title: Selenium speciation and extractability in Dutch agricultural soils.
abstract: The study aimed to understand selenium (Se) speciation and extractability in Dutch agricultural soils. Top soil samples were taken from 42 grassland fields and 41 arable land fields in the Netherlands. Total Se contents measured in aqua regia were between 0.12 and 1.97 mg kg(-1) (on average 0.58 mg kg(-1)). Organic Se after NaOCl oxidation-extraction accounted for on average 82% of total Se, whereas inorganic selenite (selenate was not measurable) measured in ammonium oxalate extraction using HPLC-ICP-MS accounted for on average 5% of total Se. The predominance of organic Se in the soils is supported by the positive correlations between total Se (aqua regia) and total soil organic matter content, and Se and organic C content in all the other extractions performed in this study. The amount of Se extracted followed the order of aqua regia > 1 M NaOCl (pH8) > 0.1 M NaOH>ammonium oxalate (pH3) > hot water>0.43 M HNO3 > 0.01 M CaCl2. None of these extractions selectively extracts only inorganic Se, and relative to other extractions 0.43 M HNO3 extraction contains the lowest fraction of organic Se, followed by ammonium oxalate extraction. In the 0.1M NaOH extraction, the hydrophobic neutral (HON) fraction of soil organic matter is richer in Se than in the hydrophilic (Hy) and humic acid (HA) fractions. The organic matter extracted in 0.01 M CaCl2 and hot water is in general richer in Se compared to the organic matter extracted in 0.1M NaOH, and other extractions (HNO3, ammonium oxalate, NaOCl, and aqua regia). Although the extractability of Se follows to a large extent the extractability of soil organic carbon, there is several time variations in the Se to organic C ratios, reflecting the changes in composition of organic matter extracted.
authors.affiliation: Department of Soil Quality, Wageningen University, PO Box 47, 6700 AA Wageningen, the Netherlands.
authors.forename: Supriatin
authors.initials: S
authors.lastname: Supriatin
authors.affiliation: Department of Soil Quality, Wageningen University, PO Box 47, 6700 AA Wageningen, the Netherlands. Electronic address: liping.weng@wur.nl.
authors.forename: Liping
authors.initials: L
authors.lastname: Weng
authors.affiliation: Department of Soil Quality, Wageningen University, PO Box 47, 6700 AA Wageningen, the Netherlands.
authors.forename: Rob N J
authors.initials: RN
authors.lastname: Comans
mesh_terms: D000383:Agriculture; D004784:Environmental Monitoring; D009426:Netherlands; D012643:Selenium / Q000032:analysis*; D012987:Soil / Q000737:chemistry*; D012989:Soil Pollutants / Q000032:analysis*
chemical_list: D012987:Soil; D012989:Soil Pollutants; D012643:Selenium
keywords: Agricultural soils; Organic carbon; Selenium; Soil extraction; Speciation