Japanese team develops method for more accurate sampling for microplastics in freshwater

Sewanee professor says methodology has limited potential in U.S. but offers sound analysis

Staff Photo / Randy Whorton, director of Wild Trails, paddles through a section of Chattanooga Creek with a thick layer of trash covering the surface in 2018 in Chattanooga.

Note: This story was updated on Sept. 13 to correct the title and affiliation of Mamoru Tanaka.

As plastic, single-use containers, cups, bags, straws and other throwaway items continue to fill the planet's landfills and waterways, worldwide concern about the health effect of microplastics -- the end result when those items degrade -- is higher than ever, but only recently have strides been made in accurately assessing the problem.

Japan-based researchers have a new method for estimating microplastic concentrations, making use of resources more efficient, sampling more accurate and assessment of the problem more meaningful, according to recent research by a team at the Tokyo University of Science.

The new study was performed by Tokyo University of Science researcher Mamoru Tanaka and researcher Yasuo Nihei, along with Ehime University researcher Tomoyah Kataoka, according to team spokesman Hiroshi Matsuda. The team has proposed a method that estimates the sampling requirements for accurate assessment of microplastic contamination in rivers.

The study, "Variance and precision of microplastic sampling in urban rivers," has been published in the journal "Environmental Pollutions," an international peer-reviewed journal that publishes high-quality research papers and review articles about all aspects of environmental pollution and its effects on ecosystems and human health. Since that publication, the work has been reviewed by numerous other scientific journals.

(READ MORE: Scientists seek clues to microplastics problem through 'pickled fish' time capsule)

The study hopes to improve accuracy in the study of the microplastic problem and its effectct on humans by helping standardize protocols for collecting samples, according to Tanaka.

"Most studies on riverine microplastics do not provide accuracy of their microplastic concentration estimates," Tanaka said in an emailed response to questions from the Chattanooga Times Free Press. "Our work proposes how to evaluate, calculate or predict accuracy of their estimates."

The extent of plastic pollution remains largely hidden from view as invisible microplastics, according to the team.

"In the years since their discovery in the early-1970s, microplastics have become a ubiquitous and global concern," Matsuda said in a news release on the study. "Microplastics are found in land, air, water and the food we eat, especially seafood."

Microplastics are present in seafood because freshwater sources, such as rivers, carry microplastics into oceans, where they accumulate, according to the team.

The team collected 10 samples in plankton nets at two sites along the Ohori River and Tone-unga canal in Chiba, Japan -- two water bodies that flow through urban areas and contain a high concentration of plastic waste -- according to Matsuda.

The team found that at high microplastic concentrations, two replicate samples are sufficient for an accurate measurement.

Research rising

Only in recent years have scientists turned a watchful eye toward microplastics, but they have been present in the environment -- and the Tennessee River -- for decades, according to research by the University of Tennessee in Knoxville, the Tennessee Valley Authority, the University of the South in Sewanee, Tennessee, and others. Scientists worldwide are concerned 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.

The Tennessee River is a prime example of microplastic pollution.

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

Fath, a professor of medical and life sciences at Germany's Furtwangen University, presented his initial findings to the Tennessee Aquarium Conservation Institute in 2018, comparing results of samples collected from Germany's Rhine River -- which Fath swam in 2014 for analysis -- to the Tennessee River, which was found to be 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 in 2021.

Fath noted microplastics were even found in Switzerland's Lake Toma at an altitude of 7,677 feet.

Compared to Germany's Rhine River with 0.2 particles per liter, the Tennessee River's concentration is about 90 times greater, Fath said in 2021. The Yangtze River, in China, has about 9 particles per liter, about half the Tennessee River's concentration, according to Fath's results. But really determining how different rivers compare is difficult because of so many variables, he said.

California effort

Martin Knoll, a geology and hydrology professor at Sewanee, helped conduct the TenneSwim survey with Fath and determined about half of the Tennessee River's microplastics pollution is polyethylene, the material used to make grocery store bags.

Knoll's research into the microplastics problem is an ongoing work, and he said meaningful research into the problem is in its infancy.

(READ MORE: Masses of plastic particles found in Great Lakes)

"The big problem with microplastic research in water is there is no standard methodology," Knoll said Friday in a phone interview between classes. "That makes it really hard to compare results from one study to results from another study."

But while the Japanese study is a small step forward for assessment accuracy and has sound analysis, the methodology might have only limited potential in the U.S., where some rivers are deep and aren't ideal for the Japanese approach of collecting samples at the surface, Knoll said. The Japanese study's use of plankton and neuston nets also don't capture the smallest microplastic particles, he said.

The neuston includes insects such as whirligig beetles and water striders, some spiders and protozoans and occasional worms, snails, insect larvae and hydras that live on the water's surface, according to the National Oceanic and Atmospheric Administration.

The state of California is employing what could be become the new standard for assessments, according to Knoll. California defines microplastics as "solid polymeric materials" measuring between one-thousandth of a millimeter and 5 millimeters, according to California's State Water Resources Control Board. Knoll said capture netting used in California is sized appropriately for the smallest particles.

Knoll said new sampling methodology in use in California stems from recent legal requirements adopted by lawmakers there to test for microplastics in drinking water and report the results to the public. He said sampling methods used in his work at Sewanee are nearly identical to California's.

"In the United States -- and probably globally -- I think the California method is going to be dominant," Knoll said. "The reason California is doing that is they're going to regulate microplastics in drinking water."

The California method has not yet been adopted anywhere else with the exception of some independent labs like Knoll's at Sewanee, he said.

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

Reduce error range

The new Japanese method hasn't been employed by others either, Tanaka said. The team felt plankton nets and neuston nets were the standard for most researchers, globally, and the aim of the new study is to reduce the error range of results, which makes it difficult to compare accuracy of estimates in other studies, according to Tanaka.

"Here our method provides how much researchers need to repeat net sampling to obtain accurate estimates of microplastic concentration in the river, based on scientific, statistical evidence. So far there has not been a method to 'scientifically' determine the number of repetitions until our article published," Tanaka said. "Our method established for microplastic collections by plankton nets and neuston nets can be applicable for microplastic studies in the U.S. and elsewhere."

Tanaka said various countries, including Japan, have passed legislation to ensure better monitoring and control of microplastics in the environment.

Although new, Tanaka hopes the team's methodology is merged into standards for future microplastics sampling while reducing the time and resources invested in microplastic assessment surveys.

(READ MORE: Yoga pants, cozy clothes may be key source of sea pollution)

Meanwhile, Knoll said he's planning a trip to Europe's Danube River -- which flows from the Black Forest in Germany to the Black Sea between Turkey and Ukraine -- to collect samples from its deepest points to assess microplastic contamination there. He said Fath recently swam the river to collect samples from the surface.

Research into the microplastics problem is gaining momentum in the scientific community, he said, and improvements and new developments should become more frequent and lead to benefits for humans.

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