Academic achievement among adolescents may be affected by early childhood lead exposure at much lower levels than previously assumed, according to a new study.
Just a small climb in blood concentrations of this toxic metal — still within the range currently deemed acceptable by public health agencies — was associated with worse performance on standardized tests, scientists found in the study, published on Wednesday in Environmental Health.
“Children’s exposure to lead has long been recognized as harmful to their health and neurodevelopment,” wrote the University of Iowa research team.
“The present work provides further evidence to support that there are no safe levels of lead and that there is a need to continue to reduce or eliminate lead exposure,” the scientists warned.
In 1991, the Environmental Protection Agency first issued a rule requiring utilities to monitor their drinking water for lead — mandating action if concentrations surpass 15 parts per billion (ppb), or 1.5 microgram per deciliter (μg/dL). Last year, the agency reduced that safety threshold to 10 ppb, or 1 μg/dL.
The Safe Drinking Water Act allows maximum lead content in pipes that touch water to be a weighted average of 0.25 percent across their wetted surfaces.
The Centers for Disease Control and Prevention (CDC) has historically published health guidelines for blood lead levels, lowering it in 2021 from 5 μg/dL to 3.5 μg/dL.
Yet the CDC and other health agencies also recognize that lower blood levels — below that 3.5 μg/dL bar — can still be harmful to child development, the authors noted.
As such, the researchers stressed the importance in understanding how blood lead concentrations that are currently considered “low” could still be impacting children.
To further that understanding, they decided to examine the association between a 1-unit change in early childhood levels within the CDC’s low range — levels less than 3.5 μg/dL — and academic performance in standardized math and reading tests taken between grades 2 and 11.
As a basis of comparison, the scientists also evaluated the effects of a similar 1-unit change in blood level levels in the range of 3.5 μg/dL or higher.
Other data informing the study came from birth certificates, as well as the standardized tests, from a broad sample pool of hundreds of thousands of students across Iowa.
Ultimately, the researchers found that a 1-unit increase in lead levels in the lower range was connected to lower math test scores by an average of -0.47 points and in reading by -0.38 points.
In the higher range, the 1-unit increase was associated with lower math test scores by an average of -0.52 points and in reading by -0.56 points.
The trend in score declines, the authors noted, applied to students across the entire study population, from grades 2 through 11.
“The declines in school tests associated with lead levels were generally steady across all grades, highlighting the persistence and permanency of the academic deficits associated with lead exposure,” the authors noted.
Emphasizing the notion that no safe lead level exists, the scientists urged policymakers to revisit current health thresholds. Those values, they explained, steer recommendations as to when individual interventions to mitigate developmental risks should occur.
“Reconsidering and potentially lowering current blood lead reference values for intervention may be needed to better address the associations of low-level lead exposures with cognitive and academic outcomes,” they added.
