Science & the Public: Redefining ?concern? over lead

Federal health agency accedes to two decades of accumulating toxicology data

Web edition : 3:58 pm

The Centers for Disease Control and Prevention announced on May 16 that it would no longer designate any particular blood-lead value in children as representing a ?level of concern.? Its justification: There is no threshold below which lead exposures are not a concern.

?Because there?s no identified safe exposure level for lead in children, ?level of concern? is a misleading statement,? explains Christopher Portier, who directs CDC?s National Center for Environmental Health and the Agency for Toxic Substances and Disease Registry.

The old term implied lower concentrations might be okay. By jettisoning the old language, federal agencies are now free to advocate broadly what a growing number of lead toxicologists have been saying for decades: That because lead poisons the brain, and because there is no safe level, all affordable means should be considered to limit every child?s exposure to lead.

Until this week, U.S. federal agencies had held onto an outmoded 10 microgram per deciliter blood-lead level as "concerning."

In January, a CDC advisory committee concluded that made no sense. It noted that blood-lead levels below 10 ?g/dl have been linked to IQ deficits, impaired attention-related behaviors and poor school achievement. It also pointed out that data demonstrating harm from what were recently considered low levels of lead extend ?beyond cognitive function to include cardiovascular, immunological, and endocrine effects.?

This realization that lead harms multiple organ systems ? and its effects appear irreversible ? ?underscores the critical importance of primary prevention,? the advisory committee concluded. Bottom line: All kids are at risk, so all should be screened. Their parents need to be given specific blood lead numbers, it said, and they should be informed that no value is ?safe.? CDC has now formally accepted those recommendations.

Federal efforts from here out will target all children in the top 2.5 percent of blood-lead values for priority attention. That top exposure group now includes some 400,000 to 450,000 kids five years old and younger ? some with blood lead values as low as 5 ?g/dl.

For the families of children who fall into this newly defined category, the advisory panel recommended enhanced education on lead risks and exposure prevention, investigations to probe the source of a child?s exposures and long-term medical monitoring for symptoms of toxicity.

CDC has now endorsed this policy. Indeed, Portier says, ?by tracking where these [most exposed] children are found, we can find communities or neighborhoods where there appear to be high levels of lead and focus resources on something broader than just the individual child.?

Every four years, childhood cumulative lead values will be assessed nationally. The expectation is that with increased monitoring, remediation of leaded paints and plumbing, and vigilance, those national averages will continue to fall. But Portier says that even if national lead averages fall, his agency will continue to focus lead-prevention efforts on kids in the top 2.5 percent, ?because our target is to push this edge ? the highest exposure group ? down as fast as we possibly can.?

In its new announcement, CDC noted that it didn?t have the money to do everything its advisory board had suggested. For instance, the panel asked CDC to develop and implement a national primary-prevention policy ?to ensure that no children in the United States live or spend significant time in homes, buildings, or other environments that expose them to lead hazards.? While CDC said it liked the idea and would work on developing such guidelines for such a strategy, it also noted that its implementation of such a strategy ?is not currently practicable.?

CDC also agreed in principle with a need for educating physicians on the extent of low-level lead risks, on the need for followup testing of kids in the upper-exposure group until they fall below the 5 ?g/dl level, and on the need to alert local or state officials about childhood patients testing in the upper-exposure category. However, Portier?s agency noted, full implementation of each of these recommendations will be ?contingent on funding.?

Even a decade ago, Joel Schwartz of the Harvard School of Public Health in Boston was warning that lead has received insufficient respect for its toxicity: Health officials err by deeming low even 2 ?g/dl in blood (5/5/01, p. 277), he argued at the time. Values then deemed fairly low appeared to slightly lower IQ. But small IQ deficits aren?t unimportant, he added, noting that one of his early analyses of lead?s impacts ?showed that if you lower the mean IQ of the U.S. population by one point, you lower the productivity of the economy by about one percent.?

In this era of economic fragility, that should serve as serious food for thought.

Found in: Body & Brain, Environment and Science & Society

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