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.