The Norfolk Southern train derailment in Ohio left behind toxic chemicals, leaving many wondering about potential health impacts though officials say it’s safe to remain in the community.

Residents temporarily evacuated because of the release of a carcinogen called vinyl chloride, but on Feb. 8, officials determined they could return, citing air quality monitoring that showed “readings at points below safety screening levels for contaminants of concern.”

Air monitoring is expected to continue, and free water well testing will also be available. 

Vinyl chloride was not the only chemical involved in the derailment. A letter that the EPA sent to the Norfolk Southern Railway Company also listed four others that were contained in cars and tankers that had been derailed, breached or on fire.

Here’s what you should know about each compound:

Vinyl chloride

Vinyl chloride is a colorless gas that burns easily and is unstable at high temperatures, with a mild and sweet odor, according to the Agency for Toxic Substances and Disease Registry.

This cancer-linked substance, which does not occur naturally, is a “volatile organic compound” — a chemical that can vaporize into the air at room temperature and can dissolve in groundwater.

Vinyl chloride is also used to make polyvinyl chloride (PVC), an ingredient in many plastics. PVC, however, is not suspected to be carcinogenic, according to the National Cancer Institute.

The institute links vinyl chloride with a heightened risk of a rare form of liver cancer, as well as primary liver cancer, brain and lung cancers, lymphoma and leukemia. 

These effects are thought to be the result of prolonged exposure to the substance.

In the short term, exposure to vinyl chloride can cause headaches, dizziness and loss of consciousness, as well as possible breathing problems and eventual death at high concentrations, said James Fabisiak, an associate professor of environmental and occupational health at the University of Pittsburgh School of Public Health. 

Over a long period of time, it can cause chronic lung problems and autoimmune diseases, in addition to cancer, Fabisiak said. 

While vinyl chloride is generally gaseous, if “it’s held under pressure, like in train car tanks,” it can also dissolve in water, according to John Bucher, former associate director of the National Toxicology Program. 

“We have a chemical that in long-term studies in animals is a very potent carcinogen,” Bucher said. 

This compound, he explained, also has “very poor warning properties” — meaning, it is difficult to smell until it reaches high concentrations. Irritation therefore suggests that exposure is “way above the levels that in long-term studies can cause cancer,” according to Bucher. 

“Of all the chemicals that I’ve seen, potentially in this accident, that’s the one that people should be paying attention to,” he said. 

Nonetheless, Bucher stressed that the possible health impacts in the Ohio derailment case remain uncertain, particularly due to the short-term, high-dose exposure that occurs during such accidents. 

“Most of the industrial chemicals, like these that have been tested for cancer, have been looked at with respect to long-term occupational settings,” he said. 

Some concern has been circulating in the media about the effects of a controlled burn that officials decided to conduct a few days following the derailment. When vinyl chloride burns, one of its byproducts can be phosgene — a chemical warfare agent used in World War I.

But Bucher said he believes the controlled burn in this case was likely a “reasonable solution,” as the temperature “would be warm enough that it wouldn’t form a phosgene cloud.” 

“Otherwise, you’ve got a highly toxic material which you’re going to have to deal with in tanks that are unstable,” Bucher added. 

However, other toxicologists did note health concerns that can stem from the byproducts generated by burning vinyl chloride. 

Keeve Nachman, an associate professor at Johns Hopkins Bloomberg School of Public Health, noted that such activity can result in hydrogen chloride and polycyclic aromatic hydrocarbons (PAHs) in addition to phosgene. 

Hydrogen chloride can, at high levels, cause severe respiratory irritation as well as respiratory hyperplasia, which can in some cases precede cancer, Nachman said. Meanwhile, PAHs can be carcinogenic. 

“In order to really make a judgment about whether those effects are likely, we need to have a better understanding of the timing and amount of exposure that people have to these chemicals,” he added.

As far as water contamination is concerned, a ruptured tank of vinyl chloride that flows into a nearby creek does create some cause for concern, according to Bucher. 

“I think it’s prudent that people requested to use bottled water for a while until they can figure out the extent of the situation,” he said. 

Murray McBride, a soil and crop scientist and emeritus professor at Cornell, also noted that if vinyl chloride gets into soil, it can remain for decades and leach into groundwater, possibly impacting people’s wells. 

On Wednesday, the state of Ohio declared that East Palestine’s municipal water is safe to drink, citing testing results that showed no contamination in water from the five wells that feed into the water system. However, residents have expressed fear and concern over the situation. 

Butyl acrylate and ethylhexyl acrylate

Butyl acrylate is used in paints, coatings, sealants and adhesives, while ethyl acrylate is used to make paints and plastics, according to the National Library of Medicine. 

Bucher, the retired toxicologist from the National Toxicology Program, described acrylates as “irritating chemicals when you run into them in high concentrations.” 

But in comparison to vinyl chloride, these chemicals have much lower odor thresholds — the point at which people can smell the chemicals, he explained. 

Some acrylates have been studied and shown to be “very weak carcinogens” under high-dose settings in long-term studies, according to Bucher.

“The primary human reaction to the acrylates has been when they’re used in things like nail polish, some of them can cause allergic contact dermatitis,” he said. 

While he stressed that he has no specific knowledge about the Ohio case, Bucher said it is conceivable that in a high-dose exposure situation, people could experience “sensitivity to a number of chemicals.”

Fabisiak said that over shorter periods of time, acrylates can irritate the skin, lungs, eyes and throat. 

There’s some evidence that ethylhexyl acrylate may be carcinogenic, but the data is not as strong as it is for vinyl chloride, according to Fabisiak. Butyl acrylate, however, is unlikely to cause cancer, he added. 

Although butyl acrylate may not pose a threat to humans, McBride said that it can “cause some pretty harmful effects in the environment on ecological systems” and said it may be responsible for killing fish in the area.

“It’s pretty toxic to aquatic and other organisms,” he said. 

Officials have estimated that the chemical spill resulting from the train derailment has killed roughly 3,500 fish.

Isobutylene 

Isobutylene is a gas that is used to make aviation fuel. It is colorless and has a petroleum-like smell, according to the National Library of Medicine. 

Fabisiak said it can have short-term impacts on the central nervous system if large amounts are breathed in. 

He said that it is prone to evaporating. 

Ethylene glycol monobutyl ether

Ethylene glycol monobutyl ether is a colorless liquid with a mild, pleasant odor that can irritate eyes and skin and may be toxic if ingested, according to the National Oceanic and Atmospheric Administration’s CAMEO Chemicals database. 

It is used as a solvent to produce paints and varnishes.

Fabisiak said that high levels in the air can cause irritation and central nervous system impacts. 

While this compound can cause the breakdown of red blood cell membranes in some species — leading to cancer — humans are more resistant to this impact, according to Fabisiak.