A further analysis of Evens’s data looked at the average blood lead level for each school in the Chicago Public Schools system. The most widely recognized standard for lead poisoning is ten micrograms per deciliter in a child’s blood. Recently the CDC lowered that standard to five micrograms per deciliter—what the agency refers to as the “level of concern.”
Taking an average of the third-graders’ blood lead levels for each school, the data showed that nearly 75 percent of schools have an average blood lead level over five. In the worst schools, average levels top ten, going as high as 16. Using this new CDC guideline, the number of children considered lead poisoned in Chicago jumped considerably—from one in 80 children to one in ten, according to data from the Illinois Department of Public Health.