ST. PAUL, Minn. (AP) — The Minnesota Pollution Control Agency unveiled a new site-specific approach Tuesday for protecting waters where wild rice grows against sulfate pollution that’s meant to replace a 1973 state law that largely went unenforced until recently.

The dispute over whether the old standard is obsolete set up a politically charged clash between the state’s iron mining industry and Iron Range legislators on one side versus American Indians who consider wild rice a sacred food source and environmentalists who support them.

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Minnesota’s current law sets the sulfate limit at a flat 10 milligrams per liter for all lakes and streams that support wild rice stands. The MPCA’s new plan, rather than relying on a single limit, proposes a complicated mathematical formula for calculating allowable sulfate levels for individual wild rice waters, based on how much iron and organic carbon are in the sediments where the plants are rooted.

The MPCA plans to begin a formal rulemaking process late this summer or early fall to change the standard, a process that could take two years from then. The agency also compiled a draft list of about 1,300 waters that would be subject to the standard, and said others could be added later.

“It’s really the beginning of our conversation about wild rice and looking at the standards we want to protect it,” MPCA Assistant Commissioner Rebecca Flood said at a briefing for reporters.

In response to pressures from the mining industry, as well as communities that operate wastewater treatment plants that would have trouble meeting the 10 milligram standard, the MPCA commissioned extensive studies to help it decide whether to revise the current standard. The MPCA also set up an outside peer review process.

Early reviews on the proposal from some key Iron Range leaders were positive. But a prominent wild rice researcher, John Pastor, a University of Minnesota Duluth biologist whose work was used to help develop the new approach, said he was “truly shocked” and called the MPCA’s equation “scientifically indefensible.”

The research found that sulfates in the water don’t harm wild rice directly, but that they become toxic when they’re converted by bacteria in the sediment to sulfides. The research found that higher iron levels in sediments bind to sulfides and neutralize them, but organic carbon in the muck feeds the bacteria and promotes sulfide production.

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The MPCA’s formula is aimed at limiting sulfide concentrations in sediment to 0.165 milligrams per liter. Katrina Kessler, manager of the MPCA’s water assessment section, said safe sulfate discharge levels could range from 0.8 to 140 milligrams per liter depending on the location.

But Pastor said the equation the MPCA developed is just a hypothesis for how sulfates, sulfides, iron and carbon interact. He said it needs to be validated against actual data that the agency didn’t collect. He also said the formula also doesn’t account for how conditions can change from one year to the next, or the possibility that iron itself can be toxic to wild rice in some circumstances.

“The onus is on them to demonstrate that it could work. They have not done that here,” said Pastor, who thinks the current standard is in the right ballpark.

But Senate Majority Leader Tom Bakk, an Iron Range lawmaker, said he’s pleased that regulators backed away from the flat standard.

“In another year or so we’ll have the remainder of the science done and we’ll know more about the whole issue of sulfates versus sulfides versus water chemistry,” Bakk said.

State Rep. Jason Metsa, another Democrat who also represents a northeastern Minnesota district, said the new path will “let the science drive the conversation.”

The federal Environmental Protection Agency must sign off on any changes.

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