In 2001, Friedland, James Kaste, a post-doctoral researcher in the Earth Sciences Department and with the Environmental Studies Program, and Stefan Sturup, Director of Dartmouth's Trace Metal Analysis Core Facility, returned to the exact plot where the lead 207 was applied on Camel's Hump, a heavily forested, undeveloped mountain near the village of Huntington, Vt. They took soil samples at the site, which is about 200 hundred yards off of a popular hiking trail at an elevation of about 3,300 feet, and brought them to the lab at Dartmouth for analysis.
"We found that the lead 207 applied in 1984 had only moved down into the soil about seven centimeters," says Kaste, the lead author on the paper. "And it will probably move slower in the future because the soil becomes denser. It's pretty rare to have a long-term study in this field, and here's a 17-year experiment that we were able to conduct."
Kaste also followed lead 210, which is a natural lead isotope that falls out of the atmosphere. He traced it to learn how long the forest floor, which is the top 10 centimeters of organic material at the top of the soil, retains it. He found that atmospherically deposited lead, like lead 210, will remain in the forest floor between 60 and 150 years, depending on the vegetation.
"The next step is to identify how the lead binds to the soil," he says. "We want to learn if it binds to organic matter, for example, or if it precipitates out."
The researchers explain that their findings are representative of deciduous and coniferous forests throughout much of the Northeastern U.S. and in some areas in Europe and Scandinavia.