Feature   |   Fall 2003

Pollution-Busters

Unlike metals, some organic contaminants are not taken up and stored by plants. In fact, it’s not the plant that degrades organic compounds in the soil, but the microbes associated with the plant’s roots. “Plants are the means by which we can deliver the microorganisms to the contaminants,” says Schwab. “Roots penetrate into parts of the soil that the microbes can’t access by themselves. Once the roots move downward, the microbes move in right along with them. That’s how phytoremediation works for the organic materials we’ve studied.”

Microbes can then degrade the organic contaminants, using the carbon as a source of energy and breaking the organics into smaller, less toxic compounds. “Plants and their associated microbes change the whole structure of the contaminated soil,” Banks explains. “We can take sludge—heavy, tar-like material from an industrial site—put a plant in it, and, after 12 months, the sludge will resemble normal soil in almost every way.”

Remediation of contaminated sites has benefits beyond cleaning up the environment, Banks says. “A real advantage to cl

eaning up these sites in urban areas is economic. An added benefit is environmental protection, but the key is that economic development is often linked to greenspace development. Property values usually increase with greenspace development, and if you’re talking about making an area green, the community’s definitely behind you,” she explains.

Purdue researchers are using a variety of plants and grasses to decontaminate sediments dredged from Milwukee Harbor. Once the contaminants have been broken down, the sediments can safely be turned into fill material.

One plant doesn’t fit all

“Part of the reason why phytoremediation needs so many people from so many different areas is precisely because it is not a one-size-fits-all approach. One discipline cannot provide all the knowledge and information you need to try to develop this approach as a solution,” says Peter Goldsbrough, professor of horticulture and another of the center’s principal investigators. “You’ve got an environment that’s not very welcoming. You have green plants living there, and you have a lot of other organisms in the soil—the bacteria and fungi—that play a role as well.”

The number of variables at work in a contaminated site means that one type of plant won’t be sufficient for every remediation project. “The ideal plant varies, depending on the contaminant and what type of resource is contaminated,” Banks says. For example, a groundwater contaminant is best cleaned up using plants with a deep taproot system, whereas plants with a branching root system are better at cleaning up contaminants that attach to the soil.

“Polluted soils exist everywhere in the world, so we’re going to need to develop a whole battery of crops,” Salt explains. “Depending on which part of the world you’re in, you’ll need different plants to suit different growing conditions.”

A business boom?

Addressing the kinds of basic research questions behind phytoremediation has led to applications beyond cleaning up polluted fields. One project that Salt spun out of his molecular work involves indicator plants, or plants that change their appearance when they detect metals in the environment. He envisions a day when, for example, factories could establish sensor plants around their perimeter to set off a visual alarm should pollutants leach into the soil or water. He is also working to develop plants that are enriched in selenium, a potent anti-oxidant with anti-carcinogenic properties.

“The capacity to clean up contaminated sites is a tremendous business opportunity that will be enhanced by Purdue’s Center for Phytoremediation Research and Development,” Woodson says. “Our hope, and the hope of the 21st Century Research and Technology Fund, is that the spin-offs from this work will help to establish unique business opportunities for companies within Indiana.”