More marine plastics than expected

Researchers led by Mikael Kaandorp from German FZ Jülich and colleagues from Utrecht University report that plastic pieces larger than 2.5 cm, which may persist longer than previously expected, made up nearly 95% of the global initially buoyant marine plastic mass in 2020 according to a modelling study published in Nature Geoscience. The findings are based on observational data from past decades (1980-2020) combined with a 3D model of the ocean.

Previously, it was estimated that 250 million kilograms (250 kilotons) of plastic pollution could be found on the ocean surface globally, but a much larger amount than this was predicted to enter the ocean on an annual basis. It had been suggested that this discrepancy is a result of an overestimation of the amount of plastic inputted from land and rivers, unknown processes removing large portions of this plastic from the ocean’s surface, or fragmentation and degradation.

To explore the cause of this discrepancy, Kaandorp and colleagues incorporated global observational data of plastic pollution into a numerical model that tracked how plastic particles moved through and were transformed in the ocean. The authors estimate that 3,200 kilotons of buoyant plastic were present in the ocean in 2020. Of this 470–540 kilotons of plastic entered the ocean in 2020, with approximately half coming directly from fishing activity and the rest from coastlines and rivers. They note that 95% of this floating plastic is larger than 2.5 centimetres, with microplastics making up only a small proportion in mass. The authors indicate that the relatively high total amount of plastic, but low inputs compared to previous estimates indicates there was no missing process removing ocean plastics; they instead suggest that the longevity or residence time of this type of plastic is high, with only 10% of the plastic likely degrading or sinking within two years.

The authors estimate that the input of buoyant plastic to the ocean is increasing by 4% each year and highlight the need for urgent action to reduce marine plastic pollution such as enzymatic recycling or circularisation of plastics production or replacement of persistent plastics that take 1,000 years to be mechanically shredded in the oceans such as polyethene, polystyrene, polyamides or polyethylene terephthalate by biodegradable alternatives.