When the catalytic converter debuted on automobiles in 1975, people everywhere breathed a sigh of relief.
Here was a device that transformed exhaust pollutants like carbon monoxide and hydrocarbons into something similar to what people exhale — plant-nourishing carbon dioxide and water vapor.
Now comes word that as the converters age, they expel tiny amounts of the very materials that make them work. In high enough concentrations, these elements could pose a health risk. But they’re also so precious that an industry could well develop to sweep up the dirt and grit along roadways to recover trace amounts.
Small amounts of platinum, palladium and rhodium — known collectively as platinum-group elements — are what make possible the conversion of auto exhaust into something far more breathable as it passes through a catalytic converter. These catalysts aren’t supposed to go out the tailpipe, but as a converters ages, tiny amounts of them do, says geologist Clive Neal, an associate professor in Notre Dame’s Department of Civil Engineering and Geological Sciences.
Consistent exposure to platinum can lead to asthma, sensitive skin and other ailments. Less is known about the effects of exposure to palladium and rhodium.
In 1998 Neal and five collaborators with Notre Dame’s Center for Environmental Science and Technology began a pilot study to see if trace amounts of the elements were accumulating on U.S. roadsides. Earlier studies had suggested that to be the case in other parts of the world. The Notre Dame study, published in the November 19, 2001, issue of the American Chemical Society journal Environmental Science & Technology, represented the most detailed look yet at roadside contamination from catalytic converters in the United States.
In samples taken along roads around campus and beside Interstate 80 between South Bend and Chicago, the researchers found concentrations of platinum as high as .1 parts per million, 100 times the background level found in nature. That’s almost certainly below the threshold to make most people sick. And it’s far below the 2 to 5 parts per million concentration considered necessary to make it viable to mine platinum from rocks.
However, Neal expects to find much higher concentrations of the elements where traffic is heavier, as in Chicago. In a three-year follow-up study, the team also hopes to determine if the elements are entering the food chain through crops growing beside highways.
“It’s not a scare tactic, it’s a cautionary tale,” Neal says of the initial findings. “We want to be sure that in fixing one problem [auto pollution], we’re not causing other problems.”
As for the possibility of prospecting for curbside platinum-group elements (platinum fetches about $460 an ounce, and rhodium is even more expensive), Neal says he has already been contacted by one potential entrepreneur.
The hope is that through roadside mining or retrofitting cars to capture the elements before they leave the tailpipe, the materials could become renewable resources.
The other authors of the study were Charles F. Kulpa Jr., professor of biological sciences and director of the Center or Environmental Science and Technology; James C. Ely, postdoctoral research fellow; James C. Seidler, undergraduate student; Mark A. Schneegurt, an assistant professor of biological sciences at Wichita State University who was a postdoctoral research associate and research assistant professor in biology at Notre Dame at the time of the study; and Jinesh C. Jain, assistant professional specialist.