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Assessment of microplastic contamination in rainbow trout (Oncorhynchus mykiss) and surface water of a high-altitude aquaculture system in the Chehel Chai River, Iran
Summary
Researchers investigated microplastic contamination in both farmed rainbow trout and the surface water of the Chehel Chai River in Iran, finding microplastics in fish digestive tracts, gills, and skin. A total of 50 fish were analyzed, revealing widespread presence of plastic particles across all tissue types examined. The study raises concerns about microplastic transfer to humans through consumption of farmed fish from contaminated waterways.
The accumulation of microplastics (MPs) in ecologically and commercially significant fish species is a growing concern, particularly those consumed by humans. This study investigated the presence of MPs in both the water and farmed rainbow trout (Oncorhynchus mykiss) a species of high commercial value collected from the upstream region of the Chehel Chai River in Golestan Province, Iran. A total of 50 fish were analyzed, with MPs examined in the digestive tract (GT), gills, and skin, revealing 55 particles in total. The frequency of occurrence of MPs in fish was 100%, indicating universal exposure among sampled individuals. MP abundance in water samples ranged from 0 to 4 items/L, with a mean ± SD concentration of 2.11 ± 1.04 items/L. In the digestive tracts of fish, MPs were detected at a mean ± SD concentration of 1.88 ± 0.94 items/g. Larger MPs (400-700 µm) were more frequently observed than smaller particles (100-250 µm and 250-500 µm) in both fish and water samples. Fibers were the most prevalent MP shape, followed by fragments and films. Micro-Fourier transform infrared spectroscopy (μ-FTIR) identified 40 MP particles, with a mean ± SD of 1.57 ± 0.29 particles per fish. Four polymer types were detected: polyethylene (PE, 44.4%), polypropylene (PP, 30.5%), polystyrene (PS, 19.4%), and polyethylene terephthalate (PET, 5.5%). Most MPs were detected in the gastrointestinal tracts (GIT) of fish, reflecting ingestion as the dominant exposure pathway. In contrast, water concentrations showed a spatial gradient, increasing from upstream to downstream sampling stations. Our findings indicate widespread plastic contamination in both fish and water across all sampling stations. These findings underscore the pervasiveness of plastic pollution even in high-altitude systems and highlight the potential for multiple exposure pathways (ingestion, respiration, adhesion) in farmed fish, with implications for ecosystem health and aquaculture sustainability.