On April 15, 2019, the Notre-Dame Cathedral caught fire and burned for nine hours. But long after the fire was extinguished, environmental effects lingered.

That’s because the cathedral contained 460 tons of lead, some of which was expelled into the air by the fire. Researchers from Columbia University wanted to investigate potential lead contamination in the area surrounding the fire, as even very small environmental exposures to lead can have devastating effects on children’s cognitive development.

In this recently published study, the scientists collected and analyzed soil samples in a one-kilometer radius surrounding the cathedral. They estimated that the cathedral fire had resulted in 1000 kilograms (one metric ton) of lead being deposited in the kilometer surrounding the fire. This amount was much greater than the 150 kilograms of lead that an early government report estimated were deposited 1 to 50 km from the fire. 

The good news is that — even with the caveat that more extensive testing should have been performed in the days after the event — the authors of the study conclude that human exposures were still likely fairly limited and probably much less problematic than exposures from leaded gasoline use in previous decades.