Plastic water bottles pollution in ocean on the shore

Study reveals ‘shocking’ amount of plastic in the Mediterranean

Image credit: Innak/Dreamstime

A new study suggests that around 3,760 metric tons of micro and macroplastic debris are currently floating in the Mediterranean Sea.

Researchers at the Hellenic Centre for Marine Research in Greece developed a model to track the pathways and fate of plastic debris from land-based sources in the Mediterranean.

The model performed a simulation over the period from 2010 to 2017, tracking plastics from rivers and coastal cities, while considering important dispersion processes such as sinking, vertical/horizontal mixing, wind, and currents.

According to the research team, the model also identified potential accumulation patterns of micro and macroplastics in the surface layer, water column, seafloor, and on beaches.

This revealed that the total annual plastic load going into the Mediterranean is approximately 17,600 tons, of which 3,760 tons are currently floating in the Mediterranean. Of the total, 84 per cent ends up on beaches and the remaining 16 per cent in the water column or the seafloor.

“Simulations of plastic distribution in marine environments are currently characterised by a large uncertainty. Experimental data on several processes that affect the fate of plastics, such as sinking, ingestion by marine organisms and fragmentation into smaller pieces are still quite limited,” said lead author Dr Kostas Tsiaras.

“Our model showed a reasonable skill in reproducing the observed distributions of plastics in the marine environment and thus can assess the current status of plastic pollution in the Mediterranean and evaluate the impact of future cleaning actions and management plans.”

The model also described biofouling as a potential mechanism for the removal of microplastics from the seawater surface. Biofouling happens when micro-organisms such as algae accumulate on floating and submerged objects, including plastic debris.

“Microplastics are less abundant on the sea surface because of their faster sinking from the attachment of heavier marine organisms (biofouling) and accumulate deeper in the water column and seafloor. On the other hand, macroplastics, such as plastic bags and styrofoam, may float around for longer time periods, and travel long distances from their sources,” said Tsiaras.

Sources of microplastics, such as wastewater treatment plants, were mainly found near metropolitan cities and heavily populated areas along French, Spanish, and Italian coasts, the research found. Larger sized microplastics were found in areas with high untreated wastewater, such as the coasts of Greece and Turkey.

According to the researchers, macroplastics were abundant in areas with important riverine input such as Algerian, Albanian, and Turkish coasts and close to metropolitan cities and the highly populated coasts of Spain, France and Italy.

Tsiaras said the model outputs can identify ecologically (bird and cetacean habitats) or commercially (aquaculture and fisheries) important areas that are potentially threatened by plastic pollution. “This is important for the design of ecosystem-based management plans and policies for the mitigation of plastic pollution, which is often a transboundary environmental problem, as floating plastics may travel long distances from their source.”

He warned that the social, political and cultural variety of inhabited countries along the coastline of the Mediterranean makes the implementation of a common marine ecosystem management policy difficult. But believes models such as the one from the study can help mitigate this problem.

"Using predictive models, like the one presented here, that can connect observed plastic concentrations with their sources, is critical for the designation of successful management plans,” he explained.

The Mediterranean Sea is considered a hotspot for plastic pollution because of its densely populated coastlines, fishing, shipping, tourism, and a limited outflow of surface water to the Atlantic. The Mediterranean is also rich in biodiversity, making it an area of concern for the conservation of marine ecosystems.

Plastic pollution affects all levels of marine biodiversity, with micro and macroplastic particles found at the sea surface, beaches, the seafloor and within the bodies of large and small marine animals. It has also been reported that humans ingest plastic through seafood consumption.

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