Thousands of people could suffer health issues due to “extremely dangerous fumes” being given off by Notre-Dame cathedral.
Over 450 tons of lead sheeting melted when the Parisian landmark caught fire in April.
Campaigners fear the city-centre area is contaminated with lead particles.
Environmental group Robin des Bois wants signs erected across the French capital to warn tourists of the continuing hazard.
Spokesman Jacky Bonnemains said: “Exposure to lead is extremely dangerous. We compare Notre-Dame to a hazardous industrial wasteland.”
The authorities have conducted a “deep clean” of nearby schools but insisted there is no danger.
There were fears the cathedral's fire-ravaged ceiling would be completely destroyed by a soaring heatwave gripping France, architects say.
Soaring temperatures amid a huge heatwave across Europe in July threatened the 850-year-old structure.
"I am very worried about the heatwave," .
"What I fear is that the joints or the masonry, as they dry, lose their coherence, their cohesion and their structural qualities and that all of sudden, the vault gives way."
Villeneuve said the vaulted ceiling "could very well" collapse and that unlike the bell towers and other parts of the cathedral, experts had still not been able to access the ceiling from above or below.
