(700f) Microplastics Characterization and Impact on Small Fish of the Thermaic Gulf

Microplastics (MPs) are detected worldwide in the marine environment. Plastic production and use have increased steadily over the past 50 years, with global production reaching 335 million tonnes in 2016 (Plastics Europe 2015). Microplastics, because of their small size, can be transferred from the marine environment to organisms, and subsequently pass through the trophic transfer. Ingestion of microplastics has been documented in many seafood species from various places around the world, including fish, bivalves, and mussels (Toussaint et al. 2019). The primary uptake pathways of MPs in the most aquatic organisms are gastrointestinal tract and gills (Su et al. 2019). MP accumulation in aquatic organisms poses an emerging food safety concern. The human health effects depend on the actual exposure concentrations and migration pathways in human body. It is inevitable that humans’ exposure to microplastics depends on the levels of seafood consumption worldwide. Therefore, human health risks assessment associated to MPs daily intake represents an important issue for public health. Moreover, the ability of microplastics to accumulate toxic chemical compounds raises a serious concern over the transfer of hazardous compounds to marine animals and subsequently to humans. The aims of this study are (i) to quantify the number of microplastics with diameter range between 100 μm to 5 cm in beach sediments and surface water of Thermaic Gulf, (ii) to identify their spatial distribution and polymeric characterization and (iii) to investigate the presence of MPs in marine organisms. Moreover, the estimation of human daily exposure to MPs due to fish consumption was conducted.

The Thermaic Gulf is affected considerably by urban, industrial and touristic activities. Additionally, the pollution levels can be increased by the re-routing of four rivers to the Thermaic Gulf. The latter is an area constituting the northwest corner of the Aegean Sea. A total of 25 water surface samples were collected at 500 m, 5 km and 10 km distance from the coast during the winter (February - March 2018). Surface samples were collected using neuston net with cod end (300 μm mesh size). For beach sediment sampling, Box Corer grabs were used. In order to ensure representativeness of the samples, 126 samples were collected from five different collection points across the coastline of the Thermaic Gulf. Finally, a total of 75 fish were sampled from Thermaic Gulf. The examined fish species were, S. colias, T. trachurus, C. linguatula, B. boops, S. pilchardus, E. encrasicolus, S. maena. The total length and wet weight of fish was recorded. The gills and the gastrointestinal tract of each specimen were separated and weighted. For plastic particle analysis, samples were observed under a stereoscope with a LED light and measured with micrometer ocular lens. Plastic particles were characterized and classified by colour, size and shape. Additionally, the polymer fingerprint was detected using RAMAN spectroscopy, and the bioconcentration factor (BCF) was also estimated. The daily intake dose of MPs concentration in fish was calculated based on the assumption that the ingestion rate is 53 g/day and the body weight is 70 kg for adults and 16 kg for children.

A total of 20000 microplastics have been isolated from all 25 surface water samples, with a range of 190 to 6500 total particles per sample. The average concentration was 1.88 items/m³or 750,846 items/km², and the highest concentrations are found within a distance of 10km from the shore and in the area of Epanomi. The most predominant color is white and the most frequently found shape is fragment. The majority of microplastics have size between 1.0 - 1.5 mm. Regarding the beach sediments the average concentration was 28.67 items/m². Plastic fragments were found to be primarily isolated plastic particles.

Polyethylene (PE) and Polypropylene (PP) were the most abundant chemical species, a fact that was in accordance with literature findings, where these polymers account for the majority of the plastic particles floating in Mediterranean Sea. The examination of seven different fish species showed the negative consequences of the microplastics presence in aquatic ecosystems. In all examined fish, microplastics were found in gills and the gastrointestinal tract. The highest concentration was found in the C. linguatula population, 0.45 ± 0.11 items/g, while Trachurus trachurus had the lowest one 0.74 ± 0.5 item/g. Therefore, this indicates that the bathypelagic fish are the most affected in comparison with the mesopelagic and the epipelagic fish. In this case, the most predominant color was white and the most predominant shape was fiber. The presence of larger microplastics in fish's organism could suggest their further fragmentation and presence in edible parts of fish. The BCF values were higher in gills than in gastrointestinal tract with average estimates of 695 and 896, respectively, for MPs < 1000 μm, whereas the estimated BCF values for MPs < 100 μm for gills were 22. The estimated daily intake of MPs (< 500 μm) in the wake of fish consumption was 15.7 p/kg/body-weight/day for adults and 9.07 for children.

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. Given the significance of Thermaic Gulf's port and its morphological features that generate important quantities of waste originating from the South European counties the evaluation of plastics’ presence in Thermaic Gulf is mandatory to apply strategies to reduce the quantity of microplastics in its waters. The results showed a higher abundance of microplastics at 5-10 km distance from the coast. Analysis of the size distribution of microplastics in surface samples showed that in the whole dataset the most abundant size class was 0.5 - 1 mm, while for sediment it was 3.5 - 4 mm. Higher concentrations of MPs in GI tract and gills were observed in size class ranging between 500 μm to 1000 μm. The results revealed high values of BCF factor, indicating that the higher absorption occurs through gills. The Estimated Daily Intake shows the quantity of MPs ingested daily by fish consumption. Although there is no standard dose for MP ingestion and information on exact toxicity of different plastic types in the human body, the consumption of high daily doses can threaten the health of consumers.

REFERENCES

Plastics Europe (2015). Plastics – the Facts 2015: an Analysis of European Plastics Production, Demand and Waste Data: 30 pp.

Su, L., H. Deng, B. Li, Q. Chen, V. Pettigrove, C. Wu and H. Shi (2019). "The occurrence of microplastic in specific organs in commercially caught fishes from coast and estuary area of east China." J Hazard Mater 365: 716-724.

Toussaint, B., B. Raffael, A. Angers-Loustau, D. Gilliland, V. Kestens, M. Petrillo, I. M. Rio-Echevarria and G. Van den Eede (2019). "Review of micro- and nanoplastic contamination in the food chain." Food Additives & Contaminants: Part A 36(5): 639-673.