Lead poisoning survey: this document presents updated results of a 1995 U.S. Government survey of the extent of lead based paints on homes and includes a critique of the methodology of lead based paint studies as well.
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Our page top photo shows a professional paint crew preparing the exterior of a historic home for re-painting. While lead levels in children in the U.S. have dropped, this environmental contaminant continues to be a concern. This website provides an overview of and links to more in-depth articles about the common lead sources, risks, and steps to take. Also see Lead Enviro-Scare.
April, 1995 (EPA 747-R-95-003), Last updated on Friday, January 27th, 2006 PUBLIC DOCUMENT - SOURCE URL: http://www.epa.gov/oppt/lead/pubs/es_epa747-r-95-003.htm provided un-edited below except for added links to key headings.
Lead is a powerful toxin that attacks the central nervous system and is particularly damaging to the developing nervous systems of young children. High levels of lead in the blood can result in convulsions, mental retardation, and even death. Further, recent medical research has found that low levels of lead exposure have more serious health consequences that previously thought. Effects include reductions in intelligence and short-term memory, slower reaction times, and poorer hand-eye coordination.1
Although there are many sources of lead in the environment, including drinking water, food, emissions from gasoline combustion, and industrial emissions, it is clear that lead-based paint plays a major role in high blood lead levels. Recent research indicates that dust and soil may be the most significant pathway for low-level lead exposure, and that lead-based paint is an important source of household dust lead.2,3
The 1987 amendments to the Lead-Based Paint Poisoning Prevention Act required the Secretary of Housing and Urban Development (HUD) to prepare and transmit to Congress "a comprehensive and workable plan" for the abatement of lead-based paint in housing and "an estimate of 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 mandate, HUD sponsored a national survey of lead-based paint in housing and delivered a Report to Congress on a Comprehensive and Workable Plan for the Abatement of Lead-Based Paint in Privately Owned Housing in December, 1990. The Comprehensive and Workable Plan report was completed under a tight, Congressionally mandated schedule and focused on motivating, developing and presenting the comprehensive plan required by Congress. As such, it only reported the estimates of the extent of lead-based paint in housing required by Congress and provided a brief description of the survey methodology.
This report, sponsored by the Environmental Protection Agency, is a comprehensive technical report on the HUD-sponsored national survey of lead-based paint in housing. It provides a detailed description of the survey methodology. It reports on wide ranging analyses of the national survey data.
It reports revised estimates of the extent of lead-based paint in housing, based on a thorough investigation of the multiple sources of error - variability and bias - in the data. These error sources include non response biases, sampling variability between housing units, sampling variability within housing units, X-ray fluorescence device (XRF) measurement error, and laboratory analysis error. The analysis underlying the estimates presented in the Comprehensive and Workable Plan (CWP) report incorporated only sampling variability between housing units.
Extent of Lead-based Paint in Housing - Revised Estimates
The number of housing units classified as having lead-based paint depends on the definition employed to classify a housing unit as having lead-based paint. The definition used here classifies a home as having lead-based paint if the measured lead concentration on any painted surface is 1.0 mg/cm2, or greater.
As reported in the CWP report, lead-based paint is widespread in housing. The revised estimate is that 64 million homes (� 7 million) 4, 83 percent (� 9%) of the privately owned housing units built before 1980, have lead-based paint somewhere in the building. (Fifty-seven million (� 5 million) homes, or 74 percent (� 6%), were reported in the CWP.) Twelve million (� 1 million) of these homes are occupied by families with children under the age of seven years old. An estimated 49 million (� 7 million) privately owned homes have lead-based paint in their interiors. There are no statistically significant differences in the prevalence of lead-based paint by type of housing, market value of the home, amount of rent payment, household income, or geographic region.
Seventeen percent of the pre-1980 housing stock have dust lead levels in excess of the federal guidelines5, independent of the presence or absence of lead-based paint. However, excessive dust lead levels are associated with the presence of damaged lead-based paint. Fourteen million homes, 19 percent of the pre-1980 housing stock, have more than five square feet of damaged lead-based paint. Nearly half of them (47 percent) have excessive dust lead levels.
Excessive soil lead levels6 are also associated with the presence of damaged lead-based paint. While 21 percent of all pre-1980 homes have excessive soil lead levels, nearly half of the 10 million homes with non-intact lead-based paint on exterior walls have excessive soil lead levels.
Although a large majority of pre-1980 homes have lead-based paint, most of them have relatively small areas of it. The average privately-owned housing unit with lead-based paint has an estimated 601 square feet of it on interior surfaces and 869 square feet on exterior surfaces.
Over half of the leaded paint is on walls, ceilings, and floors. (For comparison, the walls in a room 10' by 12', with an 8' ceiling, have an area of 352 square feet.) The amounts of lead-based paint per housing unit vary with the age of the dwelling unit. Pre-1940 units have, on average, about three times as much lead-based paint as units built between 1960 and 1979.
Lead paint is even more widespread in public housing; 86 percent (� 8%) of all pre-1980 public housing family units have lead-based paint somewhere in the building.
While most public housing units have some lead-based paint, most of them have small areas of surfaces covered with it. The average public housing unit with lead-based paint has an estimated 367 square feet on interior surfaces and 133 square feet on exterior surfaces. Most of the interior lead-based paint is on walls, while very little of the exterior walls are painted.
4. The numbers in parentheses are 95% confidence intervals.
5. The federal guidelines vary with the location of the dust: 200 micrograms of lead per square foot for floor samples, 500 ug/sq ft for window sills and 800 ug/sq ft for window wells. 6. EPA interim guidelines for soil lead action levels are 500 ppm for residential soil associated with Superfund sites.
The objective of the national survey of lead-based paint in housing was to obtain data for estimating: (1) the number of housing units with lead-based paint; (2) the surface area of lead-based paint in housing, to develop an estimate of national abatement costs; (3) the condition of the paint; (4) the prevalence of lead in dust in housing units and in soil around the perimeter of residential structures; and (5) the characteristics of housing with varying levels of potential hazard, to examine possible priorities for abatement.
The study population consisted of nearly all housing in the United States constructed before 1980. Vacant housing, group quarters, Alaska and Hawaii were excluded for operational reasons. 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 lead paint in homes survey was conducted between December 1989 and March 1990 in 30 counties across the 48 contiguous states, selected to represent the entire United States housing stock, both public and privately-owned. The total sample size is 381 dwelling units, 284 privately owned and 97 publicly owned. The sample was small, but it provided estimates that were sufficiently precise to develop the CWP for private and public housing.
Within each housing unit, two rooms were randomly selected for inspection; one room with plumbing (wet) and one room without plumbing (dry). In each of these two rooms, the field technicians inventoried painted surfaces, measured their dimensions, and assessed the condition of the paint; they measured the lead concentration in randomly selected painted surfaces; and they gathered samples of dust.
Since not all rooms in a dwelling unit were inspected, it is possible to miss lead-based paint when it is really present somewhere else in the dwelling unit. To reduce the chances of mis-classifying a dwelling unit with lead-based paint as lead-free, additional lead readings, termed purposive readings, were taken on surfaces that, in the opinion of the field technicians, were most likely to have lead-based paint. In some dwelling units, these additional purposive samples did, indeed, find lead-based paint in dwelling units where no lead-based paint had been found in the randomly selected rooms.
Exterior painted surfaces were inventoried and measured and lead readings taken according to protocols similar to those used in the interior. Soil samples were also taken at selected locations around the building exterior. Common areas were also sampled and inspected.
Lead in paint measurements were made with portable Scitec MAP-3 spectrum analyzer XRF devices (MAP/XRFs), which NIST had determined to be more accurate and more precise than the direct-reading XRFs used in earlier surveys. Although the MAP/XRFs were an improvement over the earlier direct reading XRFs, they still had limitations. In particular, MAP/XRF measurements made over brick or concrete were less accurate and less precise than those made over wood or plaster. These limitations notwithstanding, portable MAP/XRF technology was used because the survey included occupied dwellings where it was not feasible to take paint scrapings for laboratory analysis.
Data were collected on lead in dust and soil in a number of locations in each sampled dwelling unit. Dust samples were collected by vacuuming randomly selected floor locations, window sills and window wells in the wet room and again in the dry room. In addition, a dust sample was collected from the floor just inside the main entrance to the dwelling unit. Soil samples were taken outside the main entrance to the building, at a selected location along the drip line of the sampled exterior painted surface, and at a remote location away from the building but still on the property. Dust and soil samples were analyzed for lead concentration.
Analyses of the Sources of Error
An analysis was conducted of the private housing non response in the national survey to estimate the potential for non response bias. This analysis was necessary because intrusive studies that impose significant burdens on the respondents tend to have lower response rates than less burdensome studies and, therefore greater potential for non response biases. In this survey, 53 percent of the homes asked to permit the inspection visits cooperated fully with the study.
The non response analyses did not reveal any evidence of potential non-response biases associated with ethnicity, building age, or family income. There were statistically significant associations between the response rates and monthly rent in tenant-occupied housing units and current market value in owner-occupied housing; the lower ends of both distributions were somewhat under represented.
There was a strong positive correlation between inspected housing units in the same census block with respect to the presence of lead in paint, dust, and soil. On balance, these findings suggest that the potential bias due to non response is likely to be small.
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The MAP/XRF measurement equipment used to detect and quantify lead in paint tended to yield readings that were biased, i.e., systematically different from the actual lead concentrations measured. Quality assurance (QA) data collected daily during the national survey field period permitted the estimation of the MAP/XRF bias. MAP/XRF readings were made on shims of known lead concentration placed over selected substrate materials. A shim is a piece of hard paper painted with lead-based paint.
There were four substrate materials, wood, drywall, steel, and concrete, selected to represent the typical range of substrate materials encountered in residential construction. Statistical techniques were applied to the QA data to develop calibration equations for adjusting the MAP/XRF readings for measurement bias. The MAP/XRF readings taken in the housing units were therefore adjusted to statistically correct for measurement bias.
There are two major factors that induce misclassification errors. First, the MAP/XRF equipment also has random variability in its measurements.
This variation can induce a classification bias, that is, a bias in the estimated prevalence of housing units with lead-based paint. Second, the protocol for inspecting a housing unit for lead-based paint provided for sampling painted surfaces for MAP/XRF measurement, rather than measuring the lead content of every painted surface in the housing unit.
Under this inspection protocol, it is possible for a housing unit to have some surfaces with lead-based paint, other painted surfaces without lead-based paint, and only the lead-free surfaces selected for MAP/XRF measurement. Such housing units would be incorrectly classified as not having lead-based paint.
To adjust for these classification biases, the distribution of lead concentrations on the untested painted surfaces, in the sampled rooms and in the un sampled rooms, in each household was simulated. (No applicable, adequate data set existed to permit the direct estimation of these biases.)
This extension from the measured surfaces to all surfaces in the unit was based on (1) data on the number of rooms in the unit, (2) data on the number of surfaces per room, and (3) assumptions about the relationship of the lead concentrations on unmeasured surfaces to those on the sampled and measured surfaces. The model was observed to be consistent with the National Survey data.
The misclassification rates were estimated for the simulated housing units, and used to adjust the prevalence estimates accordingly.
All findings on the lead hazard in homes reported elsewhere in this report incorporate the results of this error analyses. That is, the raw MAP/XRF readings have been statistically corrected for measurement bias and the misclassifications due to measurement variation and sampling within dwelling units have been corrected.
The national estimate of prevalence of lead-based paint in privately-owned housing is 83 percent. Without the statistical corrections described above, the estimate would have been 74 percent.
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