The University Record, November 13, 1995

U scientists use chemical fingerprints to track air pollution

By Sally Pobojewski
News and Information Services

In research guaranteed to chill the hearts of polluters everywhere, U-M scientists have tested a new method of tracking the original source of trace metal pollution---like lead, arsenic and mercury---that often travels hundreds or even thousands of miles away from its point of origin.

By analyzing the relative ratios of lead isotopes in precipitation falling at collection sites around Lake Michigan and back-tracking daily meteorological records, researchers Joseph R. Graney and Gerald J. Keeler were able to identify the original point source of the lead emissions.

"Emissions from every smelter, power plant, refinery and urban area have a unique mix of isotopes," says Graney, postdoctoral scholar in public health. "Using sensitive mass spectrometers and analysis techniques, we can pick out individual chemical `fingerprints' and determine pollutants' source."

Graney presented the results of his study---the first to test the viability of the U-M pollutant tracking technique with lead isotopes in precipitation---at the Geological Society of America (GSA) meeting held in New Orleans Nov. 6-9.

Graney stressed that the amount of lead falling in precipitation over Lake Michigan is too small to create any public health danger. But success at detecting minute amounts of lead indicates that the technique could be used to identify sources for many other types of pollutants.

At the GSA Meeting, Graney presented his analysis of lead isotopes in precipitation that fell during the summer of 1994 at five collection sites near Lake Michigan in the Midwest and one near Lake Champlain in New England. Key points included:

 Most, but not all, lead pollution particles are washed out of the atmosphere when it rains.

The source of lead pollution falling at any collection site varies on a daily and sometimes even an hourly basis, depending on wind direction and weather conditions.

Lead smelters in southeast Missouri are a point source for lead particles falling in Illinois and Indiana when prevailing winds come from the southwest.

Chicago's chemical fingerprint---a unique blend of auto, industrial and power plant emissions---overpowers the weaker regional Missouri signal. Chicago is a major point source for lead pollution falling on Lake Michigan and the state of Michigan.

Depending on wind direction, lead pollution falling on Lake Champlain comes from either the United States or Canada.

If current proposals in Washington to cut EPA funding become law, the U-M technique could potentially provide an inexpensive, reliable way to monitor future pollution trends and identify those violating compliance standards, according to Graney.

Graney's research with lead isotopes was published in 1995 as part of his dissertation for a U-M Ph.D. in geological sciences. Keeler is an assistant professor of environmental and industrial health and of atmospheric, oceanic and space sciences.