A major study spanning more than four decades has traced how toxic ‘forever chemicals’ have moved through the Great Lakes, revealing a complex picture of contamination that varies dramatically between each lake and the wildlife that live there.
Researchers at the University of Notre Dame analysed 42 years of biological records, synthesising 50 studies containing 2,500 measurements of PFAs (per- and polyfluoroalkyl substances), in the region’s wildlife. Their findings provide the most comprehensive picture to date of how these persistent compounds have accumulated across the world’s largest group of freshwater lakes.
The carbon-fluorine bonds in PFAs are among the strongest in chemistry, meaning they resist heat, water and natural degradation. Instead of breaking down, they build up in soil and water, passing from algae to aquatic insects to fish, and becoming more concentrated at each step of the food chain, in a process called biomagnification.
The research, led by former undergraduate student Peter Martin, now a doctoral student at Michigan State University, focused on wildlife rather than water or sediment.
He explained: ‘We focused on the biota, not the water or the sediment, to determine what chemicals get into the organisms from algae and microbes all the way up to the top predators, like salmon and bald eagles.’
The results showed significant variation across the Great Lakes. Lake Superior had the lowest contamination levels, while Lake Ontario recorded the highest – a pattern reflecting population density and manufacturing activity, with the larger, deeper lakes Superior and Michigan showing lower concentrations.
One of the most striking findings was the inconsistency between lakes. Each of the five Great Lakes followed its own distinct contamination pattern over time, rather than a single regional trend.
Martin said: ‘There was so much variation within certain periods of time, and then across the entire 42-year timescale. And the thing that was really jarring was that there wasn’t one specific temporal trend for all five of the Great Lakes. Each lake had its own specific temporal pattern’.
The study did reveal a positive development: levels of perfluorooctanesulfonic acid, or PFOS, which was phased out of production between 2000 and 2002, declined across the Great Lakes over the study period. However, the speed of that decline varies enormously between lakes, a single drop of water spends less than three years in Lake Erie but up to 200 years in Lake Superior.
Gary Lamberti, one of the principal investigators, explains: ‘The good news is that if companies phase out a compound – even if it remains pervasive in the environment – it will eventually be flushed out of the lakes.
‘Unfortunately, the Great Lakes hold onto their water and contaminants for a very long time, meaning that there’s ample time for toxins to be taken up by the biota.’
While the decline of PFOS can be seen as a victory, Lamberti warns that new compounds continue to be developed and go untested for toxicity.
‘We hope that this paper opens the eyes of scientists, industry and the general public, as well as the government, about this persistent problem. Even if you remove a compound from production, like PFOS, it’s still there, and will be around for decades.’
The full research can be read here.
Photo: WOKANDAPIX