Biologists have dissected the digestive tracts of several fish in the collections of the Field Museum in Chicago to analyze the impact of plastic on these species over the past century. Unsurprisingly, these animals have been ingesting plastic for decades.
Recent research has highlighted disturbing effects of microplastics on marine organisms. We know they can cause aneurysms and changes in reproduction in fish, affect cognitive performance hermit crabs, or weaken mussels, to cite just these examples. But in concrete terms, since when has plastic really been a problem for fish?
“In the last ten or fifteen years, the public has sort of realized that there is a problem with plastic in the water.“Says Tim Hoellein, associate professor of biology at Loyola University in Chicago. “In fact, we believe that these organisms have probably been exposed to plastic waste since the beginning of the democratization of these materials.“. But was it really the case? And if so, to what extent?
A study on freshwater fish
To find out, Dr. Hoellein’s team relied on the collections of the famous Field Museum in Chicago, which houses around two million specimens of fish preserved in alcohol underground. As part of this work, the researchers focused on microplastics, these tiny fragments less than 5mm in size.
Thestudy focused on four freshwater species in particular: the Largemouth Bass ((Micropterus salmoides), the Straw Chub (Notropis stramineus), the Channel Catfish (ctalurus punctatus) and the Black Spotted Goby (Neogobius) melanostomus) The researchers tried to obtain at least five specimens per decade isolated between 1900 and 2017. To complete the picture, they also collected new samples of these same species.
After dissecting the digestive tracts of these fish (from the esophagus to the anus), the biologists then treated them with hydrogen peroxide, which allows the decomposition of organic matter but leaves any pieces of plastic intact. They eventually collaborated with researchers at the University of Toronto to confirm the chemical signature of these fragments using Raman spectroscopy.
Plastic on the menu for 70 years
As a result, this work did not reveal any plastic until the middle of the last century. On the other hand, pollutant concentrations began to soar in the 1950s, when the manufacture of plastics was industrialized. At the time, we started to manufacture all kinds: rigid, flexible, colored, easy to clean.
“All particles detected were fibers and represented plastic polymers (e.g. polyester) with mixtures of natural and synthetic textiles“, Emphasizes the study.
Unsurprisingly, the researchers also noticed that the further we went in time, the higher the concentrations of plastic in the digestive tracts of these fish, with a “boom” recorded over the last twenty years.