I don´t know what it mean exactly, but…
After the Fire at Notre Dame
Neighbours of the fire-stricken Notre Dame cathedral have been advised to use wet wipes to clean surfaces where lead-laden dust from the blaze may have settled.
Tests have shown that the devastating 15 April fire released particles of the toxic metal that had been present in the frame of the church and its now-levelled spire, Paris police have said.
Investigators found lead in areas near the church, “very localised” and “notably on premises that may have been standing open at the time of the fire, and where dust had settled”.
https://www.theguardian.com/world/2019/apr/28/notre-dames-neighbours-warned-of-lead-contamination-risk-after-fire