Paris officials on Tuesday downplayed the risk of lead poisoning from the massive fire that tore through 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 metres (yards) around Notre-Dame are negative, meaning there is no danger,’ deputy mayor Emmanuel Gregoire told LCI television.

Hundreds of tonnes 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 centres in the immediate area. They showed less than 70 microgrammes of lead on average per square metre.

French health officials advise blood tests for people exposed to more than 70 microgrammes -- 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-metre perimeter still showed isolated readings of more than 1,000 microgrammes 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 programmes 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 microgrammes per square meter on streets up to a kilometre away from Notre-Dame, according to a map of ARS results published by Le Parisien newspaper Tuesday.

Levels of up to 900,000 microgrammes 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.

So far 82 children or pregnant women living near Notre-Dame have undergone blood tests, with 10 showing lead levels of 25 to 49 microgrammes per litre, a level at which French health authorities urge monitoring.

One child had more than 50 microgrammes, which denotes lead poisoning, though officials later found a more likely source of exposure: parts of the balcony on his family's apartment 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, behavioural 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.