Over the past few decades, continuing efforts to eliminate lead exposure in children have dramatically reduced the incidence of elevated blood lead levels in the United States (defined by the U.S. Centers for Disease Control as greater than or equal to 10 micrograms per deciliter). But the mission is far from accomplished; the negative effects of lead are still obvious.
As researchers at Cornell University and Drexel University College of Medicine demonstrate in their recent article, a relationship between lead exposure and the academic achievement of children in New York State remains easily discernible. In New York, doctors are required by law to test children under six years of age for blood lead content; the incidence of blood lead over 10 micrograms per deciliter is recorded and published, county-by-county. And schools, in accordance with the U.S. No Child Left Behind law, are required to give their students standardized academic tests; results of these tests are similarly published, county-by-county. The authors of this article combined the two county-level data sets, wondering whether elevated lead continued to predict lower academic achievement despite the great advances made.
Their results indicated that the negative association between lead and achievement does remain quite significant. In fact, the association between the two was almost as significant as the association between two separate rounds of academic testing – lead exposure predicted later achievement almost as well as earlier academic achievement predicted later achievement.
From here, the researchers asked: could this association simply be function of the fact that higher income counties probably have higher achievement and lower lead? To answer this question, they tested for any confounding effects of income, obtaining county-level income data from the U.S. Census Bureau and statistically controlling for income. Ultimately, the association between lead and achievement remained, even after controlling for income. Differences in academic performance should most likely be attributed to the lead itself.
In and of themselves, achievement test scores are not of enormous importance. The far greater concern, of course, lies in the human potential that these scores imperfectly reveal is. And the findings presented in this article suggest that it is safe to estimate that millions of children in the United States are still having their potential reduced by lead. Vigorous efforts should be made to decrease children's exposure to lead even further; complacency should not result from the improvements that have been made to date.
Jillian C Strayhorn and Joseph M Strayhorn. Lead exposure and the 2010 achievement test scores of children in New York counties. Child and Adolescent Psychiatry and Mental Health 2012, 6:4 doi:10.1186/1753-2000-6-4.