Abundance and distribution of mesoplastics in the sediment of the southern coast of the Caspian Sea

The existence of plastic debris in the marine ecosystem is a global problem. In the present study, sediment samples were taken from three distinct areas, including recreational tourism areas (No = 24), non-tourist areas (No = 24), and the estuary of the rivers (No = 17). The sampling depth was 15 cm with an area of 20 × 20 cm (sampling volume was 0.006 m3). The combination of observational techniques and fourier-transform infrared spectroscopy (FTIR) was used to analyze mesoplastics. The abundance ranges of mesoplastics in the sediment of the recreational tourism areas, non-tourist areas, and the sediments of the estuary of the rivers were equal to 0–5, 0–3, and 0–9 (number of items per 0.006 m3), respectively. The dominant mesoplastics in the recreational tourism areas were expanded polystyrene (EPS) (33.3%), in non-tourist areas, low-density polyethylene (LDPE), and polypropylene (PP) (each one 22.7%), and the estuary of the river, PP (17.6%). On the basis of morphology, the dominant mesoplastics on the southern coast of the Caspian Sea in the recreational tourism areas, non-tourist areas, and sediments of the estuary of the river were the foam (37%), film (40.9%), and fiber (41.2%), respectively. Results from this study illustrate that the southern coasts of the Caspian Sea are a hotspot of the existence of plastic debris. Therefore, more attention to the protection of this sensitive marine ecosystem is recommended through implementing proper waste management systems by all surrounding littoral countries.