New toxin found in St. Croix River fish

High levels of “forever chemicals” in fillets point to decades of industrial pollution.




4 minute read

Black crappie. Pomoxis nigromaculatus. (Great Lakes Environmental Research Laboratory)

Fish in the lower St. Croix River can contain dangerous levels of industrial chemicals, a Minnesota state agency has found. Toxins related to products like Scotchgard and Teflon have previously been known to pollute groundwater in areas between Lake Elmo and the St. Croix, as well as across the country. Now it has been found in fish in the river at levels considered possibly harmful to human health. The affected zone is the entire 50 miles of river below Taylors Falls to the Mississippi.

The findings were part of an announcement this week by the Minnesota Pollution Control Agency, which is updating its list of impaired lakes and rivers, as required by the federal Clean Water Act. The St. Croix is among 15 lakes and rivers the agency proposes adding to the list because of PFAS, or “forever chemicals.” As a significant listing for the contaminant, the 15 would join 11 lakes previously listed, with more expected to come as additional information becomes available.

Scientists have been taking samples of fish from waters across Minnesota over the past decade and testing them for PFAS. There is not yet a statewide standard for the chemical in surface water or fish, but there are guidelines for a few lakes and rivers, primarily in Washington County.

The fish sampled from the St. Croix seem to exceed those standards by orders of magnitude.

The safe level for PFOS in fish tissue in Lake Elmo and a few other waterbodies is 0.37 nanograms per gram. Fish sampled in 2017 and 2019 from the St. Croix River had levels at 4.1 ng/g on average, with a 295 ng/g maximum. The chemicals were found in fish of several popular game species.

The MPCA’s standard for PFOS in water on selected waters is 0.05 ng/liter. This concentration of chemicals is believed to prevent fish from reaching unacceptable levels of contamination. At least one sample of the St. Croix found levels at 37.7 ng/L.

For some people, scientists say the health benefits of eating fish probably outweigh the risks posed by PFAS. But children under 15 and women who may become pregnant, or are pregnant and nursing, are a higher risk. The chemicals primarily threaten development of fetuses and children, weakening immune systems, interfering with hormone levels, and similar effects. There has not yet been solid evidence of PFAS causing cancer.

Scientists also say they simply don’t know nearly enough about the chemicals and the health risks. Studies are underway, but researchers say they need to do much more to understand the many variations on the chemical compounds and how they behave in water and organisms.

PFAS are a broad category of chemicals that were adapted for use in many products. The specific compound found in high levels in St. Croix River fish were PFOS — Perfluorooctane Sulfonate. PFOS was used in several ways, one notable product being firefighting foam used by the military and other industries. It is known to accumulate easily in fish flesh.

There are many possible sources of the chemicals in the river. A major one is hazardous waste dumps operated by 3M for many years. While the company’s headquarters in Maplewood are outside the St. Croix watershed, they transported waste to various sites that drain toward the river, particularly in Oakdale.

From those sites, a series of lakes and streams carry water southeast until meeting I-94. Flood mitigation projects in the 1980s then rerouted the flow along the freeway corridor to the St. Croix River. Contaminated groundwater from the dumps can also move through the aquifer toward the river.

The chemical has not been used in manufacturing in the United States since 2001, but PFAS are called “forever chemicals” because their atomic bonds are very strong, and they can last a long time in the natural environment.

3M’s dumps and landfills are probably not the only source, either. Scientists say the chemical may also be carried on the wind, and other sources and transportation are still being studied.

There is much more to this story than what’s in the above article. Stay tuned as St. Croix 360 begins publishing frequent articles to answer these questions and more:

  • What are the levels of PFAS in St. Croix River fish?
  • How dangerous are those levels?
  • What are the health risks of eating fish contaminated with PFAS?
  • Where did PFAS in the St. Croix River come from?
  • How can we stop more of these chemicals from contaminating our water?
  • Could recent funding for PFAS in the federal infrastructure bill help clean up the St. Croix?
  • Are certain species safer to eat than others?
  • How can we test and monitor waters to determine safe consumption?
  • Now that more waterbodies have been found to be polluted, are there new legal liabilities for companies that caused PFAS contamination?
  • What other ways are PFAS affecting people and wildlife along the St. Croix?

PFAS chemicals are complex, and there is still a lot to learn. St. Croix 360 is dedicated to following this topic and answering important questions. We need your support to do it. Please contribute today, thank you!


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3 responses to “New toxin found in St. Croix River fish”

  1. Steve Johnson Avatar
    Steve Johnson

    These numbers are startlingly high. Very concerning.

  2. John W Goodfellow Avatar
    John W Goodfellow

    Thanks Greg for being “on it”, and for your intention to cover this issue in more detail. This is an example of why SC360 is so important to our watershed.

  3. Michael J Gallagher Avatar
    Michael J Gallagher

    In the late 1970’s I worked for 3M in their Environmental Engineering and Pollution Control department. There was a big project revolving around the Oakdale dump site where lots of waste was disposed of on the ground. (landfilled). Although this type of waste disposal was legal at the time, there was concern that the groundwater under the area was being contaminated. A huge system of barrier wells were installed to try to prevent the contamination from moving with the groundwater. The water was pumped up, treated, and discharged, to parts unknown, at least to me. People at the time really should have known better, and maybe they did, but nonetheless it was legal at the time.