Microplastics Discovered in 150-Year-Old Sediments 7,000 Feet Beneath the Ocean Surface

Researchers have discovered microplastics buried in seabed sediments deep below the ocean surface that are more than 150 years old.

The team identified the tiny plastic pieces in core samples collected from the Rockall Trough—a deep-sea basin located to the northwest of Scotland in the North Atlantic.

Led by Winnie Courtene-Jones from the Scottish Association for Marine Science, the scientists examined the sediments—taken from more than 7,000 feet below the ocean surface—in order to reveal the extent and quantity of microplastics within them.

They documented the microplastics throughout the upper 10 centimeters [3 inches] of the sediment core, according to a study published in the journal Marine Pollution Bulletin.

Finding the plastics in these samples initially left the scientists baffled, given that this group of materials was not mass-produced until the mid-20th century.

"We found microplastics were distributed throughout the sediment cores, up to 10 centimeters below the seafloor, which was the deepest we analyzed," Winnie Courtene-Jones told Newsweek.

"It was very surprising to find microplastics so deep. The layers of sediment down to 4 centimeters [around 1.5 inches] deep were around 150 years old, yet microplastics were found throughout the core. Plastics were only mass produced in the 1940s and 1950s, so, therefore, based on this discovery, we found plastics were present in the sediment long before they were mass-produced."

In the study, the researchers propose a number of mechanisms for how the microplastics could have ended up in the 150-year-old sediments.

"Microplastics enter the marine environment from surface waters, either through the fragmentation of larger plastic items, or directly through the synthetic fibers which are shed from our clothing during washing," Courtene-Jones said. "Gradually the microplastics sink from surface waters through the ocean until they reach the seabed."

"Our findings that microplastics were present in sediments dating from long before mass plastic production indicate that processes within the seafloor might redistribute the microplastics deeper. Burrowing worms live in the seabed and can draw plastics deeper inside their burrows. Another mechanism is that microplastics can move between gaps, so-called pores, within the sediments and so the microplastics can move into deeper layers this way," she said.

Microplastics—tiny pieces of plastic measuring less than 5 millimeters across, according to the most recognized definition—are widely distributed throughout the marine environment, having been documented everywhere from the seafloor to the surface waters of the Arctic.

plastic pollution
Stock image: Artist's illustration of plastic pollution in the ocean. iStock

In fact, earlier this year scientists even announced the discovery of a new species of marine animal in the deepest trench on Earth, which was found to have microplastics in its body.

However, most studies into this form of pollution have focused on beaches and coastal areas, meaning the global extent of microplastics on the deep seafloor remains largely unknown. Thus the findings of the latest study could help scientists to build a better picture of microplastic pollution.

"The findings of this research indicates that microplastics can move through sediments in ways we did not know before," Courtene-Jones said. "This has implications for understanding the fate of plastics in our environment. Also microplastics could alter the properties of the sediments and cause harm to the organisms living in them."

"Other work has shown plastics can have detrimental impacts to animals, such as reducing their ability to feed and reproduce. The deep sea floor has been little studied in terms of plastic pollution, and our work indicates it could be an important accumulation site for microplastics,' she said.

The latest study builds on previous research that Courtene-Jones and colleagues conducted more than two years ago.

"In 2017, my research found microplastics contained within deep ocean water and that starfish and sea snails living on the ocean floor, over 2,000 meters deep had been eating microplastics. What's more, using historical specimens microplastics were found inside the guts of animals dating all the way back to the 1960s," she said.