The impact of lead exposure ebbs and flows during various stages of gestation.

Hu, a professor in the school of public health, and colleagues focused on a group of 146 pregnant women in Mexico City between 1997 and 1999, who were exposed to lead through their diet, air pollution and lead gasoline. Lead in gasoline was phased out in Mexico City in 1997.

The team measured the amount of lead in umbilical cord blood at delivery and when the children were 12 and 24 months of age. The results showed lead exposure during the first trimester were predictors of poor mental development index, or MDI, scores.

Likewise, lead exposure in the blood plasma during the first trimester had a more damaging influence to the developing child than second or third trimester lead. Previous research has shown children with lead in their blood fall behind intellectually, which often causes them to drop out of school or become a delinquent.

The study was published in the Environmental Health Perspectives journal.

"The bottom line is that lead is the most studied toxicant of all environmental health, and we still know so little," Hu said.

Lead interferes with the normal firing of neurons in the body, chipping away at the architecture of the nervous system in its earliest stages. Lead also travels directly to the pathways in the front of the brain that dictate executive control, the ability to learn and organize.

Their study also reinforced prior research that accumulated lead in a mother's bones leaches during pregnancy, delivering another source of the destructive metal to the fetus. A mother's bones dissolve during pregnancy as the demand for calcium increases.

Hu and his team have just completed a randomized trial to see if pregnant mothers who take calcium supplements at bedtime can reduce the lead transfer from the mother to fetus. "All I can say is it looks like there's some benefit, and stay tuned," he said.

However, there were some limitations to the research. The sample size was small, and it's possible results from the pregnant women in the study can't be generalized to other populations. More research will need to be done to confirm the results.

Hu's research should be considered by the United States when making recommendations on lead exposures for pregnant women, he said. A Centers for Disease Control and Prevention panel of experts is currently examining the issue, he said.

Lead has many effects across the spectrum of child health, both in behavior and physical ability, said Dr. Helen Binns, a professor of pediatrics and preventive medicine at Northwestern University and Children's Memorial Hospital.

But Hu's research "points to the need of a preventive approach" in dealing with lead in women of childbearing age, Binns said. Since lead builds up in the bones over time, waiting until pregnancy to be informed is too late.

The most pressing agenda should be removing lead from older homes, where it was allowed for household use until 1978. In homes built before 1940, the chances of lead paint hazards is 68 percent, Binns said -- yet many parents don't realize it.

More troubling, children with elevated lead levels don't show any physical symptoms that would suggest exposure to the metal.

"It's still a hidden issue," she said.

There need to be ways to convey lead risks when a house is sold, rented or renovated, apart from a basic pamphlet about lead. To that end, more research could focus on how to develop strategies to make lead an "open topic," Binns said.

Hu agrees more efforts need to made to give "all of our kids equal opportunities" to be healthy and productive adults.

"It's disconcerting to think about how little we know about the other artificial and manmade things we expose our children to in utero and later in life," Hu said.

The U.S. government's allowance of lead in blood has plummeted over time, from 60 micrograms per deciliter -- a metric measure of lead -- to 10 micrograms today. The U.S. Environmental Protection Agency phased out lead in gasoline in the 1980s. In 1978, around 4.7 million children had blood lead levels at or greater than 10 micrograms per deciliter due to this change -- by 1999 to 2000, this number dropped to about 430,000, according to the EPA.

"Over the past 45 years, there has been a real change and evolution in our understanding of lead," Deborah Cory-Slechta, a toxicologist at the U.S. Environmental Occupational Health Sciences Institute in New Jersey, said at an American Association for the Advancement of Science conference in St. Louis in February. "But it's not as rosy as one would like to see."

For instance, imported products continue to be a source of lead; some candies from abroad have lead in their wrappers. The metal is still unfortunately "ubiquitous" in modern society, according to Binns.

"I see this as a health concern that touches the most vulnerable proportion of the population, and it's addressable," she said.

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