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Microplastics in Surface Water and Gastrointestinal Tracts of Demersal Fishes (Oreochromis niloticus and Cyprinus carpio) in the Largest Wetland of the Philippines
Summary
Microplastics were found in 84% of fish from the Philippines' Agusan Marsh — the country's largest wetland — with up to 3.2 MPs per gastrointestinal tract on average and 20 polymer types identified in water, dominated by rayon and polyester. The pervasive contamination of a major tropical wetland and its commercially consumed fish species signals significant risks to food web integrity and human dietary exposure through freshwater fish consumption.
Agusan Marsh, the Philippines' largest wetland, is in the middle of the Agusan River and serves as a catchment basin for excess flood water from upstream tributaries. This study characterizes and quantifies the level and types of microplastics (MPs) present in the surface water and gastrointestinal tract (GIT) of demersal fish Cyprinus carpio and Oreochromis niloticus from two prominent lakes in the marsh, Lake Panlabuhan, and Lake Tugno. KOH digestion, density separation, and Fourier-Transform Infrared spectroscopy (FTIR) analysis were implemented to extract and identify suspected MP particles. Analysis of water samples found microplastic abundances at 340 ± 36.25 pa/m3 and 240 ± 33.17 pa/m3 for Lake Tugno and Lake Panlabuhan, respectively. These microplastics varied in size, shape, and color. A total of 20 polymer types were identified in water samples with Rayon (49%) and Polyester (15%) as the most abundant types. There are 13 color variations detected from water samples with yellow and black as the most dominant colors. Further, 84% of the collected fish had MPs in the GIT. The GIT of O. niloticus of Lake Tugno had the highest average MPs (3.2 ± 1.0 MP/GIT), followed by C. carpio (2.73 ± 0.55 MP/GIT) from Lake Panlabuhan. Oreochromis niloticus of Panlabuhan had the fewest MPs (1.7 ± 0.33 MP/GIT). Fragments and fibers dominate isolated MPs, while brown MPs are consistently recorded across all samples. Ten different kinds of polymers were identified from the fish GIT with Ethylene vinyl acetate (26%), polyvinyl chloride (17%), and nylon-6 polyamide (14%) as the three most prevalent types of polymers. The MPs of different types and origins in the water and demersal fish indicate that microplastic pollution is present in the lakes of Agusan Marsh. Assessment of MPs from other fish species and lakes, as well as the possible point and non-point origins of MP in Agusan Marsh is recommended to determine the extent of MP pollution in this internationally important wetland.