The air in East Palestine, Ohio, had high levels of a chemical irritant in the weeks following the February derailment of a train carrying hazardous chemicals, according to a study published Wednesday in the journal Environmental Science & Technology Letters.

Researchers from Carnegie Mellon and Texas A&M universities drove through the town in a research van following the derailment, monitoring the air for unusual concentrations of compounds that were not present before the incident.

Attention on potential hazards from the crash largely focused on vinyl chloride, a hazardous substance used in the production of plastics, which spilled in the derailment. But the team only detected vinyl chloride levels below what the Environmental Protection Agency (EPA) considers an unsafe long-term level.

However, the researchers found atmospheric concentrations of acrolein were up to six times the normal level near the crash site on Feb. 20 and 21, nearly two weeks after officials cleared evacuees to safely return home. Acrolein, which was not among the chemicals spilled in the derailment, is an irritant to the eyes, skin and nose that has been linked to increased cancer risk.

Researchers said that while the EPA has also been measuring acrolein levels in the atmosphere, the agency did not pick up the lower levels of the compound linked to long-term risk.

The study’s authors wrote that the results indicate the need for ongoing mobile air quality monitoring at the site of disasters like the East Palestine crash, particularly during the ongoing cleanup process, which may unearth contaminants in the soil.

“More broadly, this study illustrates that the ability of highly sensitive, nontargeted mobile monitoring to detect known and unknown [volatile organic compounds] can serve as a complement to the targeted and stationary monitoring typically deployed, facilitating characterization of the impacts of disasters on air quality and ultimately better protecting public health,” they wrote.

In a statement to The Hill, an EPA spokesperson said that the agency “cannot speak to the data interpretation reported by Carnegie Mellon but welcomes their scientific review and interpretation.”

“EPA has been posting air monitoring summaries and data validation reports for air, soil, and water sampling since February and researchers are free to use the EPA data that has been made publicly available,” the agency added.

– Updated 4:27 p.m.