We know that children that are exposed to lead suffer from lower IQ and decreased cognitive ability. A recent study found that children who experienced higher lead exposures saw their intellectual ability decline from their baseline starting point as time wore on---meaning that the lead exposure continued to have a negative effect on a person’s cognitive learning abilities years after the initial exposure.
The study followed 560 people in Dunedin, New Zealand from the 1970’s to present. Participants were tested on their cognitive abilities as children and again when they turned 38 years old. The tests showed that the more lead children were exposed to the less likely they were to have higher paying jobs. In addition, the dips in IQ and in socioeconomic status were found to be mild but even small changes in IQ influenced people’s lives.
Importantly, in the United Status---unlike New Zealand where lead exposure impacts all socioeconomic groups---children living in low-income areas tend to be most at risk to lead poisoning. A series of North Carolina studies of over 57,000 children found that children with a BLL as low as 4 μg/dL (40 parts per billion (ppb)) at three years of age were significantly more likely to be classified as learning- disabled than children with a BLL of 1 μg/dL (10 ppb). Researchers also found a dose-response relationship between end-of-grade test scores and BLL: BLLs of 3 μg/dL(30 ppb) and above were associated with decreases in test scores. Furthermore, children with a higher BLL were less likely to place into advanced and intellectually gifted programs. These results held true even when researchers accounted for factors such as race, family income, and other factors that might affect learning-disabled status. One of the North Carolina studies found that once BLL was taken into account, race was no longer a predictor of being classified as learning-disabled. For more information on the health effects of lead exposure on children click here.