This is unconfirmed. And the source, the Azov Battalion, is - to put it mildly - questionable.

But….sadly, it wouldn’t surprise me.

Azov are claiming that the Russians have dropped a “poisonous substance” in Mariupol from a drone, causing respiratory failure and vestibulo-atactic syndrome.
No more details were released. Big claim. pic.twitter.com/rRs8ISxT8q

— Woofers (@NotWoofers) April 11, 2022