Tons of microplastics are raining down on United States national parks

Rodiano Bonacci
Giugno 15, 2020

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.

Researchers from Utah State University found out that as much as 1,000 metric tonnes of plastic fragments (equivalent to 300 million plastic water bottles) rain down on 11 national parks and wilderness areas of the United States.

Pieces of plastic less than 5 mm in length, or microplastics, occur in the environment as a effect of plastic pollution. 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.

Secondary microplastics form from the breakdown of larger plastics; this typically happens when larger plastics undergo weathering, through exposure to wave action, wind abrasion, and ultraviolet radiation from sunlight. The new study casts light on an alternative movement of microplastics that has been overlooked. Though microplastics are found almost everywhere on Earth, the sources and processes behind their ubiquitous distribution, or the "global plastic cycle", remain vaguely understood.

How the plastic particles came to fall with rains was a little surprising, but the scientists surmised that they must have been swept into the atmosphere by storms from urban cities, and then fall to the ground when rain and snow bear down on them from the atmosphere.

"We were shocked at the estimated deposition rates and kept trying to figure out where our calculations went wrong", Brahney said. A staggering 4% of the atmospheric particulates identified collected from remote locations were plastic polymers.

The ubiquity of microplastics in the atmosphere has unknown consequences for humans and animals, but the research team observed sizes of particles that were within the ranges that accumulate in lung tissue. Moreover, the ongoing deposition of plastic in wilderness areas and national parks has the potential to influence these ecosystems from community composition to food web dynamics.

"Our data show the plastic cycle is reminiscent of the global water cycle, having atmospheric, oceanic, and terrestrial lifetimes", Brahney said. "Identifying the key mechanisms of plastic emission to the atmosphere is a first step in developing global-scale solutions".

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