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Microplastic contamination in freshwater fish: first insights from the Mekong River in Nakhon Phanom Province, Thailand
Summary
Researchers found microplastics in 100% of 89 fish gastrointestinal tracts sampled from the Mekong River in Thailand, averaging 23.76 items per individual, with fragments being the dominant shape (83%), particles under 100 µm the most common size, and 17 polymer types identified across species.
Microplastics (MPs) are emerging contaminants that cause concerns in aquatic ecosystems. Fish ingest MPs unintentionally during normal feeding because they resemble prey or by ingesting fish that has previously consumed them. The present study investigates MP contamination in the fish gastrointestinal tracts (GITs) of the Mekong River in Nakhon Phanom Province, Thailand. MP particles were identified in all 89 of the fish analyzed. In the GITs of 89 analyzed fish, the identified percentages of MP contamination were 23.76±23.14 items/individual. The most common size category identified in all samples was less than 100 μm, while the larger than 500 μm category was less predominantly observed in the GIT samples. In addition, all particles observed were fragments (83%), where 16% were fibers and the remaining 1% were spheres. The GIT of Oreochromis niloticus had the highest average MPs (63.7±32.5 items/individual), while Paralaubuca typus had the lowest (7.9±5.7 items). Fish body weight, length, and MP concentration did not differ significantly (p > 0.05). There were seven color variants observed in GIT fish samples, with blue and violet being the most dominant. The most common size category discovered in all samples was less than 100 μm, while the larger than 500 μm category was less prevalent in the GIT samples. In addition, 83% of the particles examined were fragments, with 16% being fibers and the remaining 1% being spheres. There were 17 polymer types found in fish GIT samples, with the most common being cellulose acetate (CA), glycerol triacetate, polyvinyl acetate (PVAc), cellulose acetate butyrate (CAB), and polyvinyl propionate (PVPr). This work is notable since it is the first to investigate microplastics in the Mekong River ecosystem, adding to the limited amount of freshwater research. Furthermore, it has national and international significance because of its involvement in fish production and export. To establish the level of MP pollution in this internationally significant river, it is advised that MPs from different fish species and rivers be assessed, as well as the likely point and non-point origins of MPs.