Paris health official Arnaud Gauthier said that the cleaning had been ordered "to reassure us that the risk is minimal," adding that the levels of lead pollution caused by the April fire at Notre-Dame were not a cause for alarm.
Environmental groups warned soon after the fire that 300 tonnes of lead in the roof of the Paris landmark had gone up in flames, posing a danger to residents in the area, particularly to children.
A report from the Mediapart investigative website on Thursday reported that dangerous levels of lead - as much as 10 times higher than the safe limit - had been detected in schools and creches surrounding the cathedral.
It added that Paris authorities had waited until May before conducting tests in the 10 creches and schools that are within 500 metres of the monument on the Ile de la Cite island in central Paris.
One result – in the private Sainte-Catherine elementary school – showed lead at a level of 698 microgrammes per square metre, 10 times higher than the limit of 70 microgrammes which is considered dangerous.
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During a tour of the scorched edifice on Wednesday, reporters were told by Culture Minister Franck Riester that workers inside had to wear special masks because of the presence of lead which had seeped into some of the stone during the fire.
In June, Paris health authorities urged children and pregnant women living around Notre-Dame to undergo tests to detect levels of lead in their bloodstream, after a child living locally was found with lead levels in its blood much higher than acceptable limits.
Lead pollution can cause neurological defects for humans, especially children, as well as nervous system and kidney problems.