Thousands of gallons of a toxic chemical spilled into the Ohio River between Illinois and Kentucky after a barge ran aground, environmental officials said Wednesday.

Initial estimates were that about 3,700 gallons of a petroleum-based substance called cumene had poured into the water since the barge ran aground between Brookport and Metropolis late Tuesday, Illinois Environmental Protection Agency spokeswoman Maggie Carson said.

Authorities were still trying to assess the severity of the spill Wednesday and the hazards it could pose, Carson said.

Contact with cumene can irritate skin and eyes, cause headaches in humans if inhaled, and be damaging to animals directly exposed to it. It is used in petroleum products, manufacturing, as a paint thinner and as a component of high octane fuels, according to the EPA Web site.

The Kentucky Department of Highways said it was restricting traffic on the Interstate 24 Ohio River Bridge to enable environmental officials to set up an air monitoring station.

As a precaution, local authorities also requested that a nearby park, Fort Massac State Park, be closed, said Illinois Emergency Management Agency spokeswoman Patti Thompson.