Biosolids Remediate Metalcontaminated Soils

The mining and processing of metal ores have contaminated soils in many countries. In the vicinity of lead (Pb) and zinc (Zn) mines and smelters, soils may have Pb and Zn concentrations as high as 20,000 mg/kg. These soils—with their high metals, low pH, and lack of nutrients and organic matter—are toxic to plants. Land around the mines is acidic and barren, often with blowing dust and metals leaching into ground and surface waters.

Three such sites on EPA's Superfund list— Palmerton, Pennsylvania; Leadville, Colorado; and Bunker Hill, Idaho — have demonstrated that biosolids mixtures can restore soils and vegetation. Biosolids combined with a calcium carbonate material such as lime or wood ash create a fertile soil and vigorous, self-sustaining plant growth. Iron and phosphates in biosolids adsorb lead and convert it to an insoluble compound, chloropyromorphite. Wood ash raises soil pH and prevents Zn from being taken up by plants or leached. Biosolids supply nutrients and organic matter for rebuilding soil and soil microbial communities.

Similar results have been reported in Upper Silesia, Poland, where lands have been contaminated by toxic coal and smelter wastes. New secondary treatment plants in the region will be producing a supply of biosolids for future restoration projects.

Biosolids Secondary Treatment
A douglas fir tree with (left cuts) and without (right cuts) biosolids application. There is a more than 100 percent increase in tree growth with biosolids. Each "tree ring" represents one year of growth. (King County photo by Ned Ahrens. AP/Wide World Photos. Reproduced by permission.)

has asked the U.S. National Academy of Sciences (NAS) to review the federal regulations for biosolids. The NAS review in 1995 concluded that "the use of biosolids in the production of crops for human consumption when practiced in accordance with existing federal guidelines and regulations, presents negligible risk to the consumer, to crop production and to the environment." The NAS reviewed the regulations again in 2002 and concluded, "There is no documented scientific evidence that the federal regulations have failed to protect public health."

Most researchers agree that the effects of organic compounds, metals, and microorganisms in biosolids are not harmful to humans or the environment if managed carefully. Many studies have shown that metals in biosolids are chemically bound in stable compounds and will not easily move into ground and surface waters.

Still, some land application projects are controversial, especially if they release odors. Odors at an application site can cause neighbors to raise questions about the safety and adequacy of regulations for biosolids recycling.

In response to the need for accurate and consistent information, the National Biosolids Partnership was established in 1997 by the federal EPA, Water Environmental Federation, and the Association of Metropolitan Sewerage Agencies. One of their goals is to encourage safe biosolids management practices in local communities through the use of environmental management systems. see also Beneficial Use; Clean Water Act; Ocean Dumping Ban Act; Risk; Solid WAste; Wastewater Treatment; WAter Pollution.

Internet Resource

National Biosolids Partnership Web site. Available from http://www.biosolids.org.

Peter S. Machno and Peggy Leonard

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