February 27, 2012
Three common environmental chemicals– lead, organophosphate pesticides and methylmercury– may have effects on children's IQ in the overall population to the impacts of major medical conditions such as preterm birth or ADHD – two of the most prevalent in U.S. children.
Exposure to chemicals in the environment can significantly affect a child's developing brain and nervous system. The exposures can lower IQ, alter behavior and influence social relationships. Lead, organophosphates and methylmercury are three contaminants known to harm a growing child's nervous system. Lead exposure occurs mainly through paint in older buidlings and lead-contaminated soil and dust. Organophosphate pesticides are used on crops and in homes, so children can eat or breathe the chemicals.The potential public health impacts of environmental exposures on children's nervous systems is significant, according to this study that compares the estimated drops in IQ related to exposures with those related to medical conditions.
According to the study, lead and organophosphates together would have more impact than preterm birth or ADHD, two disorders that have considerable societal burden.
The results are important because they are the first to estimate in a population the extent of cognitive losses from environmental exposures. Previous studies have evaluated IQ losses in individuals, which can vary widely in children. Examining IQ effects in populations gives a better indication of impacts on society.Medical conditions can also affect thinking and learning abilities. For instance, major health problems, including birth defects, preterm birth, ADHD, autism and brain injuries also affect cognitive and social challenges in school, family and life.
Although environmental exposures and medical conditions can both harm children's intelligence, no studies have quantified the public health impact on children's IQ at a populational level or compared the potential harm from the environment versus medical conditions.
Comparing the potential impact on children's intelligence from these sources would help determine if preventing exposures would reduce cognitive deficits in U.S. children.
Lead exposure in U.S. children could be related to about a 23 million IQ point loss in the population, making it the most harmful environmental exposure among the three examined.