Microplastic pollution in Flathead Lake, Montana

Scientists now have a better understanding of the number of microplastics polluting Flathead Lake, their likely sources, and what can be done to keep more from entering the lake's world-renowned pristine water.

Flathead Lake, Montana

They are present in our oceans and rivers. They're in the food and water we consume. They've even been found inside human bodies. Microplastics are plastic particles that are so small that they cannot be seen with the naked eye. While scientists have known for years that microplastics exist in Flathead Lake, the concentrations and sources of the microplastic pollution have remained unknown.

Scientists now have a better understanding of the amount of microplastics polluting Flathead Lake, the likely sources of these microplastics, and what can be done to prevent more from entering the lake's world-renowned pristine water, thanks to a study conducted at the University of Montana's Flathead Lake Biological Station.

This microplastics study, which was recently published in the scientific journal Environmental Pollution, was led by FLBS visiting researcher Dr. Xiong Xiong from the Chinese Academy of Science's Institute of Hydrobiology. Xiong arrived at FLBS in 2018 with the goal of learning more about microplastics in freshwater lakes in sparsely populated areas and providing insight to aid in their management.

"It appears to be quite clean, but if this clean lake is contaminated with plastics, I want to investigate," Xiong said four years ago when he began his research. "People may believe that (plastic pollution) is more severe in the ocean, but many people live inland, and we require freshwater. It may have a greater impact on our daily lives than plastic in the ocean."

Xiong worked with FLBS Director Jim Elser and a team of biological station scientists to collect surface water samples from 12 different locations around Flathead Lake over the course of a year. The samples were then examined for the presence, distribution, and types of microplastics.

The team discovered that, while levels of microplastic pollution measured in Flathead Lake were lower than in lakes in densely populated areas, Flathead had microplastic levels comparable to or higher than lakes studied in less densely populated areas around the world.

In other words, microplastics have colonized Flathead Lake, and new microplastic particles are arriving on a daily basis.

"Microplastics in lakes can disrupt food webs because animals such as zooplankton and fish can consume them," Elser explained. "They can introduce toxins into the animal, displace natural foods, and physically harm digestive tissues."

According to the study, there are three main ways for microplastics to enter Flathead Lake. Atmospheric microplastic deposition is one method. This happens when microplastics are transported by the atmosphere (e.g., wind and clouds) to Montana and then fall into Flathead Lake – either directly from the air (known as dry deposition) or through snow and rainfall (wet deposition).

Dry deposition of microplastics was highest in the fall, while wet deposition was highest in the winter.

"This study demonstrated that microplastics are literally raining – and snowing – down from the sky," Elser said.

Microplastics can also enter Flathead Lake through the lake's major river inputs, which include the Flathead River on the lake's north end and lakeside sources near larger shoreline communities such as Polson, Bigfork, and Lakeside.

The most likely source of microplastics at the Flathead River's mouth is plastic waste disposal, which in Flathead County is primarily landfill rather than recycling. Although the landfills in the Flathead Watershed are not open pits, microplastics are mobilized through leachate (contaminated water) and the soil of the landfill when winds carry dust away.

Meanwhile, researchers discovered that microplastic concentrations were particularly high along the lake's more densely populated shoreline areas. Many of today's clothes, in addition to plastic packaging, are made from fibrous plastics. These synthetic fabrics disintegrate on a microscopic level during washing and are then transported and deposited into our waters via septic drain fields and community water treatment plants.

Plastic waste generated by other human activities is also worthy of consideration. Water sports such as kayaking, sailing, speedboating, water skiing, and fishing are popular outdoor activities in the Flathead Watershed. However, these activities involve the use of plastic boats, ropes, floats, and fishing line, all of which degrade and transform into microplastics over time.

Microplastic levels in Flathead Lake are concerning, despite being relatively low. Researchers, on the other hand, are quick to point out that there is much that can be done to reduce their presence in Montana's waters.

"While we need to learn more about the effects of microplastics in our lakes, we know enough to act now to reduce plastic inputs," Elser said. "We can all reduce our use of plastics, properly dispose of them, and implement effective solutions such as laundry filters. We can also encourage businesses to follow suit, as well as governments to build facilities and systems to better manage plastics in our watershed."

Fibrous microplastics can be reduced by improving laundry practices and wastewater treatment, or by substituting natural fiber clothing and materials for synthetic fiber clothing and materials. A recent study in California, for example, discovered that installing in-line filters in washing machines had the potential to reduce annual synthetic microfiber emissions to natural environments by nearly 80%.

Further strengthening plastic waste disposal measures by both residents and visitors could significantly help reduce microplastic contamination in Flathead Lake. Better education about the dangers of improper plastic disposal, increased plastic waste recycling in the region, and reduced overall use of plastic products, such as single-use plastics common in the food service industry, are examples of such measures.

Researchers stated that extensive solutions are required to reduce atmospheric microplastic deposition. The total amount of plastic waste produced in the United States is 42 million tons per year, which is significantly more than other countries per capita. This suggests that, even in a low-population area, Flathead Lake will be vulnerable to microplastics arriving by air until national measures are implemented.

More research, according to Xiong and his research team, is needed to better understand and address our microplastic problem, not only in the Flathead Watershed but also globally. The good news is that, because human activities are unquestionably the only source of microplastics, we have the ability to solve this problem.

FLBS research scientist Tyler Tappenbeck and Chinese Academy of Sciences researcher Chenxi Wu are among the study's other authors.


Materials are provided by The University of Montana

Reference: DOI: 10.1016/j.envpol.2022.119445


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