Characterization and implication of microplastics on riverine population of the River Ravi, Lahore, Pakistan

Microplastic (MP) pollution in the aquatic environment is an emerging subject worldwide. So far, very few investigations have been reported on the riverine fish population. This study investigated the implications of microplastics for three freshwater fish species (Labeo rohita, Cirrihinus mrigala, and Sperata seenghala) as bioindicators of this pollution. Raman spectroscopy was used to confirm MP polymer type and their distribution in water, sediments, and in different organs (gut, gills, liver, and muscles) of Labeo rohita, Cirrihinus mrigala, and Sperata seenghala collected from River Ravi at two sites (site I, Dhand Nano Dogar and site II, Jhamra). These selected sites were situated predominantly near agricultural lands and received polluted water from nearby sewerage and industries that represented potential sources of microplastic pollution. Histological analysis was combined with Raman spectroscopy to assess the effects of MPs on fish organs. MPs were identified in water and sediment samples with an average load (per 0.5 L or per 0.5 kg) of 33 items and 64 items for water and sediments at site I and 27 items and 19 items at site II, respectively. Of total MPs identified, 56.9% were found in bottom feeder C. mrigala, 37.91% in column feeder L. rohita, and 5.21% in S. seenghala at site I while at site II 60% were found in C. mrigala, 29% in L. rohita and 10.34% in S. seenghala. This was linked with more plastic accumulation in sediments from the nearby residential sewerage and industrial effluent flow. In this study, the identified MPs polymers were in the order of polyvinyl chloride (PVC) > polystyrene (PS) > propylene (PP) > polyethylene (PE). Among plastic shapes, fiber (58%) was the dominant plastic in water followed by fragment (21%), sheet (12%), and cube (9%). In sediment, the fragment was the common plastic shape with 51% followed by fiber (28%), sheet (19%), and cube (2%). Fragments (62.9%) in water and fibers (68.4%) in sediments were abundant at site 2. Microplastic mean occurrence in organs was in the order of gut > gills > muscles > liver at both sites. Significant histological alterations were observed in all three species including intestinal edema, hyperplasia, hepatocyte infiltration, accumulation of lipid droplets in the liver, lamellar fusion and breakage in gills, and muscle fiber necrosis. This study showed MP occurrence in the selected freshwater fishes, so further research is needed to assess plastic pollution in the riverine fish population of Pakistan. This study appeared to be the first in the selected area, as no significant information regarding plastic pollution in that riverine system was found when this study was conducted.