Plastic pollution in the planet’s oceans is bad, which is hardly news. Yet it is far worse than commonly assumed, say scientists at the National Oceanography Centre in the United Kingdom.

The researchers, who have published their findings in a new study, say that there is up to 21 million tons of tiny plastic particles of the three most common types of plastics near the water’s surface across the Atlantic ocean.

“The combined mass of just the three most-littered plastics (polyethylene, polypropylene, and polystyrene) of 32–651 µm size-class suspended in the top 200 m of the Atlantic Ocean is 11.6–21.1 Million Tonnes,” the scientists explain. “Considering that plastics of other sizes and polymer types will be found in the deeper ocean and in the sediments, our results indicate that both inputs and stocks of ocean plastics are much higher than determined previously,” they stress.

In all, the amount of plastic particles in the Atlantic ocean as a whole is estimated to be at least 200 million tons, which is 10 times more than previous estimates had it, based on the calculations of plastic waste floating around in waters in coastal areas.

“Previously, we couldn’t balance the mass of floating plastic we observed with the mass we thought had entered the ocean since 1950. This is because earlier studies hadn’t been measuring the concentrations of ‘invisible’ microplastic particles beneath the ocean surface. Our research is the first to have done this across the entire Atlantic, from the UK to the Falklands,” explains Katsiaryna Pabortsava, a scientist the National Oceanography Centre.

She and her colleagues collected larger amounts of seawater from 12 different locations in the the Atlantic between September and November in 2016. They then filtered the samples and employed spectroscopic imaging to see how many microscopic particles of polyethylene, polypropylene and polystyrene they contained. They found that each cubit meter of seawater had as many as 7,000 particles of these three types of microplastic waste.

“[I]f we assume that the concentration of microplastics we measured at around 200 metres deep is representative of that in the water mass to the seafloor below with an average depth of about 3000 metres, then the Atlantic Ocean might hold about 200 million tonnes of plastic litter in this limited polymer type and size category. This is much more than is thought to have been supplied,” explains Prof. Richard Lampitt, another author of the study who likewise works at NOC.

Another study has recently found that microplastics accumulate in vast quantities even on the seafloor. A team of scientists behind it discovered that up to 1.9 million pieces of plastic have formed in a thin layer within just 1 square meter at certain spots on the seafloor, making for some of the highest levels of microplastic contamination ever recorded in seawater.

The situation is hardly better near the surface, Pabortsava observes. “There is an awful lot of very, very small microplastic particles in the upper Atlantic ocean, much higher than the previous estimate,” she says. “The amount of plastic has been massively underestimated.”

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