It's 1957. Dr. Herbert Needleman is on his way to see a 3-year-old patient at Children's Hospital of Philadelphia.

Needleman's a young doctor, 6 feet tall with brown eyes and dark hair. This is the first case of lead poisoning he's ever seen. And when he shows up, the girl is not in good shape.

"This girl was lethargic and almost comatose," says Lydia Denworth, who wrote a book about Needleman called Toxic Truth. Needleman has Alzheimer's disease and was unable to be interviewed for this story.

Needleman treats the girl for lead poisoning, and she starts to feel better. So he talks to the girl's mother. He tells her daughter is OK, but she was probably poisoned by lead paint or dust at home, and they can't go back there.

"The mother just looked at him and said, 'Well where am I supposed to go?' " Denworth says. "She didn't have any money, she was a single mother, and suddenly Needleman says it's like the scales fell from his eyes."

This patient marked the beginning of a lifelong crusade for Needleman. He went on to make a huge discovery that changed the way we think about the dangers of lead. But it didn't change everything.

Back in the 1950s, when Needleman was a new doctor, lead was everywhere: in paint, pipes, toys and gasoline.

Needleman became consumed by thoughts of lead.

In fact, many who know him describe him as a crusader against injustices – large and small.

His son Josh Needleman tells a story about a canoe trip the family took when he was a child. He and his father were paddling along a river when they saw a group of teenagers sitting around and smoking.

"It was generally the kind of group that I think now, as an adult, I would try to avoid," Josh says. "And they were throwing rocks at a duck that was floating in the river."

Needleman got really angry.

"He began to shout at them and said 'Leave that duck alone!' "

The teenagers were apparently so shocked that they stopped.

"He could just not hold himself back when he saw something that was unjust," Josh says.

The same thing went for lead, he says. Needleman wondered whether the small amounts of lead children were exposed to every day could damage their brains. He did a study using children's baby teeth to measure their lead levels.

The study, published in 1979, found that children "who had high lead in their teeth, but who had never been identified as having any problems with lead, had lower IQ scores, poorer language function, and poorer attention," Needleman explained years later in a Bill Moyers documentary that aired on PBS.

The findings were controversial. Critics, including companies that made lead products, said these things could be caused by other factors — like family life and education.

But the federal government had already started phasing lead out of gasoline, and in the 1980s, thanks in part to Needleman's research, it sped that up. Then it put out a plan to eliminate lead poisoning for good.

In 1991, Needleman testified in support of a bill to fund that effort.

"There is a broad consensus on the part of everybody except the lead industry and its spokesmen that lead is extremely toxic at extremely low doses," he said.

The idea was to get all the lead out of homes. But there was resistance from landlords and realtors. Congress didn't pass the bill.

The following year, however, Congress did pass the Residential Lead-Based Paint Hazard Reduction Act, which required landlords to disclose lead paint hazards to tenants. That law was hard to enforce.

Meantime, some scientists who represented the lead industry in lawsuits accused Needleman of scientific misconduct, saying he cherry-picked his data to prove a point.

In the PBS documentary, Needleman compared that accusation to a professional death sentence. "If you're found guilty of scientific misconduct, you're out of business," he said. "Your reputation is ruined. You're through."

The University of Pittsburgh, where Needleman worked, investigated for a year and found no scientific misconduct. It did say he mischaracterized some procedures in his study, but not in a way that changed the findings.

Over time, more studies showed effects of lead at low levels, but the government stopped talking about eliminating lead poisoning entirely.

Lead levels in young children have dropped by more than 90 percent since the 1970s, when Needleman published his early research, according to data from the National Center for Health Statistics. But a lot of children are still exposed to lead, and scientists say no amount of it in the blood has been proven safe.

Journalist Lydia Denworth says Needleman always felt like society hadn't done enough.

"It became old news. We thought we'd solved the problem. We never really were willing to finish it," she says.

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