A perchlorate is a chemical compound containing the perchlorate ion (ClO4−).
The carbon monoxide atmosphere of Essof IV was laced with perchlorate dust, making it toxic to oxygen-breathing lifeforms. (DIS: "The Red Angel")
In the writer's first draft script of the Star Trek: The Original Series first season episode "The Squire of Gothos", perchlorate was mentioned by Spock as one of the constituents of the fireworks that greeted the USS Enterprise upon its arrival at Gothos. However, the fireworks had been discarded from the story by the time the first draft of the teleplay was issued.