Iryna Nikolaieva sat in a stairwell of a Kyiv bomb shelter where she had been living for three days and called engineers at two chemical plants near the front lines in the country’s east during a lull between air raid warnings earlier this month. Nikolaiva was a hazardous waste expert, and she was concerned that fighting near the facilities would damage earthen dams that were holding back hundreds of thousands of tons of chemical sludge, potentially causing a catastrophic accident.

The situation was under control, according to a manager at one of the locations. The chief engineer of the other, a chemical processing plant near Toresk with waste facilities less than two miles from the front line, said he had no idea how the storage sites were holding up. “They said they couldn’t get there because of active hostilities,” Nikolaieva says from Warsaw, where she fled after living in a bomb shelter for nine days with her son, his girlfriend, and hundreds of other Kyiv residents. “It isn’t safe for people to check there.”

Millions of civilians have been forced to flee their homes as a result of Vladimir Putin’s unprovoked attack on Ukraine, with thousands more trapped under Russian shelling in cities like Mariupol. The fighting is also causing new environmental hazards, which could increase the war’s human toll. Some of these environmental risks, such as a nuclear power plant release of radiation, could have immediate and devastating consequences. Others, such as carcinogenic dust from bombed buildings, are long-term threats, with consequences that will likely last for years or decades after the fighting has stopped.

All wars endanger civilians’ health and safety, but the fighting in Ukraine could have particularly dire environmental consequences due to the country’s heavy industrialization, particularly in the east, which is considered Ukraine’s industrial heartland.

Much of that infrastructure—steel plants in the eastern Donets Basin, chemical plants near Kyiv and Korosten, and weapons factories, including facilities to manufacture intercontinental ballistic missiles—was built during the Soviet era, with some falling into disrepair or mismanagement in recent years. Warfare alters the dangers posed by such facilities dramatically. Under normal circumstances, some hazards may be relatively well-contained, but if they are damaged by bombs or shelling, they could kill or sicken thousands. Hydropower dams, for example, could fail, flooding entire towns and villages. The possibility of a toxic waste spill from one of Ukraine’s chemical facilities, such as the plant near Toresk, is one of the most dangerous threats.

That facility, in particular, could be extremely vulnerable to damage, and an accident could be devastating. The Toresk facility has two massive man-made toxic waste ponds, each of which emits sickly-sweet phenol fumes, as well as gaseous naphthalene and formaldehyde (standing close enough to cause nausea and dizziness, as well as irritation of visitors’ throats and eyes). Nikolaieva found “obvious” signs of instability in one of the dams holding back more than a quarter million tons of chemical sludge during a government-sponsored audit at the facility in 2019.

She came to the conclusion that fighting with Russia-backed rebels could set off a chain reaction disaster, as shelling could breach one of the waste storage ponds, sending thousands of tons of waste rushing downhill and flooding an even larger 8 million ton man-made lake below, which was filled with chemical byproducts. Such a surge could breach levees around the site in less than 10 minutes, dumping millions of tons of toxic sludge into the Zalizna river, knocking out bridges and electrical equipment downstream, and contaminating drinking water for the entire region. “If it’s the only water they have,” Nikolaieva says, “people will die.”