Chemical Heterogeneity of Organic Soil Colloids Investigated by Scanning Transmission X-ray Microscopy and C-1s NEXAFS Microspectroscopy

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• 作者：Marc Schumacher ; Iso Christl ; Andreas C. Scheinost ; Chris Jacobsen ; and Ruben Kretzschmar
• 刊名：Environmental Science & Technology
• 出版年：2005
• 出版时间：December 1, 2005
• 年：2005
• 卷：39
• 期：23
• 页码：9094 - 9100
• 全文大小：249K
• 年卷期：v.39,no.23(December 1, 2005)
• ISSN：1520-5851

文摘

Colloid release and deposition in soils and sorption ofinorganic and organic pollutants to soil colloids arestrongly influenced by the composition and chemicalheterogeneity of colloidal soil particles. To investigate thechemical heterogeneity of organic soil colloids at theparticle scale, we used synchrotron scanning transmissionX-ray microscopy (STXM) and C-1s near-edge X-rayabsorption fine structure (NEXAFS) spectroscopy on 49individual particles isolated from the surface horizons ofthree forest soils. Stacks of 130 images of each particle werecollected at different X-ray energies between 280 and310 eV. From these image arrays, NEXAFS spectra wereobtained for each pixel and analyzed by principle componentanalysis and cluster analysis (PCA-CA) to characterizethe intraparticle heterogeneity of the organic components.The results demonstrate that the organic matter associatedwith water-dispersible soil colloids is chemically heterogeneous at the single-particle scale. PCA-CA identifiedat least two distinct regions within single particles.However, the spectral variations between these regionswere much smaller than the variations of averaged NEXAFSspectra representing different particles from the samesoil horizon, implying that interparticle heterogeneity is muchlarger than intraparticle heterogeneity. Especially thecontents of aromatic and carboxyl carbon exhibited a largevariability. Overall, the NEXAFS spectra of water-dispersible soil colloids were similar to the NEXAFSspectrum of the humic acid fraction, but differed clearlyfrom the fulvic acid and dissolved organic matter fractionsextracted from the same soil horizon using conventionaltechniques.