Prenatal and postnatal blood lead concentrations are associated with higher rates of total arrests and/or arrests for offenses involving violence. This is the first prospective study to demonstrate an association between developmental exposure to lead and adult criminal behavior.
A cohort study done by researchers at the University of Cincinnati. Between 1979 and 1984, 376 infants were recruited. Their parents consented to have lead levels in their blood tested over time; this was matched with records over subsequent decades of the individuals’ arrest records, and specifically arrest for violent crime. Ultimately, some of these individuals were dropped from the study; by the end, 250 were selected for the results.
The researchers found that for each increase of 5 micrograms of lead per deciliter of blood, there was a higher risk for being arrested for a violent crime, but a further look at the numbers shows a more mixed picture than they let on. In prenatal blood lead, this effect was not significant. If these infants were to have no additional risk over the median exposure level among all prenatal infants, the ratio would be 1.0. They found that for their cohort, the risk ratio was 1.34. However, the sample size was small enough that the confidence interval dipped as low as 0.88 (paradoxically indicating that additional 5 µg/dl during this period of development would actually be protective), and rose as high as 2.03. This is not very convincing data for the hypothesis.
For early childhood exposure, the risk is 1.30, but the sample size was higher, leading to a tighter confidence interval of 1.03-1.64. This range indicates it’s possible that the effect is as little as a 3% increase in violent crime arrests, but this is still statistically significant.
For 6-year-olds, it’s a much more significant 1.48 (confidence interval 1.15-1.89). It seems unusual to me that lead would have such a more profound effect the older the child gets, but I need to look into it further.
We evaluate air Pb emissions and latent aggravated assault behavior at the scale of the city. We accomplish this by regressing annual Federal Bureau of Investigation aggravated assault rate records against the rise and fall of annual vehicle Pb emissions in Chicago (Illinois), Indianapolis (Indiana), Minneapolis (Minnesota), San Diego (California), Atlanta (Georgia), and New Orleans (Louisiana). Other things held equal, a 1% increase in tonnages of air Pb released 22 years prior raises the present period aggravated assault rate by 0.46% (95% CI, 0.28 to 0.64). Overall our model explains 90% of the variation in aggravated assault across the cities examined. In the case of New Orleans, 85% of temporal variation in the aggravated assault rate is explained by the annual rise and fall of air Pb (total = 10,179 metric tons) released on the population of New Orleans 22 years earlier. For every metric ton of Pb released 22 years prior, a latent increase of 1.59 (95% CI, 1.36 to 1.83, p < 0.001) aggravated assaults per 100,000 were reported. Vehicles consuming fuel containing Pb additives contributed much larger quantities of Pb dust than generally recognized. Our findings along with others predict that prevention of children's lead exposure from lead dust now will realize numerous societal benefits two decades into the future, including lower rates of aggravated assault. ► Ecological associations between lead (Pb) and violence are modeled at the scale of the city. ► U.S. cities, Chicago, Indianapolis, Minneapolis, San Diego, Atlanta and New Orleans were studied. ► The 1950–1985 fluctuation of Pb emissions explains 90% of the aggravated assault variation. ► Each 1% tonnage Pb increase 22 years prior raised aggravated assault by 0.46% (95% CI, 0.28 to 0.64). ► Childhood Pb prevention may yield numerous benefits in two decades, including less violence. PLOS Medicine – Decreased Brain Volume in Adults with Childhood Lead Exposure
Methods and Findings – Volumetric analyses of whole brain MRI data revealed significant decreases in brain volume associated with childhood blood lead concentrations. Using conservative, minimum contiguous cluster size and statistical criteria (700 voxels, unadjusted p < 0.001), approximately 1.2% of the total gray matter was significantly and inversely associated with mean childhood blood lead concentration. The most affected regions included frontal gray matter, specifically the anterior cingulate cortex (ACC). Areas of lead-associated gray matter volume loss were much larger and more significant in men than women. We found that fine motor factor scores positively correlated with gray matter volume in the cerebellar hemispheres; adding blood lead concentrations as a variable to the model attenuated this correlation. Conclusions - Childhood lead exposure is associated with region-specific reductions in adult gray matter volume. Affected regions include the portions of the prefrontal cortex and ACC responsible for executive functions, mood regulation, and decision-making. These neuroanatomical findings were more pronounced for males, suggesting that lead-related atrophic changes have a disparate impact across sexes. This analysis suggests that adverse cognitive and behavioral outcomes may be related to lead's effect on brain development producing persistent alterations in structure. Using a simple model, we found that blood lead concentration mediates brain volume and fine motor function.
The studies by Cecil and colleagues and Dietrich and colleagues expand the range of outcomes linked to increased lead exposure in the “subclinical” range and help to place the problem in a larger public health context. Lead’s detrimental effect on IQ, the outcome most often studied, is clearly only the “tip of the iceberg.”
The good news is that the blood lead levels at which reduced brain volumes and increased risk of arrest were observed are much less common among US children today than they were in the early 1980s, when the participants in the CLS were young children. The mean childhood blood lead level of CLS participants was 13 μg/dl, and ranged from 4 to 37 μg/dl. Currently, the median blood lead level among one to five-year-old US children is 1.5 μg/dl, and 5% have a level greater than 5.8 μg/dl . In Ohio, where the CLS study is based, the percentage of children less than six years of age who had a blood lead level of more than 10 μg/dl was 16.55% in 1997, but only 2.30% in 2006 . This is an impressive public health victory, but in light of clear evidence that a broad array of adverse effects occur at blood lead levels that are well below 10 μg/dl, it is a national disgrace that so many children continue to be exposed at levels known to be neurotoxic.
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