in soil organic matter via either adsorption to Fe-(hydr)oxide surfaces present in soil organic matter (Coppin et al, 2009) or via Se reduction by soil microorganisms and further incorporation into soil organic matter structure (Gustafsson and Johnsson, 1994).…”