Microplastics are raining down on protected areas in the western U.S.

Every year, more than 1,000 tons of plastic rains down on protected areas in the western United States, according to a new study from Utah State University. The research was focused on samples of microplastics and other particles collected in 11 national parks and wilderness areas. 

A team led by Professor Janice Brahney analyzed the composition of the particles to identify the sources of atmospheric plastic and to track its movement and fallout. 

“We were shocked at the estimated deposition rates and kept trying to figure out where our calculations went wrong,” said Professor Brahney. “We then confirmed through 32 different particle scans that roughly 4% of the atmospheric particles analyzed from these remote locations were synthetic polymers.”

Global production of plastic reached 348 million metric tons in 2017, and this amount continues to grow. Due to the resilience of plastic, it persists in the environment and breaks down into microplastics that accumulate in wastewater, rivers, and oceans. The new study shows that microplastics also accumulate in the atmosphere. 

“Several studies have attempted to quantify the global plastic cycle but were unaware of the atmospheric limb,” said Professor Brahney. “Our data show the plastic cycle is reminiscent of the global water cycle, having atmospheric, oceanic, and terrestrial lifetimes.”

The researchers investigated the source and life history of wet and dry microplastic deposition. The team found that cities and population centers were the initial sources of plastics that were deposited by rain. These microplastics were also redistributed by secondary sources, such as soil and surface waters. 

On the other hand, dry microplastic deposits transported by wind were associated with large-scale atmospheric patterns and showed indications they had been carried over long distances. 

Most of the plastics deposited in both wet and dry samples were microfibers sourced from clothing and industrial materials. In addition, 30 percent of the particles were brightly colored acrylic microbeads that likely originated in industrial paints and coatings. 

“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,” wrote the study authors. 

Over 14 months, the team collected wet particle samples weekly and dry samples monthly across 11 sites. Ultimately, the experts estimated that more than 1,000 tons of microplastics are dumped on protected lands in the western U.S. each year. This is equivalent to more than 123 million plastic water bottles. 

The researchers noted that some particles were excluded from the study because they did not meet the criteria for visual counting under magnification, which suggests that plastic deposition rates are even higher than what was calculated.

The presence of microplastics in the atmosphere has unknown health consequences, but the microplastics analyzed in the study were small enough to accumulate in lung tissue if ingested. The atmospheric plastic also has the potential to adversely impact ecosystems in the protected areas.

“This ubiquity of microplastics in the atmosphere and the subsequent deposition to remote terrestrial and aquatic environments raise widespread ecological and societal concerns,” said Professor Brahney. “Identifying the key mechanisms of plastic emission to the atmosphere is a first step in developing global-scale solutions.”

The study is published in the journal Science.

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By Chrissy Sexton, Earth.com Staff Writer