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Executive Summary of EPA 747-R-96-002
Distribution of Soil Lead in the Nation's Housing Stock
May 1996 (EPA 747-R-96-002)
The primary objective of this study was to supplement the prior reports on the National Survey of Lead-Based Paint in Housing through additional data analyses specifically focusing on the relationship between lead in exterior soil (a potential source of lead hazard in homes) and housing unit characteristics. The 1987 amendments to the Lead-Based Paint Poisoning Prevention Act required the Secretary of Housing and Urban Development (HUD) to "estimate the amount, characteristics and regional distribution of housing in the United States that contains lead-based paint hazards at differing levels of contamination." In response to this act, HUD initiated and conducted the National Survey of Lead-Based Paint in Housing, or the National Survey in 1990. The survey results were published in the Environmental Protection Agency's (EPA) Report On The National Survey of Lead-Based Paint In Housing document the National Survey and presented data on the extent and characteristics of lead hazards in homes.
The National Survey inspected 381 housing units (284 privately-owned and 97 public) for lead in paint on interior and exterior surfaces, lead in interior dust, and lead in exterior soil. The study population was designed to be representative of nearly all housing in the United States constructed before 1980. Newer houses were presumed to be lead-free because in 1978 the Consumer Product Safety Commission banned the sale of lead-based paint to consumers and the use of such paint in residences. The National Survey was conducted between December 1989 and March 1990 in 30 counties across the 48 contiguous states. These counties were selected to represent both the public and privately-owned housing stock across the 48 contiguous states.
The purpose of this report is to supplement discussions on soil lead prevalence in the prior reports on the National Survey by presenting findings on the prevalence and concentrations of lead in soil around private and public housing units in the United States. These findings included estimates of the number of housing units with different soil lead concentrations, nationally, by building age, by Census region, and by degree of urbanization; and summaries of the statistical associations between soil lead concentrations and soil location, building age, degree of urbanization, Census region, and the presence and condition of interior and exterior lead-based paint.
The quality of the private and public housing data was statistically evaluated to determine the suitability of the soil lead data for the analyses needed in this study. The privately-owned homes sampled in the National Survey were judged to be representative of the private housing stock nationally. Therefore, the descriptive statistics presented in the private housing data tables and the results from the analyses on the private housing data can be viewed as applicable to private housing nationally and useful in policy analysis and decision making. In contrast, the sampled public housing units were not considered representative of the public housing stock nationally, and the impact of the large amount of missing soil data (70%) on the tables and analysis results was expected to be significant. The public housing data tables and results from the analyses on public housing should therefore be viewed only as descriptive of those samples collected.
Under Section 403 of Title X, EPA has established health-based interim standards for soil lead concentrations and action recommendations for each standard. The agency recommends that "interim controls to change use patterns and establish barriers" should be implemented for areas that are expected to be used by children where soil lead concentrations are between 400 and 5,000 parts per million (ppm). Within this range, the degree of activity should be "commensurate with the expected risk posed by the bare soil considering both the severity of [lead] exposure...and the likelihood of the children's exposure." For areas where contact by children is less likely or less frequent, the "interim controls" should be implemented when soil lead concentrations are between 2,000 and 5,000 ppm. Moreover, the agency recommends the "abatement of soil" with lead concentrations above 5,000 ppm regardless of the likelihood of children's exposure.
Using the data from the National Survey, it is estimated that 23 percent, or 18 million, of the privately-owned homes in the United States built before 1980 have soil lead levels that exceed the 400 ppm "interim control" guideline. An estimated 8 percent, or 6 million, of the privately-owned homes in the United States built before 1980 have soil lead levels that exceed the 2,000 ppm "interim control" guideline. Finally, an estimated 3 percent, or 2.5 million, of the privately-owned homes in the United States built before 1980 have soil lead levels that exceed the 5,000 ppm soil abatement guideline. The prevalence and distribution of soil lead concentrations in public housing was not estimated due to the considerable number of public housing units in the National Survey for which no soil was available for sampling.
This study assessed the associations between the soil lead concentrations at different locations and the presence and condition of interior and exterior lead-based paint to determine which characteristics and factors specific to the housing unit are good predictors of soil lead. Additional variables also considered to be related to soil lead included the average daily traffic flow in the neighborhood of the housing unit (for private housing only) and the number of family units in the development (for public housing only), both of which were used to estimate the impact of the housing unit's environment on soil lead.
The strongest statistical predictor of soil lead was found to be the building age. Building age measures the length of time since the construction of the building and, in many cases, may be the last major disturbance of soil. For private housing units, soil lead around homes built before 1940 were significantly greater than lead in soil around homes built between 1960 and 1979. Similarly, soil lead around public housing units built before 1950 are significantly greater than lead in soil around homes built between 1960 and 1979.
The Census region (Northeast, Midwest, South, West) in which the housing unit was located was also an important predictor of soil lead levels. The data analysis showed that after adjusting for the age of the housing unit, soil around private housing units in the Northeast region has, on average, higher lead concentrations than in any other region, and soil in the Midwest region has on average, higher lead concentrations than those in either the West or South regions. One possible explanation is that the Northeast and Midwest are more industrialized, e.g., have the highest level of industrial productivity, of the four regions of the United States.
Another finding was soil lead levels around homes in urban, suburban, and rural areas were unexpectedly not significantly different, after adjusting for building age and other factors. Explanations of this result include one or more of the following: the distribution of privately-owned homes where soil lead measurements were not taken corresponds to sites which were expected to have high soil lead concentrations (33 of the 93 sampled private housing units in large metropolitan areas have at least one missing soil lead measurement), the correlations between the degree of urbanization and other factors, such as traffic, might be reducing the effect of highly urbanized areas, and the random variation in the data associated with the selection of the homes.
After adjusting for building age, Census region, and other factors, the presence of lead-based paint was an important predictor of soil lead at all three locations. The condition of lead-based paint, however, was not an important predictor of soil lead at any of the three soil locations.
Soil lead samples were available for only 30 percent (29 of 97) of the sampled public housing units, and the distribution of public housing units with soil lead samples was not consistent with national distributions. These problems prevented any reliable national estimates of soil lead prevalence in public housing from being calculated.
Although no estimates for the effects of the degree of urbanization could be made with respect to public housing developments, the relationship between soil lead and housing unit characteristics in public housing was analyzed with respect to building age and the presence and condition of lead-based paint. The findings showed that these relationships were similar to those in private housing data. The building age was the most important predictor of soil lead concentrations. The Census region in which the development was located was an important predictor of soil lead after adjusting for the age of the development. Housing unit variables that were correlated with soil lead but were not significant predictors of soil lead after adjusting for the age of the development and the Census region included the number of family units in the public housing development (which was slightly correlated with the development's building age) and the condition of lead-based paint in and around the housing unit.