Researchers trying to pinpoint the effects of sulfate on wild rice will update the public on their progress Thursday.
Sulfate is found in the wastewater of mining operations and sewage treatment plants. The Minnesota Pollution Control Agency is considering changing the state's current limit following industry complaints that it is not based on sound science.
The current state standard is based on research conducted by DNR researcher John Moyle in the 1940s. Moyle concluded that wild rice does not thrive at sulfate levels above ten parts-per-million in the water — which is now the standard.
University of Minnesota researcher Amy Myrbo has data so far on 160 lakes and rivers.
"We're sort of confirming Moyle's original empirical evidence that there is a correlation between sulfate and wild rice, there may be many reasons for that, but we're having trouble finding sites that are high wild rice and high sulfate," Myrbo said.
University of Minnesota Duluth biology professor John Pastor helps lead the research and said the data so far indicate that the state's current limit is in the right range.
"All three are pointing to somewhere in the range of 10-100 parts-per-million of sulfate, you start to see effects," Pastor said.
Pastor's lab experiments also yielded surprising data indicating that sulfate itself may harm growth, even without being converted to sulfide by bacteria in sediments.
He's still perfecting experimental methods, and results aren't expected until the end of the year.