After a catastrophic 38-train car derailment in East Palestine, Ohio, on February 3, some officials are raising concerns about a type of toxic substance that tends to stay in the environment. 

Earlier this month, Sherrod Brown and J.D. Vance, U.S. senators from Ohio, sent a letter to the state's environmental protection agency, expressing concern that dioxins may have been released when some of the chemicals in the damaged railcars were deliberately burned for safety reasons. 

They joined residents of the small Midwestern town and environmentalists from around the U.S. calling for state and federal environmental agencies to test the soil around the site where the tanker cars tipped over. 

Dioxins refer to a group of toxic chemical compounds that can stay in the environment for long periods of time, according to the World Health Organization. They are created through combustion and attach to dust particles, which is how they begin to circulate in an ecosystem.

Linda Birnbaum, a leading dioxins researcher, toxicologist and former director of the National Institute for Environmental Health Sciences, said that burning vinyl chloride does create dioxins.

Residents near the burn could have been exposed to dioxins in the air that landed on their skin or were breathed into their lungs, said Frederick Guengerich, a toxicologist at Vanderbilt University.

Skin exposure to high concentrations can cause what's known as chloracne – an intense skin inflammation, Guengerich said.

There is already some level of dioxins in the environment – they can be created by certain industrial processes, or even by people burning trash in their backyards, said Murray McBride, a Cornell University soil and crop scientist. 

Once they are released, dioxins can stick around in soil for decades. They can contaminate plants, including crops. They accumulate up the food chain in oils and other fats. 

In East Palestine, it's possible that soot particles from the plume carried dioxins onto nearby farms, where they could stick to the soil, McBride said. 

"If you have grazing animals out there in the field, they will pick up some of the dioxins from soil particles," he said. "And so, some of that gets into their bodies, and then that accumulates in fat tissue."

Eventually, those dioxins could make their way up the food chain to human consumers. Bioaccumulation means that a larger amount of dioxins can get into humans than what's found in the environment after the crash.

Ohio residents diagnosed with bronchitis

More residents living near the train derailment site in East Palestine have been diagnosed with bronchitis, raising concerns over the threats posed by hazardous chemicals from the accident, NBC reported on February 25. 

According to the report, a medic working for a hospital, one of the closest ones to East Palestine, told NBC that "exposure to potentially hazardous chemicals" is among possible reasons leading to ailments including bronchitis.

Apart from respiratory issues, some residents have also complained about headache, nausea and rashes.

Environmental officials suggested that nearly 44,000 animals died following the crash, with people living nearby experiencing symptoms associated with chemical exposure.

Yet the Environmental Protection Agency (EPA) and local authorities claimed the air and drinking water quality accord with relevant safety standards.

On February 16, EPA Administrator Michael Regan told the residents that the water is fit for drinking and the air safe to breathe around East Palestine, where just under 5,000 people live near the Pennsylvania state line.

"I'm asking they trust the government. I know that's hard. We know there's a lack of trust," Regan said. "We're testing for everything that was on that train."

Residents are frustrated by what they say is incomplete and vague information about the lasting effects from the disaster.

"I have three grandbabies," said Kathy Dyke, who came with hundreds of her neighbors to a public meeting on February 15. "Are they going to grow up here in five years and have cancer?"

Experts agreed that residents have reason for concern about dioxins from this accident. 

Even though they are present in small amounts from other sources, the large amount of vinyl chloride burned off from the train cars could create more than usual, McBride said. "That's my concern, that there could be an unusual concentration."

(With input from agencies)