The relationship between lead exposure and homicide.

CONTEXT Previous studies have suggested that excessive lead exposure is related to aggressive and violent behavior. OBJECTIVE To evaluate the association between estimated air lead concentrations and homicide rates. DESIGN Cross-sectional ecological study. SETTING All counties in the contiguous 48 states of the United States. EXPOSURE MEASURE: Estimated air lead concentrations and blood lead levels. MAIN OUTCOME MEASURE The homicide rate in each county. RESULTS Negative binomial regression was used to examine the relationship between air lead concentrations and the incidence of homicide across counties in the United States (N = 3111). After adjusting for sociologic confounding factors and 9 measures of air pollution, the only indictor of air pollution found to be associated with homicide rates was air lead concentration. Across all counties, estimated air lead concentrations ranged from 0 to 0.17 microg/m(3). The adjusted results suggest that the difference between the highest and lowest level of estimated air lead is associated with a homicide incidence rate ratio of 4.12 (95% confidence interval, 1.02-16.61). CONCLUSION The results of this study support recent findings that there is an association between lead exposure and violent behavior.