BUCKSPORT, Maine — Work crews on Wednesday emptied chemicals from two of the four train tanker cars that derailed on the banks of the Penobscot River last week.

Response staff with the Maine Department of Environmental Protection also said that the amount of a synthetic latex chemical that spilled from one of the tankers appears to be substantially less than originally estimated. Crews are expected to begin emptying two other cars containing a clay slurry called kaolin on Thursday.

Beginning around 7 a.m., a contractor hired by Pan Am Railways began pumping tens of thousands of gallons of a nonhazardous chemical called styrene butadiene copolymer from the derailed cars into empty tankers waiting on the tracks above. A type of synthetic latex or rubber, the styrene butadiene copolymer was contained in two tankers that went over the embankment, with one car nosing into the Penobscot.

“Everything seemed to go as planned today,” said Darian Higgins, an oil and hazardous materials responder with the DEP’s Bangor office, adding that both tankers were emptied. “So the potential for a spill of that styrene solution is gone.”

Based on the amount of chemicals pumped out, Higgins estimated that between 100 and 1,000 gallons of the styrene likely leaked from one of the tankers after the derailment. That is well below the 4,000 to 6,000 gallons initially estimated.

The two cars containing the clay slurry are at the base of the steep embankment on the river’s edge and partially submerged in the Penobscot, depending on the tide.

Massachusetts-based Pan Am Railways is investigating what caused the four cars to jump the tracks last Friday night. Roughly 200 feet of rails were damaged during the incident and had to be replaced.

A spokesman for the Federal Railroad Administration, the division of the U.S. Department of Transportation that enforces railway safety laws, said Wednesday that two inspectors with the agency are in Bucksport investigating the incident.

The 31-car train was bound for Verso Paper’s Bucksport mill at the time of the derailment. Both the clay slurry and styrene butadiene copolymer are used in the papermaking process, with the latter substance being used in coated papers. A Verso spokesman has said production was not affected by the incident, which closed the rail lines feeding the mill for several days.

Although neither substance is considered to be hazardous, the situation is being closely monitored by the DEP as well as state and federal agencies. The Penobscot River is home to Atlantic salmon and shortnose sturgeon, both of which are protected under the federal Endangered Species Act.

Steve Mierzykowski, a contaminants biologist with the U.S. Fish and Wildlife Service’s Maine field office in Orono, said now is a critical time for salmon because juvenile smolts are leaving the river for the first time while adults are swimming upstream to spawn.

Mierzykowski visited the site on Wednesday and saw a small stream of waste going into the river. The DEP will conduct sediment monitoring after the tankers have been removed but the biologist said he did not see any dead fish, wildlife or invertebrates at the site.

“From our agency’s standpoint, we are concerned about the endangered species in that area and migrating birds,” Mierzykowski said. “I looked at the site today and didn’t see any impacts to fish and wildlife.”

Cleanup work at the site is being handled by Clean Harbors, a Massachusetts-based company that does extensive work in Maine.

A Pan Am representative has said that the company hopes to have the tankers removed by the end of the week.