By Antoine Crouin and Kara Fox, CNN

(CNN) -- French health authorities are urging parents with young children and pregnant women to get their lead levels tested after April's catastrophic fire that engulfed Notre Dame Cathedral in the French capital.

The move was described "as a precaution" and came after the city's health authorities said they were investigating whether the fire was to blame for high levels of lead found in the bloodstream of a child living in central Paris.

On Tuesday, Ile de France's Regional Agency of Health (ARS), which covers Paris, said in a statement that it had learned that a child had been found to have levels of lead "higher than normal standards."

The health authority had said that in recent weeks, samples taken from the Ile de la Cite neighborhood -- where Notre Dame is located -- had shown that the risk to lead exposure had "largely disappeared."

However, on Tuesday, ARS said it had opened an investigation into the affected child's situation, saying it would also investigate if other factors, excluding the Notre Dame fire, could have caused a spike in the child's lead levels.

The agency did not give any further detail.

Lead 'didn't disappear,' group says

Lead doesn't just disappear, Jacky Bonnemains, a spokesperson from the French environmental group Robin des Bois, which estimated the blaze melted more than 300 tons of lead from the cathedral's roof and steeple.

"Public authorities are not acting at all. The lead didn't disappear, it's impossible," Bonnemains told CNN.

Days after the April 15 fire, Robin des Bois called on French authorities to "implement a protocol for health surveillance and environmental vigilance" in the locality, asking them to detoxify the tons of rubble, ash and wastewater produced by firefighters.

"Before launching a competition for the design of a new steeple, we should launch a competition to decontaminate what at the moment, alas, can be considered an industrial wasteland," the group said.

"For several months or even years, residents and people within the affected perimeter may inhale lead dust without knowing it," it added.

In May, the Paris police warned that Notre Dame's melted roof left extremely high levels of lead in the square in front of the building and the roads around it -- but said that there was no danger of toxic inhalation.

"The analysis of the samples made since Notre Dame's fire reveal that there is no risk related to lead ingestion from the air, but confirm the presence of lead dust in the immediate neighborhood of the cathedral," a police statement on May 9 said.

Police, however, did warn that children under 6 and pregnant woman were the most susceptible to lead poisoning through "multiple" inhalations and advised locals who frequent the area to regularly wash their hands and for locals to use a wet mop or cloth to wipe down their apartments.

Lead exposure can affect nearly every system in the body and can damage the brain and nervous system. It can slow growth and development and lead to learning and behavior problems including reduced IQ, attention-deficit hyperactivity disorder, and hearing and speech problems.

Children are at higher risk for lead poisoning and more susceptible to the toxic effects than adults, according to the American Academy of Pediatrics Committee on Environmental Health. The window of greatest vulnerability is in the embryonic, fetal and early postnatal periods.

There is no safe blood lead level in children, according to the US Centers for Disease Control and Prevention.