Taconite plants, the largest industrial source of mercury pollution in Minnesota, have vented the toxic metal for years into the air without enforced limits. Those days are likely coming to an end.

The U.S. Environmental Protection Agency has proposed to cut more than half the mercury emissions from the taconite industry, most of which is on Minnesota's Iron Range. The EPA's draft rule unveiled Tuesday follows years of delay and litigation, with a final rule due this fall, after a comment period.

The proposed limit affects eight taconite plants — six in Minnesota and two in Michigan — and would cut the allowable mercury from roughly 800 pounds a year to about 340 pounds. In Minnesota, taconite plants emit much more mercury than coal-fired power plants, which have had limits for years.

Mercury in the air enters the water and converts to methylmercury, which poisons ecosystems. It can damage the brains and nervous systems of animals and people who eat fish where it has accumulated. It's especially dangerous for young children, infants and fetuses.

Minnesota has a statewide fish consumption guidance for mercury. A 2012 study by the state Department of Health showed that 1 in 10 infants on Minnesota's North Shore have unhealthy levels of mercury at birth.

The EPA proposed a limit of 0.000014 pounds of mercury per long ton of taconite pellets at existing plants. How restrictive that is depends on where you stand.

To Kevin Dupuis, chairman of the Fond du Lac Band of Lake Superior Chippewa, it's not tough enough. The band and environmental groups sued the EPA in 2020 for not setting a limit for mercury and other pollutants from taconite companies.

"We welcome limits on taconite plants' emissions of mercury, which are badly needed and long overdue," Dupuis said in a statement. "EPA needs to go further, however, and set stronger limits for mercury as well as limits for dioxins and other persistent pollutants that are poisoning our fish and waterways."

James Pew, a lawyer with the environmental law group Earthjustice who represented the band in the litigation, agreed.

"EPA has let it build up and get worse over the last 20 years, so I think they should be doing everything they can to get the mercury emissions down as much as possible," Pew said.

Taconite companies said they're reviewing the draft limit.

Minnesota lawmakers set their own mercury reduction target for the industry a decade ago, but companies have faced no penalty for failing to meet it. The state required taconite companies to cut mercury emissions about 72% from 2008 or 2010 levels by 2025. Companies submitted the required reduction plans to the Minnesota Pollution Control Agency (MPCA) in 2018, but only two had a strategy to meet the requirement.

U.S. Steel, which operates the Keetac and Minntac iron ore operations and is the largest taconite producer, said in its reports that it evaluated six mercury-reduction technologies and concluded none could achieve the 72% cut. A reduction of around 30% was more realistic, the company said. The MPCA has disputed that in the past and said technologies are available.

MPCA spokeswoman Andrea Cournoyer said that everyone has been waiting for the EPA "to fulfill its congressional-mandated responsibility" to set mercury limits for the industry. Companies will have to submit updated reduction plans in the spring of 2024, after the final federal rule is adopted.

Cournoyer said the agency knows it's expensive to reduce mercury from taconite processing. Gov. Tim Walz's budget included $17.6 million in grants for taconite companies to install technology to cut mercury or sulfate, a measure still in play at the Legislature.

"Everyone recognizes that mercury contamination in our lakes, rivers and fish needs to be addressed," Cournoyer said.

Mercury contamination has shown some surprise improvements in Minnesota as the state shifts away from coal-fired electricity. But it remains a major pollutant in Minnesota waters. The vast majority of the toxin drifts into Minnesota from other states and countries — even as far away from China. Gold mining is the single largest source of atmospheric mercury globally, although coal-fired power plants remain major sources too.