Deep-Sea Plastic Debris Remains Intact After Decades

Much has been written about the fate of plastic debris on the ocean's surface. Battered by wind and wave action and exposed to sunlight, these plastics tend to break down into smaller pieces, resulting in the microplastic pollution that has become such a concern in recent years. But what happens when plastic falls straight to the ocean floor, without spending time on the surface? Less is known about this.

That is why scientists were pleased to recover two pieces of plastic debris from the bottom of the eastern Pacific Ocean, from a depth of 4,150 meters (13,615 feet), that they were able to tell had fallen straight to the bottom without being subjected to surface degradation of any kind. The items – a yogurt container and an aluminum Coca-Cola can with an Alitalia refreshment tissue enclosed inside a plastic grocery bag – had product information printed on them that allowed the scientists to estimate roughly when they were produced, sometime between 1988 and 1996. 

"We assume the deposition at the seafloor may have occurred within a matter of hours to days rather than weeks and that the polymers were subjected primarily to deep-sea conditions between discarding and retrieval, but have not been exposed to UV-light and wave action at the sea surface for prolonged times."

This allowed for a unique analysis of what happens to plastic when it stays at the bottom of the ocean for twenty years; this resulted in a study published in the journal Scientific Reports. The answer? Very little. Most of the plastic was fully intact, with almost no degradation or fragmentation. The scientists also analyzed the microbes that had grown on their surfaces over the years. From ScienceAlert:

"Even though the container and the bag were different shapes and were made from different types of plastics, their impact on the surrounding bacteria was the same; the scientists found the microbial diversity was much lower on the plastic than in the surrounding seafloor sediments."

The scientists wrote that bacterial growth was likely inhibited by hazardous chemicals leaching from the plastic over an extended period of time. This "presumably influenced the microbial surface community structure with regard to the number [of bacteria] and their distribution."

What does this research mean? 

It's helpful to know more about a substance that makes up 60 percent of ocean debris and how it behaves at various sea depths over different lengths of time. This is the first set of data to integrate the "fate and ecological function of plastic" over "more than two decades under natural marine deep-sea environmental conditions," which adds to the body of knowledge about ocean plastic pollution. It has shown that plastic items deposited on the deep-sea floor have "long-term environmental impacts creating artificial habitats with strong chemical gradients."

It is important to understand what happens to plastic because so much of it enters the world's oceans every year – an estimated 8 million metric tonnes. Next, the research team will be looking at where plastic goes, because much of it is still unaccounted for.

Read full study here.