RICHMOND, Calif. -- Thousands of gallons of a toxic solvent were released from a manufacturing plant near San Francisco Bay after thieves stripped critical valves from factory equipment, state officials said Tuesday.

But only trace amounts of the solvent, toluene, reached the bay, with most of the 3,300 gallons captured in a drainage ditch, said state Department of Fish and Game spokeswoman Carol Singleton.

The thieves stole brass valves from Reaction Products' plant in Richmond on Monday, evidently so they could sell them, but the removal of the valves caused the solvent to escape, Singleton said.

Toluene in high concentrations is "very dangerous, flammable, carcinogenic," Singleton said. "It's a nasty chemical."

So powerful are the fumes that a shelter-in-place warning was briefly issued to 1,500 homes near the plant Monday afternoon after the spill was reported.

Singleton said officials were surprised the thieves themselves were not physically affected by the toluene fumes, especially because the tanks were not empty as marked.

"I would think it would have overcome them -- the fumes would have been overpowering," Singleton said, but the thieves appeared to have completed their mission.

"They can take them to a recycling company and get maybe 10 bucks for them," Singleton said. "Yet they've unleashed a disaster that's going to cost thousands to clean up."