Previous studies have shown that chemical exposure can harm a child's individual IQ. Lead, in particular, has repeatedly been linked to developmental delays and lowered IQ. But for the first time, researchers are looking at the overall impact of chemical exposures to the IQ of all children in society — and the results are grim.
The purpose of the study, published in Environmental Health Perspectives, was to quantify the impact of chemical exposure on children's IQ at a societal — not an individual — level. To do this, researchers looked at published data from studies that evaluated the impact of environmental exposures to certain chemicals — lead, organophosphates and methylmercury — on children's IQ based on 25.5 million children under age 5 in the United States.
The results? Lead exposure was linked to the loss of roughly 23 million IQ point loss across the population, making it the most harmful environmental exposure among the three examined. Organophosphate pesticides reduced IQ by 17 million points at the population level. And methylmercury was responsible for the loss of about 0.3 million IQ points lost in U.S. children.
Combined, the three chemicals decrease the U.S.'s population-wide IQ for children by 40 million points.
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