A nearly 10-year political and legal battle over Minnesota's official state grain apparently ended Thursday when state environmental leaders announced they had reached an impasse on efforts to devise a plan to protect wild rice from pollution that comes from taconite mines and wastewater treatment plants.

"We've heard many, many voices … and the message is clear," said John Linc Stine, commissioner of the Minnesota Pollution Control Agency (MPCA). He said that the scientific research that the state has conducted in recent years is accurate and well founded, but when it comes to applying it through regulation, "we still have more work to do."

The MPCA plans to withdraw its proposed wild rice regulation from the rule-making process and will turn to the Legislature for guidance on how to move forward.

"We look forward to working with the PCA and other stakeholders to find a way to come to a conclusion that will finally provide some certainty and allow economic development projects to proceed," said Tony Kwilas, director of environmental policy for the Minnesota Chamber of Commerce, which has vehemently opposed the proposed rule and questioned the science behind it.

The MPCA's plan to protect wild rice has been in the works since 2010 and has sparked fierce political fights and multiple lawsuits along the way.

The plan was intended to regulate sulfate, a mineral salt that damages wild rice, which is produced by taconite mines, wastewater treatment plants and other industries. While the state's rule is specific to wild rice, sulfate also plays a part in converting mercury into a form that is taken up by game fish, creating significant health risks for pregnant women and children.

The issue is important "not just for people who care about wild rice, but for those who care about … the developing brains of fetuses and children," said Paula Maccabee, director of the nonprofit Water Legacy.

It is also critical to the PolyMet Mining Corp.'s controversial project near Hoyt Lakes, which would become Minnesota's first copper-nickel mine. The mining permit, still awaiting final state approval, would require the company to treat water from the open pit mine and tailings basin indefinitely, in large part to remove sulfate. Water treatment would be required for decades after the mine closes, driving the company's financial protection cost, as required by the state's permit, up to nearly $1 billion. Without a sulfate standard, the cost would be significantly less.

The state's final proposal to protect wild rice was opposed by Minnesota's Indian tribes, environmental groups, industry and wastewater treatment operators. But they opposed it for different reasons.

The highly complicated plan would have used a chemical formula to set individual sulfate limits on discharges upstream of many of the 1,300 individual lakes or rivers where wild rice grows. Industry representatives said the state's new rule would be prohibitively expensive and unworkable.

Environmentalists and the tribes said the state's existing sulfate standard of 10 parts per million, which has been in place since the 1970s, is enough to protect wild rice if the standard is enforced. With few exceptions, however, the state has not enforced it.

In January, LauraSue Schlatter, the administrative law judge charged with deciding whether the proposed rule is reasonable, agreed with both arguments. She reimposed the MPCA's original standard of 10 parts per million, saying that the state's decision to repeal it was a violation of the federal Clean Water Act. She also concluded that while the formula approach had scientific validity, the state could not effectively implement it without first conducting years of study on the 1,300 wild rice waters. It was unconstitutionally "void for vagueness," she said.

Her opinion was upheld by the chief administrative law judge, who suggested that the MPCA had the option of persuading the Legislature to approve the plan — which is highly unlikely. Republican lawmakers in both houses have proposed bills that dismiss the scientific validity of the MPCA's proposal and would require the MPCA to start over on the sulfate rule.

The proposals also would prohibit the agency from enforcing the current standard of 10 parts per million, which brings the debate back to where it was nearly 10 years ago.

"That important legislation will move Minnesota away from the narrow focus of enforcing an obsolete rule," said the Iron Mining Association in a prepared statement.

But Maccabee said that if passed, the Republican legislative proposals would violate federal clean waters standards and would likely be challenged by the Environmental Protection Agency — as was an attempt at similar legislation a few years ago — or challenged in court.

An MPCA spokesperson said environmental officials are still discussing how the current standard will be enforced.