New research helps unravel how large amounts of microplastics travel, both regionally and globally, in the wind
Carried by the wind, dust particles from places like the Sahara desert can float to the other side of the world before settling on the ground. As plastics disposed of by humans break down into small pieces in the environment, they, too, move through the atmosphere. Now scientists are one step closer to understanding how these globe-trotting microplastics travel, both locally and on long-haul flights.
The researchers spent more than a year collecting microplastics from 11 national parks and wilderness areas in the western US They separately examined particles that settled on dry days and those that fell along with rain or snow. In addition to shedding light on how microplastics move, the results, published Thursday in Science, reveal the magnitude of the problem: More than 1,000 metric tons of microplastics fall, the weight of 120 million to 300 million plastic water bottles. protected lands in the western region of the country every year. The new findings add to scientists' concern about the potential impacts of microplastic pollution on the environment and human health. "We are not supposed to breathe this material," says Steve Allen, a microplastics researcher at the University of Strathclyde in Scotland, who was not involved in the new study. Plastics in the environment "carry all kinds of pesticides, heavy metals, and all the other chemicals we've made over time," he adds. "They will take them directly to our lungs."
Since their discovery in the oceans in the 1970s, microplastics, which can be as big as a grain of rice or smaller than a particle of dust, have been found almost everywhere researchers have looked: in cities, In the arctic snow, on top of remote mountains. Their presence in areas distant from human habitation has indicated that they are carried by the winds. However, few studies have directly investigated this possibility.
Janice Brahney, a watershed scientist at Utah State University and lead author of the new study, initially set out to investigate how dust carries nutrients, not plastic. But after looking through the microscope and seeing colored beads and fibers among the pieces of dust, he refocused his efforts. To collect microplastics samples, Brahney's team used a pair of 3.5-gallon (13.2-liter) buckets with a sensor-activated lid. When rain or snow fell, the lid covered the "dry" bucket and allowed the material to enter the "wet" one. During dry weather, the lid would cover the wet bucket and allow the material to enter its dry counterpart.
Back in the lab, the researchers counted the plastic particles by hand under a microscope, using visual cues such as vivid colors and unnatural textures to distinguish them from dust and organic materials. The team independently calculated the amount of microplastics using a process called Fourier transform infrared spectroscopy, which measured how the samples absorbed and emitted infrared light to differentiate plastic from another material. The particles and fibers they captured originated as carpets, paint, cosmetics, camping equipment, and more. But the biggest contribution came from clothing. Clothes shed microfibers when washed and dried, as well as during everyday wear.
The scientists found microplastics in almost every sample they collected. In total, 4 percent of the identifiable dust particles were plastic. Brahney and her colleagues "immediately realized how serious what we were seeing," she says. "That was a moment of being completely in awe."
By analyzing weather patterns and dust accumulation in national parks and wilderness areas, the team was able to observe the effects of pollution from nearby cities and better understand the “plastic cycle” that transports synthetic materials around the globe, by just like the "dust cycle" It transports the dust. Microplastics that fell to the ground during storms tended to be larger and arrived when winds blew from populated areas. This observation indicated that the “wet” plastics originated in those nearby cities and that the larger plastics fall out of the atmosphere closer to where they are emitted. On the other hand, the microplastics that fell during dry conditions were smaller but more numerous. They also corresponded with higher air currents in the atmosphere, suggesting that these plastics had traveled long distances.
The new research "expanded significantly" on previous studies of microplastics in remote areas, Allen says, including a paper that he and his wife, Deonie Allen, also at the University of Strathclyde, published last year in Nature Geoscience. "They've done a good job especially figuring out where it comes from and the kind of distances it can travel," he adds. Deonie Allen, who was not involved in the Brahney project, says that the separation of dry and wet microplastics represents an important advance in understanding how atmospheric conditions affect the flight paths of these particles.
For Brahney and others, future research will focus on discovering the ways that microplastics enter the atmosphere. "We are only beginning to really scratch the surface of what is in the atmosphere and how it moves," he says.