BUCKSPORT, Maine — Work is expected to begin Wednesday to remove tens of thousands of gallons of chemicals from railway cars that derailed in Bucksport and crashed into the Penobscot River last week.

The derailed tankers, meanwhile, may be removed from the river bed and embankment later this week.

Pan Am Railways has hired an environmental cleanup contracting firm to pump chemicals still inside four tanker cars into empty cars. At least one of the cars leaked an estimated 4,000 to 6,000 gallons of a nonhazardous chemical into the Penobscot River after Friday’s derailment.

On Tuesday, Department of Environmental Protection officials corrected the name of the chemical suspected of leaking into the river. The chemical, called styrene butadiene copolymer, is a type of synthetic latex used to make the coated paper produced at the Verso Paper mill in Bucksport, where the train was headed at the time of the incident. The car was believed to be carrying 23,000 gallons at the time.

DEP staff initially had identified the leaking chemical as kaolin, which is a type of clay that also was being carried in some of the Pan Am Railways cars that derailed near the Bucksport-Orrington town line. Four cars in a 31-car train headed to the Verso mill derailed during the Friday evening incident, tearing up roughly 200 feet of track in the process. There were no injuries.

Styrene butadiene copolymer is a type of synthetic rubber commonly used in tires and shoe soles as well as in some papermaking applications. Samantha DePoy-Warren, a DEP spokeswoman, said the nonhazardous chemical is heavier than water and has likely dispersed given the location of the spill and the strong tidal currents in the Penobscot.

Other than a milky, bluish color in the water near the tankers, DEP staff have not observed any environmental effects from the spill. But DePoy-Warren said DEP staff as well as biologists from the Maine Department of Inland Fisheries and Wildlife will be looking for possible effects on wildlife or aquatic life.

“We will be monitoring that very closely but so far we haven’t seen anything,” she said. That stretch of the Penobscot is home to at least two federally protected fish: Atlantic salmon and shortnose sturgeon, both of which are considered endangered species.

Cynthia Scarano, executive vice president of Pan Am Railways, said Tuesday that the company hopes to have the tankers removed from the site by Friday. Pan Am reopened the rail lines on Monday after crews replaced a 200-foot section of track.