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.