The Flint, Michigan, pediatrician who first connected the city's water to high lead levels in children tells 60 Minutes early results from extensive neuropsychological assessments of 174 kids have found 80% will require services for a language, learning or intellectual disorder. Dr. Mona Hanna-Attisha speaks to Sharyn Alfonsi for a report on the lead crisis in Flint to be broadcast on 60 Minutes, Sunday, March 15 at 7 p.m. ET/PT on CBS.

Mismanagement following a switch in the city's water supply in 2014 caused lead in old pipes to enter the drinking water. Despite complaints by residents of discolored water, Michigan and Flint officials insisted there was no threat to public health. When Dr. Hanna-Attisha heard that independent testing detected lead in the water, she searched for the truth by examining her patients' medical records. In 2015, she found the percentage of kids with elevated blood lead levels had increased since the water switch. Two weeks later, Michigan Governor Rick Snyder ordered Flint to switch back to the Great Lakes water source.

"There is no safe level of lead… It is an irreversible neurotoxin. It attacks the core of what it means to be you, and impacts cognition-- how children think," Hanna-Attisha says. "[Lead] actually drops IQ levels. It impacts behavior, leading to things like developmental delays." She estimated that 14,000 Flint children under the age of six were exposed.

Last year, Hanna-Attisha began the Flint Registry to track them, part of a state and federally funded program to assess those exposed and get them help.

The pediatrician and her research team learned that 80% of those kids who underwent neuropsychological assessments will require assistance such as speech and behavioral therapies. Before the crisis,15% of Flint children required special education services.

"But we also realized that our research, our science, this data and facts was also an underestimation of the exposure," says Hanna-Attisha. "Because we were looking at blood lead data… done at the ages of one and two. Lead in water impacts… the unborn," she tells Alfonsi.

To determine that impact, a study on children's baby teeth is being conducted because the teeth begin to grow in the womb. Rings like those in tree trunks are found in teeth, too, trapping lead that researchers can see with lasers. The technology allows researchers to identify exactly which children were exposed to the lead-contaminated water, when and at what level.

Last year, lead levels four times higher than the federal limit were found in New Jersey's largest city, Newark. "Newark, New Jersey is like living Flint all over again," says Hanna-Attisha.

"There's no antidote. There's no cure. We can't take away this exposure," Hanna-Attisha says.