Scientists seek clues to microplastics problem through 'pickled fish' time capsule

TVA's 56-year-old collection offers look back for human connection

Photo contributed by the Tennessee Valley Authority / Dr. Ben Keck, curator of the University of Tennessee Knoxville's David A. Etnier Ichthyological Collection, is using 3,000 "pickled fish" collected from as far back as 1965 to look at the history of microplastics in the Tennessee River.

Looking like a cupboard full of preserves made by a river-faring grandmother, the University of Tennessee-Knoxville's collection of thousands of "pickled" fish could offer a 56-year look back to when microplastics, fish and humans were first becoming connected in the Tennessee River Valley.

Microplastics are the end result of degrading plastic - soft drink bottles, straws, grocery bags and other packaging products thrown on the ground, into water or discarded in landfills - that ends up as tiny particles in freshwater streams where they are ingested by fish, according to the Tennessee Valley Authority.

Until now, there have been no long-term, freshwater studies on microplastics pollution, but TVA and the University of Tennessee in Knoxville are trying to change that.

Scientists on the environmental front are concerned that microplastics can act as super magnets, absorbing concentrated amounts of toxins suspended in public drinking water sources.

A study published in 2019 in the "Environmental Science and Technology" peer-reviewed scientific journal estimated Americans each consume 39,000-52,000 microplastic particles per year. Those numbers increase to 74,000-121,000 when microplastics that are inhaled are included.

It's important because the Tennessee River is one of the most bio-diverse freshwater natural resources in the world, according to TVA. Health and environmental impacts are largely unknown, but UT-Knoxville and TVA scientists have hopes of luring clues from the guts of the preserved fish.

They already know the Tennessee River is loaded with microplastics.


Over 34 days in the summer of 2017, German scientist and long-distance swimmer Andreas Fath set a world record as he swam the 652-mile Tennessee River, end to end, with gear to collect water samples and draw attention to the microplastics issue in what was dubbed "TenneSwim."

Fath is a professor of medical and life sciences at Germany's Furtwangen University. He presented his initial findings to the Tennessee Aquarium Conservation Institute in 2018, and those findings would catch the eye of a UT scientist.

When Fath compared the results with data from Germany's Rhine River, which he swam in 2014 for analysis, the Tennessee River was much more polluted.

"We found a bunch of different chemicals from household, industry and agriculture in the Tennessee River together with a high amount of microplastic particles in the size range from 25-300 [microns]," Fath said Friday in an email.

The plastics detected were mainly polypropylene and polyethylene, used in packaging.

TVA points to work by Dr. Martin Knoll, the University of the South geology and hydrology professor who helped conduct the TenneSwim survey and determined about half of the Tennessee River's microplastics pollution is polyethylene, the material used to make the common grocery store bag.

"The quantity of 18 particles per liter can have an ecological impact on aquatic life," Fath said.

(READ MORE: U.S. aquariums increase push to drastically reduce use of plastic straws)

Compared to Germany's Rhine River with 0.2 particles per liter, the Tennessee River's concentration is about 90 times greater, Fath said. The Yangtze River, in China, has about 9 particles per liter, about half the Tennessee River's concentration, he said. But really determining how different rivers compare is difficult because of so many variables.

"The question of which of these rivers is the most polluted by microplastics is not that easy to answer because there are several parameters to consider which are: depth of water filtration, depth of the river and its current with turbulence, discharge and range of particle size," he said.

'Pickled fish'

The study uses UT's David A. Etnier Ichthyological Collection, essentially a 45,000-jar library containing an estimated 420,000 specimens from the Tennessee River originally collected by TVA biologists and university students.

It's a time capsule that could reveal whether decades of a disposable society is leading to microplastics entering food sources. Ben Keck, lecturer and curator of the Etnier Collection, said specimens have been added to it since the mid-1960s, first as part of namesake Etnier's inventory and exploration of the state, and then of his students, TVA, the Tennessee Wildlife Resources Agency and others.

Keck said the idea to launch the study came from Fath's 2017 swim.

"When I read the reports of Dr. Fath's swim, I thought that we might have a unique opportunity to look at microplastics in fishes through time, not just contemporary levels," Keck said Friday. "Natural history museums have way more information in them than the specimens themselves. Here we have the ability to answer a question about microplastics in fishes that wouldn't be possible without the collection.

"The collection enables us to ask questions about the past 50-60 years," Keck said. "We're not sure what we'll see as there haven't been other studies of similar systems through time."

The collection probably can't show the first instances of microplastics in the river since plastics were already in wide use by the 1960s, but it can help show how fish are exposed.

"Right now we are focused on species from different feeding groups, such as bottom feeders and surface feeders, to see if there's a difference in how many and what type of microplastics they ingested or were exposed to," he said.

The study will lead to more questions since it starts with the simple query, "Are there microplastics in these fishes and does it vary through time, by feeding behavior and locality?" Keck said.

Those answers could come in the years ahead when other researchers and institutions take up the cause.

What to study?

Fath said other U.S. rivers should be studied with an eye toward how the states those rivers run through manage waste "because most of the particles in the river have their origin from littering and landfill. The plastic gets brittle by [ultraviolet] light, and weathering and the wind takes it everywhere."

When it rains, plastics can be carried in streams and rivers, he said.

States with a waste management system that separates plastics from household trash, or that have high recycling rates among residents, should be compared with states that have no such systems, he said.

On a global scale, most of the world's largest rivers have been studied but only in select locations, Fath said. That brings up the problem again of variability impacting results. Future study should be narrower, he said.

(READ MORE: Plastic waste fills much of Chattanooga Creek)

"Tributaries should be investigated because they are smaller with lower discharge and decreased depth," he said. "This investigation would give us a better overview of the whole situation."

Another way to look at the problem is to look back in time as the TVA/UT study does.

"I just read a paper about the investigation and results of microplastic concentrations in freshwater fish looking at museum specimens over the last 100 years and it turned out that the researcher found microplastic particles in fish bodies since 1950," Fath said. "That was the year when mass production of plastics starts. The authors made a direct correlation between plastic production and accumulation in freshwater fish."

What's next?

"Next is the investigation and swimming of the Danube [River], which will be very interesting and exhausting because this international river passes 10 countries with different cultures and different waste managements," Fath said Friday.

"Rivers are a mirror image of society," Fath said. "You find microplastics everywhere."

A major unavoidable source is wheel friction from the motoring public, but other sources could be addressed, he said. Microplastics in cosmetic products could be eliminated, plastic consumption could be reduced and recycling could be increased.

(READ MORE: Chattanooga's 'Conservation Kid' adds to impressive year, publishes book about aquatic conservation, plastic pollution)

Scientists aren't sure about microplastics in the atmosphere but the tiny particles have been found in some surprising places.

"We even found microplastics in Lake Toma at an altitude of 2,340 meters" or 7,677 feet, Fath said. "This lake is considered a source of the River Rhine in the Alps. The lake feeds itself with melting water from the surrounding snow fields and glaciers."

Fath's next project is coming in January 2022 when "we investigate the snow in North Norway," he said. "The project is called 'PUREICE.'"

Keck said after the current work is done, others at UT will pick up where the current study leaves off.

"Several undergraduates working on this study have developed their own questions and will be conducting that research over the next year or so," he said. "These mostly focus on urban vs. rural settings and finer time scales. The goal of these studies in the end is to provide a robust understanding of what has been and what is happening so that any policy is well informed."

Contact Ben Benton at or 423-757-6569. Follow him on Twitter @BenBenton or at