The Neurotoxin Vats are tall buildings used by the Scorpion Cell to store the namesake neurotoxin substances created by Rashidi that, despite of being fatal if used for extended periods, are capable of countering Yuri's mind control technology.
In Obsidian Sands, multiple Neurotoxin Vats are scattered inside the Scorpion Cell's base. Yuri first thought that these vats were just another variation of the Bio Reactor that powers the Scorpion Cell's base. He later knew that it was filled with unidentified toxins that the Proselyte must be careful about.
In the Covert Ops mission Survivors, the objective is to extract neurotoxin from 7 out of 13 Neurotoxin Vats controlled by Epsilon loyalists by capturing them and protecting Drillers sent to extract them until the extraction is complete. Therefore, at least 7 Neurotoxin Vats must remain intact during the mission.