French authorities are under growing pressure over possible health risks from the Notre Dame cathedral fire after an environmental group filed a lawsuit saying swift action was not taken to contain potential lead poisoning, and a firefighters’ union raised concerns.

Hundreds of tonnes of lead in the cathedral spire and roof melted in the extreme heat of the fire in April, dispersing lead particles into the air that settled on streets and buildings in surrounding neighbourhoods.

Officials have insisted there was no danger to residents but pressure has mounted on Paris authorities and health officials in recent days over the safety of schools in the surrounding area as well as the health of hundreds of firefighters who fought the blaze and the construction workers shoring up the site.

The French environmental campaign group Robin des Bois this week filed a lawsuit saying: “The relevant authorities, including the diocese .… neglected to assist residents, visitors and workers, allowing them to be exposed to the toxic fallout.”

The lawsuit accuses health agencies, government officials and the city of Paris of “deliberately putting people in danger” by not immediately taking measures to limit exposure to the contamination.

Environmental campaigners have said there were potentially high levels of lead in dust at ground level at schools and creches near the site and swift remedial action was not taken.

Clean-up work at Notre Dame was halted last weekend with workers sent home from the site after a leading government official acknowledged that anti-contamination measures were insufficient.

The Paris prefect, Michel Cadot, the government’s top official for the Paris region, said strict controls should have been introduced in the heavily contaminated interior of the cathedral, as well as in surrounding areas. Increased safety precautions are being put in place.

Paris city hall has closed a nursery and primary school that were jointly hosting a holiday club for 180 children in Paris’s 6th arrondissement “as a precautionary measure” after tests revealed high levels of lead in their shared playground.

Several other schools are being “deep cleaned”, with walls and furniture to be wiped and playgrounds hosed down during the summer holidays to remove dust. Local officials said this was being done to reassure residents “the risk is minimal”. Tests are continuing at other schools.

Facebook Twitter Pinterest An aerial view of Notre Dame under reconstruction after it was badly damaged by fire last April. Photograph: Kenzo Tribouillard/AFP/Getty Images

The investigative website Mediapart this month said Paris authorities were not being open enough about risks and had waited a month after the fire before conducting tests in the nearest schools. Health officials insisted they had been transparent about testing for lead levels and were keeping parents informed.

Sébastien Delavoux, a firefighter and representative of the CGT union, said he was concerned that not enough had been done to decontaminate fire engines and equipment used to put out the fire and questioned whether sufficient health support and testing had been given to fire officers.

He said his union had written to the authorities. “Has adequate medical follow-up been put in place? We haven’t had an answer,” he told France Info. “There must be transparent and public information made available.”

Shortly after the fire, the Paris police advised locals to clean surfaces with a damp cloth and pregnant women and children to wash their hands frequently. Police issued a statement shortly afterwards saying there was no risk of toxic inhalation from the air and that high lead levels found on the ground were limited to the area immediately surrounding the cathedral – which is closed to the public – and not further afield. Pregnant women and children in the area were later advised to get tested for lead levels in their blood.

Environmental groups have warned that potential health risks should have been taken into account immediately, likening the site of the cathedral to “toxic waste”.