Comparison of the spectroscopic speciation and chemical fractionation of chromium in contaminated paddy soils.
Sequential extraction has been widely used to classify metal species in soils and sediments; however, the lack of selectivity in extraction reagents may lead to the misinterpretation of metal speciation. In this study, we used X-ray absorption near edge structure (XANES) spectroscopy to classify Cr species based on its molecular form. These results complement the conventional Cr fractionation derived from the Tessier extraction method. The linear combination fitting (LCF) for the Cr-XANES spectra indicated that the Cr species in the soils could generally be described as Cr(III) sorbed on ferrihydrite (Cr-FH), Cr(III) complexed with humic acid (Cr-HA), and precipitated Cr. While the sum of the adsorbed Cr(III) and Cr(III)/Fe coprecipitates showed a nearly 1:1 relationship with reducible Cr, the total of Cr precipitates and organic Cr also followed the same trend with oxidizable Cr. This result indicated that there might be a underestimation in the reducible fraction as pure Cr(III) precipitates associated with surfaces of Fe minerals would not be extracted in the reducible process. Instead, such pure Cr(III) precipitates were dissolved during the oxidizable process, resulting in a overestimation in the fractionation of organic-related Cr.
Department of Soil and Environmental Sciences, National Chung Hsing University, 250 Kuo Kuang Rd., Taichung 40227, Taiwan, ROC.
Liang-Ching
LC
Hsu
Department of Soil and Environmental Sciences, National Chung Hsing University, 250 Kuo Kuang Rd., Taichung 40227, Taiwan, ROC; Department of Environmental Science and Engineering, Tunghai University, Taichung 40704, Taiwan, ROC. Electronic address: ytliu@thu.edu.tw.
Yu-Ting
YT
Liu
Department of Soil and Environmental Sciences, National Chung Hsing University, 250 Kuo Kuang Rd., Taichung 40227, Taiwan, ROC. Electronic address: ymtzou@dragon.nchu.edu.
Yu-Min
YM
Tzou
D005591:Chemical Fractionation / Q000379:methods*; D002857:Chromium / Q000032:analysis*; D004784:Environmental Monitoring / Q000379:methods*; D006812:Humic Substances / Q000032:analysis; D012989:Soil Pollutants / Q000032:analysis*; D013624:Taiwan; D056928:X-Ray Absorption Spectroscopy / Q000379:methods*
D006812:Humic Substances; D012989:Soil Pollutants; D002857:Chromium
Chromium; Sequential extraction; Spectroscopic speciation; XANES