The fire at Notre-Dame in April destroyed the cathedral’s roof and spire, which were covered with 460 tons of lead tiles. Tiny particles of some of that lead mixed with the plume of smoke that drifted over Paris.
Then that lead-laced dust settled on buildings, squares, parks, and plazas, test indicate. It also is likely to have made its way through open windows, air conditioning ducts and other building ventilation systems.
Here is what we found out about the potential risks, how the French authorities handled them, and what you need to know if you have visited Paris since the fire, or are considering going.
The authorities were slow to respond
The first indications that lead contamination was a problem were discovered two days after the fire, at a day care center at the Police Headquarters across the street from the cathedral.
Yet the response was halting:
The authorities closed two day care centers for officers’ children, while allowing other children from the broader public to play for weeks or months in schoolyards and day care centers, and to sit in classrooms, whose surfaces were tainted.
The authorities waited a month before conducting the first lead tests in nearby public schools, leaving children — who are most at risk — exposed to high levels of lead.
City and health authorities failed to get a full picture of the schools that could have been contaminated, conducting tests as late as the end of July, more than four months after the fire.
The authorities failed to clean the surroundings of the cathedral in the immediate aftermath of the fire, waiting more than four months to complete a total decontamination of the neighborhood.
For more than three months, the Culture Ministry, responsible for the Notre-Dame construction site, failed to heed warnings from labor inspectors that safety measures were not being followed by workers, who were exposed to alarming levels of lead.
The authorities minimized health risks
Even as problem became clearer, the French authorities delayed exposing its scope to avoid alarming the public, and instead issued reassuring statements that played down the risks.
According to one participant Culture Ministry officials minimized the risks in meetings as late as May with city, labor and police officials. The ministry denies this.
Health authorities have refused to share any blood lead test results for workers who operated in a highly contaminated zone, citing the confidentiality of medical records.
The authorities decided against compulsory blood lead tests for the thousands of children who live in the area or go to nearby schools.
With the exception of residents of the Île de la Cité, where Notre-Dame sits, parents who wanted to have their children tested — or their schools — faced delays and obstacles.
Of roughly 400 children who have been tested, 8.5 percent showed levels at or above risk thresholds, according to the Regional Health Agency.
Is it still safe to visit Paris?
All experts consulted by The Times said yes, though they differed on the level of precautions that should be taken.
Experts in France said that the risks from the lead were low, and advised against “paranoia.”
Businesses in the area of the cathedral have been cleaned. Eating a croque-monsieur at a restaurant on the Île de la Cité, where Notre-Dame sits, or drinking a glass of rosé on a restaurant terrace, is unlikely to result in lead contamination, French experts said.
Yet while no one suggested canceling a trip to Paris or, for residents, leaving the city, all the health experts consulted by The Times suggested a range of measures, out of prudence.
What precautions might I take?
Some experts recommended staying away from the immediate vicinity of Notre-Dame, particularly if you have children under age 6.
“I would be saying to parents, ‘Don’t panic, these are the three or four things you should do,” said Dr. Sean Palfrey, a professor pediatrics and public health at Boston University and director of the Boston Lead Poisoning Prevention Program, a state public health service.
Dr. Palfrey said that residents should be careful to wash their infants’ hands, so that they don’t pick up dust and put it in their mouths.
He also urged parents to be sure that their children had a diet with a good, nutritional dose of iron and calcium, which can displace lead in the body and make the body less likely to absorb it.
Residents should be sure to clean their apartments with wet mops or cloths, not brooms, which can simply stir up the dust. Vacuum cleaners with special filters, called Hepa filters, can also be used, experts said.
“If I could tell parents one thing, it’s that they should leave shoes at the door, keep the house really clean of dust and make sure everyone washes up before they eat,” said Jessica Wolpaw Reyes, a professor of economics at Amherst, in Massachusetts, who has done extensive studies on lead.
And everyone said that the government needed to clean up the city and its schools as soon as possible.
What if I have visited Paris since the fire?
Given the fragmentary information that has been made available, health experts vary on how dangerous they believe exposure to the lead dust has been.
“We must put things into perspective: Lead is a problem in France, like elsewhere, and we must deal with contaminations,” said Philippe Glorennec, a professor of health risk assessment at the École des Hautes Études school in Paris.
“We should pay attention to the Notre-Dame situation,’’ he said. ‘‘But be alarmed? No.”
Local authorities in Paris say they have encouraged parents of children who might have been affected to get their children’s blood lead levels tested, yet they have refused to make such tests compulsory.
French experts and regional health authorities who have urged restraint said they believed that the children who had been the most exposed had been tested, and that for the others, an exposure to lead dust presented minor risks.
“A high level of lead on a surface doesn’t mean the child is going to be automatically contaminated,” said Fabien Squinazi, a Parisian doctor and prominent expert on lead who advised the authorities against generalized and compulsory testing.
Those statements have come under scrutiny from other officials.
In a phone interview, the Paris deputy mayor in charge of health, Anne Souyris, said that she had been in favor of compulsory testing, but that health authorities had decided otherwise.
Dr. Palfrey also said that France has an obligation to screen as many children as possible.
Others, too, encouraged erring on the side of caution.
The best way for people to know their exposure is to get tested, said Dr. Morri Markowitz, director of the lead treatment and poisoning prevention program at the Children’s Hospital at Montefiore in New York.
“While the transient tourists probably did not accumulate much lead, the same might not be true for those that live and work close by,” Dr. Markowitz said.
Who is most at risk?
Among the groups at highest risk are children who still put their hands on floors, toys and other surfaces — all of which might be contaminated — and then put their hands in their mouth.
If pregnant or nursing mothers have been exposed to lead, their born or unborn children can also be at risk, said Dr. Markowitz.
Lead passes through the placenta, so the blood lead levels of mother and fetus tend to be correlated, he said. And during nursing, if a mother has high blood lead levels, some of that lead can be passed to the baby in her milk.
Professor Reyes said that no level of lead was safe for a child.
Her studies have shown that a level of 5 micrograms per deciliter could lead to a significant increase in behavior problems, juvenile violence and risky teen behavior.
“Lead is very toxic and very damaging to people,” Ms. Reyes said. “There are well established effects on I.Q. and behavior.”