Ocean interior has accumulated "missing" plastics

Approximately 51 trillion microplastics –  tiny fragments measuring less than five millimeters in length and originating from various types of plastics – are floating in the surface waters of seas and oceans all over the globe, negatively impacting a large variety of ecosystems. While hundreds of scientific studies have surveyed the plastic debris on the surface or near the surface of oceans, they are still far from providing a full picture of marine microplastic pollution.

A new study led by the Florida Atlantic University (FAU) has found that microplastics are in fact present in the entire water column within the Southern Atlantic Ocean, suggesting that ocean interiors are just as polluted as their surfaces. According to the researchers, the study indicates that the ocean interior is a crucial pool of “missing” plastics.

Moreover, weak ocean current systems are shown to contribute to the formation of microplastic hotspots in the depths of the ocean, where they can significantly affect zooplankton populations.

“Our study highlights the urgency for more quantification of the deep-ocean microplastics, especially the smaller size fraction, to better understand ecosystem exposure and to predict the fate and impacts of these microplastics,” said study senior author Tracy Mincer, an assistant professor of Biology at FAU. 

By sampling plastic particles in the South Atlantic Subtropical Gyre, Professor Mincer and her colleagues found that abundances and distribution patterns of small and large microplastics varied geographically and vertically due to complex and diverse redistribution processes. 

“Small microplastics are different from large microplastics with respect to their high abundance, chemical nature, transport behavior, weathering stages, interactions with ambient environments, bioavailability, and the release efficiency of plastic additives,” explained study first author Shiye Zhao, a postdoctoral fellow at FAU. “These distinct characteristics impact their environmental fate and potential impacts on marine ecosystems.” 

Compared to larger microplastics, the smaller ones are more highly oxidized and seem to have a longer lifetime in the water column, suggesting increased risks for ocean ecosystems.

“As plastic particles disintegrate into smaller size fractions, they can become harmful in different and unpredictable ways that are only now beginning to be understood,” said Professor Mincer.

“These micron-size microplastics can move across the gut epithelium, become trapped in biomass, and have the potential to transfer through marine food webs, posing an unknown ecological risk and biogeochemical impacts.” 

Further research focusing on smaller microplastics ingestion by various animals are urgently needed in order to assess the extent of plastic contamination in biomass.

The study is published in the journal Global Change Biology.

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By Andrei Ionescu, Earth.com Staff Writer