Science: Effects of Sulfate Pollution

What does the science say about sulfate and wild rice?

The Minnesota Pollution Control Agency (MPCA) adopted the wild rice sulfate standard limiting sulfate in wild rice waters to 10 parts per million (ppm or mg/L) in 1973. The standard was based on scientific field research done by the Minnesota Department of Conservation (the predecessor to the Minnesota Department of Natural Resources) from the 1940’s through the 1970’s.

In 2011, the Minnesota Legislature funded new scientific research with the goal of weakening or repealing the wild rice sulfate standard. However, the new research – in the field, in test tubes, and growing wild rice in tanks and buckets – all confirmed that the 10 mg/L wild rice sulfate standard was needed and reasonable.

What recent scientific research supports the wild rice sulfate standard?

This slide from John Pastor’s technical review shows the impact of sulfate on wild rice. Orange healthy roots (left) are from wild rice grown under low sulfate concentrations at or near the current standard. The black iron sulfide coating on roots (right) are from plants grown in water with high sulfate concentrations and high levels of iron. The iron sulfide coating on wild rice roots interferes with nutrient uptake and wild rice seed development.
John Pastor, PhD, now an emeritus professor at the University of Minnesota Duluth (UMD), studied the ecology of wild rice for more than a decade. His experimental research and that of UMD masters and doctoral degree candidate, Sophia LaFond-Hudson demonstrated that increased sulfate in surface waters impairs and, eventually, kills wild rice.
  • Dr. Pastor found in a series of controlled experiments in outdoor mesocosms (large tanks) that adding sulfate to the water resulted in increased sulfide in the sediments and a decline in wild rice. Dr. Pastor explained:
Wild rice seedling emergence, seedling survival, biomass growth, viable seed production, and seed mass all declined with sulfate additions and hence sulfide concentrations in sediment. These declines grew steeper during the course of the 5 yr [years] of the mesocosm experiment.
  • Dr. La-Fond Hudson tested the hypothesis that high levels of iron would protect wild rice. This hypothesis was proposed by the mining industry and the MPCA as justification for weakening the wild rice standard. But Dr. Hudson found – in a series of experiments that involved growing wild rice in buckets — that high levels of iron did not protect wild rice from harm caused by sulfate. Instead, iron sulfide accumulated on wild rice roots, interfering with nutrient uptake. As a result, wild rice seeds were fewer, lighter, and thus, less likely to generate new plants.
  • Dr. Pastor explained the implications of this research in an expert opinion provided to the Administrative Law Judge in support of preserving Minnesota’s wild rice sulfate standard:

The MPCA assumes that any precipitation of sulfide by iron helps to protect wild rice. Our experimental mesocosm research has substantially undermined this assumption.

We learned that iron sulfide precipitates rapidly on wild rice roots in midsummer at the time when the plants are beginning to flower and take up additional nutrients for the ripening seeds. The iron sulfide precipitates gave the roots a black appearance, compared to amber or rust colored roots on healthy plants exposed to sulfate concentrations near the current fixed standard of 10 mg/L.  Seed nitrogen, seed count and seed weight were all markedly reduced in plants with back root surfaces exposed to high sulfate surface water concentrations (300 mg/L) because these black iron sulfide precipitates inhibit the uptake of nutrients necessary for the filling and ripening of seeds necessary for propagation of wild rice.

[B]ased on my training and experience, it is my opinion that the weight of the scientific evidence supports retaining Minnesota’s existing sulfate standard of 10 mg/L to protect wild rice.

  • University of Minnesota (U of M) mathematics professor emeritus, Joel Roberts, PhD, also analyzed the MPCA’s proposed equation that would replace Minnesota’s 10 mg/L wild rice sulfate standard. He pointed out that the mathematical formula “is inadequate for explaining the data from the Wild Rice Field Study” and “inadequate for protecting Minnesota’s Wild Rice.”
  • Administrative Law Judge LauraSue Schlatter disapproved the MPCA’s proposed rule to repeal Minnesota’s wild rice sulfate standard. She concluded that the equation proposed by the MPCA to allow more sulfate in waters with a high concentration of iron was not protective of wild rice:
[T]he Administrative Law Judge further concludes that the MPCA has not presented facts adequate to support the reasonableness of the proposed repeal of the 10 mg/L sulfate standard without a replacement standard that is equally or more protective of wild rice waters.  Therefore, the proposed rule repealing the 10 mg/L sulfate standard is defective.

Dr. Pastor’s continuing mesocosm research has indicated that, while increased iron may counter the toxicity of sulfide to wild rice seedlings in the springtime, iron sulfide plaques form and precipitate on the plants’ roots during the flowering and seed production phases of the wild rice life cycle.  These plaques result in fewer and smaller seeds, with reduced nitrogen content, leading to extinction of the wild rice plant within 4 or 5 years at about 300 mg/L of sulfate, and greatly reducing wild rice plant population viability at lower concentrations of sulfate.

The MPCA disregarded scientific evidence that its proposed rule repealing Minnesota’s wild rice sulfate standard was defective and would not protect wild rice. In fact, this evidence was provided to MPCA before the rule was proposed. For more information on this scientific evidence:
News articles in 2016 summarized the scientific research MPCA disregarded.

The Duluth News Tribune discussed on July 19, 2016:

Paula Maccabee, attorney for the environmental group WaterLegacy, said the [M]PCA appears to be ignoring new research that shows iron may not play any beneficial role in reducing the impact of sulfate. That research, by Prof. John Pastor at the University of Minnesota Duluth and funded by Sea Grant, concluded there is no buffering impact by iron on the sulfate/sulfide conversion.

“We already know that the existing sulfate limit is effective and reasonable. But [M]PCA, ignoring evidence that the equation they are developing is flawed, continues down this path and away from protecting wild rice,” Maccabee said. “They are developing this very complex and flawed process based on pressure from the mining industry and Iron Range lawmakers when their primary concern should be protecting wild rice.”

What scientific research supported the wild rice sulfate standard in 1973?

The wild rice sulfate standard was adopted by the MPCA and approved the by the EPA in 1973 on the basis of scientific field research conducted by John Moyle on hundreds of water bodies from the 1940’s through the 1970’s. Dr. Moyle wrote in 1944:

No large stands of rice occur in water having sulfate content greater than 10 ppm [parts per million, or mg/L], and rice generally is absent from water with more than 50 ppm.

Dr. Moyle confirmed in a 1975 memo to MPCA, after decades of additional research:

There are no large stands in waters in which the concentration of the sulfate ion exceeds 10 parts per million.

What contributions did citizen scientists make early in the review process?

In 2010, the MPCA floated a trial balloon proposal to weaken the wild rice standard without rulemaking, by administratively allowing five times as much sulfate in wild rice waters (50 parts per million) as the standard permitted (10 parts per million). That fall, northern Minnesota citizen scientists working in partnership with WaterLegacy prepared a report to challenge MPCA’s proposal to informally weaken the wild sulfate standard.

Len Anderson, a biology teacher and experienced hunter, fisher, and ricer, canoed the Partridge River with retired mine engineer and outdoorsman, Bob Tammen, to sample water quality and document conditions of wild rice beds. Upstream, they found plentiful, healthy natural wild rice beds. But downstream, the beds were damaged from decades of mine wastewater discharges. Anderson and Tammen concluded that current field data required preservation of the wild rice sulfate standard.

Len Anderson found impaired wild rice in the Partridge River downstream of historical sulfate pollution from mining.

How does sulfate affect mercury contamination of fish and harm Minnesota lakes?

Blue-green algae in Voyageurs National Park in mid-September. Photo by Mark Edlund, St. Croix Watershed Research Station.
In addition to impairing natural stands of wild rice, recent U. of M. scientific research in mesocosms led by Amy Myrbo, PhD, has confirmed that sulfate pollution increases mercury contamination of fish and algae blooms in lakes.
  • Sulfate more than doubles the release of inorganic mercury from sediments as compared to a low-sulfate control. With sulfate levels of either 100 mg/L or 300 mg/L, methylmercury increased 5.9 times as compared to the low-sulfate control. Methylmercury is the form of mercury that accumulated in the food chain and contaminates fish.
  • In addition, higher sulfate released nutrient chemicals – nitrogen and phosphorus – from sediments to water. Excessive nitrogen and phosphorus contribute to algae blooms in once-clear Minnesota lakes.

The plain English summary of Dr. Myrbo’s article states:

This study demonstrates that adding sulfate to a wetland can not only produce toxic levels of sulfide but also increase the surface water concentrations of nitrogen, phosphorus, mercury, and methylmercury.

Information on the risks of methylmercury to human health, particularly harm to the developing brains of fetuses, infants, and children is summarized in Expert Opinion of Duluth child psychiatrist Dr. Margaret Saracino.