Embargoed until 2 p.m. EDT
NSF PR 02-80 - September 26, 2002
Study Sheds Light on Mess in Polluted Streams
Downstream from mining sites, a suffocating gel forms
in the water of creeks and rivers. A new study by
an international team of researchers details the processes
that make that gel and should advance our understanding
of the damaging environmental effects of mine drainage
and acid rain.
"This new nanoscale level of understanding of trace
metal pollution of streams opens new doors for addressing
the problem of contaminated waters in affected areas,"
says Sonia Esperanca, program director in the National
Science Foundation's (NSF) division of earth sciences,
which funded the research.
According to the team's report in this Friday's issue
(Sept. 27) of the journal Science, the gel
results when runoff made acidic by mining or acid
rain collects aluminum from local soils and then mixes
with stream water that is less acidic. In subsequent
chemical reactions, aluminum molecules link together
to form polymer gel.
Scientists call the gel "floc" and say its influence
is widespread: Mining disrupts about 240,000 square
kilometers of the Earth's surface (about 93,000 square
miles, an area roughly the size of Oregon).
The gelatinous floc is bad enough by itself; it gums
up the gills of fish and suffocates them, and is equally
deadly to other aquatic animals and plants. But it
also possesses another dangerous quality: It binds
to toxic metals, including mercury, lead and cadmium,
and transports them far downstream.
"This combination of floc and metals pollutes streams,"
said William Casey, a University of California at
Davis geochemist and an author of the new report.
"Bad things adsorb into this gel and then it travels
forever."
Knowing how floc forms at the molecular level may suggest
some practical solutions, Casey said. One such solution
might be to stop aluminum from migrating into streams.
"Now we know how these pollutants enter the watershed,
how fast they move and perhaps how to prevent the
reactions by cutting off the ingredients. Detailing
the molecular pathways helps us better understand
the pollutants' source and their fate," Casey said.
The paper, "The origin of aluminum flocs in polluted
streams," was written by Casey; Gerhard Furrer of
the Institute of Terrestrial Ecology in Switzerland;
Brian Phillips of State University of New York at
Stony Brook; Kai-Uwe Ulrich of Technical University
of Dresden, Germany; and Rosemarie Pothig of Leibniz
Institute of Freshwater Ecology and Inland Fisheries,
Berlin.
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