Over 1,000 tons of plastic rains into protected areas and national parks in western US annually: Study

Roughly 4% of the atmospheric particles analyzed from these remote locations are synthetic polymers

                            Over 1,000 tons of plastic rains into protected areas and national parks in western US annually: Study
(Getty Images)

Delivered like dust by the wind and rain, researchers estimate that more than 1,000 tons of plastic microparticles, roughly the equivalent of 120-300 million plastic water bottles, falls upon national parks and protected wilderness areas in the western US annually.

According to researchers, the results show that atmospheric transport is an important mechanism in the global distribution of microplastic pollution, including remote locations, and they underscore the importance of reducing pollution from such materials, which in the analysis were small enough to accumulate in lung tissue. “We approximate that over 1,000 tons of plastic from the atmosphere are delivered to western protected areas in the US, including national parks and wilderness areas, each year. This is equivalent to approximately 120 to 300 million plastic water bottles. Deposition rates averaged 132 plastics per square meter per day,” says the team in their findings published in Science. It includes experts from Utah State University, Salt Lake Community College, and Thermo Fisher Scientific, all based in the US. 

The study says that the world produced 348 million metric tons of plastic in 2017 and global production shows no sign of slowing down. It says that 11 billion metric tons of plastic are projected to accumulate in the environment by 2025. In the US, the per capita production of plastic waste is 340 grams per day. High resilience and longevity make plastics particularly useful in everyday life, but these same properties lead to progressive fragmentation instead of degradation in the environment, say experts. These microplastics are known to accumulate in wastewaters, rivers and ultimately the worlds' oceans. But while microplastics are found nearly everywhere on Earth, the sources and processes behind their ubiquitous distribution, or the “global plastic cycle” remain vaguely understood. Recent studies have suggested that long-range atmospheric transport plays an important role in carrying microplastic pollution vast distances and to remote locations.

To understand the reach of microplastics to conservation locations, the research team evaluated the transport and accumulation of microplastics in 11 remote and protected areas across the western US. They used high-resolution atmospheric deposition data and identified samples of microplastics and other particulates collected over 14 months. The results highlight the source, transport, and fate of plastics on surfaces as well as the contamination of US protected environments.

Plastic fibers and beads in dust collected from remote national parks and wilderness areas in the US. (Janice Brahney, Utah State University)

The researchers identified plastic and polymers' composition to detect sources of plastic emitted into the atmosphere and track its movement and fallout. By comparing the size and shape of the particles deposited during wet and dry weather, the team was able to identify atmospheric transport processes and deposition patterns.

Examination of weekly wet and monthly dry samples from the 11 sites allowed the authors to estimate that more than 1,000 tons of microplastics are deposited onto the protected lands annually. A staggering 4% of the atmospheric particulates identified collected from remote locations were plastic polymers. The study notes that clear and white particles were not included because they did not meet the researchers' criteria for visual counting under magnification, suggesting that their “estimates of plastic deposition rates based on counts are conservative.” 

Researchers examined filters from field sites in several national parks and wilderness areas and did visual counts of microplastic beads and fragments deposited by wind and precipitation. The pennies are used to hold each filter in place on the microscope stage. (Brian Kartchner, Utah State University)

The study examined the source and life history of both wet (rain) and dry microplastic deposition. Cities and population centers were found to serve as the initial source of plastics associated with wet deposition, but secondary sources included the redistribution of microplastics re-entrained from soils or surface waters. In contrast, dry deposition of plastics showed indicators of long-range transport and was associated with large-scale atmospheric patterns. Plastics deposited dry were smaller in size and traveled farther, “reminiscent of the global dust cycle but distinctly human in origin.” This suggests that microplastics are small enough to be entrained in the atmosphere for cross-continental transport, says the study. 

Most of the plastics deposited in both wet (66%) and dry (70%) samples were microfibers sourced from both clothing and industrial materials. Approximately 30% of the particles were brightly colored microbeads, but not those commonly associated with personal care products, these microbeads were acrylic and likely derived from industrial paints and coatings. Other particles were fragments of larger pieces of plastic. “This result, combined with the size distribution of identified plastics, and the relationship to global-scale climate patterns, suggest that plastic emission sources have extended well beyond our population centers and, through their longevity, spiral through the Earth system,” conclude the researchers.

Total, wet, and dry deposition separated by fiber and particle components for each site. (Science)

The finding that microplastics are ubiquitous in the atmosphere and are transported to distant locations has widespread ecological implications, say experts. The authors suggest that sensitive mountain ecosystems with simple food webs and shallow soils could be particularly sensitive to microplastic deposition. “Though the literature is still sparse on the effects of microplastics on terrestrial organisms, accidental ingestion of plastics by aquatic organisms has been shown to lead to blockages in the intestinal tract causing internal injury, reduced energy, and behavior modifications. In some cases, ingested plastics have been shown to transfer up the food chain. Less is known about the influence of microplastics on microbes, but recent work has suggested that plastics can influence microbial community composition,” they explain. 

According to the team, understanding the key mechanisms underpinning plastic emissions to the atmosphere is the first step in developing scalable solutions. “If the potential dangers posed by environmental microplastics are to be mitigated, both the scale of the solution and the level of cooperation that will be required call on the engagement of the global community,” say experts.

In a related perspective, experts from the University of Toronto, Canada, and Loyola University, Chicago, write that a key insight from the new work is that fundamental tools for studying global dust transport can be applied to microplastics. “Like dust, most particles measured were within the size range typical of global transport. However, microplastics are less dense than soil and, therefore, might travel longer distances than natural dust particles. Future research should test hypotheses about the distances that microplastics can travel atmospherically and the processes that entrain microplastics in the air, such as sea spray and dust storm,” say experts.

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