Risk Assessment of Microplastics Influenced by Human Activities along the Gorganroud River (Iran) and its Estuary to the Caspian Sea

Rivers are an increasing source of MPs (microplastics) destined to the marine environments. Gorganroud River is passing through many kinds of land uses; including agriculture, forest and urban areas and could be one of the MPs pollution drivers to the Caspian Sea. The abundance and distribution of MPs in sediments and some fish of the Gorganroud River assessed. Also, characteristics of microplastics with attached elements revealed and confirmed by SEM, EDX, ATR and Raman analysis. The average abundance of MPs along the River sediments ranged from 220 ± 66 to 2460 ± 444 items/Kg. The most abundant of MPs reported from stations situated in urban areas, which suggests great amount of MPs in the Gorganroud River originates from cities wastewater effluents. Over 80% of these MPs was less than 2 mm. What's more, the majority shapes of MPs were fiber, followed by fragment and film. Black and gray were the dominant color among sediment MPs. Whereas the most common polymer types of these MPs in sediments were polypropylene (39%), polyethylene (26%), polyamide (16%), polystyrene (14%) and polyester (5%). Main type of polymers found in the digestive tract of fish were polypropylene (37%), polystyrene (29%), polyethylene (25%) and polyester (9%). Regard to the fish, the most abundant MPs detected in Neogobius melanostomus (0.72 n/g) caught mainly from stations situated along areas of agricultural fields. The same as sediment samples, prevalence shapes within digestive tract identified as fibers, followed by fragments and films. Although MPs size ranged from 0.1 to 3 mm, dominant MPs size was less than 1mm. Moreover, the frequent color detected within fish digestive tract was black. This survey demonstrated characteristics of MPs contamination along the Gorganroud River and revealed significance of the River as a sinking MPs pathway to the Caspian Sea ecosystem.