A train carrying hazardous chemicals derailed on Friday in East Palestine, Ohio, resulting in a large fire, and to prevent an explosion, crews this week began to expel the chemicals from the train cars in a “controlled release,” reports The Washington Post.

The release was to drain the cars of vinyl chloride, a highly unstable compound that is carcinogenic. If inhaled, it could cause respiratory illness, skin burns, and even death. Firefighters controlled the flames, allowing the chemical to burn off. The release went through Monday, however, evacuated residents have not been permitted to return. “We really don’t have a time frame right now,” said Mayor Trent Conaway.

The Environmental Protection Agency has been monitoring the chemicals released both into the ground and the air. There is a risk that vinyl chloride, hydrochloric acid, and phosgene, which is a World War I-era chemical weapon that is also sometimes used as a pesticide, could be released from the burning, the Post continues. 

Citizens have since become concerned about the potential contamination of the environment. “If a water supply is contaminated, vinyl chloride can enter household air when the water is used for showering, cooking, or laundry,” explains the National Cancer Institute. Vinyl chloride is used to make PVC and is used in many household products. 

“Scientists have been telling us for years that PVC is the most environmentally damaging type of plastic,” explained Emily Jeffers, an attorney at the Center for Biological Diversity. The EPA also has regulations on vinyl chloride because it’s been “implicated as the causal agent of angiosarcoma and other serious disorders, both carcinogenic and noncarcinogenic.”

Currently, residents of East Palestine are still under evacuation orders.