A research team from the University of Wisconsin-Madison found levels of radium in groundwater from public water supply wells in much of Wisconsin have risen over the past 18 years.
According to the National Academy of Sciences, radium is of concern because long-term exposure to elevated levels of this contaminant in drinking water may result in an increased risk of bone cancer.
Radium occurs naturally in some Wisconsin groundwater. As the water moves through the underground aquifer system, minerals and other elements — including radium — dissolve out of the rock and into the groundwater. Some rocks transfer radium more effectively than others into groundwater.
In Wisconsin, the highest radium levels occur in water from two types of rock aquifers: the deep sandstone in Wisconsin’s eastern quarter and the crystalline granite found in the north-central part of the state. Water softeners can lower radium levels in drinking water, as can diluting it with water containing lower radium concentrations.
Information was gathered from a long-term, publicly available dataset gathered by the Wisconsin Department of Natural Resources. Numbers from the year 2000 through 2018 were examined for trends in radium levels, focusing on the most-problematic deep sandstone aquifer.
Previous studies have shown that elevated radium occurs in groundwater that is old, has elevated dissolved solids, or is anoxic. Coauthor Madeleine Mathews said all those conditions are found below the regional confining unit in eastern Wisconsin.
“We found that, overall, the radium levels are increasing more in the confined region in the eastern part of the state,” added coauthor Amy Plechacek. “However, we still see increases in radium from 2000 to 2018 in the rest of the state, regardless of if there is a confining unit or not.”
The average radium level in the confined region increased from 5.5 to 7.9 picocuries per liter (pCi/L) over this time period, and the level in the unconfined region increased from 4.8 to 6.6 pCi/L. The maximum contaminant level set by the U.S. Environmental Protection Agency for drinking water is 5 pCi/L.
Mathews said they aren’t sure why the increase is happening. “We have all this data, but it doesn’t give much of an explanation,” she said. “It’s just kind of the tip of the iceberg, so we’d like to use this dataset to explore that in another study.”