About two weeks after a train carrying toxic and combustible materials derailed just outside a small town near the Ohio-Pennsylvania border and filled the skies with black smoke, questions abound over the health and environmental impacts of the disaster.

The February 3 derailment of the train, operated by Norfolk Southern, near East Palestine, Ohio, sparked a massive fire that sent fumes from several toxic chemicals into the air. To reduce the risk of an explosion, on February 6 officials released at least one chemical from five derailed tanker cars. (About 50 of the train’s 150 cars were involved in the accident.) Some of the substances were diverted into a designated trench, where they were burned off, the Environmental Protection Agency wrote in a February 10 letter to the train company.

But even now scientists are still struggling to understand the chemicals’ short- and long-term health implications for residents of the 5,000-person town and its surrounding region. Many reports have focused on vinyl chloride—a clear, flammable gas used to produce polyvinyl chloride (PVC) plastic, which is used in everything from piping to packaging to flooring. Scientists have known for decades that high doses of vinyl chloride can cause liver cancer. And even lower doses, particularly over long periods of time, may be dangerous to a person’s health. People can be exposed to the chemical as a vapor or from drinking contaminated water.

“We study concentrations that are currently considered safe, and in our studies, what we have observed is that these low doses can enhance underlying diseases—talking about liver diseases here,” says Juliane Beier, a hepatologist at the University of Pittsburgh, who studies vinyl chloride exposure in animals.

It’s not clear how much risk vinyl chloride might pose at this point, now that much of what was on the train has burned away. Of course, setting a hazardous material on fire is far from an ideal method of disposal. The problem is that by the time a train car full of vinyl chloride actually derails, there usually aren’t any better options available. (Investigators at the National Transportation Safety Board continue to search for answers about what caused the derailment in the first place.)

“In environmental risk assessment, we have to make a lot of decisions that we don’t want to have to make,” says Kim Garrett, an environmental toxicologist at Northeastern University.

In this case, that meant choosing to burn off the vinyl chloride rather than letting the chemical seep into the environment and waiting to see whether one or more of the train cars might explode.

Garrett says the key risk involved in a vinyl chloride burning, controlled or not, is the production of two nasty chemicals: phosgene, which both Germany and the Allies deployed during World War I to kill trenches full of soldiers, and hydrogen chloride, which, when inhaled, can turn into hydrochloric acid—a key component of stomach acid—within the lungs. By intentionally burning off the vinyl chloride in this case, however, responders could evacuate residents long enough for these two short-lived chemicals to break down or otherwise change form rather than risk an unpredictable explosion occurring with people nearby.

Vinyl chloride wasn’t the only chemical on the train: A partial manifest shared by the EPA offers more insight into some of the other materials it carried. And the agency’s February 10 letter said, “Cars containing vinyl chloride, butyl acrylate, ethylhexyl acrylate, and ethylene glycol monobutyl ether are known to have been and continue to be released to the air, surface soils, and surface waters.” All three chemicals are known irritants to humans, although scientists don’t have evidence that they can cause cancer.

But these documents raise as many questions as they answer, Garrett says. “I can be concerned about a chemical as I see it written down and as I know how it behaves in a laboratory setting. But I don’t know how every chemical reacts in the environment or every chemical reacts with each other, how it reacts in large quantities,” she says. “There’s a lot of toxicological nuance here, and I know that that’s not the answer the public deserves, that it needs.”

In response to a request for comment from Scientific American, a Norfolk Southern representative pointed to the company’s February 15 statement, as well as statements from state and federal government agencies about drinking water tests and home inspections.

To get the public the answers it needs, scientists will have to better establish what’s happening on the ground—and that means a lot of monitoring, experts say. EPA personnel have been on the scene since the day after the derailment, and the agency is sharing air-monitoring data publicly. Experts are also testing local well-drawn drinking water and encouraging residents to rely on bottled water until that work is complete.

“Officials are testing the outdoor air, and they are reporting no concerns, and that’s good news,” Beier says. But she adds that testing should continue for at least a year—and longer if any concerning compounds appear. “I think the air and the water, but also particularly the indoor air of any enclosed spaces around, should be monitored longer,” Beier says, “not just this one snapshot.”

It’s not yet clear whether the EPA has examined the site for other concerning chemicals, according to Nesta Bortey-Sam, an environmental toxicologist at the University of Pittsburgh, which is located about 50 miles from the derailment site. These substances include dioxins, a type of pollutant known to build up over time in animals and humans. When exposed to high levels of dioxins, people can develop chloracne (a skin disorder similar to acne), liver problems and elevated blood fats, which can increase the risk for heart disease and stroke, according to the Centers for Disease Control and Prevention.

“My recommendation is to broaden the scope and look at more chemicals because I believe there is a longer list than what is currently being looked at,” Bortey-Sam says.

Garrett says it’s important that independent groups, as well as the EPA and Norfolk Southern, monitor the situation. She also hopes that residents gather together to do their own science, mapping where people experience headaches or see dead fish, for example. Garrett notes that this sort of work can help give residents political power after a chemical disaster.

But people living near the crash site may need support to monitor their health as well, she adds. “In the region generally, rural health care has been an issue. Hospitals close; people don’t have access to doctors as they used to,” Garrett says. “Making sure everyone is able to access health care for complaints and issues that they notice is definitely important in the region.”