The April 15 blaze sent tons of toxic lead from the cathedral's burnt-out roof into the air, later sinking to the ground as dust.
The agency said it has identified a child from the area with "a blood lead level above the regulatory threshold". Soil samples and some administrative buildings nearby tested positive for high levels of lead.
The agency said recent samples show there is "no risk linked to air quality".
Paris authorities have begun a cleanup of lead dust in the remaining cordoned-off parts of Notre Dame's forecourt with a vacuum-style machine.
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