Research Highlights - September 2004

It is well known that children are harmed by exposure to lead in their environments. Programs to reduce lead in paint, gasoline, and drinking water have greatly reduced childhood exposures to those sources, but lead in soil remains a challenging health risk. This is particularly true for children in urban environments where aging buildings and concentrations of industry can result in soil-lead levels up to 100 times higher than those found in agricultural soils. Traditional methods for treatment of these contaminated soils include excavation, disposal and replacement with clean soil–all very disruptive and expensive. US EPA soil scientists, in cooperation with other researchers, have developed an innovative treatment that converts the harmful chemical form of soil-lead into an environmentally stable and biologically inert mineral, and does it on site with minimum disruption and at lower cost.

Lead poisoning is the most common and serious environmental disease affecting children, according to the U.S. Centers for Disease Control and Prevention. In 1991, accumulated data on blood-lead levels in children and childhood cognitive development caused that agency to revise its standard of elevated blood-lead levels downward from the 1970 definition of 25 micrograms of lead per deciliter of blood to 10 micrograms. By 1994, median blood-lead levels in young children had dropped to 2-3 micrograms per deciliter. Yet more than 2 percent of children ages 1-5 still have blood-lead concentrations of over 10 micrograms.

One way to reduce the risk of childhood exposure to lead is to change its chemical form. After determining that soil-lead mineralogy could easily be altered under laboratory conditions, EPA risk management researchers formed a collaborative field study with the DuPont Company and other researchers to test the hypothesis that adding reactive materials to lead-contaminated soil would result in less-hazardous lead forms.

Immobilized soil-lead crystals after the addition of phosphorus. Photo provided by US EPA.

The potential toxicity of lead in soil depends on its chemical form: some lead species are insoluble and pose little harm to human health and the environment, while other forms can be very harmful because of their ability to be easily absorbed into our bodies when ingested. To alter the toxicity, EPA researchers added phosphorous, a common component of fertilizers, as a reactive material. The addition of phosphorous to lead has a very rapid two-fold effect: 1) it sequesters the lead in soil, and 2) it significantly reduces the bioavailability of lead, meaning that if a child ingests contaminated soil treated in this manner, the lead should potentially pass through the child’s body without harmful effects.

The EPA risk management research, conducted over several years at a lead-contaminated Superfund site in Missouri, successfully immobilized lead in soil, reducing its bioavailability as much as 72 percent over a 32-month period. Costs of this innovative treatment–for which EPA holds a patent–were estimated at thousands of dollars per acre foot (an amount covering one acre to a depth of one foot), a very favorable contrast to the million dollars per acre foot typical of traditional remove-and-treat technologies. The results suggest that this approach has great merit for cost-effective in-place immobilization of lead in contaminated soils and wastes. Complete information about this project is available in the American Chemical Society’s publication, Environmental Science & Technology, January 1, 2004, pp.19A-24A.

To access the EPA publication on the same topic titled, "Providing Solutions for a Better Tomorrow," click on this link: http://www.epa.gov/ORD/NRMRL/Pubs/600F01014/600F01014.pdf .

Contact: Patricia Schultz, Office of Public Affairs, 513-569-7966, or e-mail to: schultz.patricia@epa.gov.

NRMRL Meetings

"Pit Lakes 2004" is a conference to exchange scientific information on the characterization, modeling and remediation of pit lakes to be held in Reno, NV, November 16-18. Registration information is available at the conference web site http://www.epa.gov/ttbnrmrl/pitlakes.htm. Or contact Alina Martin, SAIC, at 703-318-4678.

Other Meetings

The Environmental & Water Resource Institute (EWRI) of the American Society of Civil Engineers (ASCE) is holding its annual World Water & Environmental Congress in Anchorage, Alaska on May 15-19, 2005. The meeting will be organized around the theme "Impacts of Climate Change," and will include Continuing Education seminars and short courses with opportunities to accumulate professional development hours. The flyer announcing the 2005 World Water & Environment Congress is currently posted on the ASCE web site: http://www.asce.org/conferences/ewri2005. Environmental and water resource professionals are invited to submit sessions or papers.

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