Three toxins that have been found to affect children’s developing brains and nervous systems—lead, organophosphate pesticides, and mercury—have been found to impact children’s IQ in the overall population, according to a recent study published online in the journal Environmental Health Perspectives.

Most studies evaluating the effects of toxins look at one toxin in a relatively small group of people. This new study instead analyzed published data on the impact of environmental exposures and medical conditions on childhood intelligence in 25.5 million children under age 5 in the United States.

The researchers found that lead exposure in U.S. children was related to about a 23 million IQ point loss in the population, the highest of the three toxins analyzed. Organophosphate pesticides represented a 17 million point loss in IQ over the population. Methylmercury accounted for 0.3 million IQ points lost, population wide.

When comparing these amounts of IQ loss to those from other medical conditions, the researchers found that preterm birth, which affects 12 percent of newborns, accounted for 34 million IQ points lost. ADHD (Attention-deficit hyperactivity disorder) accounted for 17 million points lost, and autism and traumatic brain injuries each accounted for 7 million IQ points lost across the population. 

When combined, toxin exposure from lead, organophosphate pesticides, and mercury, account for more loss in IQ in U.S. children under 5 than does ADHD or preterm birth. This is a substantial effect in our children, yet, what is being done to reduce this exposure? Not enough, I say.