A toxic spill from a tanker truck closed the northbound lanes of Interstate 5 through Seattle for more than an hour Wednesday afternoon, backing up traffic.

The Seattle Fire Department says the spill, originally estimated at 50 gallons, is about two gallons of a sodium borohydride and sodium hydroxide solution. The chemicals are used for bleaching pulp and wood products.

All northbound lanes of I-5 were closed just before 2 p.m. and two lanes reopened around 3:15 p.m. A third lane reopened about 4 p.m., easing the backup. Fire crews spread sand on the spill and worked with state Ecology Department officials on the cleanup.

Fire Department spokesman Kyle Moore says a person would definitely not want to breathe the spilled substance. He says the truck driver stopped when he noticed something leaking from his 5,000-gallon truck.