In the early evening of April 15, 2019, the 800-year-old wooden beams supporting the roof of Paris' Notre-Dame Cathedral caught fire and eventually consumed the building's iconic spire before local firefighters could extinguish the flames.

The cathedral sits on the Île de la Cité, an island in the middle of the Seine river in the heart of Paris, in close proximity to schools and parks.

The smoke from the fire scattered dust containing 460 tons of lead across the central city, possibly exposing up to 6,000 children under the age of 6 to unsafe levels of toxic chemicals, an investigative report from the New York Times found.

French authorities have not properly alerted the Parisian public to health risks associated with the fire, the Times reported.

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In April, the world watched in anguish as the Notre Dame — situated in the heart of Paris — went up in flames.

By the time the blaze had been extinguished, the cathedral's iconic spire had collapsed, and much of its roof and wooden internal structure destroyed. Politicians, celebrities, and companies from around the globe immediately pledged support and funds to help rebuild the landmark and French President Emmanuel Macron set an ambitious timeline, saying he wants renovations completed in five years before Paris hosts the Summer Olympics in 2024.

But as the French set their eyes on rebuilding their national pride, the possible health risks from the fire took a seat on the back-burner, an investigation from the New York Times revealed.

Read More: Why Notre-Dame Cathedral, a medieval stone church, burned so quickly

According to confidential documents, including warnings by labor inspectors, a police report and previously undisclosed lead measurements by the Culture Ministry, smoke from the April fire scattered toxic dust that contained 460 tons of lead to surrounding parks, schools, and homes.

The dust came from the collapsing cathedral spire and roof, and contaminated parts of central Paris with lead levels up to 1,300 times higher than French safety guidelines, the Times reported.

"It's almost a no-brainer that if you incinerate hundreds of tons of lead, you're going to have some significant deposition of particles in the neighborhood," Matthew J. Chachère, counsel to the New York City Coalition to End Lead Poisoning, told the Times.

More than 6,000 children under the age of 6 live within half a mile of areas in Paris that were found with lead levels outside the acceptable range of safety guidelines.

The French authorities knew about the lead problem just days after the fire but didn't inform Parisians of the health risks

The Times confirmed through a series of interviews that French authorities were aware of the possible levels of lead exposure within 48 hours of the fire. But a month passed before the first lead test was completed in the area, and the public was not immediately alerted to the health risks associated with the fire's fallout.

Current tests reveal that at least 18 schools and daycares in the area have unsafe lead levels and dozens of public spaces have 60 times the acceptable levels of lead. Areas surrounding Notre Dame were hit hardest, according to the report, as up to 1,300 times more lead than regulatory standards permit, and authorities didn't decontaminate the area until four months later.

"These are astronomical levels, and the attitude of health authorities is inexplicable," Annie Thébaud-Mony, a public health expert in France, told the New York Times.

In this image taken from France Televisions video, firefighters stand at an entrance and look at the fire damage inside the Notre Dame cathedral in Paris, Monday April 15, 2019. France Televisions via AP

The Times added that hundreds of children continued to go to school in contaminated areas after the fire before lead testing and clean-up efforts began.

"Lead affects children more than it does adults," according to the US Centers for Disease Control and Prevention (CDC). Children tend to show signs of severe lead toxicity at lower levels of exposure, the CDC reports; lead poisoning has occurred in children whose parents accidentally brought home lead dust on their clothing.

Regardless of whether a person breathes-in or swallows lead particles, the chemical gets stored in the body's bones, blood, and tissues — potentially causing kidney and brain damage. According to the CDC, lead exposure can cause miscarriage, stillbirths, and infertility, and ill-health effects can pass from pregnant women to their unborn children. Lead poisoning can damage developing babies' nervous systems and later affect behavior and intelligence.

'They thought that they would protect people by not communicating about the lead issue'

Just days after the fire, a lead test at a daycare center across the street from Notre Dame revealed unsafe levels of the toxic chemical, the Times reported, citing a confidential police document. Another test at a second daycare center yielded similar results. Despite those tests, the two daycares (along with other public schools near the Île de la Cité) weren't closed until May — and French authorities didn't sound the alarm.

City officials like Anne Souyris, Paris' deputy mayor in charge of health, told the Times that they were following the lead of regional and national agencies: "They thought that they would protect people by not communicating about the lead issue."

The Île-de-France regional health agency released a statement to the public on May 9 that confirmed the presence of lead dust near the cathedral, but also stated that their analysis "indicates that there are no risks associated with [lead] absorption."

Souyris added, "The state was afraid to make people afraid."