Officers responded to reports of a suspicious package at Antioch Fire Department Station 81, located at 315 W. 10th St., at around 7:25 a.m., according to the Antioch Police Department.
Firefighters had found a lunchbox sealed with duct tape with the word "danger" written on it. The package was left anonymously on the fire station doorstep.
Police evacuated Station 81 and requested assistance from a Walnut Creek Police Department bomb squad. The bomb squad inspected the package and found it to contain two smaller containers filled with an unidentified liquid.
The Contra Costa Health Department responded and determined the liquid to be mercury, which was taken by health officials for disposal.
Station 81 personnel were directed to work out of another station, according to police, and there was no interruption in service.
Traffic was diverted around the area until around 11 a.m. when the mercury was safely removed. No one was injured during the operation.
The incident is being investigated as a hazardous materials case, since malicious intent does not appear to be a factor, according to police.