A knockout punch
 |
| Roots from plants that were used to degrade
PAHs in the soil at a site in Bedford, Ind., are analyzed in
the lab. A root scanner generates a digital image of the roots,
(visible on the computer screen); then a software program analyzes
the image to give total root length, surface and volume. |
Metals, of course, aren’t the only type of contaminants in soil.
Organic compounds—essentially any compound containing carbon—are
other sources of soil and water contamination. Some of the most ubiquitous
organic contaminants, known as “polycyclic aromatic hydrocarbons,”
or PAHs, are produced as byproducts of the process of oil refining
or gasoline combustion and are a problem nearly everywhere in the
world.
“It’s hard to find a place without
some degree of PAH contamination,” says Paul Schwab, professor
of agronomy and a principal investigator with the center. “PAHs
are a combustion product—when we burn gasoline, they come
right out of the tailpipe. They get into the air, they fall to the
ground and they find their way into the soil and watersheds.”
While these compounds are a widespread problem,
it turns out that PAHs make ideal candidates for phytoremediation.
“Some petroleum products are easy to degrade, but PAHs are
more difficult” Schwab says. “However, if you put appropriate
plants in the soil, and they establish a good root system, they’ll
remove the petroleum contamination by degrading it. Even the PAHs
can be degraded in this way.”
Schwab and Kathy Banks, professor of civil engineering
and co-director of the center, are experts in remediating field
sites contaminated with organics. Their combined expertise in the
fields of soil chemistry and microbial degradation of organic compounds
has been a central component of their success in cleaning up contaminated
sites all over the country, from an oil pipeline spill in Texas
to PAH-contaminated groundwater in southern Indiana.
Their latest research project involves using
plants to decontaminate dredged sediments that have been removed
from Wisconsin’s Milwaukee Harbor and stored in a large facility.
“The idea is, rather than leave the sediments in storage indefinitely,
it’s better to remove the water, decontaminate the sediments
and then turn them into something useful, like fill material for
construction or landscaping,” Schwab says.
Schwab and Banks are currently studying methods
for establishing plants in these sediments. “It’s challenging
to establish plants on a large scale under these conditions, especially
on material that is essentially very wet mud. We’ve been using
some innovative methods to get the plants in there,” Schwab
says. Ultimately, they hope to establish a wetland that will first
remove the excess water from the sediments and then will begin the
process of breaking down the organic contaminants.
|
