The insidious spread of microplastics through our environment is something that we really don't know enough about. Tons and tons of plastic waste washes into the ocean every year, much of which is broken down into pieces smaller than a fingernail that become very difficult to track, with untold consequences for marine life and organisms that consume it (us included). Researchers have now found unexpected quantities of microplastics are lodged in Arctic sea ice, shedding new light on how microplastics move through the ocean.

The study was carried out by a team from Germany's Alfred Wegener Institute (AWI) who retrieved ice samples during three Arctic expeditions in 2014 and 2015. Their collection was made up of ice blocks from five different regions of the Arctic Ocean along the Transpolar Drift Stream and Fram Strait, passages that carry sea ice from the central Arctic to the North Atlantic.

These samples were then analyzed using a device called a Fourier Transform Infrared Spectrometer, which works by blasting infrared light onto the ice and then measuring the radiation that is bounced back. This enabled the scientists to not only assess the concentration and size of plastic particles within, but because the different chemical composition of different particles will reflect different wavelengths of light, they can even determine the types of plastic.

The samples contained up to 12,000 particles per liter of ice (0.26 US gal), which is two to three times higher than what has been measured in the past. Two thirds of these particles measured 50 micrometers or smaller in size.

"During our work, we realized that more than half of the microplastic particles trapped in the ice were less than a twentieth of a millimeter wide, which means they could easily be ingested by arctic microorganisms like ciliates, but also by copepods," explains first author of the study Dr Ilka Peeken, a biologist at AWI. "No one can say for certain how harmful these tiny plastic particles are for marine life, or ultimately also for human beings."

The unique optical signatures of the particles allowed the scientists to distinguish 17 different types of plastic, including common packing materials like polyethylene and polypropylene, along with polyester, nylon, paints and cellulose acetate. Together, these six materials made up around half of the total microplastics detected.

And by determining what type of plastics they are, the team can deduce where they might have come from. The paint and nylon, for example, may well be from ships and nets respectively, possibly as a direct result of intensified shipping and fishing activities in parts of the Arctic. The polyethylene, on the other hand, is assumed to have washed in from the Great Pacific Garbage Patch.

"The sea ice binds all this plastic litter for two to a maximum of eleven years – the time it takes for ice floes from the marginal seas of Siberia or the North American Arctic to reach the Fram Strait, where they melt," explains Dr Peeken.

But what happens after that remains unclear. It is possible that they continue their journey south through the ocean or stick around the Arctic, where they would likely start to sink at a pretty rapid rate. Earlier research conducted by the scientists found concentrations of up to 6,500 plastic particles per kilogram (2.2 lb) of seafloor.

"Free-floating microplastic particles are often colonized by bacteria and algae, which makes them heavier and heavier," says AWI biologist and study co-author Dr Melanie Bergmann. "Sometimes they clump together with algae, which makes them drift down to the seafloor much faster."

The team's research was published in the journal Nature Communications.

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