Ocean floor a ‘reservoir’ of plastic pollution, study finds

Researchers have taken a deep dive into plastic pollution, and found up to 100 times more of the synthetic material blankets the ocean floor than floats on the surface.

Alice Xia Zhu, a PhD candidate from the University of Toronto who led an international study, said earlier studies have focused more on the plastic floating on the surface but over the decades tonnes of plastic have drifted down to the bottom, and their research shows the amount is significantly higher than previously thought.

“When it accumulates on the ocean floor, there is a potential threat to sensitive ecosystems,” said Zhu in an interview. It can also interfere with the ocean’s capacity to absorb and sequester carbon dioxide, which could accelerate the climate crisis.

Zhu, along with researchers at CSIRO, Australia’s national science agency, used data from remote operated vehicles and from bottom trawls. From this data they estimated there is between three and 11 million metric tonnes of plastic residing on the ocean floor. That’s up to 100 times more plastic on the bottom of the sea than floating on the surface, she said.

The study was published this week in Deep Sea Research Part 1: Oceanographic Research Papers.

While she wasn’t surprised to find there was more on the ocean floor, she was startled by the enormous amount of plastic trash.

“It was definitely a shocker because no one wants to see that much plastic ending up in our oceans,” said Zhu, adding that every minute the equivalent of a full garbage truck of plastic enters the ocean.

“The ocean is really becoming a big trash pit for our waste and that’s not a good finding.”

Most of the plastic rubbish comes from derelict fishing gear but also from plastic bottles, bags and other disposable items, she said .

The data also show much of the plastic clusters around continents, with nearly half (46 per cent) of it residing above 200 metres, said Zhu. The remainder was found as deep as 11,000 metres.

“People living on land are the main sources of plastic to the environment. So a lot of this plastic is just clustered around where we live,” she said.

Zhu said the study adds to the growing research about the damage that plastic is doing to the marine environment. Scientists are trying to figure out how much plastic is ending up in marine animals’ stomachs and which ecosystems are most at risk.

Last year, an international team of scientists, including researchers from B.C., discovered disturbing levels of microplastics in Antarctica, one of Earth’s most remote ocean regions. They found the tiny plastic particles in every water sample collected. And earlier this year, UBC and Ocean Wise scientists found that plastics can harm or even kill zooplankton, reducing a food source for many types of fish, including salmon.

Studies have also shown that plastics are harming the gut biomes of seabirds, and are prevalent in Galápagos Islands penguin prey.

“The statistics are shocking. Just how much waste we produce on a daily basis. We all need to work together — people, communities, industry, government to really tackle this issue,” said Zhu, adding one idea that is on the table is a global plastic tax.

“The burden can’t all be on consumers, it has to be on industry as well.”