This is Your Soil on Acid

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Could increased nitrates in soil be leading to an increase in uranium in groundwater? A pair of UW Stevens-Point researchers are digging into the question.

While Nitka and McGinley don’t expect their research to reveal a one-to-one relationship between increases in nitrate and increases in uranium, both contaminants bear close watching.
Credit: Amy Nitka

March 29, 2017

By Aaron R. Conklin

Call it nature’s sense of irony, Wisconsin edition: The natural process that gives the Badger State’s groundwater its clear taste and beneficial health effects is the same thing that could be putting it at potential risk for contamination.

We’re talking about the way in which natural acidity from carbon dioxide present naturally in soil can be amplified by acidity from external sources like agricultural fertilizer to increase rock dissolution. In areas of the state where the groundwater aquifer includes glacial deposits of carbonate rock and granite —think central and northeastern Wisconsin–that increased dissolution can result in the release of calcium and magnesium, a pair of elements with human health benefits.  But could that same dissolution also be leading to increased dissolution of uranium, a known kidney toxin, into the groundwater supply?

Amy Nitka, a research specialist with the University of Wisconsin-Stevens Point Center for Watershed Science and Education, and Paul McGinley, a UW-Stevens Point professor of water resources, have teamed up to measure the relationship between levels of nitrate and uranium using samples taken from  several groups of monitoring wells  in Portage, Waupaca and Shawano counties. Their work is supported by the Wisconsin Water Resources Institute.

“We have historical data for uranium in Wisconsin,“ explained Nitka, whose research background is in environmental chemistry. “It does have health concerns associated with it, but it’s not something a homeowner would typically test for. Are there areas that are likely to be more susceptible to uranium contamination?”

UW- Stevens Point water resources students Andrew Wick and Nick Salewski have collected water and soil samples, and the research team is in the process of evaluating them in the lab.

UW-Stevens Point water resources students Andrew Wick and Nick Salewski collect water and soil samples in the field.
Credit: Amy Nitka

Nitka and McGinley agree that it’s unlikely their research will determine a direct one-to-one relationship between an increase in nitrate and an increase in uranium.  So far, the levels of uranium concentration the team has measured haven’t exceeded the state’s 30 micrograms/liter standard.  That doesn’t mean they’re not worth tracking.

“The development of a groundwater’s chemistry depends on a combination of factors, so we do not expect a very simple correlation,” said McGinley.  “But nitrate is a contaminant that already has implications for human health and groundwater quality. If we do have increased rock-dissolution  occurring, would the concentrations of these other substances be something we’d have to worry about? You might also have to us a different type of treatment if you had to remove two contaminants instead of just one.”

In fact, the eventual results of Nitka and McGinley’s project, expected sometime later this year, could open the door for similar studies focused on other groundwater contaminants also released through rock dissolution. That list could include everything from molybdenum and strontium to cobalt and chromium.

‘If nitrate is impacting these other elements of concern, that’s another reason we’d want to keep an eye on it,” said Nitka.