Ecological risk and trophic transfer of microplastics in freshwater fish from the Sutlej River stretch in Punjab, India.

Evidence proved that untreated wastewater, sludge, and industrial waste are the root causes of microplastic (MP) influx into Sutlej River a major tributary of Indus River system, which threatens the aquatic ecosystems. In the present study, bioaccumulation, biomagnification, trophic magnification factor (TMF), and the relationship between body weight and body length vs. MPs abundance were studied in three major commercial fish species representing different trophic levels and feeding habits, namely, Labeo rohita (herbivorous column feeder), Cyprinus carpio (omnivorous bottom feeder), and Wallago attu (predatory carnivorous bottom feeder). Samples collected from selected stretch-Phillaur to Walipur Kalan of the River Sutlej in Punjab (India). The average abundance of MPs in water samples from Phillaur and Walipur Kalan was recorded as 10.24 and 12.20 MPs/L with mean concentration of 9.99 MPs/L. The average abundance of MPs in L. rohita, C. carpio and W. attu collected from Phillaur was 0.12, 0.26, and 0.40 MPs g⁻1, respectively, whereas corresponding abundances in fish collected from Walipur Kalan were 0.43, 0.39, and 1.02 MPs g⁻1, respectively. Surface characteristics of retrieved MPs suggested that complete degradation had occurred. Based on FTIR analysis, polypropylene comprised the majority of the abundance of polymers. MPs were found in higher concentrations in fish gills and intestines than in muscle tissue. Although bioaccumulation factor (BAF) values indicated limited accumulation of microplastics (MPs) from the surrounding water, biomagnification factor (BMF) values greater than 1 were observed in the predator-prey relationships, suggesting potential trophic transfer and localized trophic enrichment of MPs. However, the observed differences in BMF were not statistically significant, indicating that the findings represent a possible trend rather than conclusive evidence of ecosystem-wide biomagnification. Overall, the results highlight the occurrence of microplastic trophic transfer within the selected Sutlej River food web and emphasize the need for improved waste management practices and continuous environmental monitoring to protect aquatic biodiversity.