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History of the sulfate standard

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Sulfates are ions containing sulfur that can come from decaying plants and animals as well as from industrial processes such as mine discharges, mine stockpiles and waste piles, tanneries, steel mills, pulp mills, textile plants and wastewater treatment plants.

High sulfate levels are known to coincide with damage in plants. But it’s not completely clear how much sulfate is too much for wild rice or even how the stuff actually causes problems with rice.

Minnesota has seen generally declining wild rice stands, state officials note, but there may be no single culprit. Higher temperatures, more droughts and floods, shoreline development and other water quality issues may be limiting factors for rice.

In the 1940s, a state natural resource scientist named John Moyle found that the best wild rice lakes and rivers generally had water with less than 10 parts per million of sulfate. In areas of high sulfate, wild rice didn’t grow well. There appeared to be a direct correlation between naturally higher sulfates in waters to the south and west in Minnesota and reduced or no wild rice to the south and west.

“No large stands of rice occur in water having sulfate content greater than 10 ppm, and rice generally is absent from water with more than 50 ppm,” Moyle concluded.

But Moyle’s research didn’t actually determine what higher sulfate actually did to damage rice, or at what level serious harm began. Nor did it rule out other factors such as pH, temperature or even rainfall totals that also changed from northeast to southwest in a similar patterns as sulfate across the state.

Still, Moyle’s work was just about all Minnesota had on wild rice water ecology in the early 1970s as the federal Clean Water Act was put into action by state resource agencies. Minnesota officials used Moyle’s research to set a Clean Water Act standard for “wild rice waters” in the state.

For many years, sulfate was a background pollutant that spurred little interest. Now, nearly 40 years after the wild rice standard was first set, it has become a major controversy in the debate over how to balance a rapidly growing northern Minnesota mining industry and efforts to protect the water-rich environment that has defined the region for centuries.

When state regulators began to enforce the 1973 standard in recent years, mining companies cried foul. State lawmakers and the Minnesota Chamber tried in 2010 and 2011 to weaken the sulfate standard to protect mines and potentially other industries. Lawmakers even tried to order the PCA not to enforce the old standard.

Those efforts failed on two levels. A state judge upheld the sulfate standard as state law, and the federal Environmental Protection Agency said lawmakers can’t change the Clean Water Act rice standard unless it can show a scientific reason why.

That’s where the current sulfate study comes in.