Plastic accumulation in the Mediterranean sea.

Andrés Cózar,Marina Sanz-Martín,J Ignacio González-Gordillo,José Á Gálvez,Carlos M Duarte,Bárbara Ubeda,Elisa Martí,Xabier Irigoien,Erik V Thuesen

doi:10.1371/journal.pone.0121762

Abstract

Concentrations of floating plastic were measured throughout the Mediterranean Sea to assess whether this basin can be regarded as a great accumulation region of plastic debris. We found that the average density of plastic (1 item per 4 m2), as well as its frequency of occurrence (100% of the sites sampled), are comparable to the accumulation zones described for the five subtropical ocean gyres. Plastic debris in the Mediterranean surface waters was dominated by millimeter-sized fragments, but showed a higher proportion of large plastic objects than that present in oceanic gyres, reflecting the closer connection with pollution sources. The accumulation of floating plastic in the Mediterranean Sea (between 1,000 and 3,000 tons) is likely related to the high human pressure together with the hydrodynamics of this semi-enclosed basin, with outflow mainly occurring through a deep water layer. Given the biological richness and concentration of economic activities in the Mediterranean Sea, the affects of plastic pollution on marine and human life are expected to be particularly frequent in this plastic accumulation region.

Highlights

Recent studies have demonstrated the existence of five large-scale accumulation regions of floating plastic debris in the oceans corresponding to each of the subtropical gyres located at either side of the Equator [1,2,3,4,5,6]
We found plastic debris in all surface net tows carried out in the Mediterranean Sea
We identify the Mediterranean Sea as a great accumulation zone of plastic debris

Summary

Introduction

Recent studies have demonstrated the existence of five large-scale accumulation regions of floating plastic debris in the oceans corresponding to each of the subtropical gyres located at either side of the Equator [1,2,3,4,5,6]. Ocean currents transport floating plastic released from terrestrial (e.g., coastal cities, rivers, and tourist beaches) and maritime (e.g., vessels, and at-sea platforms) sources to central convergence zones in the open ocean where these materials accumulate [7,8,9]. This process results in surface concentrations of buoyant plastic up to the order of kilograms (or millions of pieces) per km in the center of ocean gyres, while open-ocean concentrations outside the gyres only occasionally reach a few grams (or thousands of pieces) per km2 [1,2,3,4,5, 10, 11].

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Conclusion