David Stonehouse Science & Health

Getting the lead out

A new study questions the levels of safe exposure in children

By David Stonehouse

A study of IQs in young children has given rise to new concerns about exposure to lead, even at levels currently considered acceptable.

Researchers at Cornell University found that children with lead levels of 10 micrograms per decilitre of blood -- the limit traditionally viewed as tolerable -- saw a noticeable drop in brain power when compared with children with minimal lead exposure.

The dramatic findings -- published in the New England Journal of Medicine -- surprised the researchers and has prompted calls in this country for federal health authorities to re-examine their stance on lead.

"It's a bit shocking when you think how could such low levels cause problems," says Kapil Khatter, a Toronto family doctor and executive director of the Canadian Association of Physicians for the Environment.

"Certainly, the fact that lead causes IQ problems isn't surprising because we know that's what lead does. But the fact that it could be that low is surprising -- and kind of frightening."

For decades, health authorities have been scaling back limits of lead exposure because of the naturally occurring metal's toxic effects, particularly in children.

Short-term exposure to high levels of lead can bring on problems ranging from vomiting to coma or even death. Over the long run, low levels of lead exposure can cause neurological damage. Children are most susceptible because they absorb lead much faster than adults.

Exposure dropped drastically over the last generation as lead was removed from gasoline and paint. But sources of lead remain everywhere -- in air, water, soil, food and even household dust.

The study, published last month, tracked the blood-lead levels of 172 children in the Rochester, N.Y., area over a five-year period -- testing IQ at the age of 3 and then again at 5.

The findings suggest that there is reason for worry with even the smallest levels of exposure in children. In fact, the study suggests that lead may do the most damage to the brain through low-level exposure.

Children with lead levels of 10 micrograms per decilitre of blood had IQs that were 7.4 points lower than those of children with only one microgram of lead per decilitre. But those with lead counts of 30 were only two to three more IQ points lower.

Richard Canfield, a senior researcher of nutritional sciences at Cornell University and the study's lead author, says the findings were unexpected.

"The size of the difference was very surprising," Dr. Canfield says.

"Some people are arguing that there are no safe levels of lead and we should strive to reduce all exposure to zero. I would agree, as a general principle, that we should do that," he says, but cautions that more study is needed to back up the findings of harm at the lowest lead levels.

Dr. Khatter says more needs to be done in Canada to discover the extent of lead poisoning in children and to reduce their exposure. He is calling for wider screening.

"If you live in downtown Baltimore in the U.S., your kids will all get screened for lead as long as they get health care. That isn't true in Canada," he says. "Almost no child gets tested for lead in Canada."

In the United States, children found with lead levels above 10 trigger an automatic investigation by health authorities into the possible source. Although Canada traditionally follows the U.S. limits, there is no formal standard for acceptable exposure. And with no routine testing, officials have no way of knowing if there is a problem to investigate.

Lead exposure could be the hidden cause of some learning disabilities in children, Dr. Khatter says. "We can't prove that lead is causing that problem, but we are certainly stupid if we wait around and not do anything about it. We may have a clue as to what one of the causes is, and that's lead."

Kelly O'Grady, a spokeswoman for the non-profit group Lead Environmental Awareness and Detection, wants to see broader testing of infants -- particularly those living in homes built before 1950, where lead paint may still be present. She says doctors often see signs of lead poisoning, but don't realize it.

"They are treating lead toxicity, but they are not calling it lead toxicity," says Ms. O'Grady, a nurse in Pembroke, Ont.

Charles Ethier, director-general of the product safety program for Health Canada, admits that the government department does not have an accurate picture of the extent of lead exposure in children without mandatory testing. But he notes that regulations will be brought into force within the next year banning the import and sale of products such as lead jewellery and leaded candles. Both pose a high hazard to children.

"Our premise is that there is no safe level," Mr. Ethier says, but he acknowledges that he holds little hope of banning lead. "Ultimately, that would be a pretty ambitious undertaking."