Microplastics Equivalent to 120-300 Million Plastic Bottles Travel and Fall From Our Sky

Microplastics are floating and falling from the sky, along with dust particles that float and travel halfway across the globe. Researchers have collected microplastics for more than one year from some wilderness areas and national parks in the western part of the US. They examined particles that settled down during dry days and the ones that settled together with snow and rain.

They published their results in the journal Science. The study showed how these microplastics traveled, revealing that microplastics amounting to over 1,000 metric tons and weighing an equivalent of 120 to 300 million plastic bottles disperse into protected areas in this region every year.

This raised concerns on the impacts of microplastic pollution on human and environmental health. University of Strathclyde, Scotland microplastics researcher Steve Allen says that it is not healthy to breathe this kind of material. He says plastics carry various chemicals such as heavy metals and pesticides, which are directly brought into our lungs when we inhale them. Allen was not involved in the study.

Microplastics range in size from being smaller than a dust particle to as large as a rice grain. They are present almost everywhere that researchers looked for them - in the cities, in the Arctic region, and on the remotest mountaintops. Because they have been seen in areas where no humans are present, scientists concluded that they could be transported through the air.

Lead study author and Utah State University watershed scientist Janice Brahney originally intended to determine how nutrients are carried by dust. However, after she saw colored fibers and beads in the dust samples she put under her microscope, she shifted her focus.

The research team collected microplastics by using two buckets with a capacity of 3.5 gallons (or 13.2 liters) and equipped them with a lid with a trigger sensor on them. As snow and rain fell, the bucket designated as dry was covered while the bucket designated as wet was allowed to collect material in it. Conversely, on dry weather, it was the wet bucket that was kept lidded while the dry bucket allowed entry of materials.

The team manually counted the particles of plastic with the use of visual clues like unnatural textures and vivid colors so that they can be distinguished from organic materials and dust. They estimated the amount with the use of Fourier Transform Infrared Spectroscopy. This process measured the absorption and emission of infrared light, which serves to differentiate plastics from other objects. They captured fibers and particles which originally belonged to carpets, paints, camping gear, cosmetics, and others. The source with the most significant contribution they found is clothing. Our clothes shed these microfibers as they are used and washed. Four percent of all dust particles were plastic.

The team found that microplastics which fell during storms were larger and came from winds that originated from populated places. "Wet" plastics came from nearby cities while larger plastics fall closer to their source of emission. Meanwhile, microplastics falling during dry weather were more numerous but smaller. These corresponded with higher air currents, which suggested that they came from far away.

Allen's wife, Deonie Allen, who is also affiliated with Strathclyde, says that this research advances our understanding of the way atmospheric conditions influence the dispersion of these particles.