Background: Exposure to environmental levels of lead (Pb) and manganese (Mn) has been associated with detrimental effects to neurodevelopment. However, little is known about the potential association between environmental levels of Pb and Mn on intelligence of children. The aims of the study were to investigate the association of community level of Pb and Mn with the intelligence of school-aged children, and to explore the implications of joint exposure to these two heavy metals.
Methods: A cross-sectional examination of blood Pb and Mn concentrations was performed, and the intelligence quotient (IQ) was determined for 261 Korean children aged 8-11 years.
Results: The mean blood concentrations of Pb and Mn were 1.73 microg/dL (SD=0.8; median=1.55; range=0.42-4.91) and 14.3 microg/L (SD=3.8; median=14.0; range=5.30-29.02), respectively. Both Pb and Mn showed significant linear relationship with full-scale IQ (Pb, beta=-0.174, p=0.005; Mn, beta=-0.123, p=0.042) and verbal IQ (Pb, beta=-0.187, p=0.003; Mn, beta=-0.127, p=0.036). Blood Pb (DeltaR(2)=0.03) and Mn (DeltaR(2)=0.01) explained 4% of the variances of the full-scale IQ and 5% of the variances of the verbal IQ. When Pb and Mn levels were entered as predictive variables, additive increase in the explained variances was observed. Finally, full-scale IQ and verbal IQ of the children with blood Mn>14 microg/L showed significant association with Pb, whereas group with Mn<14 microg/L did not, suggesting effect modification between Pb and Mn.
Conclusions: The present study suggests the presence of additive interaction and effect modification between Pb and Mn on the intelligence of school-aged children, suggesting more attention should be paid to preventing the exposure of disadvantaged children to various combinations of toxic materials.