Our oceans are littered with plastic – this can be seen around the world. However, it is difficult to determine how great the level of pollution is now. Now, for the first time, researchers have examined the entire Atlantic from north to south for microplastics. The analyzes showed that 12 to 21 million tons of plastic particles of the three most common types of plastic swim around in the upper 200 meters of water alone. Most of this microplastic is smaller than 100 micrometers and therefore largely “invisible”. The scientists estimate that the true extent of plastic pollution could be far greater than previously thought.
Around 400 million tons of new plastics are manufactured worldwide every year – the majority of them for short-lived products such as packaging. As a result, most of it ends up in the garbage very quickly and also in the environment. Plastic bottles, bags and other plastic waste are now collecting in several huge garbage whirlpools in the Atlantic and Pacific. Many plastics cannot be biodegraded, but break down into smaller and smaller particles over time. This microplastic spreads with the ocean currents in almost all marine regions. Plastic remains can even be found in the Arctic and Antarctic, in deep-sea trenches and other remote areas. “The amount and distribution of this microplastic, especially below 250 micrometers, is almost unknown,” explain Katsiaryna Pabortsava and Richard Lampitt from the National Oceanography Center in Southampton. This is because so far mainly local samples and the water surface or the sediment have been examined. What is going on in the whole water column in between is in the dark.
Up to 7000 particles per cubic meter of water
To change that, the two researchers took part in the Atlantic Meridional Transect Expedition in 2016. Scientists sailed across the Atlantic from north to south and took measurements and took samples at regular intervals. During these stops, Pabortsava and Lampitt collected microplastic samples from three different depths with the help of special filter pumps: one in ten meters of water, one 10 to 30 meters below the lower limit of the mixed water zone and another around 100 meters below this layer boundary. Using special spectroscopic techniques, they then determined in the concentrated samples how many particles of the three most common plastics – polyethylene (PE), polypropylene (PP) and polystyrene (PS) – were contained in the water. Together, these plastics make up around 56 percent of global plastic waste, as the researchers explain. Their analytical method enabled them to detect particles as small as 25 micrometers.
As it turned out, there was no water sample in which no microplastic was found. “We detected PE, PP and PS at all stations, but the quantities and mass differed by several orders of magnitude depending on the location and water depth,” report Pabortsava and Lampitt. In most cases, the concentration of microplastics was highest in the uppermost water layer. There the density ranged from 990 to 6999 particles per cubic meter of water. This has been proven significantly more than in previous studies. Concentration usually decreased with increasing depth. As in the overall plastic waste, polyethylene was the most common in the water samples, followed by polypropylene and polystyrene. Contrary to expectations, however, the geographic distribution of the microplastics did not show any higher densities in the vicinity of the large garbage vortices. “We cannot yet explain why this is so,” the researchers said.
Too small for most sample methods
Another observation was very illuminating: As the measurements showed, most of the plastic particles were very small – the proportion of particles with a diameter of 50 to 80 micrometers was the largest. “This supports the assumption that smaller microplastics make up the largest proportion of ocean plastic waste,” say Pabortsava and Lampitt. However, it is precisely these very small particles that are usually not recorded with current sampling methods. “They are therefore not yet included in the estimates of plastic pollution in the oceans,” the researchers said. According to their evaluations, the Atlantic could contain 11.6 to 21.1 million tons of the three types of plastic examined in the size of 30 to 650 micrometers in the upper 200 meters alone. “If we assume that the microplastic concentrations we have measured are also representative for the water column down to the sea floor at a depth of around 3000 meters, then the Atlantic could contain a total of around 200 million tons of microplastic of this size and of these three types of polymer ”Says Lampitt.
However, it is more likely that contamination is lower in deeper water layers than in the upper ones. Nevertheless, in the opinion of the scientists, there will still be enough left to significantly exceed previous estimates. As they determined, the amount of microplastics in the Atlantic could then be between 17 and 47 million tons. “Our results suggest that both the inputs and the amounts of oceanic plastic are far higher than previously determined,” they state. At the same time, the study reveals that very small plastic particles floating below the surface of the water play a decisive role in contamination – not least because it is precisely this microplastic that can be easily absorbed by marine animals.
Source: Katsiaryna Pabortsava and Richard Lampitt (National Oceanography Center, Southampton), Nature Communications, doi: 10.1038 / s41467-020-17932-9