7 March 2013. A new study from Detroit has linked early childhood data on blood-lead concentrations to educational assessment scores from school grades 3, 5, and 8 during 2008-2010. The researchers managed to obtain both sets of results for over 21,000 students. The highest blood-lead concentration before age 6 years averaged just above 7 microgram per deciliter (ug/dL). These elevated exposures are thought to be mainly due to lead paint in old housing. Detroit in fact ranks fourth among large US cities in regard to frequency of lead poisoning.
The researchers found that proficiency in reading, mathematics, and science clearly declined at higher lead exposures. Compared with children with the lowest exposure (blood-lead below 1 ug/dL), those with levels between 1 and 5 ug/dL had a 40% increased risk (computed as an odds ratio) of being less than proficient in the three tests, the risk doubled for lead levels between 6 and 10, and it further increased at higher exposures. In this study, 90% of children were African-American, and 80% qualified for free school lunch. The children with complete data did not differ from other Detroit school kids. But the results may reflect more serious outcomes of brain drain in disadvantaged children.
In a more general sense, the findings on poor academic achievement are in agreement with many previous reports on decreased scores on IQ tests at higher lead exposures. Thus, children who do poorly on cognitive tests are also more likely to do poorly in school. And both are related to lower education and lower lifetime income.
The World Health Organization concluded in 2011 that there is no safe limit for lead exposure, as had also been concluded in other recent expert reports. The following year, the US Centers for Disease Control and Prevention lowered its reference level to 5 ug/dL. This limit is clearly not protective.