Soil selenium fractionation, depth profiles and time trends in a vegetated site at Kesterson Reservoir

Land disposal of San Luis drain sediments: Progress Report October 1998 through November 2000

“…A sequential extraction procedure was developed from previous techniques used for Se fractionation and speciation (Weres et al, 1989a,b;Velinsky and Cutter, 1990;Lipton, 1991;Tokunaga et al, 1991). Table 5.1 contains the sequence of extractions and the target species each extraction is designed to remove.…”

“…Sequential, or selective extraction techniques are commonly used for Se fractionation (Weres et al, 1989a;Lipton, 1991;Tokunaga et al, 1991), but provide only an approximation of the distribution of Se (or any other element) among species. This is due to the inability of wet extraction procedures to objectively discriminate amongst Se species without affecting the redox status, pH, and physical state of the sediment sample, which can in turn cause changes in Se speciation (Tokunaga et al, 1994).…”

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

“…Methodology to determine Se speciation in soils has been explored intensively either using various single step soil extractions (Yamada and Hattori, 1989;Abrams et al, 1990a;Kang et al, 1991b;Gustafsson and Johnsson, 1992;Johnsson, 1992;Gustafsson and Johnsson, 1994;Alam et al, 2000;Keskinen et al, 2009;Tolu et al, 2011;Qin et al, 2012;Stroud et al, 2012) or sequential soil extractions (Chao General introduction and Sanzolone, 1989;Tokunaga et al, 1991;MacLeod et al, 1998;Mao and Xing, 1999;Wang and Chen, 2003;Hagarová et al, 2005). In general, these soil extractions represent different Se pools or Se fractions present in soils that are removed by the corresponding extractants, such as soluble Se, exchangeable Se, Se adsorbed to metal-(hydr)oxides or carbonates, and Se bound to organic matter or humic compounds, instead of specific Se species (Tokunaga et al, 1991).…”

“…In general, these soil extractions represent different Se pools or Se fractions present in soils that are removed by the corresponding extractants, such as soluble Se, exchangeable Se, Se adsorbed to metal-(hydr)oxides or carbonates, and Se bound to organic matter or humic compounds, instead of specific Se species (Tokunaga et al, 1991). In comparison with single step soil extractions, the sequential soil extractions seem inappropriate for low Se soils and increase the risk of Se contamination, loss and Se species redistribution (Tolu et al, 2011).…”

“…Sequential extraction schemes fractionate Se into e.g. soluble Se, exchangeable Se, Se adsorbed to (hydr)oxides or carbonates, and Se bound to organic matter or humic compounds (Chao and Sanzolone, 1989;Tokunaga et al, 1991;MacLeod et al, 1998;Mao and Xing, 1999;Wang and Chen, 2003;Hagarová et al, 2005). Single step extractions using (hot) water, mild salt solution or mild phosphate solution has been proposed to estimate soluble Se in soils (Yamada and Hattori, 1989;Johnsson, 1992;Keskinen et al, 2009;Tolu et al, 2011;Stroud et al, 2012), whereas extractions using phosphate buffers and ammonium oxalate have been used to determine exchangeable Se (Alam et al, 2000;Keskinen et al, 2009;Tolu et al, 2011) and Se adsorbed to metal oxides (Keskinen et al, 2009), respectively.…”