A year ago I wrote a long post on lead poisoning in Chicago, inspired in part by the attention Mother Jones's Kevin Drum has brought to the connection between lead and violence; the disappearance of lead from gas and paint is one of the more compelling theories for the decline of violent crime in America, especially in cities—big cities, with their density and traffic, were particularly vulnerable to airborne lead. The problem was intense in Chicago:

[B]etween 16 and 46 young Chicagoans died from accidents each year between 2002 and 2006, the leading cause of death in the 1-14 age group. In a 1962 Trib report, a board of health poison control pilot study found 35 deaths [from lead poisoning] from 1959 to 1961: "Most of the victims were from 1 to 5 years old and came from rundown slum area buildings…." 465 cases were treated at County Hospital in those two years, and another 65 suffered severe brain damage.

Lead paint was banned in 1972; between 1970 and 1973, the Trib reported that 18 cases of lead poisoning had been traced to buildings under one ownership alone. According to a 1980 Trib piece by Anne Keegan, Chicago didn't see any lead fatalities among children from 1974 through 1980, when poisoning from lead paint killed a toddler on South Ridgeland.

Lead abatement was one of the great achievements of 20th-century social policy (and it's relatively new, in the grand scheme of things). But fatalities and severe brain damage were only part of the problem; scientists are trying to figure out its effects at lower intensities, and where the bar should be set for a level of exposure that's considered dangerous. In October, the Chicago Reporter's Megan Cottrell looked at the lead situation right now in Chicago for the Reader, and found that bar is continuing to lower, meaning more kids are at risk for the more subtle, insidious effects of lead than you might think (full disclosure: I did an informal edit of an early version):

A recent study out of the University of Illinois at Chicago examined the blood lead levels of third graders between 2003 and 2006—students now likely to be roaming the halls at CPS high schools. It turns out that at three-quarters of Chicago's 464 elementary schools, the students' average blood lead level was high enough to be considered poisoned, according to standards set by the Centers for Disease Control and Prevention. And although lead poisoning is rarely mentioned in the debate on how to improve schools, the UIC research shows just how much it may be damaging kids' ability to succeed. According to the study, lead-poisoned students in Chicago Public Schools are more likely to fail the third grade and score notably lower on their yearly standardized tests.

Even though there's less lead in the environment than just a few decades ago, the problem hasn't gone away, largely because as we learn more about lead, the threshold for what's considered safe has declined significantly:

A further analysis of Evens's data looked at the average blood lead level for each school in the Chicago Public Schools system. The most widely recognized standard for lead poisoning is ten micrograms per deciliter in a child's blood. Recently the CDC lowered that standard to five micrograms per deciliter—what the agency refers to as the "level of concern."

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Emile Jorgensen, an epidemiologist with the Chicago Department of Public Health…. estimates that the number of children with lead rates five and above is more like one in 12.

"When you think about all the challenges that our kids have in terms of performing in school—poverty, gang violence, the list goes on and on—lead is something you can actually do something about and have an impact," Evens says. "It just seems crazy, as a community that cares about school performance, not to invest in preventing it."

Kevin Drum recently turned his ongoing interest in the subject into a longform piece on lead poisoning and its effects, and it's a must-read. Here's how lead actually does its work in the brain:

A second study found that high exposure to lead during childhood was linked to a permanent loss of gray matter in the prefrontal cortex—a part of the brain associated with aggression control as well as what psychologists call "executive functions": emotional regulation, impulse control, attention, verbal reasoning, and mental flexibility. One way to understand this, says Kim Cecil, another member of the Cincinnati team, is that lead affects precisely the areas of the brain "that make us most human."

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In other words, as Reyes summarized the evidence in her paper, even moderately high levels of lead exposure are associated with aggressivity, impulsivity, ADHD, and lower IQ. And right there, you've practically defined the profile of a violent young offender.

Cottrell's article focuses on lead in old housing stock, and what the city does (and doesn't) do to combat it. But it's also in the soil, and it gets kicked up periodically, particularly in the summer, when airbore lead is at its peak (PDF).

Lead contaminated urban soil is implicated as the major source for atmospheric Pb aerosol loadings. A consequence of the resuspension of Pb contaminated soil is that it has significant repercussions for ongoing adverse Pb exposures in urban dwelling US children. Pingitore et al. (2009) observed that if Pb contaminated urban soil is the principal source for airborne Pb in urban settings, then “contaminated soil may set a practical lower limit for future decreases in regulation of airborne lead levels” (Pingitore et al., 2009, p. 5). The Centers for Disease Control and Prevention (CDC) acknowledges that along with Pb-based paint and Pb dust, soil is a major Pb source; the agency does not provide a single recommendation about soil Pb in their guidelines (CDC, 2007).

Drum calculates that abatement of lead and soils would cost $10 billion each every year (though the estimates for soil lead abatement are rough), with an estimated return of $210 billion a year from lowered crime and higher IQs (see "School Testing and the Burden of Childhood Lead Exposure"), and wonders why it hasn't been part of federal policy (or, say, an infrastructure trust?). My guess actually goes back to the crime aspect of lead abatement. Lead was banned from paint in the 1970s, and gas in the 1980s; violent crime didn't begin its current downward trend until the mid-1990s, and lead abatement has really only become vogue as a cause in the past few years—a delay of several decades between cause and effect. It's invisible, expensive work that takes years to show an effect, an unsexy form of infrastructure work.

Photograph: taberandrew (CC by 2.0)