The FBI says a possible hazardous material that prompted the evacuation of a Minneapolis apartment complex and injured a University of Minnesota student could be ricin.

The bureau said Wednesday that a preliminary test of the material found in an apartment “indicated the presumptive potential presence of ricin.” The FBI also says the female student “may have been intentionally handling the material.”

Ricin is a poison found naturally in castor beans. The FBI says evidence will be sent to the bureau’s lab in Virginia for positive identification.

Emergency crews were called Tuesday to The Marshall, a 316-unit complex that caters to students at the nearby university. The complex was evacuated but residents were allowed to return after authorities determined there was no danger to the public.

The student remains hospitalized.