Fish and plastics is an old tale
A Field Museum study has found that fish have been ingesting microplastics for decades
“The big takeaway would be: We need to be conscious about our everyday choices. People might make the argument of, ‘Well, if I don’t use this plastic straw, what is that going to have to do with, you know, finding plastic in fish?’ Well, if everyone skips on using that plastic straw, it’ll actually make an impact.”
To prove that fish ingestion of microplastics is more than just an ocean story and more than just a modern story, Loren Hou used an unusual technique.
Transporting the digestive tracts of four freshwater fish species she was studying from the Field Museum, where she dissected specimens dating back to the 1900s, up the lakefront to Loyola University Chicago, where she would analyze what was in the fishes’ guts, Hou sometimes took the Red Line.
So if at some point you noticed a young woman whose Trader Joe’s bags seemed to jangle a bit as the train rounded corners — as if full of Mason jars — that might have been Hou, en route to earning a master’s degree in biology and proving something valuable to the increasing concern about what plastic is doing to our environment and the organisms in it.
Dating back to the dawn of the plastics age, freshwater fish from Illinois have been found with rising numbers of plastic particles in their digestive tracts, according to Hou’s first-of-its-kind new study, “A fish tale: A century of museum specimens reveal increasing microplastic concentrations in freshwater fish.”
She found fragments of the petroleum-based substances in fish beginning in the 1950s, and their concentration has increased along with the profound increase in plastics production and use worldwide since then, said the study, published in Ecological Applications, the journal of the Ecological Society of America.
“Plastic pollution in common freshwater fish species is increasing and pervasive across individuals and species, and is likely related to changes in environmental concentrations,” says the abstract of the paper, whose authors after Hou include Field Museum ichthyologist Caleb McMahan and Loyola biology professor Timothy Hoelllein.
That trio gathered this week in the museum’s vast underground specimen storehouse — a kind of biological library through time — to talk about the methodology and the findings and, sure, also to look at some of the specimens McMahan keeps handy to share with visitors.
You want to see an electric eel, no longer amped but ready for scientific inquiry? McMahan can put on an industrial rubber glove, reach into a metallic tank filled with preservative alcohol, and display the roughly 4-foot-long South American specimen, which is actually a fish.
Hou, despite all the time she spent at the Field’s fish laboratory for her research beginning in 2017, hadn’t seen the eel before, and she snapped a picture on her phone.
The concern about environmental microplastics, which include the tiny and enduring fragments that plastic products from baggies to polyester clothing break down into, has been growing over the past decade. A 2019 study showed them to be prevalent in human food sources, and one from this year reported that humans “constantly inhale and ingest” microplastics, while noting the impact on human health is still under research.
Plastic in the oceans — and in marine fish — has been one of the hottest study topics in recent years, helping to raise alarm about humans’ willingness to just keep using and discarding more and more of the product category that has been seen as both miracle substance and, increasingly, scourge.
But this study is the first to look at microplastic consumption in freshwater fishes over time, the authors say.
Over the long term in fish, eating microplastics has been shown to lead to digestive tract breakdown and general stress, said Hou.
“The big takeaway would be: We need to be conscious about our everyday choices. People might make the argument of, ‘Well, if I don’t use this plastic straw, what is that going to have to do with, you know, finding plastic in fish?’ Well, if everyone skips on using that plastic straw, it’ll actually make an impact,” said Hou, who grew up in the Bridgeport-Chinatown area and graduated from the city’s Whitney Young Magnet High School. The study was her Loyola master’s thesis, and she now works a medical research job with Abbott Laboratories in Lake County.
The Field’s vaults, which include some 2 million fish specimens under McMahan’s care, were perfect for the study, which chose four common species, channel catfish, largemouth bass, sand shiners and round gobies, trying to use five specimens per species per decade. Where there weren’t enough samples from a particular decade, the study added fish from the Illinois Natural History Survey and the University of Tennessee, and from researchers’ own fishing, in 2018.
“We have things we collected last year, things going all the way back to the mid-1800s,” said McMahan, standing in an aisle filled with shelves full of labeled glass jars, holding up a jar from almost 50 years ago containing sand shiners.
“So this jar of 16 minnows from Illinois, this is like a time capsule. We can go back to this spot in Illinois and see if we get the same species. But what we cannot do is go back to this spot in 1976. We can look at change over time, not only for the fish but in this context the environment as a whole, based on this little time capsule. So that’s what’s really exciting about this project.”
After dissecting the fish in the Field’s lab, and removing their digestive tracts “from esophagus to anus,” Hou put them back into their ethanol-filled jars, their scars barely visible, where their other tissue and genetic material remain available to science.
Once the fish guts were at Loyola, she painstakingly broke down what they contained, work that Hoellein, her adviser, described as incredibly painstaking and detail oriented. It took microscope work to spot the plastic particles, a great many of which turned out to be clothing fibers.
Perhaps the most telling chart in the study shows the amount of plastic in the freshwater fish almost exactly matching the rising curve of plastic production over time.
While science was the goal, it isn’t the only thing that crosses a researcher’s mind. Asked if she had a favorite of the four species she studied, Hou said, “I would have to say the round gobies. They’re invasive. I know they’re bad. But I like them. They look cute.”
— Loren Hou