Purpose
Because lead is a toxin that can have long-term impacts on physical health and brain development, understanding the sources of exposure is vital to identifying lead risks and preventing further exposure. Lead-based paint in homes built prior to 1978 is a known exposure source. Deteriorating lead-based paint can be toxic to people, and young children are particularly vulnerable. While there are many potential sources of lead exposure, living in older housing and in low-income households are known risks for childhood lead exposure.
History
We created Version 1 (V1) of the Lead Exposure Risk Index in 2016 after reviewing multiple possible geospatial risk factors for estimating geographic lead exposure risk. The Washington State Department of Health (DOH) Childhood Lead Poisoning Prevention Program, in collaboration with the State Health Officer and a multi-expert review panel, identified age of housing and poverty as primary risk factors for lead exposure. Poverty is closely linked to housing conditions, as households with limited financial resources may be more likely to live in older homes with deteriorating paint and deferred maintenance. This increases the risk of lead exposure.
There are many known risk factors for exposure, including having a sibling or playmate with an elevated blood lead level, parents who work in an industry where lead is used, some traditional spices and cosmetics, and even imported cookware. However, we did not have sufficiently high-quality data to include these variables as risk factors.
V1 of the map used 2010 census tract boundaries.
In 2024, we developed Version 2 (V2) of the Lead Exposure Risk map to incorporate updates to the housing-related lead risk measure. These included using 2020 census tract boundaries and new data on lead exposure risk by decade of housing construction.
Data Sources and Weighting
The Lead Exposure Risk Index combines the age of housing and poverty into a single map at the community level. The map represents the combined risk from both poverty and the age of housing.
Age of housing. Data on housing age comes from the U.S. Census’s American Community Survey’s 5-year rollup (2018-2022). This dataset provides the total number of houses and proportion of houses by year of construction.
Age of housing weights. We multiply the number of homes in each age group by a weight from zero to one. A weight of one means 100 percent of homes in this age category are estimated to be at risk of significantly deteriorated lead-based paint (LBP). The estimates we use come from U.S housing surveys. For V1 we used a housing survey conducted 1998 to 2000 from a publication by Jacobs, et al.[1] For V2 we used weights from the American Healthy Homes Survey II, which was conducted 2018 to 2019 (see Table 1).[2]
After multiplying the weights, the number of homes at risk are added up, and divided by the total number of homes for a given geography to get percentage of homes with significant lead risk.
|
Table 1: The biggest change in weights between Housing Surveys is for built from1940 to 1959 |
||
|
Age of Housing |
Jacobs et al. Survey |
American Healthy Homes Survey II (2018-2019) |
|
1960 to 1977 |
.08 |
.075 |
|
1940 to 1959 |
.43 |
.309 |
|
Before 1940 |
.68 |
.619 |
Figure 1 shows an example of how lead risk from age of housing was calculated for a fictitious census tract.
Fig. 1: Example calculation of lead risk from age of housing using a fictitious census tract:
| Construction Year | Number of Houses | Percent with Lead Hazards | Estimate of Homes with a Lead Risk |
|---|---|---|---|
| After 1978 | 100 | 0% | 0 |
| 1960-1977 | 100 | 7.5% |
7.5 |
| 1940-1959 | 100 | 31% | 31 |
| Before 1049 | 100 | 62% | 62 |
| Total | 400 | 100.5 | |
| Proportion of Homes with a Lead Risk | 100.5/400 | 25% |
Poverty. We used poverty data from the U.S. Census’s American Community Survey’s 5-year rollup (2018-2022). This dataset provides the total number of households living at or below 125% of the federal poverty line. There is a significant association between poverty and elevated blood lead levels.[3] Children who live below the poverty line in pre-1950 housing are at the greatest risk for lead exposure. These homes are more likely to have aging lead paint that is in poor condition.
Additional weighting. In V1, we used data from the Center of Disease Control’s Morbidity and Mortality Weekly Report (CDC’s MMWR) report on childhood blood lead testing. This reports age of housing and household poverty levels for those children tested.[4] We used this data to calculate the difference in likelihood of an evaluated blood lead test between exposure to old housing and poverty. We weighted poverty and age of housing data by these prevalence risk differences to calculate a combined overall rank.
However, for V2 we determined that the risk differences in poverty compared to age of housing were not stable over time. As a result, we decided to weight these two data measures equally in the index.
Information By Location (IBL) Rankings
IBL combines age of housing and poverty into a single into a single map at the community level. Each census tract is ranked from one to ten for how much lead exposure risk there is. Each ranking number represents one tenth of all census tracts in Washington (a decile).
Caveats
The rankings help to compare health and social factors that may contribute to disparities in a community. Rankings are relative, and do not represent absolute values. The rankings should not be used to diagnose a community health issue or to label a community.
This indicator models potential lead exposure based on the age of housing. The age of a building by itself does not reflect the actual exposure to lead. Some older homes have had lead paint removed through a process called remediation.
While the age of housing is an individual-level risk factor, this indicator summarizes the data at the census tract level, which may present challenges for interpretation. The aggregation of housing data to a larger geographic area means that not all homes within a census tract share the same risk. Since localized or household-level conditions can vary widely, people should consider checking the specific age of their own homes and their lead status.
[1] Jacobs, D. E., Clickner, R. P., Zhou, J. Y., Viet, S. M., Marker, D. A., Rogers, J. W., Friedman, W. (2002). The prevalence of lead-based paint hazards in US housing. Environmental Health Perspectives, 110(10), A599.
[2] U.S. Department of Housing and Urban Development, Office of Lead Hazard Control and Healthy Homes. American Healthy Homes Survey II: Lead Findings Report. October 29, 2021. https://www.hud.gov/sites/dfiles/HH/documents/AHHS%20II_Lead_Findings_Report_Final_29oct21.pdf.
[3] Centers for Disease Control and Prevention (CDC. (2013). Blood lead levels in children aged 1-5 years-United States, 1999-2010. MMWR. Morbidity and mortality weekly report, 62(13), 245.
[4] Pirkle, J. L., Kaufmann, R. B., Brody, D. J., Hickman, T., Gunter, E. W., & Paschal, D. C. (1998). Exposure of the US population to lead, 1991-1994.Environmental health perspectives, 106(11), 745.