Long-term effect of increased lead absorption on intelligence of children

The authors examined the reversibility of cognitive impairment caused by a mild increase in lead absorption among children. The results of our initial study revealed that air and soil outside a lead-recycling plant in Taiwan were seriously contaminated by lead, which was associated with lowered inte lligence quotients of 32 children who attended a nearby kindergarten (i.e., kindergarten A). Thirty-five children-who were comparable with respect to age, sex, birth order, sibling number, and parental education level-from an other kindergarten (i.e., kindergarten B) located 5 km from the plant were enrolled as the reference group. Following the initial study, kindergarten A school children moved 2 km from the lead-recycling plant. Twenty-eight ch ildren in each group were followed successfully 2.5 y later. Blood lead, in telligence quotient, and intelligence quotient-related factors were reasses sed. The results showed that the average blood lead level of the exposed pu pils dropped 6.9 mu g/dl (standard deviation [SD] = 3.9 mu g/dl) (p < .001) , and the average intelligence quotient increased 11.7 points (SD = 13.2) ( p < .01), compared with the results of the initial study. The average blood lead level of the reference group decreased by 1.7 mu g/dl (SD = .1.3) (p < .001), whereas the average intelligence quotient increased by 4.2 points (SD = 13.8) (p = .115). There was a significant difference in intelligence quotients between the two groups during the initial study, but the differen ce subsequently disappeared during the follow up. The authors concluded tha t intelligence quotient impairment, caused by a mild subclinical elevation of blood lead (i.e., likely no more than 30 mu g/dl) for a period of 1-3 y in 3- to 5-y-olds, is at least partially reversible.