A Cardassian colony in the Demilitarized Zone which Michael Eddington's Maquis render uninhabitable to Cardassians with a biogenic weapon in the episode For the Uniform.
In For the Uniform, set in 2373, the Maquis leader and former Starfleet officer Michael Eddington steps up his campaign against the Cardassian settlements of the Demilitarized Zone. His ships release cobalt diselenide, a nerve agent lethal to Cardassians but harmless to humans, into the atmosphere of Veloz Prime.
The colonists are forced to evacuate, and Eddington makes clear that he means to treat every Cardassian world in the zone the same way, leaving them open to human settlement. Quatal Prime suffers the same fate soon afterwards.
Sisko, humiliated by Eddington at every turn, answers in kind by poisoning the Maquis colony of Solosos III against human life. When the crisis ends, the displaced Cardassian and Maquis colonists are left to resettle on each other's former worlds.