Quantification and characterization of microplastics in the Thermaic Gulf, in the North Aegean Sea

The abundance and distribution of microplastics has largely increased during last years and the respective implications on the environment and human health is an emerging field in research. In addition, recent studies in the enclosed Mediterranean Sea in Spain and Italy have shown an extended occurrence of microplastics (MPs) in different sediments of environmental samples. This study is focused on the quantification and the characterization of MPs in the Thermaic Gulf in northern Greece. Briefly, samples from different environmental compartments such as seawater, local beaches and seven commercially available fish species collected and analyzed. MPs particles extracted and classified by size, shape, colour and polymer type. A total of 28,523 microplastic particles recorded in the surface water samples, with their numbers ranging from 189 to 7714 particles per sample. The mean concentration of MPs recorded on the surface water was 1.9 ± 2 items/m³ or 750,846 ± 838,029 items/km². Beach sediment sample analysis revealed 14,790 microplastic particles, of which 1825 were large microplastics (LMPs, 1-5 mm) and 12,965 were small microplastics (SMPs, <1 mm). Furthermore, beach sediment samples showed a mean concentration of 733.6 ± 136.6 items/m², with the concentration of LMPs being 90.5 ± 12.4 items/m² and the concentration of SMPs being 643 ± 132 items/m². Concerning fish deposition, microplastics were detected in intestines and mean concentrations per species ranged from 1.3 ± 0.6 to 15.0 ± 1.5 items/individual. The differences in microplastic concentrations between species were statistically significant (p < 0.05) and showed that mesopelagic fish contained the highest concentrations, followed by epipelagic species. The most common size fraction found in the data-set was 1.0-2.5 mm, and polyethylene and polypropylene were the most abundant polymer types recorded. This is the first detailed investigation of MPs in Thermaic Gulf, which raises concerns on their potential negative effects.