Although this brochure contains widely-applicable information about the ris

the hydroxyapatite treatment technique described within is primarily aimed 

Superfund sites; the use of the patented hydroxyapatite technique does not s

residential soil remediation under the Toxic Substances Control Act. This br

peer and administratively reviewed and approved for publication as an EPA 

NOTE 

US EPA Office of Research and Development 
“Nearly 1 million children living in the United States have lead levels 

in their blood that are high enough to cause irreversible damage to 

their health.” 

Centers for Disease Control and Prevention, 1998 

Introduction vitamin D and calcium. Lead can cause reproductive 

Flaking paint, decades of leaded gasoline use, mining toxicity (i.e., it can be transferred easily to the developing 

operations, smelter and industrial emissions, waste fetus via the placenta), impaired tooth and bone developincineration, and application of insecticides and fertilizers ment, kidney damage, and anemia. Other adverse effects 

have all contributed to elevated lead levels in soils. Urban which may result from elevated blood lead levels include: 

environments, with their higher concentrations of indus- lower IQ scores; poor attention levels; hearing, speech 

tries, aging buildings, and vehicular traffic, have corre- and language problems; reading disabilities; reduced 

spondingly higher levels of lead in soil. To complicate motor skills; and poor hand-eye coordination. 

matters, lead seems to remain near the surface of the soil Although no safe lower threshold level for these 

where it is deposited — increasing the chance of expo- effects has been established, available evidence suggests 

sure. that lead toxicity may occur at levels as low as 10-15 

The quote highlighted at the top of this page brings micrograms of lead per deciliter of blood (μg/dL). The 

the risks associated with lead exposure into perspective. current level of concern established by the Centers for


The U.S. Environmental Protection Agency (EPA) has Disease Control and Prevention (CDC) and the American


acknowledged these significant risks and the need for a Academy of Pediatrics is 10 μg/dL. According to recent


better understanding of the associated issues. EPA’s CDC estimates, 890,000 U.S. children under age 6 (i.e.,


Office of Research and Development, in cooperation with 72 months) have elevated blood lead levels. In light of


other scientists and engineers, has developed risk assess- these statistics, lead poisoning is expected to cost billions


ment tools that estimate the risks associated with lead of dollars in medical and special education expenses and


exposure and a cost-effective management technique to decreased future earnings.


reduce the risks associated specifically with exposure to


lead in soil. The following information is presented to Why Children are at Greater Risk


better inform citizens, decisionmakers, and remediation Compared to adults, children proportionately eat


engineers of these risks and give them some tools to help more food, drink more fluids, breathe more air, and play


solve the problem. outside more. Natural curiosity and the tendency to 

explore leaves children open to health risks that adults can 

Effects Associated with Exposure to Lead more easily avoid. In crawling on the ground and playing 

Whether lead enters the body through ingestion or with and in soil, ingestion of contaminated soil and dust 

inhalation, the biological effects are the same: normal cell (by chance and on purpose) can occur more often (Fig. 1). 

function and a number of physiological processes can be Children’s bodies are not yet fully developed, so 

disrupted. In humans, lead primarily affects the nervous exposure to contaminants may affect their growth and 

system, blood cells, and processes for the metabolism of development. Children may be more or less sensitive than 

Common Sources of Lead Exposure 

Air 

Paint 

Food 

Water 

Dust on 

Pets 

Auto 

Emissions 

Auto 

Emissions 

Soil 

Industrial 

Emissions 

Dust on 

Toys 

Dust on 

Hands 

Figure 1. Some of the sources of lead exposure are 

shown at left. Since children are more often in 

direct contact with potentially-contaminated soils, 

they face greater risk of exposure to soil-related 

contaminants. Children younger than 6 years are 

most at risk for exposure to lead in soil. 
adults when confronted with an equivalent level of 

exposure to pollutants. These age-related variations in 

susceptibility are due to many factors, including body 

composition, metabolism, state of the immune system, 

and differences in the way the body absorbs, distributes, 

transforms, and excretes a contaminant. 

With exposure to lead, children absorb into their 

blood and retain more of the contaminant in proportion to 

their weight than adults. Nutritional deficiencies such as 

inadequate iron and calcium may increase the chances for 

lead absorption. Depending on a child’s stage of development at time of exposure, lead-damaged cells can hinder 

development of important body systems. 

Bioavailability and Its Importance 

The risk associated with a contaminant depends on 

how easily an individual absorbs it; this measure of 

absorption by the body defines contaminant “bioavailability.” Another important factor is how easily the contaminant is delivered to the part of a body (e.g., brain) where 

its toxic action can occur. 

Should a heavy metal like lead be bound to other 

molecules when ingested, it might pass through the body 

without being absorbed into the blood. While absorbed 

lead has toxic effects, not all soil lead is bioavailable. 

Three factors contributing to varying bioavailability are: 

the size of the lead-containing particle (i.e., perhaps the 

particles are too large to be dissolved and/or absorbed); 

the chemical form of lead in the soil; and the geochemical 

matrix incorporating that form of lead (i.e., lead may be 

entrapped in a less soluble compound). 

Contaminant bioavailability is important when 

considering remediation needs. Historically, remediation 

decisions have been based on an assumed bioavailability 

level (30% is the accepted default level) for all forms of 

lead in soil. Using the integrated exposure uptake 

biokinetic (IEUBK) model developed by EPA’s National 

Center for Environmental Assessment, blood lead levels 

can be predicted for a population given the amount of soil 

ingested and its bioavailability. 

Figure 2 demonstrates how the bioavailability of lead 

in soil affects estimates of lead concentration in the body. 

Using EPA’s IEUBK model, if the lead bioavailability is 

decreased (e.g., through soil treatment techniques), higher 

exposures would result in the same blood-lead effect as 

exposure to lead species with greater bioavailability. Such 

a finding could translate into significant savings in 

cleanup costs. 

Determining Bioavailability 

Even with the IEUBK model, direct bioavailability 

estimates are not easily obtained. Clearly, children cannot 

be used as test subjects to determine the amount of lead 

absorbed through exposure to local soils; surrogate 

measures must be used that best estimate lead uptake. 

EPA Region VIII scientists have used immature swine to 

examine oral lead bioavailability. They have completed 

test studies using swine dosed with soils containing 

varying levels and species of lead. Soil lead bioavailability ranged from 6% to 86% relative to freely soluble 

(aqueous) lead acetate. 

Scientists from EPA’s Region VIII have been 

focusing on the use of site-specific risk-based information 

in determining the level of cleanup needed. For instance, 

by first determining that the bioavailability of lead 

contaminants in soil at a Bingham Creek, Utah, site was 

lower than the default level (19% instead of 30%), less 

cleanup was necessary to manage the risk at the site. With 

less disruption of the site, an estimated $4 million was 

saved through this refinement of evaluation techniques. 

Building on Region VIII’s in vivo (live animal model) 

studies, an in vitro (artificial, non-animal) chemical 

extraction approach has been devised to imitate the 

physiology of human and animal digestive tracts. Results 

from this chemical method, using the same soil samples, 

have compared well with the results of the swine study. 

Such good correlation may make further animal bioavailability testing unnecessary. A Solubility-Bioavailability 

Research Consortium is currently verifying and standardizing this in vitro approach. 

Figure 2. Information on the 10


bioavailability of lead in soil at


a specific site provides a more 8


accurate representation of the


risk at that site. The chart at 6


right (based on EPA’s IEUBK


model) shows that if a treatment 4


method reduces the bioavail­


ability of lead in soil (e.g., from 2


the 30% assumed value to 5%),


the risk from exposure can be 0


reduced and less remediation


may be needed. This can result -2


in lower cleanup costs and less 0 500 1000 1500 2000 2500 3000


disruption of the environment. Lead Concentration (mg/kg) in the Ingested Soil


10% bioavailability 

5% bioavailability 

30% bioavailability 

20% bioavailability 

15% bioavailability 

2 

Percentage of Exposed Population with 

Blood Lead Levels > 10 

μg Pb/dL 
Reducing the Risks Associated with 

Lead Contaminants in Soil 

In 1992, the Remediation Technologies Development 

Forum (RTDF) was organized by EPA to foster collaboration between the public and private sectors in developing 

innovative solutions to mutual problems of contaminated 

materials. EPA’s National Risk Management Research 

Laboratory (NRMRL) and the DuPont Corporation 

formed the “In-place Inactivation & Natural Ecological 

Restoration Technologies” (IINERT) Soil-Metals Action 

Team in November 1995, under the RTDF. The ‘IINERT’ 

Soil-Metals Action Team includes representatives from 

industry and government who share a common interest in 

developing and validating surrogate measures of bioavailability. Through this effort, the Team supports the 

Solubility-Bioavailability Research Consortium mentioned earlier. 

The IINERT team also has as objectives developing 

and validating in situ (in-place) techniques as viable 

technologies for eliminating the hazards of metals in soils 

and surface materials. Their purpose is to develop and 

demonstrate in-place inactivation and natural ecological 

restoration technologies that reduce or eliminate the 

human health and ecological risks of heavy metals in soil 

and to achieve regulatory and public acceptance of these 

technologies. 

The ‘IINERT’ Soil-Metals Action Team concluded 

that if soil-lead species can be converted to less bioavailable forms, the overall lead risk of the soil can be reduced. Therefore, three facets of the issue are being 

studied: 1) innovative approaches to reduce lead bioavailability; 2) techniques to measure the conversion of lead to 

less bioavailable forms; and 3) identification and quantification of soil lead forms in intact soil systems and their 

relationship to bioavailability. 

Developing Innovative Alternative 

Remediation Methods 

Efficient remediation treatments for soils attempt to 

capitalize on the differences in physical and chemical 

properties between a contaminant and soil constituents. 

For example, remediation efforts for metal-contaminated 

sites use properties such as solubility, density, particle size 

distribution, surface chemistry, boiling point or magnetic 

susceptibility to allow separation and recovery. 

Metals found as relatively soluble species or weakly 

bound to other soil components might be dissolved by 

applying mild acids. If the metals are present as separate 

mineral particulates, their typically higher density might 

permit the physical separation of these species from the 

less dense soil constituents. If the metal species are 

volatile, then a soil heating method might allow recovery. 

Separation methods relying on the magnetic susceptibility 

of ferromagnetic or strongly paramagnetic metal species 

have also been attempted. If separation techniques are not 

feasible, the metals can be bound in a solid cement or 

vitreous (glass) matrix. 

Soil-lead remediation has typically been accomplished by soil removal for off-site disposal, covering, or 

diluting by mixing with uncontaminated soil. Cost 

(approximately $1.6 million per acre foot), logistical 

concerns, and regulatory requirements associated with 

excavation, ex situ (off-site) treatment and disposal can 

make in situ treatment an attractive option. Current 

understanding of lead exposure, associated bioavailability 

factors, and environmental chemistry may allow development of less costly and environmentally less disruptive 

methods of remediation. 

Innovative Approach 

NRMRL, as part of its effort within IINERT, has 

demonstrated that by adding phosphorus (P) to leadcontaminated soil, lead can rapidly and effectively be 

bound into a stable compound called pyromorphite (see 

Fig. 3) that will rarely be absorbed if ingested. Also, 

hydroxyapatite has proven to be an effective source of 

phosphorus for binding with and reducing bioavailable 

lead in contaminated soil to below the U.S. EPA action 

level of 15 micrograms of dissolved lead per liter of 

drinking water. 

NRMRL scientists have demonstrated that hydroxyapatite effectively immobilizes lead in soil even in the 

presence of interfering elements and compounds (e.g., 

anions, cations, and metals such as zinc, cadmium, 

nickel, copper, iron, and aluminum). The completeness 

and rate of this transformation have been found to depend 

upon the lead species, amount of hydroxyapatite added, 

and the pH (acidity/alkalinity) of the soil system. The 

speed at which soluble lead and phosphorus from 

hydroxyapatite react to become pyromorphite illustrates 

that the reaction can potentially occur during transit 

through the gastrointestinal tract — further reducing the 

potential exposure to bioavailable lead. 

Figure 3. Pyromorphite crystals. Phosphorus from a 

hydroxyapatite additive can immobilize soil-based lead 

into this stable compound and make it less bioavailable. 

3

The hydroxyapatite in situ inactivation technique (for 

which EPA was awarded a patent) has captured the 

interest of industry and the remediation research community. As tested in field studies by EPA’s Region VII, the 

cost for this innovative, less disruptive method is in the 

thousands of dollars per acre foot of treated soil (in 

contrast to traditional treatment costs of more than a 

million dollars per acre foot). The technique, employing 

common agricultural application and tilling approaches 

for the addition of hydroxyapatite, leaves the treated soil 

capable of sustaining plant growth, which can in turn hold 

the soil in place and act as a barrier against contact with 

soil contaminants. 

Conclusion 

Efforts to reduce exposure to lead contamination 

have been very effective in the last two decades. EPA’s 

ban on lead in gasoline and the Consumer Product Safety 

Commission’s ban on lead in paint have reduced potential 

exposure considerably. Since lead solder is no longer used 

in the canning of foods, another avenue of exposure has 

been closed. Declining reliance on lead solder and lead 

pipes for the distribution of drinking water has further 

reduced exposure potential. 

Some simple remedies can reduce the risk of exposure to lead in soil and dust. Careful handwashing should 

become a practice after contact with soil and before 

eating. Toys, bottles, and pacifiers should be cleaned — 

especially after use outside. Floors, window sills, and 

other surfaces should be cleaned regularly to reduce the 

risk of exposure to lead-contaminated dust. Deliberate 

ingestion of soil and paint chips should be strictly 

discouraged or prevented. Prior to commencing renovation in homes built before 1978, the surfaces to be 

disturbed should be tested for the presence of lead-based 

paint. If lead-based paint is found above the regulatory 

limit, contact the National Lead Information Center at 

1-800-424-LEAD for guidance on how to proceed. 

Additional information on evaluation and control of leadbased paint in homes can be found in EPA publications at 

the following website: 

http://www.epa.gov/lead/leadpbed.htm 

In spite of lead bans and behavior precautions, lead 

poisoning remains a significant threat to human health — 

especially for children. Although the symptoms of 

moderate exposure may be subtle, the damage can be 

irreversible. Local health agencies can provide useful 

information on the need for blood lead testing. Should 

unsafe lead levels be discovered, medical treatment 

should be sought at once and the sources of exposure 

must be identified and dealt with carefully. 

EPA’s National Risk Management Research Laboratory, in cooperation with many other scientists and 

engineers, is working to better understand the scientific 

issues surrounding exposure to lead in soil. By continuing 

to develop and refine assessment and remediation tools, 

EPA will be better poised to offer real solutions — like the 

patented hydroxyapatite treatment process — to high 

priority risks faced by our society. Through increased 

awareness of the dangers associated with lead exposure, 

and continued innovative risk management research, a 

safer environment can be provided. 

EPA’s National Risk Management Research


Laboratory Lead Remediation Contact:


Jim Ryan, Ph.D.


513/569-7653 (Telephone)


513/569-7879 (Fax)


Email: ryan.jim@epa.gov


For additional information about U.S. EPA’s risk 

management research, visit the following internet 

web site: 

http://www.epa.gov/ORD/NRMRL 

To learn more about lead bioavailability and 

related topics, visit the following U.S. EPA 

Technical Workgroup for Lead internet web site: 

http://www.epa.gov/superfund/programs/lead/ 

For more information on the risks and control of 

lead hazards, visit the U.S. Dept. of Housing and 

Urban Development’s Office of Lead Hazard 

Control internet web site: 

http://www.hud.gov/offices/lead/index.cfm 

4

This publication was written and produced by Patrick Burke and 

Ryan of USEPA’s National Risk Management Research Laboratory 

(NRMRL) within the Office of Research and Development. Comme

were provided by Rufus Chaney, U.S. Department of Agriculture’s 

Agricultural Research Services, and Bill Berti, DuPont Company an

IINERT RTDF. 

An electronic version of this publication can be viewed and 

downloaded from the Office of Research and Development’s Intern

website at http://www.epa.gov/ORD/ (in the “Publications” section). 

Printed copies can be requested from USEPA’s Publications Cente

calling 1-800-490-9198.