Seven of the 82 cars derailed, and a tanker car that fell into Mantua Creek leakedvinyl chloride into the waterway, which feeds into the Delaware River near Philadelphia, said Deborah Hersman, chairwoman of the National Transportation Safety Board.
More than 12,000 gallons (45,425 liters) of the highly toxic and flammable industrial chemical leaked from a gash in the car's side, local officials said.
Twenty-two people were examined at a nearby hospital as a precaution and were doing fine, said Larry Ragonese, a spokesman for the New Jersey Department of Environmental Protection.
Ragonese said the health danger and environmental impact were minimal.
"Initially there was a release of gas into the air that affected some nearby residents and people working right in that area," he said.
