Irreversibly (or irrevocably) contaminated was a Peacekeeper term for an individual who had come into contact with an unknown life form, either willingly or unwillingly. When something of the like occurred, Peacekeepers risked being tagged "irreversibly contaminated".
When a Peacekeeper was "irreversibly contaminated" they often shared the same fate as the being with whom that person had come into contact. In the case of Aeryn Sun, the subject she had encountered was the human John Crichton who was to be executed and dissected. Therefore, she would meet a similar fate.