Paris officials on Tuesday downplayed the risk of lead poisoning from the massive fire that tore through the Notre-Dame cathedral in April, as tests continue to show worrying levels of the toxic metal at nearby schools.

"All the tests we've carried out in a radius of 500 meters around Notre-Dame are negative, meaning there is no danger," deputy mayor Emmanuel Gregoire told LCI television.

Hundreds of tons of lead in the roof and steeple melted during the April 15 blaze that nearly destroyed the Gothic masterpiece, releasing lead particles that later settled on surrounding streets and buildings.

Work at the gutted monument was halted on July 25 after officials found that anti-contamination measures were insufficient to keep the lead from spreading, and it is only expected to resume next week.

On Monday evening, the city posted the results of new tests at schools and daycare centers in the immediate area. They showed less than 70 micrograms of lead on average per square meter.

French health officials advise blood tests for people exposed to more than 70 micrograms – a level that has been far surpassed in parts of central Paris since the disaster.

But the city also revealed that some schools and daycares beyond the 500-meter perimeter still showed isolated readings of more than 1,000 micrograms on playgrounds or windowsills.

Gregoire vowed the sites would be "rigorously cleaned" before the school year resumes in September, and would welcome children back only if approved by the regional health agency ARS.

"The city is not going to take any risks," he said.

But he rejected calls by some residents and parent associations to shroud the entire church site with protective cladding to contain the particles, a system often used when removing asbestos.

"From a technical and financial point of view, such a move would be an incredibly complex decision to carry out," Gregoire said.

Alarming tests

After weeks of saying residents were not at risk, Paris authorities suddenly shut two schools on July 25 that were running summer holiday programs for children, after tests found alarming lead levels.

That prompted a lawsuit from an environmental group alleging that officials failed to contain the contamination quickly, while others accused the city of failing to notify the public about the test results.

As recently as June 5, tests were showing lead readings of up to 7,500 micrograms per square meter on streets up to a kilometer away from Notre-Dame, according to a map of ARS results published by Le Parisien newspaper Tuesday.

Levels of up to 900,000 micrograms were found on the square just in the front of the cathedral in the days following the fire and this area has remained closed to the public since.

The ARS said Tuesday that the number of children so far tested doubled to more than 160 by end-July.

Among the some 80 children tested last month, six showed lead levels of 25 to 49 micrograms per liter of blood, a level at which French health authorities urge monitoring.

One child had more than 50 micrograms per liter of blood, which denotes lead poisoning, but officials said it was possible that in this case there were other causes because a sister came in at below 25 micrograms.

Of the 82 children tested up to June 30, 10 were in the 25-49 micrograms category, while one was about 50 micrograms. But in this case officials said a more likely source of exposure was the balcony in his family's apartment which contained lead.

The World Health Organization warns that "There is no known safe blood lead concentration," saying even trace amounts may be linked to "decreased intelligence in children, behavioral difficulties, and learning problems."

Children are more vulnerable because they are more likely to touch contaminated objects and then put their fingers in their mouths, it says.