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Plants—The Hard-Core Cleaning Machines! Heavy Metal Plants Are Hard-Core Cleaners! S ome people think playing soft, peaceful music to their plants will get them to grow taller and healthier. But don’t play that stuff around plants with names like Alpine Pennycress or Golden Tufted Madwort. They like heavy metal. In fact, they eat it up (real metal, that is, like zinc, cadmium, and nickel—not “hard rock” music). zinc and nickel that would kill or sicken nearly all other plants. But why “hunger” for heavy metals? Rufus Chaney, an Agricultural Research Service (ARS) agronomist in Beltsville, Maryland, studies these metal-hungry plants, called “hyperaccumulators” (say, Hyper Ak-Yoom You Laters). He says, “The metal in the leaves kills chewing insects and also prevents certain plant diseases.” At polluted sites, a crop of pennycress could be grown, harvested, and then burnt to remove and recycle its stored metals. This type of plant-powered clean up is called “phytoextraction.” The cost is $250 to $1,000 per acre per year. That’s a lot cheaper than $1 million—the per-acre cost of current methods. These involve scooping up polluted soil and replacing it with clean soil. So rock on little plants! —Adapted from the ARS Science for Kids website by Jan Suszkiw, USDA, Agricultural Research Service, Information Staff For further reading Durham, Sharon. “Dainty Plant Outpowers Cadmium-Contaminated Soils,” Agricultural Research magazine, USDA-ARS Information Staff, Beltsville, Maryland, September 2004, p. 22. www.ars.usda. gov/is/AR/archive/sep04/plant0904.pdf. Becker, Hank. “Phytoremediation: Using Plants To Clean Up Soils,” Agricultural Research magazine, USDA-ARS Information Staff, Beltsville, Maryland, June 2000, pp. 4−9. archive/jun00/soil0600.pdf. Comis, Donald. “Metal-Scavenging Plants to Cleanse the Soil,” Agricultural Research magazine, USDA-ARS Information Staff, Beltsville, Maryland, November 1995, pp. 4−9. is/AR/archive/nov95/cleanse1195.pdf. QUIZ Why do these plants store heavy metals? (Pick all that apply.) A) Scientists believe it makes the plants less tasty to hungry insects. B) It makes them more valuable. C) It may help them fight off diseases. D) It prolongs their blooming season. Answer: A and C are both correct! Long ago, European prospectors used these shrubs as a sign that metals lay hidden beneath the soil. Today, scientists want to use plants like pennycress to clean up soils contaminated with heavy metals. Landfills and old mines are two examples of such sites. Hyperaccumulator plants don’t actually eat the metals, though. Instead, they use their roots to draw in large amounts of the metals, which are then carried to the stems and leaves for storage. Pennycress may look small and dainty with its pretty white flowers. But its leaves can store toxic amounts of

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