A white, powdery substance found by a Boone mail worker Monday is harmless, an Iowa Department of Public Safety official said late Monday.

“We are confident that the substance poses no threat,” said Special Agent In Charge Jim Saunders of the Department of Public Safety’s public information office.

That preliminary analysis still needs to be confirmed by the Iowa Hygienic Laboratory in Iowa City, Saunders said.

“The focus now turns to investigation into the individual or individuals responsible for mailing this letter,” he said.

The suspicious white powder was found by a worker at Communications Data Services in Boone as she was sorting through mail.

The woman who discovered the powder was taken to the hospital as a precaution and was later released after showing no signs or symptoms of illness, said Des Moines Fire Inspector Brian O’Keefe. The woman’s name has not yet been released.

Saunders said he couldn’t release many of the specifics about the incident while the investigation continued.

“Officers are pursuing leads as we speak,” he said.

Saunders also said nothing was known about the substance, other than it was not dangerous. The tests were performed at Communications Data Services, 2005 Lakewood Drive, by a mobile laboratory from the National Guard’s 71st Civil Support Team.

Nine local, state and federal agencies assisted in the investigation.

Early Monday, the woman was sorting mail in a cubicle in an open area of the plant, O’Keefe said.

Boone police officers responded to a call at about 7:30 a.m., and management decided to send the workers home soon after.

Later in the morning, a hazardous materials team from the Des Moines Fire Department was sent to Boone.

If a suspicious powder is found in a mail facility, O’Keefe said, a hazardous materials team is always sent as a safety precaution.

Forty-six employees and first responders were decontaminated Monday as a precaution.

Communications Data Services, a part of the Boone Business Park just south of U.S. Highway 30, is an international data management company owned by the Hearst Corporation. The plant in Boone has about 350 employees who process bills, subscriptions and direct mail products.

— Lucas Grundmeier contributed to this article from Boone.The Associated Press also contributed.