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Lush, Indigenous Plants Rise From Brown Landscape

By Sharon Durham
July 18, 2002

Land around former metal-mining operations can become a dead ecosystem where plants can't grow. A team of scientists from the Agricultural Research Service, the U.S. Environmental Protection Agency (EPA) and the University of Washington has found a method to help plants flourish again. Adding biosolids and alkaline industrial byproducts--such as wood ash, woody debris and paper pulp--improves soil quality and boosts plant growth.

ARS agronomist Rufus Chaney led the team, which demonstrated successful revegetation of a Bunker Hill, Idaho, site that was a former zinc and lead mining and smelting operation and is now an EPA Superfund site. Due to dispersal of mine wastes and smelter fumes, more than 3,700 acres remained barren and toxic to plants, even 30 years after closing of the smelter. Methods to revegetate sloping, contaminated soils at this Superfund site were needed to reduce the costs of its remediation.

Zinc, lead and cadmium were present in elevated levels in the acidic soil, allowing virtually no vegetation to grow. Chaney and his colleagues used the biosolids, rich in phosphorous and organic nitrogen, and lime-rich waste materials such as wood ash to raise the pH in the soil to 7.5. This made the zinc, lead and cadmium much less soluble and thus less toxic to plants. The biosolids used at this test site consisted of treated sewage sludge, which meets strict EPA standards for use on cropland.

Because of the site's sloping terrain, erosion and runoff were a concern. However, a cementlike reaction occurs with the biosolid/lime-rich combination of materials, keeping the mixture in place, while allowing water to percolate into the soil.

This method is an alternative to removing contaminated soil and replacing it with clean soil from elsewhere, an expensive and time-consuming method. The soil improvements can prevent solubility of the metals for a long period of time--possibly centuries--making it a long-term means to revegetate metal-toxic soils around the world.

ARS is the chief scientific research agency of the U.S. Department of Agriculture.

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