The U.S. Centers for Disease Control and Prevention has revised its blood lead reference value, which determines when children aged 1-5 are considered to have high lead exposure. Since 2012, this level was set at 5 micrograms of lead per deciliter of blood; children at or above this level were in the top 2.5% for the highest blood lead levels nationally. Now, influenced by recent federal health surveys, the CDC has lowered this threshold to 3.5 micrograms per deciliter. Environmental scientist Gabriel Filippelli, an expert on urban lead poisoning in children, explains the public health implications of this change. The Centers for Disease Control regularly evaluates national data on children’s blood lead levels. This new, lower value represents the average blood lead level that 2.5% of tested children surpassed. Many clinics have on-site screening devices that use electrochemical detection to quickly test a small blood sample from a fingertip prick. If these tests are positive, doctors refer children for a larger blood sample drawn from a vein for analysis in a diagnostic lab. Although the clinical test is quick, inexpensive, and relatively painless, the venous blood draw is considered the benchmark for diagnosing lead poisoning.
On-site clinical devices typically detect lead at concentrations as low as 3.2 micrograms per deciliter, so the new CDC guidelines mean that nearly all children showing positive screening results will be referred for additional testing. This approach is more protective from a public health standpoint. However, this update will approximately double the number of children classified as having the highest risk for lead poisoning. Previously, children needed at least 5 micrograms per deciliter of lead in their blood to be in that category; now, it will include many more children with slightly lower blood lead levels. The increased number of affected children means many states will struggle to afford testing and follow-up care, which can involve dietary changes, medications, and removing lead exposure sources unless Congress increases federal funding for lead poisoning prevention and treatment programs.
The most widespread source, especially in urban settings, is soil and dust originating from soil. Urban soils typically have lead concentrations that range from harmless to hazardous due to years of emissions from deteriorated lead-based paint, leaded gasoline, and industrial sources. Children may come into contact with lead by playing in or touching contaminated dirt or inhaling the dust. The U.S. Environmental Protection Agency sets the limit for lead in soils at public play areas at 400 parts per million, which is much higher than typical background levels of about 20 to 50 parts per million. This action level has been in place for decades, despite studies suggesting it is too high as a public health guideline. Some U.S. states, like California, have much lower limits. In my experience, urban soils, particularly near building exteriors where lead accumulates from degraded paints or dust, can have much higher levels. Neighborhoods in cities with the most lead contamination are often the poorest and have the highest percentage of nonwhite children. This situation is a result of historical racist housing practices that concentrated people of color into less desirable areas. Residents in these areas can have significantly higher rates of elevated blood lead levels than those in wealthier neighborhoods. Lead-based paint also poses a significant exposure risk, especially in poorly maintained buildings.
Since lead paint is sweet-tasting, children may chew on paint chips or painted wood. Lead water pipes are a third source, though less common than paint or soil. Many cities and towns across the U.S. have lead service lines delivering water to homes. When appropriately treated, water forms a protective plaque on the inside of pipes, keeping lead out of the water. However, some cities like Washington, D.C., Newark, New Jersey, and Flint, Michigan, have altered water sources or treatment methods in ways that removed this protective plaque, allowing lead to reach household taps. These water crises disproportionately impacted communities of color. Historically, public health efforts targeted children with acute lead poisoning who displayed clear neurocognitive issues such as attention deficit, memory problems, agitation, and tremors. As lead was phased out from most household uses in the mid-20th century and the U.S. population’s blood lead levels dropped, these apparent clinical symptoms of lead poisoning became less common. Now, more subtle neurocognitive deficits are observed, assessed by scientists and medical experts through neurological and behavioral tests. A child diagnosed with high blood lead levels today might perform poorly on standardized tests, act disruptively at school or home, or struggle with information retention.
Follow-up research in Flint shows many infants and toddlers exposed to lead-contaminated water in 2015 face challenges in school today. These tests demonstrate that blood lead levels even below the new standard can impact performance, supporting the conclusion by researchers and the CDC that no safe blood lead level exists for children. Blood lead levels have been declining since major environmental sources of lead were eliminated starting in the 1970s, such as leaded gasoline, lead-based paints, and industrial emissions. Recent analyses indicate the median blood lead level for U.S. children aged 1-5 is approximately 0.7 micrograms per deciliter today, compared to 15 micrograms per deciliter in the late 1970s. Yet, Black children and those living in poverty have average blood lead levels 13% higher than this national average, placing many at risk. For instance, in a 2019 study, my colleagues at Notre Dame and I analyzed blood lead levels of over 18,000 children in St. Joseph County, Indiana, including the town of South Bend.
In some areas, over 30% of children had blood lead levels above 5 micrograms per deciliter, and over 65% of census tracts had average blood lead levels exceeding that safety limit. We also found no systematic, risk-informed approach to testing. In areas with the highest potential risks based on poverty, less than 6% of eligible children had lead test results reported to the county health department comparable to other, wealthier census tracts. Without more screening and efforts to eliminate lead exposure in at-risk communities, this issue won’t be resolved soon. This article has been updated to include a link to an article advocating for lower limits on lead in soils at public play areas.