Background and Objectives: The abstract is one of the most important parts of a paper. The abstract must be presented on a Plastic products have a growing trend in the world due to ease of production, flexibility, strength and economic efficiency. These products are used in a wide range of industries, including construction, automobiles, marine industries, aerospace, electricity and electronics, transportation, medicine and pharmaceuticals, cosmetics, paints, agriculture, home appliances, etc. It can be said that today, plastic has become a part of human life, and no one can claim that who don’t related to plastic on a daily basis. This is illustrated that our environment is facing a huge amount of plastic pollution in air, soil and water. Also this concern is exacerbated by the slow rate degradation of these compounds in nature. The presence of compounds such as phthalates and bisphenols in the structure of plastics, that their carcinogenic effects and hormonal disorders have been reported in humans, can also intensify human concerns in the public health along with environmental issues. Scientists attempts to control the unbridled expansion of plastics in the environment, by changes in the chemical structure of them into biodegradable forms, finding alternative products, and also categorizing main sources of contamination. The largest enclosed water body of the Caspian Sea, with its unique sturgeon fish species and fragile ecological conditions, is one of the most important habitats. Due to the growing trend of development in the surrounding countries of the Caspian Sea, microplastic pollution is increasing in this ecosystem. Owing to ecological importance of this habitat, the present study was conducted on the southwestern shores of the Caspian Sea in the province of Guilan

Methods: In this study, sampling of surface sediments from the southwestern coastlines of the Caspian Sea was performed at 13 stations in September and October 2016.  About 3kg of Sediment samples were collected from the surface section of 0-5 cm at each station.  After dewatering, the samples were dried at 60 ° C and then passed through a sieve with a 5 mm mesh for homogenization. In order to separate the microplastics from the sediment samples, a two-step extraction method based on density was done by two saturated solutions prepared from NaCl and NaI. Number of fragments, shape and color separation of microplastics were performed using stereo microscope. The Fourier transform infrared spectroscopy device was also used to identify the chemical structure of microplastics.
Findings: A total of 909 microplastic fragments were obtained from sediment samples of the region. The results showed that the amount of microplastics in tourist and commercial centers such as Astara, Bandar Anzali, Caspian free zone and Chamkhaleh regions were more than other stations. Studies have demonstrated that in terms of shape, microplastics separated in three categories including: filaments, disintegrating fragments and membranes. The consequences of spectroscopy demonstrated that the microplastics in the study area are composed of 4 different types of polymers: polyethylene, polypropylene, polyester and polystyrene. The outcomes also displayed that the average microplastic particle size is 1.43 ± 1.06 mm in the region.
Conclusion: According to the results, commercial and tourist sectors have a major role in the spread of micro-plastics in the study area. The continued use of fishing nets and plastic ropes in the fishing industry are other sources of this type of pollution in the region.  Among the collected samples, microplastics with polyethylene structure had the highest amount between the groups of polyester, polypropylene and polystyrene. This, illustrates the use of large amounts of plastic bags and bottles in tourist areas has important role in increasing of this type of polymer. The small size of microplastics, in addition to greater ability to be swallowed by aquatic animals, also shows their extraordinary potential as a substrate for the absorption of other pollutants.