(CNN) -- A suspicious white substance in an airplane bathroom?

It could be anthrax, could be explosive residue or -- as authorities in California learned Friday -- it could be toilet paper.

The white dust appeared in the back lavatory of Alaska Airline's Flight 508 soon after it took off Friday afternoon from Seattle, said Bobbie Eagan, a spokeswoman for the carrier. Sometime during the 1,000-mile flight, the flight's crew notified authorities about the unknown substance and asked for help.

Fire department crews, law enforcement officers and hazardous materials experts circled the plane soon after it touched down shortly after 4 p.m. at John Wayne Airport in Santa Ana, California, according to Federal Aviation Administration spokesman Mike Fergus.

The aircraft's 151 passengers and six crew members deplaned, and authorities climbed on board. They included members of the Orange County Fire Authority, who along with members of the county's sheriff department tested the suspicious substance.

Capt. Greg McKeown, the fire department's spokesman, said that authorities eventually determined that white dust actually was a "cellulose paper material" -- or, in other words, what appeared to be toilet paper.

With that potential mess cleared up, the aircraft went back into service, said Egan.

CNN's Anna Rhett Miller and Marlene Baldacci contributed to this report.