A study just published in the journal PLoS Medicine (and written up in the LA Times) suggests a link between childhood lead exposure and adult arrests for violent crimes. Studying 250 adults for whom they had prenatal and childhood blood lead level measurements, University of Cincinnati researchers found that each 5-microgram-per-deciliter increase in blood lead levels at age 6 was associated with a nearly 50% increased risk of arrest as a young adult (the risk ratio was 1.48).

The good news is that overall, U.S. children’s blood lead levels have dropped dramatically since manufacturers started phasing lead out of paint and gasoline in the mid-1970s. The bad news is that 40% of the nation’s housing still contains lead-based paint, and hundreds of thousands of children still have blood lead levels associated with neurological problems.

When we as a society consider whether or not to regulate hazardous substances, we need to remember that allowing their continued use can have severe consequences. The lead saga demonstrates that even when environmental and health advocates succeed in getting hazardous substances out of consumer products, the damage can be extremely costly and long-lasting.

This study linking early lead exposure to adult arrests has several strengths. Instead of using indirect measures of childhood lead exposure (such as bone-lead levels in young adults) it relied on actual blood-lead measures taken when the subjects were young. Researchers recruited subjects from the parts of Cincinnati with concentrations of older, lead-contaminated housing, so the cohort was relatively homogenous with respect to socioeconomic status and ethnicity.

The researchers also noted some limitations related to their use of arrests as a measure of criminality: most criminal behavior doesn’t result in arrests; the study only looked at arrests in one county; and average follow-up time (years after the subjects’ 18th birthdays, when their arrest records would have been available to researchers) was under five years. Such limitations are hard to avoid in this kind of long-term epidemiological study, though, which is why it’s important to have multiple studies addressing the same topic from different angles, and to see what we can gather from the body of research.

In short, the body of research on childhood lead exposure tells us that lead harms children’s neurological development in ways that can have serious consequences. The authors explain the link between their study and previous research this way (references omitted):

The neurodevelopmental consequences associated with lead exposure in previous studies, such as lower IQ, less tolerance for frustration, deficits in attention, hyperactivity, and weak executive control functions, are potent predictors of delinquent and criminal behaviors. Attention deficit hyperactivity disorder (ADHD) is a common finding among juvenile delinquents, and those with ADHD are more likely to have severe cognitive impairments. ADHD is also a known risk factor for criminal behavior in adulthood. A recent analysis of data from the third National Health and Nutrition Examination Survey (NHANES-III) found that higher blood lead concentrations were significantly associated with ADHD. Children with blood lead concentrations greater than 2 μg/dl were at a 4.1-fold increased risk of ADHD. Similarly, in experiments with rodents, felines, and nonhuman primates, early lead exposure was associated with increased impulsivity, aggression, antagonistic interactions, reduced social play and abnormal mother–infant interaction. Childhood lead exposure therefore seems to place individuals at risk for multiple underlying neurobehavioral deficits associated with a higher probability of later criminal behavior.

They also note that the overall drop in crime in this country – which parallels the reduction in lead pollution – wasn’t uniform, and that lead might be one of the reasons:

Crime and violent crime are concentrated in urban centers in the US where many poor African-Americans reside. One factor in the disproportional representation of African-Americans in crime statistics could well be the historically higher exposures to lead in these communities.

This doesn’t mean that lead plays as much of a role as other factors. But unlike the complex social and economic forces that raise the risk of criminality, we know exactly how to solve the problem of lead exposure: rehabilitate homes with lead paint in them, and keep lead out of children’s products.

Removing lead from paint and gasoline brought us huge economic gains. Researchers from the CDC and Harvard’s School of Public Health quantified the overall IQ-point increase that we gained from reducing childhood lead exposure and estimated that a single birth cohort – children who reached age 2 in 2000 – will enjoy between $110 billion and $318 billion more in lifetime earnings than they would have if they’d experienced the same level of lead exposure as their counterparts in the mid-1970s.

This public health victory and resulting economic boon came later than it should have, and we’re still seeing the consequences in many of today’s adults, and in many of the children who live in the 38 million homes that still contain lead-based paint. A 2005 Journal of the American Medical Association editorial by Bruce Lanphear points out that many European countries banned leaded as early as 1909, but the U.S. took until 1978, because of marketing and lobbying efforts by the lead industry. It also notes that our idea of what constitutes a too-high lead level has dropped dramatically, from 60 µg/dL in the 1960s to 10 µg/dL (the current CDC action level). Recent research finds adverse effects at levels as low as 5 µg/dL.

So when an industry tells us that its product or byproduct isn’t harmful at the low levels currently seen in the population, and that eliminating or controlling the substance would be too costly, remember the case of lead. If we realize a few years from now that today’s low levels do indeed cause problems, we could have already committed ourselves to decades of consequences to the tune of hundreds of billions of dollars.