The Environmental Protection Agency should expand air monitoring activities to more Illinois industrial sites emitting ethylene oxide after agency data appeared to show links between the probable carcinogen and a facility emitting the gas, the two senators from the state said.

Ethylene oxide is a flammable, colorless gas used to sterilize medical equipment and make products such as antifreeze. According to the EPA, breathing air containing elevated levels of the chemical over many years increases the risk of some types of cancers, including non-Hodgkin lymphoma and breast cancer.

EPA data released March 21 showed ethylene oxide emissions...