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Science 27 September 2002:
Vol. 297. no. 5590, pp. 2245 - 2247
DOI: 10.1126/science.1076505
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Reports

The Origin of Aluminum Flocs in Polluted Streams

Gerhard Furrer,1* Brian L. Phillips,2 Kai-Uwe Ulrich,3 Rosemarie Pöthig,4 William H. Casey5*

About 240,000 square kilometers of Earth's surface is disrupted by mining, which creates watersheds that are polluted by acidity, aluminum, and heavy metals. Mixing of acidic effluent from old mines and acidic soils into waters with a higher pH causes precipitation of amorphous aluminum oxyhydroxide flocs that move in streams as suspended solids and transport adsorbed contaminants. On the basis of samples from nine streams, we show that these flocs probably form from aggregation of the epsilon -Keggin polyoxocation AlO4Al12(OH)24(H2O)127+(aq) (Al13), because all of the flocs contain distinct Al(O)4 centers similar to that of the Al13 nanocluster.

1 Institute of Terrestrial Ecology, Eidgenössische Technische Hochschule Zürich, Grabenstrasse 3, CH-8952 Schlieren, Switzerland.
2 Department of Geosciences, State University of New York, Stony Brook, NY 11794-2100, USA.
3 Technical University of Dresden, Ecological Station Neunzehnhain, D-09514 Lengefeld, Germany.
4 Leibniz Institute of Freshwater Ecology and Inland Fisheries, Müggelseedamm 310, D-12587 Berlin, Germany.
5 Department of Land, Air, and Water Resources and Department of Geology, University of California, Davis, CA 95616, USA.
*   To whom correspondence should be addressed. E-mail: furrer{at}ito.umnw.ethz.ch (G.F.); whcasey{at}ucdavis.edu (W.H.C.)

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