Contamination of the Caspian Sea Southern coast sediments with microplastics: A marine environmental problem

Marine ecosystem pollution with microplastics (MPs) is a global problem. The current study aimed to assess the occurrence of MPs in the sediments of the Caspian Sea southern coasts. For sampling, two distinct areas were selected including recreational-tourism areas (No = 24), and non-tourist areas (No = 24). MPs were studied in 5 and 5-15 cm from the top sediment surface. All 96 samples were taken and analyzed according to the methodology provided by the US national oceanic and atmospheric administration (NOAA). The combination of observational techniques, FTIR, and SEM analysis was applied to identify MPs. MPs were classified into two categories in terms of size: small MPs and large MPs. The average, maximum, and minimum abundance of MPs (based on dry weight) in sediments of the southern coast of the Caspian Sea was 183.5 ± 154.4 MP/kg, 542 MP/kg, and 13 MP/kg, respectively. On the basis of morphology, fragment-shaped (30.3%) MPs showed the highest prevalence, while film-shaped (18.7%) MPs were the least contributory. Polyethylene (PE) and polyethylene terephthalate (PET), each of them with a 20% share, were the most common MPs found in the studied samples. The distribution of MPs on the southern coasts of the Caspian Sea revealed a sporadic and irregular spatial pattern. Correspondingly, it can be concluded that probably environmental factors (the current of the sea surface water from west to east), enclosed environment of the Caspian Sea, anthropogenic activities (e.g., industrialization and urbanization, improper waste management, fishing, and tourism activity, residential wastewater), and also discharging of rivers (which can carry plastics) into the sea, have all influenced the abundance and polymer diversity of MPs in the sediments of the southern coast of the sea. More attention should be paid to the health and environmental effects of MPs and to the protection of this sensitive marine ecosystem through implementing proper waste management system by all surrounding littoral countries.