The toxic chemical acrolein was found to be six times higher than usual near the train derailment in East Palestine, Ohio, even after officials told residents they could return.
A study by scientists at Carnegie Mellon and Texas A&M published Wednesday found those shocking results while looking for evidence of another toxic substance — vinyl chloride — with a mass spectrometer.
The researchers warned that long-term exposure to acrolein might be a health concern, with animal studies showing a higher likelihood of lung damage, abnormal lesions, and nasal tumors.
"The acrolein was a little bit surprising," study contributor Albert A. Presto, an associate research professor in mechanical engineering at Carnegie Mellon, told NBC News.
The Environmental Protection Agency previously confirmed that the substance was discovered during its tests following the derailment. However, the agency was unaware of how bad it truly was.
"For some compounds, including acrolein, concentrations that would have been potentially health-harmful were below what EPA could measure," Presto noted. "We were more sensitive."
The news comes as the local, state, and federal effort to clean up East Palestine from a dangerous Norfolk Southern train derailment in February continues.
At the time, local authorities evacuated the area and approved controlled burns — an attempt to prevent a potential explosion — that released hydrogen chloride and phosgene into the air.
NewsNation reported that removing contaminated soil and debris is an ongoing priority, with several plans also approved to ensure surface and groundwater safety.