About 4,000 gallons of a toxic solvent combined with lye spilled onto the Interstate 20 bridge and into the Mississippi River in a multiple vehicle pileup that halted traffic on the bridge for 17 hours Wednesday, Louisiana State Police said Thursday.

The thousands of gallons of a solution of acetonitrile and sodium hydroxide spilled out of a tanker truck driven by Jethro McIntosh, 60, of Mobile, Ala. at about 4 a.m. Tuesday that was in the middle of the pileup, said Albert Paxton, spokesman for LSP.

Acetonitrile, also known as methyl cyanide, is a solvent most frequently used in the production of rubber, pesticides, batteries and some pharmaceuticals. Sodium hydroxide, also known as lye or caustic soda, is sometimes added to acetonitrile to degrade the chemical into acetic acid — one of the primary components of vinegar — and ammonia, thus making it less toxic.

The environmental impact of the spill is still unknown though the chemical should have been diluted greatly by the flow of the Mississippi River, said Greg Langley, a spokesman for the Louisiana Department of Environmental Quality.

“We do know that the material when released in the water does biodegrade to a moderate extent,” Langley said.

The flow of the river should have flushed the chemical solution away from Vicksburg, but LDEQ hasn’t fully examined the extent of the impact south of the bridge, Langley said.

“We’re still investigating the incident,” he said.

The chain reaction of crashes that caused the spill began when a westbound tractor-trailer rig driven by Koffi Akollor, 48, of Hampton, Ga., struck a patch of ice and jackknifed on the Louisiana side of the bridge, Paxton said.

Akollor’s vehicle was followed by McIntosh and another semi driven by 31-year-old Michael Lesko of Flagstaff, Ariz.

“McIntosh, the tanker drive, and Lesko were able to stop,” Paxton said.

Stopping, however, was a futile attempt at averting a pileup. Both trucks were struck in the rear by an 18-wheler driven by Michael Lampkin, 33, of Como, Paxton said.

“He ran into the two of them and knocked them into the first truck,” Paxton said.

Donald Ross, 41, of Hazlehurst was driving a Ford F-350 with a car-hauling trailer and was able to stop before rear-ending the pileup, but he was hit from behind by a semi driven by David Christian, 39, of Memphis, Paxton said.

Christian and Lampkin both received citations for careless operation of a vehicle, Paxton said.

Eastbound traffic was halted until 5 p.m. Wednesday, and westbound lanes opened at 7 p.m., about 13 hours after the initial spill.

A crew from U.S. Environmental Solutions, a private company, cleaned up the spill on the icy bridge using soap and water, LDEQ officials said.

River traffic was also at a standstill until 11:30 a.m. when the water was deemed safe for barge traffic, U.S. Coast Guard officials said.

Initially, the chemical in the spill was reported to be isopropyl 2-chloropropionate, which is insoluble in water.

The United Nations Committee of Experts on the Transport of Dangerous Goods requires trucks hauling hazardous materials to display a numbered and color coded placard indicating the dangers of the chemicals inside.

Acetonitrile containing sodium hydroxide falls into a category of otherwise unspecified chemicals for which trucks must have a red placard bearing number 2924.

Isopropyl 2-chloropropionate has the same red placard with number 2934 printed on it.

Officials have said spills of both chemicals require similar cleanup protocol.