This paper is the first to report on the role of a wastewater treatment plant (WWTP) in Sari, as a source of microplastics (MPs) in the Caspian Sea. Composite 270-liter/24-hour samples were taken the treated effluent of the WWTP in winter and spring, two seasons with different levels of human activity. The effluent contained 380±52.5 and 423±44.9 MPs/m3 in winter and spring, respectively, with the total numbers of MPs/m3 not differing between the two seasons. The dominant type of MPs in the effluent was microfibers with 237±68.7 and 328±33.4 per m3 in winter and spring, respectively. In both seasons, fiber sizes of

This paper presents concentrations and sources of Aliphatic and Aromatic Hydrocarbons in the sediments from Babolsar coastal area and the inlet of Babolrood River in the southern side of the Caspian Sea. The concentration of hydrocarbons in 13 sediment samples from the study area were measured by gas chromatography (GC). Total Petroleum Hydrocarbon (TPH) concentrations in sediment samples in the coastal area ranged from 115 to 201 μg/g. In the inlet samples, TPH concentrations were close to each other and ranged from 294 to 367 μg/g. The TPH results showed moderate level of oil pollution in the study area. Total Polycyclic Aromatic Hydrocarbons (ΣPAHs) concentrations in sediment samples inside the inlet ranged from 498 to 702 ng/g, indicating moderate level of pollution. Concentrations of ΣPAHs in sediment samples in the coastal area ranged from 341 to 1703 ng/g, indicating moderate to less than significant level of pollution. Developed indices for pollutant origins showed that hydrocarbons in all sediment samples collected in the study area had petrogenic origin. The results also showed the Babolrood River as the main source of oil pollution in the sediments in the study area.

The present study aimed to reveal correlations between environmental events and geochemistry variation and ecological risks of the coastal Tajan River. Sediment quality indices (Cf, Cd, Er, and RI) were applied to achieve the research objectives based on the concentration of toxic metals (As, Cd, Cr, Cu, Ni, Pb, Zn). The probably effective level is based on the concentration of As, Cr, and Ni observed. The coastal zone and the urban sector of the river have experienced a moderate ecological risk since 1975, especially during wet seasons (1988–1997) with a mean sedimentation rate of 2 cm/year. A significant correlation (r=0.439–0.633, p-values < 0.0001) between the toxic metal concentration and the Caspian Sea level fluctuation was obtained. The lowest concentration of toxic metals coincided with the high stand water level. Management practices recommend controlling toxic metals (As, Cd, Ni, Cr, Pb) from the sources and dredging of retention pounds along the Tajan River.

Given the increase in plastic production, persistence, and toxicity in the environment, understanding the probability of microplastics (MPs) accumulation in the sediments of the rivers' estuary is urgently needed. In this study, sediments of the estuary of 17 rivers, ending to the Caspian Sea, were evaluated at two depths (0–5 cm and 5–15 cm). Plastic particles were categorized into two groups in terms of size: small MPs and large MPs. The combination of observational techniques, FTIR, and SEM analysis was applied to identify MPs. The mean of MPs in 17 rivers was obtained at a depth of 0 to 15 cm of sediments 350.6 ± 232.6 MP/kg. The fiber was identified as the predominant particles in sediments, and foam-shaped particles were the least amount in the sediment. In terms of polymer structure, polyethylene (PE) (20%) and polyvinyl chloride (PVC) (2%) showed the highest and lowest prevalence, respectively. In the current study, the number of MPs was higher than the average of MPs in sediments of recreational-tourist areas and non-tourist areas of the southern Caspian coast. Results from this study indicate that sediments of the rivers' estuary are a hotspot of plastic particle pollution. Therefore, plastic management in the path of the Caspian catchment area of Iran, and cleaning rivers coast and rivers mouth from plastic is recommended.

The occurrence of microplastics (MPs) in nearshore zones of the southern Caspian coasts is well documented; however, no data are available on MP occurrence in offshore sediments. In this study, six sandy beach stations and 18 inshore-offshore stations (six transects) were surveyed. MPs were detected in all sediment samples. The mean abundances of MPs in the beach and inshore-offshore stations were 196.67 ± 11.58 and 103.15 ± 7.21 MPs/kg, respectively. Fibers constituted the most common shape of MPs. Polystyrene (PS) and polyethylene terephthalate (PET) were the major polymer types found in the beach and inshore-offshore sediments, respectively. In most transects, negative MP gradients were observed from nearshore to offshore, which showed that coastal fishing, tourism, and rivers were the main sources of MPs in this area. These results will improve our understanding on MPs pollution in the marine ecosystem. We recommend further MP studies in different parts of the Caspian Sea to develop appropriate management programs.

This study assesses the frequency, distribution, characteristics, and chemical composition of microplastics (MPs) in the gut of highly consumed fish species, namely leaping mullet (Chelon saliens), common carp (Cyprinus carpioi), and Caspian kutum (Rutilus caspicus), in the southern Caspian Sea biome. Fibers are found to be the only shape of MPs. Black MPs and polystyrene, polypropylene, and polyethylene terephthalate polymers are dominant. MP frequency is highest in leaping mullet's gut, while kutum specimens exhibited the lowest MP frequency, reflecting that leaping mullet is a neritic species and thus highly exposed to MP influx in shallow coastal water, while the other species are benthopelagic. The estimated condition index reflected a significant difference between the species, implying that MPs may pose adverse health impacts on leaping mullet and common carp, with no undesirable effect on Caspian kutum. No significant relationship exists between biological parameters and the MP frequency in the fish gut.

Microplastic pollution is a growing, yet poorly understood problem. Here, we assessed the relationship between microplastic concentration and distance to rivers, shorelines, cities, sediment grain size or water depth in sediments of the world's largest (semi-)enclosed aquatic basins. Microplastic was extracted from sediment using density separation, elutriation and hydrophobic adhesion. Fibers and transparent or white microplastic particles were the most abundant shape and color. The microplastic concentration in sediments of the Black Sea was about twice as high compared to that in the Caspian Sea. Fragment concentrations decreased with depth, while fiber concentrations were independent of depth. Overall, no relationship with distance to shores, rivers and cities or with grain size was observed. However, within some depth classes concentrations were related to the distance from rivers, shores and cities.

This study aims to inspect the oil spill propagation in the Caspian Sea using Sentinel-1 data as well as wind and observation data. Detection processes clearly show that although the north and middle basin are the main sources of oil pollution, the southern basin would be the final destination of these oil slicks. Comparison of oil spill clusters in the southern and on the Apsheron indicates that the size of these clusters decreases under the physical process of the southern basin like eddies. Further, the mixed layer is estimated at 25–35 m in the southern basin. After applying the analytical formulas, the eddy diffusivity profile is plotted, leading to an estimate of nearly 5 × 10⁻⁴ m²/s on the surface water. The droplet oil diameters are calculated which vary from 150 μm to 250 μm based on an analytical model in a steady-state mode.

Southern parts of the Caspian Sea have been faced with a diverse range of oil pollutants. Therefore, this study was designed to evaluate the effects of relevant environmental concentrations of benzo[α]pyrene (BαP) on liver, gill, and blood of Caspian White fish. To this end, 150 fingerling fish (6.5 ± 0.8 g) were exposed to under, near and over environmental concentrations of BαP (i.e. 50, 100, and 200 ppb, respectively) and two control groups for 21 days. Following exposure to BαP, generally, DNA damage increased in the liver and gill cells as well as the frequency of micro- and bi-nucleated erythrocytes in a time and concentration-dependent pattern. In addition, the liver and gill tissues displayed several histopathological lesions. Together, the findings are warning the health status of the Caspian Sea due to an ever-increasing concentration of BαP through using Caspian White fish as an ecological model.

The coastal pollution has been evaluated using indexes like Clean Coast Index (CCI) in many countries. In this study, several coasts and urban areas in northern of Iran along the Caspian Sea, were assessed in terms of number and composition of litters. Furthermore, Clean Environment Index (CEI) was used for the first time to interpret the results. The results indicated that 60% of the coasts and 50% of the urban areas were in a dirty status and only 22% of the total surveyed areas were found to be in a clean status. The highest number of litters observed in the study areas was cigarette butt. Due to the impact of risk factor of different types of littered waste, it was obviously clear that CEI offers a more realistic and rigorous interpretation than CCI. Therefore, this new index can be considered to evaluate litters pollution in various areas.