Minnesota health officials are adjusting acceptable levels for two troublesome pollutants found in drinking water supplies in the east Twin Cities metro area, based on new scientific data.
The chemicals are part of a family of compounds known as per- and polyfluoroalkyl substances, or PFAS, found in products ranging from nonstick cookware to firefighting foam.
On Wednesday, the Minnesota Department of Health lowered slightly the health-based advisory values for perfluorooctane sulfonate, or PFOS, to 15 parts per trillion, down from the previous level of 27 parts per trillion set two years ago. The levels are used to determine whether water from public systems and private wells is safe to drink.
State health officials use scientific research to set what are known as health-based advisory values for a variety of chemicals at levels that are likely to pose little or no risk to human health. The state Pollution Control Agency uses the values to determine whether cities and other public water suppliers must treat their drinking water to reduce contaminants.
The impact of the change announced Wednesday is minor, but will allow health officials to more accurately evaluate the potential health risks of exposure to the chemicals, said Jim Kelly, manager of environmental surveillance and assessment at the state health department.
"It's a tweak, it's a slight adjustment, in our minds," Kelly said. "That's really a very small difference when you're talking about low, low parts per trillion."
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The health department for the first time also set a value for perfluorohexane sulfonic acid, or PFHxS, at 47 parts per trillion. Until now, there hasn't been enough scientific data available to set a value for PFHxS, Kelly said, so the health department was using the PFOS value of 27 parts per trillion as a substitute.
PFAS compounds were manufactured beginning in the 1950s for a variety of industrial and consumer products, including nonstick cookware, stain and water repellents for clothing and furniture, food wrappers and firefighting foam.
About 20 years ago, studies found that PFAS were showing up around the globe: in water, soil, wildlife and even in humans. Scientists are still studying the health effects of the chemicals, but research has linked prolonged exposure to PFAS to health problems including some cancers, thyroid disease and infertility.
States are struggling with how to regulate PFAS chemicals, which are showing up in drinking water supplies across the nation.
The U.S. Environmental Protection Agency has established a non-binding advisory level of 70 parts per trillion for two of the chemicals, PFOA and PFOS. Other states, including Minnesota, have set more stringent levels.
The latest change is a less drastic action than in 2017, when Minnesota health officials cut the health-based values for PFOA and PFOS in half. The cities of Cottage Grove, Oakdale, Woodbury, St. Paul Park and Bemidji had to take action quickly to ensure their drinking water supplies met the new standards.
The new values won't affect any public drinking water systems, Kelly said. But the health department will issue advisories notifying the owners of six private wells in the east metro area that their wells are above the recommended level. Those well owners will be provided with an alternate water supply, Kelly said.
Since 2002, state officials have issued nearly 1,100 private well advisories due to PFAS levels.
Minnesota's 3M Company manufactured PFAS at its plant in Cottage Grove, Minn., for decades beginning in the 1950s.
The company legally disposed of its waste containing PFAS in landfills in the eastern suburbs of the Twin Cities metro area. The chemicals leached into the groundwater in nearby cities like Woodbury, Oakdale, Cottage Grove and Lake Elmo.
In 2010, Minnesota sued 3M for natural resource damages. The high-profile case settled last year when 3M agreed to pay $850 million to provide safe drinking water and clean up contamination in the east metro.
Kelly said he thinks the new values will be helpful as state and local officials try to figure out how to use the 3M settlement money to come up with long-term drinking water solutions for the east metro.
"That depends on a really accurate picture of where the groundwater is impacted to the point where it can't be used in an untreated manner for drinking," he said.
On the federal level, the EPA in February released an action plan aimed at moving toward setting safety limits nationwide for PFAS. Environmentalists and some members of Congress said the strategy wasn't aggressive enough.