(166d) Microplastic Environmental Effect on the Aquatic Ecosystem of the Thermaic Gulf

The aim of this study is to quantify the abundance of floating microplastics in sediments and surface water of Thermaic Gulf, Greece and to identify the spatial distribution of the microplastic particles and their polymeric characterization. Moreover, the frequency of occurrence of ingested microplastics in marine biota also was examined. Microplastics are now found worldwide in all aquatic compartments such as surface water, water column, and sediments (Ivar do Sul and Costa, 2014). Recently, it has been estimated that 5 trillion microparticles are floating globally, while up to 890,000 plastic particles/ km² were predicted in the Mediterranean surface waters. (Eriksen et al., 2014).

Thermaic Gulf is a gulf constituting the northwest corner of the Aegean Sea. The city of Thessaloniki is at its northeastern tip, and it is bounded by Pieria and Imathia on the west and the Chalkidiki peninsula on the east, with Cape Kassandra at the southeasternmost corner. It is about 100 km long. Water surface samples were realized during the winter (February–March 2018). A total of 25 samples were collected at 500 m, 5 km and 10 km distance from the coast. Surface samples were collected using neuston net with cod end (300 μm mesh size) equipped with a flowmeter and towed on the water surface at 2–3 knots for 20 min. At the end of the samplings, the nets were rinsed thoroughly from the outside to ensure that both plankton and debris were washed into the end of the net and to prevent any contamination by rinsing water. Organic matter attached to the surface of microplastics was removed to allow clear identification of the type of plastics, using a solution of 30% H₂O₂. For sediment sampling, boxcorer grabs were used and to ensure representativeness of the samples, at least five sample replicates (5 m between replicates) were collected. Density separation of microplastics were carried out with a Munich Plastic Sediment Separator. After separation and purification, target microplastics were sorted from the remaining matrix. Large plastics were sorted out directly, while smaller-sized ones needed further observation under a dissection microscope. For plastic particle analysis, samples were observed under a stereo-microscope with a LED light and measured with micrometer ocular lens. Plastic particles were characterized and classified by colour, size and shape. The particles were dried at room temperature and weighted in analytical balance. Additionally, the polymer fingerprint was detected using Fourier Transform Infrared (FT-IR) spectroscopy.

A total of 15 sea bass was sampled from Thermaic Gulf. The fish were collected during the winter of 2018. The total length (TL) and total wet weight (TWW) of fish were recorded. The fish were stored at −20 °C prior microplastic detection. Also, the tissues from sea bass were analyzed.

A total of 1200 microplastics have been isolated from all 25 surface water samples, with a range of 13 to 520 total particles per sample. The minimum concentration was 13752 particles/km² and the maximum was 420513 particles/km². Regarding the sediments the minimum concentration was 0.02 MPs / g dry sediment and the maximum was 0.1 MPs/g dry sediment. Analysis of the size distribution of microplastics in surface samples showed that the most abundant size class is 1–2.5 mm both in the whole dataset. This finding suggests a potentially higher hazard or zooplankton organisms (Fossi et al., 2012). Plastic fragments were found to be primarily isolated plastic particles. Polyethylene (PE) and Polypropylene (PP) were the most abundant chemical species, in good agreement with the literature where these polymers account for the majority of the plastic particles floating in Mediterranean Sea. The results showed a higher abundance of microplastics at 5-10 km distance from the coast. Microplastics were also detected in in the guts, skin and muscles of sea bass collected at an amount that ranged from 0.08 g^-1 to 1.1 g^-1.

This study reports the results of a monitoring campaign of microplastics in three different media. These data represent the first attempt to present the current state of microplastics in the Thermaic Gulf and to establish the baseline level for a future study. Being a Thermaic Gulf an important port within the European countries and because of its morphological features generate important quantities of waste originating from the South European counties so the evaluation of the presence of plastics is mandatory to apply strategies to reduce the quantity of microplastics in Thermaic Gulf.

REFERENCES

ERIKSEN, M., LEBRETON, L. C. M., CARSON, H. S., THIEL, M., MOORE, C. J., BORERRO, J. C., GALGANI, F., RYAN, P. G. & REISSER, J. 2014. Plastic Pollution in the World's Oceans: More than 5 Trillion Plastic Pieces Weighing over 250,000 Tons Afloat at Sea. PLOS ONE, 9, e111913.

FOSSI, M. C., PANTI, C., GUERRANTI, C., COPPOLA, D., GIANNETTI, M., MARSILI, L. & MINUTOLI, R. 2012. Are baleen whales exposed to the threat of microplastics? A case study of the Mediterranean fin whale (Balaenoptera physalus). Marine Pollution Bulletin, 64, 2374-2379.

IVAR DO SUL, J. A. & COSTA, M. F. 2014. The present and future of microplastic pollution in the marine environment. Environmental Pollution, 185, 352-364.