Abstract
The composition, size distribution, and abundance of floating plastic debris in surface waters of the Mediterranean Sea were analyzed in relation to distance to land. We combined data from previously published reports with an intensive sampling in inshore waters of the Northwestern Mediterranean. The highest plastic concentrations were found in regions distant from from land as well as in the first kilometer adjacent to the coastline. In this nearshore water strip, plastic concentrations were significantly correlated with the nearness to a coastal human population, with local areas close to large human settlements showing hundreds of thousands of plastic pieces per km2. The ratio of plastic to plankton abundance reached particularly high values for the coastal surface waters. Polyethylene, polypropylene and polyamides were the predominant plastic polymers at all distances from coast (86 to 97% of total items), although the diversity of polymers was higher in the 1-km coastal water strip due to a higher frequency of polystyrene or polyacrylic fibers. The plastic size distributions showed a gradual increase in abundance toward small sizes indicating an efficient removal of small plastics from the surface. Nevertheless, the relative abundance of small fragments (< 2 mm) was higher within the 1-km coastal water strip, suggesting a rapid fragmentation down along the shoreline, likely related with the washing ashore on the beaches. This study constitutes a first attempt to determine the impact of plastic debris in areas closest to Mediterranean coast. The presence of a high concentration of plastic including tiny plastic items could have significant environmental, health and economic impacts.
Highlights
The quantity of plastic entering the ocean from waste generated on land has been recently estimated as on the order of millions of tons per year [1]
It seems that the fragmentation of large plastic manufactured objects was the main source of microplastics
We show a coherent large-scale pattern, spanning from hundreds of meters to hundreds of kilometers for the distribution of floating plastic debris in the Mediterranean Sea in spite of the high spatial heterogeneity at small scales
Summary
The quantity of plastic entering the ocean from waste generated on land has been recently estimated as on the order of millions of tons per year [1]. Several surveys have shown the global scale of the marine plastic pollution, with large accumulations of floating debris in distant offshore regions of surface water convergence [6,7,8,9,10]. Maritime activities can scatter important amounts of plastic waste over the sea and it seems evident that a fraction of the marine floating debris can be moved onto the coasts by wind and waves [11]. The distance from coast can be regarded as a proxy of the time at sea of the plastic [12], and the changes in abundance, size or composition of floating plastic debris could help to understand the processes controlling distribution of the plastic pollution in the surface waters
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