WILLOWBROOK — The U.S. Environmental Protection Agency says it may have overstated the emissions of a cancer-causing gas from a suburban Chicago plant that sterilizes medical instruments.

The agency released a statement Wednesday saying it recently discovered a problem with the way the gas, ethylene oxide, has been measured outside the Sterigenics plant in Willowbrook. It says another chemical, trans-2-butene, can be incorrectly identified as ethylene oxide when air quality samples are analyzed in a laboratory. Trans-2-butene can be released from petrochemical industrial processes and the burning of fossil fuels.

The EPA says it will host a community forum on the matter Nov. 29.

An email seeking comment was sent to Sterigenics.

Democratic Attorney General Lisa Madigan and Republican DuPage County State’s Attorney Robert Berlin recently sued Sterigenics over the emissions.

RELATED: EDITORIAL: Shut medical equipment sterilization plant until air around it safe