Selenium Speciation of Soil/Sediment Determined with Sequential Extractions and Hydride Generation Atomic Absorption Spectrophotometry

Abstract

Understanding the speciation of the multioxidation states of selenium is vital to predicting the mineralization, mobilization, and toxicity of the trace element in natural systems. A sequential extraction scheme (SES) was developed for identification of Se oxidation states that first employed 0.1 M (pH 7.0) K 2 HPO 4 -KH 2 PO 4 (P-buffer) to release soluble selenate (Se +VI ) and selenide (Se -II ) and ligandexchangeable selenite (Se +IV ). The second step involved oxidation of organic materials with 0.1 M K 2 S 2 O 8 (90°C) to release Se -II and Se +IV associated or occluded with organic matter. The final step used HNO 3 (90°C) to solubilize insoluble Se remaining in the sample. The solubilized Se compounds were speciated by a selective hydride generation atomic absorption spectrophotometry technique. Accuracy of the developed SES method (96-103% recovery) was verified by use of prepared Se compounds of known speciation, NIST standard reference materials, and existing seleniferous soils. The average precision (relative standard deviation) for the P-buffer extraction ranged from 5.5 to 7.7% (n ) 12); the precision of the persulfate extraction ranged from 2.6 to 8.4% (n ) 12); and the precision of the nitric acid extraction ranged from 2.8 to 7.4% (n ) 12) for three soils extracted at four different time periods.The method was applied to analyze Se species in seleniferous plant, soil, and sediment samples.

Selenium behavior in the soil environment and its implication for human health

“…In this context, Se forms may affect Se mobility. Thus, studies evaluating the speciation of Se have received attention in the literature (Martens and Suarez, 1997;Li et al, 2010). In this context, after the advent of synchrotron facilities, one easy way currently available to measure oxidation states of different elements (e.g., As, Fe, Mn, Cr, and others), including Se, is using the technique termed as X-ray Absorption Spectroscopy (XAS).…”

Determining the fate of selenium in wheat biofortification: an isotopically labelled field trial study

“…Soil texture was determined by laser granulometry following initial treatment with 40% H 2 O 2 and dispersion in 25 mL Calgon™ solution (3.5% sodium hexametaphosphate and 0.7% sodium carbonate). Following the study of Konert and Vandenberghe (1997) Zhao and McGrath (1994) for sulphate extraction, which was later adapted by Martens and Suarez (1997) for Se extraction. The extractable soil Se was solubilised by suspending 3.0 g (± 0.3 g) of air-dried <2 mm sieved soil in 9 mL 0.016 M KH 2 PO 4 in 50 mL polypropylene centrifuge tubes and shaking end-over-end for 1 h at 27 rpm.…”

Selenium in agriculture, food, and nutrition

“…Extraction of soils and sediments with neutral phosphate or citrate/phosphate buffer solutions yields an exchangeable fraction, which can be investigated for further speciation in solution [54][55][56][57][58]. After removal of solubles and exchangeables, oxalate pH 3 selectively extracts selenite bound to iron hydroxides, which is the main fraction in acid soils.…”