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Science 12 November 1999:
Vol. 286. no. 5443, pp. 1335 - 1337
DOI: 10.1126/science.286.5443.1335
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Reports

Imaging of Humic Substance Macromolecular Structures in Water and Soils

S. C. B. Myneni, 13* J. T. Brown, 2 G. A. Martinez, 4 W. Meyer-Ilse 2

Humic substances (HSs) are the natural organic polyelectrolytes formed from the biochemical weathering of plant and animal remains. Their macromolecular structure and chemistry determine their role in biogeochemical processes. In situ spectromicroscopic evidence showed that the HS macromolecular structures (size and shape) vary as a function of HS origin (soil versus fluvial), solution chemistry, and the associated mineralogy. The HSs do not simply form coils in acidic or strong electrolyte solutions and elongated structures in dilute alkaline solutions. The macromolecular structural changes of HSs are likely to modify contaminant solubility, biotransformation, and the carbon cycle in soils and sediments.

1 Earth Sciences Division,
2 Center for X-ray Optics, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
3 Department of Geosciences, Princeton University, Princeton, NJ 08544, USA.
4 Agriculture Experimental Station, University of Puerto Rico, Rio Piedras, PR 00928, USA.
*   To whom correspondence should be addressed. E-mail: smyneni{at}princeton.edu

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