A white powdery substance that prompted a partial evacuation of the Cobb County courthouse Friday morning turned out to be toothpaste, authorities said.

The first floor of the Cobb Superior Court building was evacuated about 11 a.m. when a male employee in the clerk’s office opened a letter and was exposed to the suspicious substance, Marietta fire Chief Tim Milligan said. The employee was taken to the hospital as a precaution and three other employees were evaluated at the scene.

Several downtown Marietta streets were shut down for hours as firefighters in white hazmat suits were called in to investigate. After evacuating the building, shutting down its HVAC system and analyzing the mystery substance, officials determined it was likely just toothpaste that had been used to seal the mailed envelope.

“We sent our teams in to identify the substance, and what we’re finding is that substance consisted with the makeup of toothpaste,” Milligan said. “It was a white, crusty, pasty substance.”

Cobb County Sheriff’s Office Col. Nat Nation said the innocuous letter was simply an open records request that had been mailed to the clerk’s office from a Georgia prison inmate.

“It’s common for inmates to use toothpaste to seal envelopes, and that’s what it was,” he said.

Authorities did not disclose which prison the letter came from. The scene was cleared about 2 p.m. and normal operations resumed at the courthouse.