"Not safe": Parents wary of Malibu school's handling of toxic chemicals

Building materials used in a California school are sparking a nationwide debate about the safety of students. The dispute involves toxic chemicals known as PCBs that were discovered in Malibu classrooms about three years ago.

School officials in the wealthy beach community say they have a plan to deal with the problem, but many parents don't believe them, reports CBS News correspondent Danielle Nottingham.

Jennifer deNicola withdrew her daughter from Malibu Middle School because of fears about PCBs, but her son, a sophomore, remains enrolled at the high school, partly because he didn't want to leave.

"We know there are PCBs in there. The district has tested, and the highest results in the entire nation -- some people say in the entire world -- has been found in our schools. That's not safe," deNicola said. "I worry about my child that's still in that environment every day."

deNicola , who heads a group suing the Santa Monica-Malibu Unified School District. She's gotten support from Malibu A-listers, like Cindy Crawford, who pulled her two children from Malibu High School.

"My husband and I have decided that we would happily pay for proper and thorough testing of all pre-1979 classrooms," Crawford said back in 2014.

PCBs - or polychlorinated biphenyls - are carcinogenic. They can also cause problems with the reproductive, nervous and immune systems. Before they were banned in 1979, PCBs were widely used to make caulk, sealants and other building materials.

"There could be as many as about 25,000 schools that contain those materials," said Robert F. Herrick of the Harvard School of Public Health.

The problems in Malibu were discovered after three teachers were diagnosed with thyroid cancer within months of each other in 2013.

The district says contaminated materials will be removed in the coming years as the schools undergo renovations. In the meantime, it has a plan -- approved by the EPA -- to continuously clean and monitor affected areas.

"We followed what we truly do believe is the science, and we really do believe that what we've done is health protective," said Laurie Lieberman, president of the Santa Monica-Malibu Unified School Board. But she said it would take years to replace the materials because "it requires people being out of the classrooms" and "changing out windows and all the caulking surrounding them."

Since implementing its plan, the district has tested more than 1,000 samples and detected no excessive PCB levels. But some public health experts remain critical.

"You have to remove the source. The cleaning is really just treating the symptoms," Herrick said.

deNicola also wants the district to do more tests to determine all the sources of PCB contamination.

"What we do here, we hope that it sets precedents to protect every child in every classroom. All those kids deserve toxic free schools," deNicola said.