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Great Lakes cooperation helps solve PFAS in smelt mystery

In 2021, Wisconsin fish researchers identified a big mystery in a tiny fish.  Sampling data from rainbow smelt caught in Lake Superior showed unusually high levels of perfluorooctane sulfonate (PFOS), a harmful chemical that is part of a group of compounds known as per- and polyfluorinated substances (PFAS). As a result, both Wisconsin and Michigan notified the public about this discovery and issued a Consumption Advisory which included the risks of eating those fish too often. 

EGLE staffer processes smelt.

An EGLE staffer processes smelt.


These high levels of PFOS in these little smelt raised questions for state scientists – “Where did this PFOS come from?” and “Why was it so high in smelt?”  There were many possible reasons to be investigated. It was possible that the amount of PFOS in Lake Superior varied around the lake; it was possible that smelt had a feeding behavior that exposed them to greater amount of PFOS than other fish; or it was possible that smelt retained PFOS more than other Lake Superior fish.  It has long been known that PFOS bioaccumulates differently in fish than other persistent chemicals (such as mercury), and that fish lower in the food chain can have some of the highest PFOS concentrations.

These questions led the Michigan PFAS Action Response Team, MPART, scientists on a three-year journey that involved collaboration with Tribal governments, Great Lake States, and the U.S. Environmental Protection Agency (EPA).   Based on Wisconsin’s initial results, MPART conducted sampling to also evaluate smelt within Lake Superior. The Michigan smelt results mirrored those found in Wisconsin, however, other researchers had results that showed much lower levels of PFOS in Lake Superior smelt.

Scientists shared data and observed that a specific sub-type of PFOS called “branched-PFOS” was high in Michigan data but not in the other researchers’ data sets.

In 2023, scientists from EPA sought to determine why smelt from Lake Superior had drastically lower PFOS concentrations along the northern shorelines compared to those collected from the southern shorelines. 

Reviewing all the Lake Superior smelt data available, they surmised that a naturally occurring bile acid in smelt, known as taurodeoxycholic acid (TDCA), could be interfering with the laboratory method. This interference could cause branched-PFOS to be reported in much higher amounts than is actually present in the smelt.

According to EPA, TDCA/bile acids have nearly the same molecular mass as branched-PFOS in addition to containing a sulfonate group, another marker for PFOS. Because of those characteristics, the lab equipment couldn’t previously separate the bile acids from the branched-PFOS.

Michigan has reanalyzed some smelt samples with a new lab method and found low-levels of branched-PFOS and confirmed that bile acids were interfering with the branched-PFOS levels. The reanalyzed smelt samples had PFOS concentrations in line with those being reported by the other researchers.

“Providing answers to these complex PFAS questions can only be solved in cooperation with our many partners” Abby Hendershott, MPART executive director, said. “The collaboration and data sharing between Great Lakes partners have led to this major finding.” 

Michigan will be using the reanalyzed data to update the 2024 Eat Safe Fish Guidelines in accordance with their fish consumption programs.

“For the past 50 years, the Eat Safe Fish Guidelines have been designed to be protective of everyone, including the most sensitive populations,” said Dr. Natasha Bagdasarian, chief medical executive. “Michigan continues to be a national leader in PFAS research and understanding and will continue directing resources to protect Michiganders from PFAS and other contaminants.”

MPART will continue to collaborate with federal and state agencies, Tribal governments and academia to use the best methods to understand this group of chemicals as the science evolves.