The concern is growing over the handling of toxic chemicals by U.S. authorities after a freight train derailed in the village of East Palestine, Ohio, earlier this month.

　　About 50 Norfolk Southern freight train cars derailed on the night of Feb. 3 in East Palestine, a town of 4,800 residents near the Ohio-Pennsylvania border, due to a mechanical problem on an axle of one of the vehicles.

　　There were a total of 20 hazardous material cars in the train consist, 10 of which derailed, according to the National Transportation Safety Board (NTSB), a U.S. government agency responsible for civil transportation accident investigation.

　　Five of derailed hazmat cars, the NTSB said, were carrying vinyl chloride, a colorless gas that burns easily and is produced industrially for its commercial uses.

　　After hundreds of residents evacuated their homes, emergency crew conducted a controlled release of the chemicals on Feb. 6 to avert a possible explosion, but the operations were said to have discharged toxic and potentially deadly fumes into the air.

　　Vinyl chloride exposure is associated with an increased risk of a rare form of liver cancer, as well as primary liver cancer, brain and lung cancers, lymphoma, and leukemia.

　　The controlled burn would also release phosgene and hydrogen chloride. Phosgene is a highly toxic gas that can cause vomiting and breathing trouble and was used as a weapon in World War I.

　　A group of state, federal, and local officials issued a statement on Feb. 8, saying that "evacuated residents in and around East Palestine can now safely return home."

　　"Air quality samples in the area of the wreckage and in nearby residential neighborhoods have consistently shown readings at points below safety screening levels for contaminants of concern," they alleged.

　　"This is one of the deadliest environmental emergencies," U.S. Congressman Jamaal Bowman, a New York Democrat, tweeted on Monday. "And no one is talking about it."