According tomedia reports, the problem of plastic waste has become one of the world’s most concerned environmental issues. About 8 million tons of plastic waste enter the ocean each year. Yet what scientists can see and measure on dumps and beaches is only a fraction of the amount of plastic that enters the water. So where is the remaining 99% of marine plastic? Disturbing answers have recently begun to surface.
Erik Van Sebile, an oceanographer at the University of Utrecht in the Netherlands, says what we usually see is what accumulates at sea “less than the tip of the iceberg, probably 0.5% of the total”. “I often joke that it should be easy to be a marine plastics scientist, because wherever you are, you can find something,” says Van Sebille. But, he adds, the reality is that there is a lack of actual amounts of plastic in any one location. It is becoming increasingly clear that plastic eventually accumulates in large quantities in the deepest reaches of the ocean, buried in sediments on the ocean floor.
Helge Niemann, a biogeochemist at the Royal Netherlands Institute of Oceanography, said perhaps the most frightening thing was that it could break into tiny pieces that could be almost impossible to detect. At this point, Niemann says, it becomes “more like a chemical dissolved in water than a chemical floating in water.”
From the narrow estuary of San Francisco Bay to the open waters of Monterey Bay to the scenic mountains and the redwood forests of Big Sur, the 276-mile-long land boundary is the largest national marine reserve in the United States. It seems unspoiled for anyone visiting a beach near Santa Cruz or driving along a coastal road. But that’s not all.
For the past two years, scientists at the nearby Monterey Bay Aquarium Research Institute have been using custom-built remote-controlled submersibles to collect near-invisible plastic samples far below the surface of the water. “Just because you don’t see it doesn’t mean it doesn’t exist,” said Anela Choy, a professor of oceanography at the University of California, San Diego and lead researcher on the project. Beneath her so-called ocean “surface,” the submersible carefully filters the water and takes a snapshot of it.
Her team found that at a depth of 200 metres, there were nearly 15 pieces of plastic per litre of water, similar to the amount on the surface of so-called garbage blocks. The remote sampler still finds plastic at a maximum depth of 1 km. But this is only the beginning of the search. “After two or three years of effort, we have come up with the fact that we have only a set of samples from a part of the entire ocean of the world,” she said. “
The team’s work was one of the first to calculate the exact amount of plastic below the ocean surface and to show that plastic waste was abundant at lower depths. Scientists have speculated for years. Oceanographer Richard Thomson first coined the term “microplastic” in 2004 to describe hard-to-capture plastics less than 2 mm in length, and he believes large quantities of microplastics can be found in the deep sea and the sea floor.
In a paper published in 2017, Van Sebille’s team predicted that 196 million tons of plastic could sink from the surface to the deep ocean, based on the amount of plastic entering the ocean since 1950 and known ways of sinking. The researchers’ next plan is to show the source of the plastic and determine how it moves from a surface that is relatively easy to find and track to a depth.
Traditionally, it is difficult to trace marine microplastics back to their source. However, even small plastics do not necessarily look the same. By studying how lasers scatter when they encounter different pieces of plastic, researchers can create “fingerprints.” For example, the plasticfound found in Monterey Bay is different from the plastic used in local fishing equipment, but is mainly used in single-use packaging of polymer polyethylene glycol (PET), indicating that it may have come from land.
How plastic falls into the deep sea is largely a mystery. Choy’s team found two species of animals, red crabs and translucent, filter-fed creaturegiant sheetceans, which consume plastic and move them into deeper water. This has been observed in many species. A 2011 study looked at plastics in fish in the North Pacific, estimating that they consume about 12,000 tons of plastic each year. Van Sebille’s team pointed out in a later paper that if the plastic was preserved throughout the ocean, 100,000 tons of plastic could be placed in animals at any time.
The search for missing offshore plastics has opened up new research areas. Ten years ago, the discovery of microplastics led to a fundamental shift in the concept of plastic pollution. Scientists have found that billions of pieces of plastic are almost invisible, absolutely never caught, and easily eaten by the smallest marine organisms. Now they have made amazing new discoveries about the extent of plastic contamination.
Alexandra Ter Halle, a researcher at paul Valeri University in Montpellier, France, last year sat on a sailboat and took water samples from the River Thames. It was the first time it had visited 10 European estuaries, and other scientists on board were doing familiar work, counting microplastic particles with microscopes and identifying the bacteria in the sample.
However, Ter Halle had to return to her university before she could study the samples, where she had the special equipment to detect that nanoplastics – nanoplastics – the size of which had been broken down to less than one thousandth of a millimeter, less than a unit. Two years ago, her team was the first to find these particles in seawater. Ter Halle uses techniques similar to forensic scientists’ detection of chemicals at crime scenes: igniting samples into gases, bombarding them with electrons, and then separating them in electric fields to measure their weight and charge. They are often not visible and can only be detected.
Nanoplastics research is still in its infancy. But laboratory tests have shown that, unlike microplastics, nanoplastics are small enough to accumulate in the blood flow and cell membranes of various organisms, and even pass through the blood-brain barrier when testing Japanese fish, and can cause toxic effects, including nerve damage and reproductive abnormalities.
“It’s about the location of all the plastic in the ocean… For 40 years, we’ve been looking for plastic that can be seen. Now that we have reached a very special, very responsive nanoscale, we have to start over. Ter Halle said.