A pair of environmental advocacy groups sued the U.S. Environmental Protection Agency to tighten national emissions standards for toxic pollution from steel mills, including some in Indiana that still use an outdated, heavily polluting process.

The Indianapolis-based Hoosier Environmental Council and the Sierra Club filed suit to force the agency to set emissions limits on two pollutants that are hazardous to human health but were omitted from the EPA’s original 2003 rule that regulates emissions from iron and steel manufacturing.

“Steel mills, not surprisingly, emit a huge amount of hazardous air pollutants,” said Hoosier Environmental Council staff attorney Kim Ferraro. “Nationwide, the estimates are 227 tons from their smokestacks and another 295 tons per year for what are called fugitive emissions.”

The EPA’s 2003 National Emissions Standards for Hazardous Air Pollutants: Integrated Iron and Steel Manufacturing rule placed emissions limits on metal hazardous air pollutants, particulate matter and some volatile organic compounds from steel mills.

The rule did not regulate, or mention, the emission of a chemical compound and a gas used in steelmaking processes currently used only in Indiana.

Carbonyl sulfide and hydrogen chloride, also known as hydrochloric acid, are naturally occurring, but have been found to negatively affect human health in large quantities.

Both the chemical compound and gas smell like rotten eggs, but people lose the ability to smell them at high concentrations. The federal government warns that people may falsely believe the two are no longer present, increasing their exposure risk to air levels that may cause serious health effects.

Both can have serious respiratory and neurological effects on people at high concentration levels.

The Hoosier Environmental Council said carbonyl sulfide and hydrogen chloride are used in a stage of the steelmaking process that is unique to the mills in Burns Harbor, East Chicago and Gary.

“The Indiana steel mills include the only three steel mills nationwide that still operate what are called sinter plants that are used to burn off impurities from the blast furnace where the steel is made,” said Ferraro. “And all of the emissions, which include 72 tons per year of the carbonyl sulfide, 12 tons per year of hydrogen chloride, all of that comes from the sinter mills in Indiana.”

Both substances were acknowledged in a review of the 2003 rule released in August but were not submitted for regulation.

Ferraro says this omission has seriously affected the health of Hoosiers and will continue until it’s corrected.

“Indiana, specifically northwest Indiana, in the communities of Gary, East Chicago and Burns Harbor are home to the mills that produce the vast majority of hazardous air pollutants. This should raise a really huge red flag for people that this is an environmental injustice issue,” said Ferraro. “These communities are largely poor, minority and are clearly suffering an undue burden that EPA should take seriously and correct.”

Since 2003, Lake County, Porter County, and several neighboring counties have failed to meet federal hazardous air pollution emissions standards several times.

That means facilities in those counties have emitted pollutants known or suspected to cause cancer and other serious health effects at levels beyond those permitted by federal law.

That could be having a negative effect on the health of the state’s second most populous county.

Lake County has approximately 484,411 residents, or about half of the 954,670 people living in Marion County, the state’s most populous county.

Despite the difference in population, Lake County has similar incidence numbers for some types of cancer.

According to Indiana State Department of Health statistics, between 2011 and 2015 Marion County reported 1,857 cases of prostate cancer while Lake County reported 1,519. In that same time period, Marion County reported 1,761 colon and rectal cancer cases while Lake County reported 1,401 cases.

The Hoosier Environmental Council and Sierra Club lawsuit was filed in the U.S. Court of Appeals for the District of Columbia Circuit. The court has ordered the EPA to begin responding to the suit by mid-November.