It's well known that exposure to lead can harm young children's brain development. Now a new study suggests that racial segregation may be compounding the detrimental effects of lead on Black children.
The study, of close to 26,000 schoolchildren, found that Black children with elevated blood lead levels had worse scores on standardized reading tests. And that effect was made worse when they also lived in neighborhoods that were highly racially segregated.
The specific reasons for the findings are unclear, researchers said. But neighborhood segregation has deep roots in history, where practices such as "redlining" isolated many Black Americans in areas with high poverty rates and little to no investment.
"Residential segregation is not an accident," said lead author Mercedes Bravo, an assistant research professor at the Duke Global Health Institute in Durham, N.C. "It's the result of many years of structural racism that separated people into different neighborhoods."
Lack of investment in predominantly Black neighborhoods has historically meant fewer businesses, fewer job opportunities, poorer housing and difficulty accessing basics ranging from grocery stores to health care.
The new findings suggest that those factors can "interact" with lead exposure to worsen Black children's reading performance, according to Bravo.
Lead is a naturally occurring metal that can cause serious health effects if it accumulates in the blood. Children under 6 are particularly vulnerable, as lead can damage their developing brains and cause learning or behavioral problems.
Lead was once widely used in house paints and gasoline. While those practices were phased out decades ago in the United States, there are still many ways for children to be exposed, according to the U.S. Centers for Disease Control and Prevention.
Children living in homes built before 1978 -- when lead-based paint was banned -- can be at risk if that old paint is still in place, and is chipped or peeling.
Kids can also be exposed by playing in lead-contaminated soil -- near highways, factories or airports, for example -- or by drinking water that flows through lead pipes.
It all means that Black children living in poverty are at increased risk of being exposed to lead. A study last year found that 58% of children from predominantly Black neighborhoods had detectable levels of lead in their blood, compared to 49% of kids in mostly white neighborhoods.
"That's what makes this new study so important," said David Cwiertny, director of the University of Iowa's Center for Health Effects of Environmental Contamination. "These are kids who are already more vulnerable to lead exposure."
If other factors in their environment "compound" the effects of lead, that's worrying, said Cwiertny, who was not part of the new research.
There is no "safe" blood lead level in children, Cwiertny said. But the CDC considers a level of 3.5 micrograms per deciliter (mcg/dL) to be higher than normal.
The current study, published Aug. 15 in the Proceedings of the National Academy of Sciences, involved 25,699 North Carolina children who had their blood lead levels screened at some point. They all took standardized reading and math tests in fourth grade.
Bravo's team found that when Black children had relatively lower lead levels (1 to 3 mcg/dL), neighborhood segregation had no bearing on their reading test scores. But among Black kids with higher lead levels (4 mcg/dL or more), those living in highly segregated neighborhoods had worse reading scores. And the higher kids' lead levels were, the greater the impact of neighborhood segregation.
Bravo noted that the bigger picture is not all bleak: Kids today are exposed to less lead than their counterparts decades ago.
But, she said, the "enduring legacy of structural racism" means that Black children have greater exposure to lead and other environmental hazards and stressors.
"That's not acceptable," Bravo said.
"We haven't done enough to reduce sources of lead exposure," he said. Leaded gasoline, for example, is still used in aviation because alternatives have not been developed. And lead service lines (underground water pipes) put in place in the early 20th century remain in many cities and communities.
The U.S. Environmental Protection Agency has estimated there are between 6 million and 10 million lead service lines nationwide. Federal funding is available to assist states and utilities in replacing them.
But, Cwiertny said, local authorities often don't even know where their lead service lines are located.
The U.S. Centers for Disease Control and Prevention has more on lead exposure.
SOURCES: Mercedes Bravo, PhD, assistant research professor, Duke Global Health Institute, Duke University, Durham, N.C.; David Cwiertny, PhD, professor, civil and environmental engineering, and director, Center for Health Effects of Environmental Contamination, University of Iowa, Iowa City; Proceedings of the National Academy of Sciences, Aug. 15, 2022