A metal recycling company with a history of air pollution violations is suing one of its competitors and state environmental regulators, saying Minnesota needs to subject all operations to the same rules.

Northern Metal Recycling relocated from Minneapolis to Becker, Minn., under pressure from neighbors and increasing scrutiny from the Minnesota Pollution Control Agency. The company installed several pollution controls on its new shredding facility.

The suit, filed earlier this month in Ramsey County District Court, argues that the MPCA needs to hold Crow Wing Recycling to the same standard. Crow Wing recently opened a new operation in Ironton, roughly 12 miles northwest of Mille Lacs Lake.

The suit names as defendants Crow Wing and a subsidiary as well as the MPCA and its commissioner, Katrina Kessler. It does not ask for monetary damages but seeks multiple injunctions and declarations, which would impose a more stringent air permit on the Ironton site. The suit also asks that the court order the shredding site to stop operations until an enclosure is built and several environmental tests are completed.

Northern Metal is by far the state's biggest shredding operation, but no other metal recycler in Minnesota has the same air permit. It requires the removal of polluting components before cars and other items are shredded, as well as several devices to capture contaminants that could still escape. MPCA revealed earlier this year that it was reviewing air emissions at all the state's shredders.

Northern Metal Chief Operating Officer Scott Helberg said in an interview that his firm was told by MPCA when it relocated and installed various air filters and controls that "this is what every shredder was going to have to do in the future in Minnesota." But he said that hadn't turned out to be the case.

"We tried everything to try and get this resolved without getting to this point," he added.

MPCA declined to comment on the suit. A spokeswoman for Crow Wing wrote in an email that the company is properly permitted and in compliance with environmental rules.

No other shredder in the state has the history of Northern Metal. Neighbors in north Minneapolis complained for years about its pollution. A whistleblower claimed the company had falsified its emissions records. Fires have broken out at company facilities in Minneapolis and Becker.

Helberg said he has repeatedly flown planes over the sites of competitors to capture pictures of their operations, showing that several of them, including Ironton, have no enclosure around their shredder and that the operations are effectively open to the air.

This means it's easy for airborne contaminants to escape, but it also makes it nearly impossible to test what's actually being released because there's no stack to put a sensor on, state officials have said.

Generally, air regulators rely on equations that estimate how much soot, gaseous pollutants and heavy metals might come out of a shredder. These equations are based on the rare cases where a shredder has been tested and include assumptions about what kinds of materials — cars, appliances, or leftover metal from manufacturing — are sent into a hammermill to be pounded apart.

Metal shredders can release lung-damaging fine particulate matter, or soot. The heating of old motor oil and other fluids as shredders tear apart cars creates a group of gaseous pollutants known as volatile organic compounds, or VOCs. Mercury switches in old cars can also lead to emissions of that heavy metal.

The U.S. Environmental Protection Agency has acknowledged that some excessive emissions may be escaping, sending out an enforcement alert to the metals recycling industry in 2021 that focused on VOCs.

Andrea Cournoyer, a spokeswoman for MPCA, wrote in an email that the agency "is currently working with the U.S. EPA to apply its most recent data for metal shredders to our permitting process to ensure that every shredding facility operates under permits appropriate for its size and potential to pollute the air."

Northern Metals' lawsuit alternately hails the role of metal shredding in saving resources and managing the combustion-engine cars that will be phased out as the United States moves to electric vehicles, and argues that the recycling industry can pollute air and water when not regulated.

In particular, it says the amount of mercury coming from the Ironton site far exceeds MPCA's limit of 3 pounds per year. Nearby Mille Lacs Lake is considered an impaired waterbody by MPCA because of high mercury levels in the fish there. Mercury is also released by fossil-fuel burning power plants.