Local families along with the Paris branch of the CGT trade union and the anti-pollution association Henri Pezerat, have filed the legal complaint alleging city and public health authorities endangered lives.

“Despite the scale of the fire and knowledge about the risk of pollution and contamination… no precaution in particular was taken by the authorities involved for more than three months after the fire,” according to a copy of the complaint seen by AFP.

It says 400 tonnes of lead from the roof of the Gothic masterpiece melted or were dispersed as microparticles over the French capital during the blaze on April 15, 2019.

“Children (in crèches and schools), neighbours and workers have clearly been exposed to the risk of lead” pollution, the complaint adds. “These facts amount to the crime of endangering the lives of others.”

The square in front of the cathedral was closed again to the public in May this year after tests revealed high concentrations of toxic lead particles.

Several months after the fire, city authorities ordered a deep-clean of schools in the area, while children and pregnant women were urged to have blood tests.

The complaint says the city withheld information from school directors and failed to act promptly. It also targets the police department, the culture ministry and regional health authorities.

The efforts of firefighters ensured the great medieval edifice survived the fire despite the collapse of the spire and much of the roof being destroyed.

But the lead risks delayed work on clearing debris and launching the restoration effort for the landmark, which President Emmanuel Macron wants open for visitors in time for the 2024 Olympic Games in Paris.

Investigators have yet to determine the cause of the blaze, but they have said an accident, possibly caused by a short circuit or discarded cigarette butt, remains the most likely explanation.