Modern scientific techniques are rapidly improving our understanding of how plastic pollution can impact marine organisms, and a new study has demonstrated how they can also be used to understand the plight of creatures past. Scientists have used museum collections to step back in time and study the guts of freshwater fish over the past century, which revealed not just that they've been swallowing plastic waste for decades, but that the concentration in their bellies has skyrocketed in recent times.
This study by biologists at the Loyola University Chicago focuses on microplastics, which are tiny fragments of broken down shopping bags, soda bottles and other plastic items, smaller than 5 mm (0.2 in) in size. Recently, scientists studying the effects of microplastics on marine organisms have made some concerning discoveries, finding that they can cause aneurysms and reproductive changes in fish, affect the cognitive performance of hermit crabs and weaken the physical performance of mussels, just to list a few examples. They've also uncovered evidence of microplastics traveling up the food chain, while studies on the potential effects on humans has found they may alter the shape of lung cells.
The authors of the new study set out to understand how microplastics have built up over the past century, and what that means for the fish of the past. This led them to to Chicago's Field Museum, where around two million fish specimens are preserved in alcohol and stored in an underground collection.
"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," says Tim Hoellein, an associate professor of biology at Loyola University Chicago. "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. Looking at museum specimens is essentially a way we can go back in time."
The study focused on four species in particular: largemouth bass, channel catfish, sand shiners, and round gobies, all of which have records dating from 2017 back to 1900. To complete the picture, the team also collected fresh samples of these same species for study.
"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," says Loren Hou, the paper's lead author. "We tried to get at least five specimens per decade."
These digestive tracts were then treated with hydrogen peroxide, which breaks down all the organic matter but leaves any potential plastics in tact. The scientists used microscopes to identify materials with suspiciously smooth edges that might be indicative of microplastics, and then collaborated with researchers at the University of Toronto to confirm their chemical signature using Raman spectroscopy.
This revealed no plastics up until the midway point of last century, but then when plastics manufacturing was industrialized in the 1950s, these concentrations began to skyrocket. The plastics were found to be in fiber form, and were derived from polymers and a range of natural and synthetic textiles. The researchers describe the discovery and this significant increase in concentration as "alarming" and a "wakeup call."
"We found that the load of microplastics in the guts of these fishes have basically gone up with the levels of plastic production," says Caleb McMahan, an ichthyologist at the Field Museum. "It's the same pattern of what they're finding in marine sediments, it follows the general trend that plastic is everywhere."
The research was published in the journal Ecological Applications.
Source: Field Museum via EurekAlert
