"It's pretty shocking," said Lake County resident Penny Bosch.
Thousands of people living and working in the area are being exposed to ethylene oxide (EtO), which is frequently used to sterilize medical instruments and pharmaceutical drugs.
This is the same toxin that is allegedly polluting the air in Willowbrook, emitted by Sterigenics, another medical sterilization company.
WATCH: Andrea Thome believes Sterigenics emissions sickened her family
Illinois Attorney General Lisa Madigan recently filed a lawsuit against that company, asking the court to limit or prohibit the company's EtO emissions in order to protect residents' health.
On Friday, the U.S. Environmental Protection Agency confirmed that Medline Industries, located in Waukegan, is one of the polluters allegedly releasing more than 3,000 pounds of toxic gas in 2014 alone.
"We always are in compliance with all standards of any organization," said Blair Klein, vice president of corporate communications for the company.
Vantage Specialty Chemicals, another medical manufacturing plant, may pose an even greater danger: Based on published reports, their Gurnee plant released twice the amount of EtO as Medline.
A manager at Vantage released a statement saying the company "is committed to ensuring the health and safety of our employees, neighboring communities and the local environment... and take this matter very seriously."
Up to now, authorities had not issued any warnings about the company in part because the state EPA failed to provide the data. There also has been no indication that either Medline or Vantage violated any rules.
"The U.S. EPA is working with the state and these facilities to evaluate their emissions calculations, stack test results, and pollution controls to further assess and address risk," a spokesperson for the U.S. EPA said in an emailed statement.