Estimation of the quantity of plastics entering to the Caspian Sea and investigation of microplastics distribution in southern coasts sediments

Abstract

Background: It has been proven that there is an extensive bulk of plastic debris in marine ecosystems, that it is considered a global problem. But the estimation of the quantity of plastics entering the Caspian Sea and investigation of microplastics (MPs) distribution in southern coasts sediments, not specified yet. Therefore, the aim of this study estimates the plastic waste Input to the Caspian Sea and is an investigation of MPs distribution in its southern coasts sediments. Methodology: This study consists of two sections. The first part is the estimation of the quantity of plastic waste entering the Caspian Sea, which in this section, first, the trend of plastic waste production in northern Iran was examined. Then the quantities and quality of municipal waste produced, and also the management and final disposal of waste in the Caspian littoral states (Iran, Russia, Kazakhstan, Turkmenistan, and Azerbaijan) were investigated. In the next step, the quantity of plastic wastes that are mismanaged was determined. Then, using three assumed conversion rates (15%, 25%, and 40% of plastics that are mismanaged and therefore have high potential to enter the marine ecosystem) the amount of plastic waste Input to the Caspian Sea was estimated.In the second section of this study, the distribution of MPs in the sediments of the southern coast of the Caspian Sea was investigated. First, three separate areas (recreational-tourism areas [24 samples], non-tourist areas [24 samples], and the estuary of rivers [17 samples]) were selected for sampling. Sampling was performed from two different depths (0-5 cm and 5-15 cm). Generally, the number of 130 samples was taken according to the method presented by the National oceanic and atmospheric administration (NOAA) and was analyzed. To identify and analyze MPs the techniques including density separation (using NaCl and ZnCl2), method of digestion (using H2O2 30%), observational (with the unaided eye and using an optical digital microscope), polymer type determination (by FTIR), and determination of surface morphology of MPs (by SEM) was applied. Results: The study results of the trend of plastic waste production in northern Iran showed that the annual growth rate of plastic waste in the north of the country is on average 0.535 percent. On average, about 90% of waste in the Caspian Sea countries is managed inadequately and incorrectly. The amount of plastic waste generated by the Caspian Sea littoral states (Iran, Russia, Kazakhstan, Turkmenistan, and Azerbaijan) in 2016, were obtained about 425 kt, that of this amount about 58-155 kt was able to enter the sea.The average number of MPs on the sediments of the recreational-tourism, nonuse (non-tourism) areas, and the estuary of the rivers were obtained 227.1±173.8 and 139.9±120.7 and 350.6±232.6 MP/kg, respectively. In the present study, eight polymer groups were identified in the studied samples, that included PE (20%), PET (18%), PP (16%), PS (16%), EPS (12%), LDPE (6%), HDPE (4%), PVC (2%) and other (6%). Also in terms of shape, the MPs found in the sediments included fragments (30%), fibers (26.5%), foams (23.1%), and films (20.4%). Conclusion: According to the results of this study, plastic wastes input to the sensitive ecosystem of the Caspian Sea is increasing. On the other hand, MPs are present in all samples collected from the southern coasts of the Caspian Sea. Most of the plastics entering the marine ecosystem derive from rivers and this has probably led to a high accumulation of plastic particles in the estuarine sediments. In terms of polymer type, the most dominant MPs identified on the southern coasts of the Caspian Sea were PE. In the plastics industry, the highest volume of consumption of plastics is in the packaging part, and PE is the most used in the packaging industry. Therefore, it is possible that the abundance of PE in the sediments of the southern coasts of the Caspian Sea has been high. In terms of shape, most MPs identified on the southern coasts of the Caspian Sea are related to the fragments. Given that fragment-shaped MPs are derived from both primary and secondary MPs, it is likely that the abundance of this type of MPs are higher than other MPs found in sediments.

Keywords: Caspian Sea, Plastic, Microplastics, Sediment