Racial segregation makes consequences of lead exposure worse

Growing evidence shows how residential segregation can contribute to racial disparities in health. Real Window Creative / Shutterstock

Racial residential segregation—in which racial or ethnic groups live in separate, unequal neighborhoods—tends to concentrate factors that contribute to racial disparities in health. These include socioeconomic and environmental stressors. Racial residential segregation is associated with differences in death rates, pregnancy outcomes, and chronic diseases.

Researchers have been exploring the relationship between racial residential segregation and children’s cognitive development. Lead exposure is known to cause cognitive and developmental problems in children. Kids can be exposed to lead via lead-based paint, lead pipes, or proximity to sources of lead pollution. These factors tend to be more prevalent in poor neighborhoods. But few, if any, studies have evaluated the complicated relationships between residential segregation, lead exposure, and cognitive development.

An NIH-funded research team from Duke University, Rice University, and the University of Notre Dame linked detailed birth records with lead screening and standardized testing data for almost 26,000 children in North Carolina. The children were all born in the year 2000. Standardized testing occurred 10-11 years later, at the end of fourth grade. The researchers also developed a measure of racial residential segregation in different areas. Results appeared in the Proceedings of the National Academy of Sciences on August 23, 2022.

Overall, non-Hispanic Black children had higher median blood lead levels than non-Hispanic white children. More than 80% of the Black children experienced economic disadvantage. Black children also lived in areas with greater racial residential segregation than white children, both at birth and at the time of the standardized testing.

Reading test scores declined with higher levels of either blood lead or racial residential segregation at the time of testing. The researchers also found that blood lead levels and residential segregation interacted to affect reading test scores among the Black children. For those with low blood lead levels, test scores were not affected by racial residential segregation. However, among those with higher blood lead levels, test scores decreased as racial residential segregation increased. This effect became more marked as blood lead levels increased.

Math test scores also declined as blood lead levels increased. But the researchers didn’t find an interaction between blood lead levels and racial residential segregation on math scores.

The findings suggest that racial residential segregation may compound the harms of lead exposure and impede children's cognitive development. Black children were more likely than white children to experience the worst of both. This understanding may lead to better targeting of interventions.

“This study reminds us that there is an enduring legacy of structural racism and environmental injustice that may be systematically disadvantaging specific groups and communities of children,” says lead author Dr. Mercedes Bravo at Duke University. “Taking a more holistic approach to examining what children are exposed to in their physical and social environments is critical to addressing health disparities and advancing health equity.”

—by Brian Doctrow, Ph.D.