How dangerous is lead?

How dangerous is lead?

How dangerous is lead?

Health and medicine explained.
May 19 2004 1:30 PM

Heavy Metal

How dangerous is lead?

Illustration by Mark Alan Stamaty

Last January, the Washington Post revealed that corroding lead pipes were contaminating the city's drinking water. Officials at the local Water and Sewer Authority had known about the lead in the water since 2002 and had quietly notified those whose drinking water had been found to have elevated lead levels. But it was after the Post"broke" the story that Washingtonians evinced the type of righteous indignation that often accompanies perceived cases of bureaucratic indifference to the public's health.

Lead, after all, has a terrible reputation. One need only do a quick Web search to learn that the element has been blamed for everything from the fall of Rome to the fact that kids are "loosing [sic] their minds." So, many Washingtonians understandably jumped to the worst-case scenario: Was the water silently emitting toxic levels of lead into the locals' bodies, and, more ominously, into the brains and tiny bodies of their children?

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In one of a host of stories—many more than 100 to date—the Post has published on the topic, a reporter summarized the metal's myriad nasty effects: "Studies have shown that children exposed to lead have reduced potential for lifetime achievement and increased risk of social and behavioral problems. ... Some epidemiologists report evidence that lead's effects on children can remain undetected for decades until psychiatric diseases, such as schizophrenia, emerge. Others have attributed impulsive and antisocial behavior and juvenile delinquency to lead exposure."

Schizophrenia, underachievement, delinquency—obviously scary stuff. But is the amount of lead in the D.C. water—many of the thousands of homes tested this year have levels only a few micrograms over the Environmental Protection Agency's legal limit of 15 parts per billion—really as menacing as all that?

To get a sense of the potential risks posed by lead, as well as the debate that informs reactions to even relatively low-level exposures like this one, you first need to know one thing: It is, basically, all about children (and pregnant or breast-feeding women). Experts, it seems, don't worry much about the effect of low-level lead exposure on adults. (At higher levels, however—such as those found in many workplaces, like construction sites or lead-recycling plants, where lead is utilized—the metal may, according to an expert paraphrased in the Post, "affect fertility and sexual function, interfere with kidney function, cause muscle aches and possibly act as a carcinogen.")

Beyond the fact that environmental workplace-conditions rarely trigger the type of public outcry they might deserve, there are some scientific reasons to focus on children's lead exposure. Because children are nearer to the ground—where soil and dust laced with lead can accumulate—and are more likely to "mouth" their (lead-contaminated) fingers, they are considered more vulnerable. A child's still-developing nervous system may also be more susceptible to lead's ill effects. Furthermore, children under the age of 6 apparently absorb far more lead in proportion to their size than do older kids or adults. But what does this mean for those D.C. children whose drinking water flows through lead pipes?

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First, a bit of history is in order. Lead has been used for thousands of years for everything from bullets to fancy crystal tableware to water pipes. Today, lead is integral to umpteen useful products: the bibs that shield you from X-rays, the screen on your computer, the battery in your car. Given its wide use, lead is ubiquitous—found in air, soil, dust, paint, and water contaminated by corroding pipes. (Lead dust and lead paint are considered the most prevalent source of contamination.) Therefore, humans can't really avoid inhaling or ingesting it. And because the metal somehow "mimics" the essential mineral calcium, the human body apparently doesn't register that lead is toxic. Instead, lead moves in the body as calcium does: coursing through the blood, finding its way into soft tissues of the liver, kidneys, and the brain, where it may disrupt normal functioning; settling into bones and teeth, where it can be stored for decades.

This all sounds bad, particularly if you're talking about a child. But our instinctively emotional reaction might just be preventing us from keeping current lead scares in perspective. The amount of lead most children today are exposed to is, by and large, small compared with the amount of lead to which American children were historically exposed.

Indeed, bans on leaded gas and leaded house paint, initiated in the 1970s, have resulted in dramatic declines in children's blood-lead levels. (In 1986, Congress amended the Safe Drinking Water Act to limit, though not ban, the use of lead in plumbing, but obviously many old lead pipes and fixtures, such as those in D.C., remain.) Whereas in 1976 nearly 90 percent of American children ages 1 to 5 had blood levels of lead higher than 10 micrograms per deciliter—the standard of "concern" recognized by the Centers for Disease Control—by 2001, the percentage was down to 2.2 percent. Extreme cases of lead poisoning—marked by blood levels higher than 70 micrograms per deciliter, and characterized by terrible symptoms such as brain swelling and coma, sometimes death—were, in the early 20th century, a relatively commonplace occurrence in children but are now rare.

In D.C., it's unclear whether lead in the water is affecting children's blood-lead levels. Not every District child has been tested, but of the 1,692 kids under age 6 who were evaluated as of late-April, 35—2.1 percent of those tested—had blood-lead levels higher than 10 micrograms per deciliter. Among the 13 children living in houses where the water-lead levels were more than 20 times the EPA-threshold, none had elevated blood-lead levels.

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What sort of effects might be experienced by those 35 kids? In some ways, this is an unanswerable question, since lead does not seem to affect all children equally. It may be that malnourished children lacking in calcium and iron are more vulnerable to the ill effects of lead. This may also explain the strange fact that the blood-lead levels of poor children living in lead-paint-infested housing are, on average, higher than the levels of better-off kids—call them the children of renovation-minded Bobos—who live in antique homes equally slathered with lead paint.

Furthermore, though lead is one of the most studied environmental toxins, the literature is suggestive, but not necessarily conclusive. Consider those studies linking lead exposure with juvenile delinquency. While parents of those with serious lead poisoning sometimes report that their kids are markedly aggressive, only four human studies have investigated the link so far. A 2001 University of Cincinnati study, for instance, reported a "modest" association between adolescent delinquent acts (aka the kind of thing that could get you arrested, like disorderly conduct) and childhood blood-lead levels at age 6. And so, while a  2002 delinquency study reported that youths with "elevated" bone-lead levels (which may indicate cumulative lead-exposure) were four times more likely to have been arrested, researchers are careful not to
overinterpret the findings. David Bellinger, Ph.D., a Harvard neurologist and prominent lead expert, recently wrote in the journal Pediatricsthat "much work" is needed to "clarify" the "potential" contributions of lead to childhood psychiatric problems. (As for schizophrenia, only one study so far has examined its potential association with lead, and it was conducted on subjects for whom complete family histories of mental illness—potentially a major contributor to disorders like schizophrenia—were not available.)

For now, perhaps the sturdiest sheaf of studies supports the link between moderately diminished IQ in children and high blood-lead levels—though even these findings have been questioned: Some of the early studies, critics have argued, did not adequately "control" for other risk factors for lower intellectual achievement, like having a parent with a low IQ or growing up in a low-income household. A 1994 roundup of those lead-IQ studies that did take these factors into account concluded that a rise in lead blood-levels from, say, 10 micrograms per deciliter to 20 might indeed cause a "small" IQ deficit of perhaps one to two points in childhood. (By way of comparison, researchers have observed slightly larger IQ deficits in later life among those who were low birth-weight babies.) And a 2003 study, published in the New England Journal of Medicine, counterintuitively suggested that blood-lead levels below 10 microgramsper deciliter, the CDC threshold, might somehow lead to more dramatic IQ deficits than those above 10 micrograms per deciliter.

In any event, the lead crisis in Washington has mobilized environmentally minded politicians. Sen. James Jeffords, I-Vt., recently introduced a bill called the Lead-Free Drinking Water Act, which would ban lead plumbing fixtures and would allocate $200 million to the nation's capital to help it yank its remaining lead pipes. With fervor (and less than felicitous phrasing) Jeffords proclaimed, "It is time to get the lead out of our pipes, out of our water, out of our families, and out of our lives."