PROVIDENCE -- A pediatrician who is one of the country's leading experts on childhood lead poisoning testified here yesterday that the chief cause of the lead poisonings of Rhode Island children was the lead that was long used as paint pigments.

"In the United States, lead-based paint is the overwhelmingly predominant source of lead exposure in all 50 states, and since Rhode Island is one of the 50, we know that lead-based paint is the predominant form of exposure here," said Dr. Philip J. Landrigan, a professor at the Mount Sinai School of Medicine in New York City.

Landrigan said the fact that Rhode Island, as one of the original 13 colonies, has some of the oldest housing in the country reinforces his conclusion about the source of lead poisonings.

He said the most effective way to protect children was to get the lead paint out of houses.

Landrigan was the state's first witness as it launched its second trial of four major corporations that once produced lead-based paint pigments. The state of Rhode Island has accused the companies of creating a public nuisance by producing the paints that have poisoned nearly 35,000 Rhode Island children since the early 1990s.

The first trial, focusing solely on the nuisance allegations, ended in a hung jury. In this second trial, issues of liability and remedies will be woven in, so some expect the testimony to take as long as four months. The state wants the companies to inspect each of the estimated 250,000 houses treated with lead paint and remove the paint that remains.

For its first witness, the state selected an expert with credentials that he earned over several decades. Landrigan, a Harvard Medical School graduate, is a certified pediatrician, epidemiologist, and an expert in preventative and environmental medicine.

He had a long career with the U.S. Public Health Service for which he was sent around the world in response to medical emergencies. He heads the special clinic set up to treat and monitor some 12,000 people who worked in the contaminated conditions around the World Trade Center after the terrorist attack four years ago. And he has written two books and dozens of peer-reviewed academic papers about toxic threats to children.

Landrigan, under questioning from lawyer Jack McConnell for the state, spent the day explaining exactly how lead affects children who consume it.

Apparently in response to a defense argument that almost any material can be toxic, Landrigan said the difference with lead is that it is toxic at even minute quantities.

A chip of lead paint half the size of his finger nail, he said, could cause a child to go into convulsions and coma.

Occasionally children will eat paint chips, Landrigan said. But far more commonly lead paint dust falls to floors from window and doors. Young children play in that dust, get it on their hands, and put their hands in their mouths.

Because of that unusual route of exposure, Landrigan said the greatest risk of lead poisoning starts for children at about 10 months, when they become mobile, and continues until about age 5 or 6, the ages when kids typically stop putting their hands in their mouths.

Landrigan said there are other differences between children and adults that make small children far more susceptible to lead poisoning.

The stomachs and intestines of small children tend to absorb about half the lead a child ingests, a rate that is five times higher than what an adult would absorb.

The kidneys of small children are much less efficient at removing contaminants, so more lead stays in a child's system, Landrigan said.

Most important, Landrigan said, is that the brains of small children are still developing -- nerve cells are making billions of connections. Lead interrupts that process, he said, causing lower intelligence, shortening attention spans, and affecting behavior.

The damage is permanent and irreversible, Landrigan said.

"It's sort of a perfect storm," said Landrigan. "Little children crawling on floors, taking the chips into their bodies more, with organs more susceptible."

The vast majority of victims show no symptoms and their cases go unreported, Landrigan said.

No level of lead in children is now considered safe, Landrigan said.

Landrigan said there was little chance of people being affected by lead that was once used in gasoline in the United States. The last leaded gasoline was sold more than 15 years ago, he said. Any lead that was left in the environment would have washed away by now.

Paint company lawyers raised numerous objections to Landrigan's testimony, arguing several times that he was testifying on issues that weren't disclosed during discovery depositions earlier this year.

Judge Michael A. Silverstein rejected many of the objections. McConnell said the company lawyers could challenge Landrigan in cross-examination, scheduled to begin this morning.

In response to a question from McConnell, Landrigan said he was paid $400 an hour for his testimony, which he said was average for a medical expert.

FIND TIPS on removing lead-based paint, and other resources for dealing with the toxic material, at:

http://projo.com/extra/lead/