To: "S.M. Mandaville"
Date: Sat, 31 Aug 2002 01:07:06 -0400
Nitrates Affect Arsenic Pollution in Lakes
CAMBRIDGE, Massachusetts, August 30, 2002 (ENS) - A common pollutant may change the behavior of arsenic and other toxic metals in some lakes, say researchers at the Massachusetts Institute of Technology (MIT). Their findings are adding to scientists' understanding of how such elements move through the water.
"The work shows that nitrate pollution, which arises from sources such as automobile exhaust, wastewater disposal and fertilizers, is more important in lake dynamics than had been thought," said Harry Hemond, an MIT engineering professor and author of a paper on the work that appeared in the June 28 issue of the journal "Science."
"This is a linkage we need to understand if we want to manage water quality," Hemond explained.
Hemond said nitrate pollution, which is also associated with noxious impacts such as excessive algal growth, was found to help reduce arsenic pollution in lakes. It reacts with naturally occurring iron to create iron oxides that absorb arsenic.
"The result is a suppression of seasonal arsenic release into the water," said Hemond.
Hemond and coauthor David Senn focused their studies on Upper Mystic Lake. The lake is part of the Aberjona Watershed, a 25 square mile drainage basin that includes parts of seven Massachusetts communities.
For more than a century, hundreds of tons of toxic wastes from leather, chemical and other industries were dumped into the waterways of the Aberjona, the real world setting of the movie "A Civil Action." Today the dumping has stopped, but the pollutants remain, including considerable amounts of solvents, chromium and arsenic.
For the last 14 years, MIT researchers have been exploring the fate of these wastes and the chains of events that can lead to effects on human health. Earlier studies showed that iron and arsenic in water sampled from the cold depths of Upper Mystic Lake in summer were not in the chemical forms researchers expected.
Senn and Hemond had a hunch that nitrate pollution was responsible for the anomalous forms of iron and arsenic. Over several months they tracked the concentration of nitrate, along with the concentrations and chemical forms of arsenic and iron.
Higher nitrate concentrations did indeed coincide with the unexpected particulate forms of iron and arsenic. Culture studies in the lab, and thermodynamic calculations, supported the effects observed in the field.
The work aids scientists' understanding of how arsenic moves through polluted, stratified lakes, and has implications for other pollutants, including phosphate and toxic metals like lead, cadmium and zinc. These contaminants are also absorbed by iron oxides, so they are expected to have similar behaviors in lakes.
Hemond expects that nitrate pollution could be important in groundwater or marine systems contaminated by arsenic.