MASON CITY — Emergency authorities are working on Mason City’s south side after an anhydrous ammonia leak at the Five Star Co-op on 245th Street. Cerro Gordo County authorities were called to the co-op at about 9:30 this morning when a valve on an anhydrous tank was sheared off, with employees not able to stop the leak. The Mason City Recycling Center and Cartersville Elevator were evacuated but no homes in the area adjacent to the co-op were impacted. With winds blowing from the northeast to the southwest, authorities were planning to allow the ammonia to dispense out of the tank. Roads in the area of the co-op have been closed for the time being.