Global plastic production has increased every year since the 1950s, with 368 million tonnes of plastic produced in 2019. A high proportion of these pollutants end up in seas and oceans, and estimates suggest that more than 250,000 tonnes of waste Plastics currently float in the world’s oceans. Now, a new study published in the journal Frontiers in Marine Science estimates that around 3,760 metric tons of micro and macroplastic debris would currently float in the Mediterranean Sea.
Plastic pollution hot spot
The Mediterranean Sea is considered a plastic pollution hotspot, due to factors such as its densely populated coastline, fishing, shipping, tourism, and limited surface water outflow to the Atlantic. At the same time, the Mediterranean is rich in biodiversity, which is why the conservation of its ecosystems is of concern to the scientific community.
Plastic pollution affects all levels of marine biodiversity, with micro and macroplastic particles found on the sea surface, beaches, the seabed, and within the bodies of large and small marine animals. In addition, humans are also known to ingest plastic through the consumption of shellfish.
The researchers, from the Hellenic Center for Marine Research (Greece), tracked the routes and the final destination of plastic in the Mediterranean Sea using a simulation that took data from the period 2010 to 2017, tracking plastics from land-based sources such as rivers and coastal cities, taking into account important dispersal processes such as subsidence, vertical / horizontal mixing, wind and currents. Potential patterns of accumulation of microplastics and macroplastics were also identified in the surface layer, the water column, the seabed and on the beaches.
The results revealed that the total annual load of plastics entering the Mediterranean is approximately 17,600 tonnes, of which 3,760 tonnes currently float in the Mediterranean. Of the total, 84% ends up on the beaches and the remaining 16% ends up in the water column or at the bottom of the sea.
“Simulations of plastic distribution in marine environments are currently characterized by a high degree of uncertainty. Experimental data on various processes that affect the fate of plastics, such as sinking, ingestion by marine organisms and fragmentation into smaller pieces, are still quite limited, ”explains lead author Kostas Tsiaras. “Our model showed a reasonable ability to reproduce the observed distributions of plastics in the marine environment and therefore can be used to assess the current state of plastic pollution in the Mediterranean and assess the impact of future clean-up actions and plans for management”.
The model also described biofouling as a potential mechanism for the removal of microplastics from the surface of seawater. Biofouling occurs when microorganisms such as algae accumulate on floating and submerged objects, including plastic debris.
Plastics distribution
Microplastics sources (such as sewage treatment plants) were found primarily near metropolitan cities and densely populated areas along the coasts of France, Spain, and Italy. Larger microplastics were found in areas with a high level of raw sewage, such as the coasts of Greece and Turkey.
Macroplastics were abundant in areas with important river contributions such as the Algerian, Albanian and Turkish coasts, and near metropolitan cities and densely populated coasts (Spain, France, Italy).
Management recommendations
“The results of the model can be used to 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 can travel long distances from their sources ”, explains Tsiaras .
Referencia: Tsiaras et al, 2021. Modeling the Pathways and Accumulation Patterns of Micro- and Macro-Plastics in the Mediterranean. Frontiers in Marine Science. DOI 10.3389/fmars.2021.743117
