Microplastic Contamination and Species-Specific Vulnerability of Freshwater Fish in Sardaryab Stretch of the Kabul River, Pakistan

Abstract

Microplastic (MP) pollution has emerged as a critical environmental concern in freshwater ecosystems, particularly in developing countries where untreated waste discharge is common. This study evaluates the susceptibility of selected fish species Clupisoma naziri (Sher Mahi), Cyprinus carpio, Cirrhinus mrigala, Garra gotyla, Crossocheilus diplocheilus, and Barilius vagra to microplastic contamination in the Sardaryab region of the Kabul River, Pakistan. Water, sediment, and fish gastrointestinal tract samples were analyzed using digestion and microscopy techniques. Results indicated a higher abundance of microplastics in sediments (ranging from 210±45 to 610±140 MPs/kg) than in water (150±40 to 510±130 MPs/m³), with fibers and fragments being the dominant morphological types (80-92% fibers across matrices). Bottom-feeding fish exhibited significantly higher microplastic ingestion compared to pelagic species. Clupisoma naziri showed elevated contamination due to trophic transfer, with overall fish contamination ranging from 6±2 to 18±9 MPs/individual. The progressive downstream increase in microplastic concentrations underscores the cumulative impact of urbanization, agricultural runoff, and recreational activities along the river corridor. Sediment acting as a long-term reservoir of microplastics poses a chronic exposure risk to benthic organisms and facilitates continuous recontamination of the water column through resuspension events. The predominance of fibrous microplastics in fish gastrointestinal tracts raises concerns about physical blockage, reduced nutrient absorption, and potential translocation to muscle tissues consumed by humans.  Furthermore, the detection of microplastics in multiple commercially valuable species highlights the urgent necessity for developing dietary exposure assessments and implementing source-specific mitigation strategies to safeguard both aquatic ecosystem integrity and public health in the region. The findings highlight ecological risks and potential human health concerns due to consumption of contaminated fish. This study emphasizes the urgent need for pollution control and species-specific monitoring strategies in the Kabul River basin.

Keywords: Microplastics; Benthic feeders; Trophic transfer; Sediment contamination; Aquatic pollution; Bioaccumulation.