Microplastics have been abundant in fish guts since the 1950s

In a new study from the Field Museum, experts have discovered that fish have been swallowing microplastics since the 1950s. The researchers examined the guts of freshwater fish preserved in museum collections, and found that concentrations of microplastics have dramatically increased over time.

“For the last 10 or 15 years it’s kind of been in the public consciousness that there’s a problem with plastic in the water. But really, organisms have probably been exposed to plastic litter since plastic was invented, and we don’t know what that historical context looks like,” said study co-author Professor Tim Hoellein of Loyola University Chicago. “Looking at museum specimens is essentially a way we can go back in time.”

Study co-author Caleb McMahan is an ichthyologist at the Field Museum who cares for two million fish specimens, most of which are preserved in alcohol and stored in jars in the museum’s underground Collections Resource Center. 

McMahan explained that these specimens are more than just dead fish – they are a snapshot of life on Earth. “We can never go back to that time period, in that place.”

The study was focused on four common fish species that the museum had chronological records of dating back to 1900: largemouth bass, channel catfish, sand shiners, and round gobies. 

“We would take these jars full of fish and find specimens that were sort of average, not the biggest or the smallest, and then we used scalpels and tweezers to dissect out the digestive tracts,” said study lead author Loren Hou. “We tried to get at least five specimens per decade.”

To find microplastics inside of the fish, the team treated their digestive tracts with hydrogen peroxide. 

“It bubbles and fizzes and breaks up all the organic matter, but plastic is resistant to the process,” explained Hou. “It just looks like a yellow stain, you don’t see it until you put it under the microscope.”

“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 most likely microplastic.” 

To determine where the microplastics came from, the researchers teamed up with collaborators at the University of Toronto to examine the samples using Raman spectroscopy, a technique that uses light to analyze the chemical signature of a sample.

The amount of microplastics present in the fish guts was found to drastically increase over time. There were no plastic particles before mid-century, yet these concentrations skyrocketed in the 1950s – when manufacturing was industrialized.

“We found that the load of microplastics in the guts of these fishes have basically gone up with the levels of plastic production,” said McMahan. “It’s the same pattern of what they’re finding in marine sediments, it follows the general trend that plastic is everywhere.”

One of the major sources of plastic particles found in the fish guts was fabric. 

“Microplastics can come from larger objects being fragmented, but they’re often from clothing,” said Hou.

“It’s plastic on your back, and that’s just not the way that we’ve been thinking about it,” said Hoellein. “So even just thinking about it is a step forward in addressing our purchases and our responsibility.”

While it is not clear how ingesting microplastics affected the fish in this study, the outcome was probably not great. 

“When you look at the effects of microplastic ingestion, especially long term effects, for organisms such as fish, it causes digestive tract changes, and it also causes increased stress in these organisms,” said Hou.

The researchers hope the stark findings will serve as a wake-up call. “The entire purpose of our work is to contribute to solutions,” said Hoellein. “We have some evidence that public education and policies can change our relationship to plastic. It’s not just bad news, there’s an application that I think should give everyone a collective reason for hope.”

The researchers noted that the study highlights the importance of natural history collections in museums. 

“Loren and I both love the Field Museum but don’t always think about it in terms of its day-to-day scientific operations,” said Hoellein. “It’s an incredible resource of the natural world, not just as it exists now but as it existed in the past. It’s fun for me to think of the museum collection sort of like the voice of those long dead organisms that are still telling us something about the state of the world today.”

“You can’t do this kind of work without these collections,” said McMahan. “We need older specimens, we need the recent ones, and we’re going to need what we collect in the next 100 years.”

The study is published in the journal Ecological Applications.

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By Chrissy Sexton, Earth.com Staff Writer