For days, authorities have been telling residents of the area around East Palestine, Ohio, in the United States that it is safe to return home after a 150-car train carrying hazardous chemicals derailed on Feb 3.

However, concerns remain among the public that the government or railroad is not telling them the entire truth about the pollution or potential harm.

About 50 cars, including 10 carrying hazardous materials, derailed in the fiery crash, which investigators said was caused by a broken axle.

After hundreds of residents evacuated their homes, emergency crews conducted a "controlled burn" 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.

The Ohio Department of Natural Resources said the chemical spill had killed an estimated 3,500 small fish along 12 kilometers of streams as of Feb 8.

Ohio Governor Mike DeWine said on Tuesday that the pollution didn't pose a serious threat to the 5 million people who rely on the Ohio River for drinking water.

However, he and several Ohio health and environmental officials cautioned at a news conference that residents using private wells near the derailment site should use only bottled water.

Reporters pressed DeWine and other officials on Tuesday about some residents' complaints of headaches and concerns over the situation.

US Representative Jamaal Bowman, a Democrat from New York, said on social media on Monday: "This is one of the deadliest environmental emergencies. And no one is talking about it."

Sil Caggiano, a hazardous materials specialist, warned: "There's a lot of what-ifs, and we're going to be looking at this thing five, 10, 15, 20 years down the line and wondering. Cancer clusters could pop up, you know, well water could go bad."

Wang Wenbin, spokesman for China's Foreign Ministry, said on Tuesday that some Western media chose to ignore the derailment at the time it happened, adding that this was not the first time they have done so, despite their boasts of being free, professional and fair.

Railroad union officials said they have been warning that such an accident could happen because, they alleged, railroad cost-cutting has harmed safety measures.

According to the US Department of Transportation, about 4.5 million metric tons of toxic chemicals are transported by rail each year, with an average of 12,000 rail cars shipping the materials through cities and towns each day.

The incident is "the tip of the iceberg", Ron Kaminkow, general secretary of the cross-union group Railroad Workers United, was quoted by The Guardian as saying. "If something is not done, then it's going to get worse, and the next derailment could be cataclysmic."