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Adjusting pH boosts plant's metals uptake.

One of the most promising low-cost technologies for remediating soils contaminated by metals such as cadmium and zinc is cultivation of plants called "hyperaccumulators." Alpine pennycress (Thlaspi caerulescens) is one of these plants with a penchant for sucking up metals and storing them. It can concentrate cadmium in its leaves up to about 100 times the levels in soil.

Reducing soil contamination with the use of metal-storing plants is called "phytoremediation," or "phytoextraction," and it costs about $250 to $1,000 an acre per year. When the accumulated metal is recovered for industrial use, the process is called "phytomining," and it's already being done for nickel retrieval.

Now tests have shown that, for strains of alpine pennycress from southern France, slightly increasing the soil acidity--from the neutral pH of 7 to 6--raised the cadmium concentration in the plant's shoots. But at a pH below 6, soils were so acidic that the pennycress yields fell.

Most highly contaminated soils can be deemed safe after 3 to 10 years of plant-based phytoextraction. The University of Maryland filed a patent in 2000 on use of T. caerulescens for this purpose. Rufus L. Chaney, USDA-ARS Animal Manure and Byproducts Laboratory, Beltsville, Maryland; phone (301) 504-8324, e-mail
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Title Annotation:Science Update
Author:Chaney, Rufus L.
Publication:Agricultural Research
Date:Nov 1, 2005
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