MPCA to act on wild rice sulfate standard

Public comments accepted by December 18

The Minnesota Pollution Control Agency (MPCA) is considering amendments to the state’s water quality sulfate standard to protect wild rice.

Minnesota has a 42-year-old rule limiting how much sulfate can be discharged into wild rice waters. The current standard of 10 milligrams per liter (mg/L) is not consistently enforced, and there has been significant discussion on whether the standard is scientifically supported. Minnesota is the only state with a wild rice sulfate standard.

Based on recent research, the MPCA has concluded that sulfate is not directly toxic to wild rice but that elevated sulfide can be toxic to wild rice. Under certain conditions, sulfate can be converted to sulfide in the sediment where wild rice grows. To replace the current 10 mg/L sulfate standard, the MPCA proposes a standard that takes into account the sulfide-producing characteristics of a water body and its sediment to calculate a “Protective Sulfate Concentration” to protect wild rice.

A key to the new standard is defining the toxicity of sulfide to wild rice. The MPCA funded research by University of Minnesota-Duluth Biologist Dr. John Pastor to address that issue. A peer review panel convened by the MPCA made seven specific recommendations to improve the accuracy of the results.

Responding to the peer review panel recommendations, a 2015 study was conducted by Fort Environmental Laboratories, a nationally renowned environmental toxicology laboratory. The study followed all seven peer review panel recommendations and is being submitted to a peer reviewed journal for publication.

The study concluded that sulfide is significantly less toxic to wild rice than was indicated by Dr. Pastor’s tests, and not toxic at levels that typically exist in Minnesota wild rice waters. The study also confirmed that the presence of iron in the sediment where wild rice grows significantly reduces the toxicity of sulfide.

This new scientific evidence confirms that Minnesota’s current wild rice sulfate standard of 10 mg/L is wrong. The ramifications of enforcing an incorrect water quality standard are enormous and would negatively impact communities throughout our state.

The MPCA is accepting public comments on the wild rice sulfate standard until December 18. Share your thoughts with the MPCA through our action center.