Forget diamonds – plastic is forever. It takes decades, if not centuries, for plastic to break down, and almost every piece of plastic ever made still exists in some form or another today. We’ve known for some time that large chunks of plastic can harm wildlife – think seabirds stuck in six-pack plastic rings – but in recent years, scientists have found microscopic pieces of plastic in it. water, soil and even the atmosphere. To find out how these microplastics have accumulated over the past century, researchers examined the guts of freshwater fish in museum collections; they found that fish have been swallowing microplastics since the 1950s and that the concentration of microplastics in their intestines has increased over time.
“Over the last 10 or 15 years, the public has sort of realized that there is a problem with plastic in the water. But the reality is, organisms have probably been exposed to plastic waste since plastic was invented, and we don’t know what it is. the historical context looks like this, ”says Tim Hoellein, associate professor of biology at Loyola University in Chicago and corresponding author of a new study in Ecological applications. “Looking at museum specimens is essentially a way of stepping back in time.”
Caleb McMahan, an ichthyologist at the Field Museum, looks after some two million fish specimens, most of which are preserved in alcohol and stored in jars in the museum’s underground collections resource center. However, these specimens are more than just dead fish – they are a snapshot of life on Earth. “We can never go back to that time, to that place,” says McMahan, co-author of the article.
Hoellein and his graduate student Loren Hou wanted to examine the buildup of microplastics in freshwater fish in the Chicagoland region. They contacted McMahan, who helped identify four common fish species that the museum had chronological records dating back to 1900: largemouth bass, river catfish, sand slickers and round gobies. Specimens from the Illinois Natural History Survey and the University of Tennessee also filled the sampling gaps.
“We would take these jars full of fish and find specimens that were sort of average, neither the biggest nor the smallest, and then we would use scalpels and forceps to dissect the digestive tract,” says Hou, the lead author. of the article. “We tried to get at least five specimens per decade.”
To actually find the plastic in the fish’s intestines, Hou treated the digestive tract with hydrogen peroxide. “It bubbles and fizzes and shatters all the organic material, but the plastic resists the process,” she explains.
The plastic left behind is too small to be seen with the naked eye, however: “It looks like a yellow spot, you don’t see it until you put it under a microscope,” Hou says. Under magnification, however, it is easier to identify. “We look at the shape of these little pieces. If the edges are frayed, it’s often organic material, but if it’s really smooth, then it’s probably microplastic.” To confirm the identity of these microplastics and determine their origin, Hou and Hoellein worked with collaborators at the University of Toronto to examine the samples using Raman spectroscopy, a technique that uses light to analyze the signature. chemical of a sample.
Researchers found that the amount of microplastics in fish intestines increased dramatically over time as more plastic was made and accumulated in the ecosystem. There were no plastic particles before mid-century, but when plastic manufacturing was industrialized in the 1950s, concentrations skyrocketed.
“We found that the microplastic load in the guts of these fish basically increased with the levels of plastic production,” McMahan says. “It’s the same pattern as what they find in marine sediments, it follows the general trend that plastic is everywhere.”
Analysis of microplastics revealed an insidious form of pollution: tissue. “Microplastics can come from the fragmentation of larger objects, but they often come from clothes,” Hou explains – every time you wash a pair of leggings or a polyester shirt, tiny little threads come loose and flow into the skin. the water.
“It’s plastic on your back, and that’s just not the way we think about it,” Hoellein says. “So even thinking about it is a step forward in dealing with our purchases and our accountability.”
It’s unclear how ingesting these microplastics affected the fish in this study, but it’s probably not great. “When you look at the effects of ingesting microplastics, especially the long term effects, for organisms like fish, it causes changes in the digestive tract, and it also leads to increased stress in those organisms,” explains Hou.
While the results are striking – McMahan described one of the graphs in the paper showing the surge in microplastics as “alarming” – researchers hope it serves as a red flag. “The aim of our work is to contribute to solutions,” says Hoellein. “We have evidence that education and public policy can change our relationship with plastic. It’s not just bad news, there is an app that I think should give everyone a reason to hope. collective. “
The researchers say the study also highlights the importance of natural history collections in museums. “Loren and I both love the Field Museum, but we don’t always think about its day-to-day science activities,” says Hoellein. “It is an incredible resource of the natural world, not only as it exists now, but as it existed in the past. It’s funny for me to think of the museum’s collection, kind of like the voice of those long-dead organisms that still tell us something. on the state of the world today. “
“You can’t do this kind of work without these collections,” McMahan says. “We need older specimens, we need newer specimens, and we will need what we collect in the next 100 years.”