Even Low Lead Levels Pose Perils for Children

August 5, 2003

JANE E. BRODY, New York Times

You have no doubt heard of similar situations in the past. A substance known to be hazardous above a certain level is deemed safe below that, only to discover years later that the so-called safe level was not safe at all.

Such has repeatedly been the case with children's exposure to lead, a substance known since 1923 to damage the brain.

Years ago, doctors worried only about what is called frank lead poisoning ? blood levels of 60 micrograms or higher. Since 1943, it has been known that the brains of children exposed to these high levels never recover from the damage.

Then, more careful studies of children living in lead-contaminated environments showed that blood levels from 40 to 60 micrograms also took a significant toll on the developing brain, lowering I.Q. scores and causing language and attention problems, as well disturbing behavior.

Repeatedly over 30 years, follow-up studies of lead-exposed children have demonstrated I.Q. reductions and other memory and learning disturbances associated with successively lower blood lead levels.

Those findings prompted long-delayed federal action, bans on lead-based paint, lead in gasoline and lead solder used to seal food cans.

Later findings also led to a reduction in the "level of concern" for blood lead levels in infants and young children, the point where efforts should be made to identify the source and reduce exposure. That level today, set by the Centers for Disease Control and Prevention, is 10 micrograms a deciliter.

If a child tests below that, parents are told that there is no cause for concern.

Less Lead, More Damage

Now, however, findings published in April in The New England Journal of Medicine strongly suggest not only that any amount of lead is harmful to a child's brain, but also that greater damage seems to occur at levels below 10 micrograms than above that.

In other words, there is no threshold for lead's effects on the brain, and just small amounts seem to have relatively large effects.

If a blood level of, say, 15 micrograms can shave 2 points off a child's I.Q., then a level of 5 micrograms might reduce I.Q. by 5 points or more.

The new study, headed by Dr. Richard L. Canfield, a developmental psychologist in the division of nutritional sciences at Cornell University, followed 172 children from relatively poor families in Rochester whose blood lead levels were repeatedly measured from age 6 months to 5 years.

In 101 children, blood levels never exceeded 10 micrograms.

Although levels above 10 micrograms were associated with a 4.6-point I.Q. loss for every additional 10 micrograms, a lifetime average level below 10 micrograms was linked to a decline of 7.4 I.Q. points.

The researchers took into account many factors known to influence a child's I.Q. to isolate the effects of lead itself. Still, skeptics might wonder, Are only children living in poverty at risk?

No, says Dr. Herbert L. Needleman, professor of psychiatry and pediatrics at the University of Pittsburgh School of Medicine, who has studied the effects of lead on the brain and behavior for 31 years.

Dr. Needleman and Dr. David C. Bellinger of Boston Children's Hospital and the Harvard Medical School studied 249 mostly middle-class children in the Boston metropolitan region, measuring blood levels levels seven times from birth to age 10.

Prompted by the Canfield study, they reanalyzed findings among the children whose blood levels never rose above 10 micrograms and found the same effects ? proportionately greater harm at the lowest levels.

Ideally these findings should be confirmed by other larger studies, but the cost and time involved are somewhat prohibitive, and the delay could mean that millions of children continue to be harmed by very low lead levels.

Dr. Canfield said in an interview: "Our research suggests that nontrivial damage is occurring below the C.D.C. level of concern. Both the C.D.C. and the World Health Organization need to reassess their policies in light of this research."

The researchers are to to discuss their data with the Centers for Disease Control.

So what do a few lost I.Q. points mean? Well, it could make the difference between average and below average intelligence requiring remedial education or it could mean a potential genius is just very bright. And it could mean that more than 90 percent of American children, all with lead levels below 10 micrograms, are being harmed by lead.

Furthermore, these effects are permanent. Attempts to remove lead from children through a chemical process called chelation succeeds in lowering blood levels but does nothing to restore a child's lost intelligence.

Effects on Society

Perhaps more important from a societal view are the links between lead exposure in childhood and later delinquent and criminal behavior. In a study directed by Dr. Needleman of 300 students in the Pittsburgh region, teenage boys with elevated lead levels were more likely to have committed antisocial acts like bullying, vandalism, arson and shoplifting.

Dr. Kim Dietrich, a developmental psychologist at the University of Cincinnati, has been following 300 children recruited before their births in 1981.

The average blood level of the children, who lived in an area with a historically high incidence of lead poisoning, was 10 to 40 micrograms a deciliter from birth to 5 years.

By 16, those with elevated lead levels were more likely to have committed antisocial and criminal acts like assaults, property damage, chronic truancy, disorderly conduct and vandalism. Girls were as likely as boys to have exhibited those behaviors, Dr. Dietrich said in an interview. He added, however, that he had no information on the behavioral effects associated with lead levels of less than 10 micrograms.

Indeed, some lead experts suggest that the recent decline in violent crime is a function not of law enforcement, but of the falling lead levels in children born after 1980. At that time, 88 percent of children younger than 6 had blood lead levels greater than 10 micrograms, Dr. Bruce P. Lanphear of the Children's Hospital Medical Center in Cincinnati said in an interview.

What Parents Should Know

While sources of lead encountered by American children have declined greatly, they have not beeneliminated. One-quarter of American homes with children younger than 6 contain lead-based paint. Children can be exposed to lead-containing dust when windows are opened and closed, when old paint on walls, ceilings, radiators or floors chips or is sanded or scraped off, or when old bathroom tiles are demolished.

Renovations of older houses, especially by do-it-yourselfers, can leave lead-contaminated residues in the air and on surfaces handled by babies and toddlers. The best way to contain lead-painted surfaces is to seal them with several fresh coats of nonleaded paint or have a certified lead-abatement service remove the old paint.

In addition, Dr. Canfield said, parents should be sure that babies and toddlers are periodically tested for lead and not be satisfied with an "O.K." result. Find out the number.

If his own children had a reading of 5 or more micrograms, Dr. Canfield said, he would want to find the source of their exposure and eliminate it.