Why, observing dirt age in a hurry, according to a team at the Pacific Northwest National Laboratory that can speed soil's natural aging process to sponge up and trap organic contaminants.
In nature, dirt is said to age as water-resisting organic compounds accumulate in mineral pores and organic matter of sediments. The PNNL group, based in Richland, Wash., helps the process along by injecting soils with a contaminant dissolved in carbon dioxide in its so-called supercritical form-a fluid that shares properties of liquids and gases.
"We believe the supercritical-fluid aging process can simulate decades of contaminant exposure in just a few hours," said Christopher J. Thompson, PNNL senior research scientist and project leader, who reported his results Wednesday here at the national meeting of the American Chemical Society.
"Such fluids have the strong penetrating ability of a dense gas, making them ideal for carrying contaminant molecules deeply into the microscopic pores and organic components of soil grains," Thompson said.
He and colleagues have enlisted a technique called Fourier-transform infrared spectroscopy to monitor accelerated soil-aging in real time, enabling them to measure the soil-absorption rate of carbon tetrachloride and other volatile organic compounds.
"Initially, the soil is contaminant-free," Thompson said, "and all of the contaminant is dissolved in supercritical carbon dioxide. In a few hours, the concentration of contaminant in the carbon dioxide decreases, which means the contaminant is being taken up by the soil."
PNNL is a DOE Office of Science laboratory that solves complex problems in energy, national security, the environment and life sciences by advancing the understanding of physics, chemistry, biology and computation. PNNL employs 3,800, has a $600 million annual budget, and has been managed by Ohio-based Battelle since the lab's inception in 1965.