LITHIA (FOX 13) - Federal authorities are investigating after a letter containing an unknown substance was sent to Mosaic's offices in Hillsborough County.
Firefighters responded Friday after the letter was discovered at Mosaic's corporate offices on Circa Crossing Drive in Lithia.
According to the FBI, an unknown substance was found inside the letter. Firefighters did field testing, which showed that the substance was not hazardous. Investigators are doing additional testing to determine what the substance is.
The phosphate-producing company has been highly criticized since a sinkhole opened on the facility's property in late August. The sinkhole resulted in 215 million gallons of contaminated water spilling into the Florida aquifer.
Mosaic and the Department of Environmental Protection did not notify the public of the sinkhole until mid-September, prompting outrage from many residents who live near the facility.
The company and the DEP insist that the contaminated water is not affecting local water supplies and that it has "not migrated beyond the immediate area of the water loss incident."
The FBI will continue to investigate the letter and substance.