An In-depth Study of Meso- and Microplastics Contamination in Sediments of Southern Coasts of the Caspian Sea

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Abstract
Plastic products are essential materials that play critical roles in people's lives in the modern world. However, plastic pollution is a growing global challenge due to the fact that its durability and long life span make it a persistent problem. In the present study, we aimed to analyze the contamination of meso- and microplastics (MPs) through separation based on density differences in sediments from the southern coasts of Caspian Sea. We found that the plastic contents of meso- and MPs were 14-38 and 100-286 particles kg−1 dry weight (dw) sediments, respectively. The size of debris was detected in the range of 0.1-15 mm. The relationship between meso- and MPs, the distance to coastline was investigated. In general, there was no correlation between distance to coastline and the concentration of meso- and MPs in the sediments from the southern coast. The plastic particles had a high variety of colors, but they were mainly transparent, black and gray, respectively. Polyethylene (PE), polyamide (PA), polyethylene terephthalate (PET), polystyrene (PS), polypropylene (PP), polyurethane (PU), and polyacrylonitrile (PAN) were identified in the samples using FTIR analysis. Contrary to previous reports, more meso- and MPs were found in the west and east coasts sediment samples from the southern Caspian Sea basin. Our findings suggest that environmental conditions may play a more important role in the accumulation and distribution of MPs along the coasts of Iran. These findings provide new information to evaluate the environmental effects of MPs in future research.

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