Microfiber plastics appear to tumble, roll and move slowly in the environment

The findings are published in a journal, water resources researchmeaning fibers are easily trapped in sediments. This work helps improve understanding of the exposure risks and possible health effects of ubiquitous plastic debris, which is the world’s largest mass pollutant.

“Fibers tend not to want to move. If anything, they want to stay in place and attach to something,” said Nick Engdahl, associate professor in the Department of Civil and Environmental Engineering at Washington State University and corresponding author of the paper.

In the new study, the researchers carefully inserted 1,200 pieces of fishing line, one at a time, into a thin vertical sheet of material with four holes representing spherical gravel particles. Fluorescent fishing lines between three and eight millimeters in length were chosen as study material because they are easy to see. Video recordings of fiber movement show that the fragments tend to alternate between short periods of tumbling or rolling and longer periods of smooth motion.

In recent years, microplastic fibers in the environment have attracted increasing attention. These thread-like fibers are less than five millimeters in size and come from synthetic clothing materials such as wool, cosmetics, packaging materials and carpets. Other studies estimate that about 90% of global water contains microplastics, with 91% of plastics consisting of microfibers. The fibers have been found to negatively impact small marine life, but it’s unclear how they affect human health and ecosystems, in part because researchers don’t know their ability to move.

“We need to know how they move and where they end up to really see their impact on the environment,” said the paper’s lead author, Tyler Fouty, who recently earned his Ph.D. Worked at WSU and is now a water resources engineer at Jacobs.

In recent years, Engdahl developed a computer model to simulate how fibers move. The researchers also ran plastic fibers through columns of soil, which provided some information, but they couldn’t actually watch the fibers move. In the environment, researchers can find where pollutants start and end, but not how they got there.

“These experiments don’t provide any sense of the mechanisms that actually cause the fibers to move,” Engdahl said.

The researchers extracted the fibers’ travel paths from the videos and analyzed them to determine their travel times compared with microbeads. The researchers found that the fibers moved more slowly than the beads, and that the longer the fibers, the slower they moved. Through their analysis, they also found that the most common numerical models available to describe fiber motion were inaccurate.

Directly capturing the movement of microfibers is not easy, Foti said.

“The most important lesson we learned in this work is that it is difficult to obtain direct observations of transport behavior,” he said. “We anticipate that the challenge of trajectory capture can be greatly simplified if relatively large fibers and relatively large domains are used, but even then unexpected behavior will be encountered.”

The researchers hope to continue investigating other aspects of transport, including controlling flow more precisely and using different types of fibers. This work was supported in part by the National Science Foundation.