The authors estimate that the dangerous levels of lead in these low- and middle-income countries cause a loss of five to eight IQ points across the population as well as more than 51,000 DALYs. They estimate that the exposure in these settings causes mild mental retardation in roughly six out of every 1,000 people. Those numbers sound reasonable based on the scale of the work, says Bruce Lanphear, professor of children's environmental health at Simon Fraser University in Vancouver, who is not involved with the study.
Clearly, the impact of this kind of toxic exposure is worrisome, Chatham-Stephens says. “If you lose one IQ point, it’s important to think about how much that reduces lifetime learning, and to think about its economic impact. With this data we can start to think about the economic losses at these sites and how much it costs to clean them up—and then how much you will save by cleaning up these sites and not having these exposures.” Most of these places have no waste cleanup programs, the authors note.
Although the scientific community is generally aware of the issues, “no one has tried to document these exposures in terms of what happens, and this first step is a reasonable approach,” says Kyle Steenland, an environmental health professor at Emory University’s Rollins School of Public Health who studies occupational lead exposure. He cautioned that because the studies rely so heavily on estimates, the data must be considered as just a first attempt to quantify the issue. “There is a large amount of uncertainty at each step here.”