Quantitative and qualitative assessment of microplastics pollution in the Blackfin barracuda (Sphyraena genie) in the Oman Sea

Introduction: The abundance and durability of plastic wastes in the environment, especially in the marine environment, comes with extensive environmental threats to the ocean and its biodiversity. Microplastic (MP; 1 µm to 5 mm) is an important component of marine plastic pollution. The concerns about the negative effects of MPs on human health have raised attention to the presence and physiochemical properties of MPs found in aquatic environments and inside body of edible aquatic animals. Therefore, the main goal of this study is to investigate the quantity (presence, abundance, and size), and quality (shape and color) of MPs found in the digestive tract of Blackfin barracuda (Sphyraena genie) living in the Oman Sea.
Materials and methods: For this study, 27 pieces of S. genie (average total length: 42.5 cm ± 5.36 and total weight: 353.5 g ± 2.5) were collected from the northern shores of the Oman Sea during the winter of 2020 by gill nets. The fish were bioassayed and then dissected in the laboratory. To extract MPs, each digestive tract was digested with a 10% KOH solution and then vacuum filtered. Identification, counting, and determination of the characteristics of MPs (shape, size, and color) were done by a stereomicroscope. Particle dimensions (μm) were measured using ImageJ software.
Results and discussion: All the examined fish had MPs in their digestive tracts (100%). 285 MPs were found in the S. genie samples. The MP average abundance was 10.5 ± 5.19 particles per individual and 0.8 ± 0.2 particles per gram of wet weight. The most identified microplastics were in the form of fiber (abundance: 73%), irregular fragments (26%), and films (1%). The MP colors ranged from light to dark color spectrum. The color combination according to abundance was black > gray > transparent > creamy > red > blue and dark red > green and brown > pink and white > dark blue, and peach. Around half of the MPs were shorter than 300 µm in length, while only about 9% of the MPs were longer than 1 mm. In terms of size, microplastics were classified into eight groups: category one (size: 1 - 100 µm; N: 64 MPs), category two (100 - 300 µm; N: 85 MPs), category three (300 - 500 µm; N: 45 MPs), category four (500 µm - 1 mm-; N: 66 MPs) category five (1 - 2 mm; N: 19 MPs), category six (2 - 3 mm; N: 5 MPs), category seven (3 - 4 mm; N: 1 MP) and category eight (4-5 mm; No MP). The size of the irregular fragments was smaller than the fibers, mostly less than 100 µm. Considering the shape and small size of dominant MPs, the presence of small fish remains (skulls, scales, and gill fibers) and shell fragments in the digestive tracts, and also the carnivorous diet of the S. genie, it can be assumed that these degraded secondary MPs might have been transferred through the food chain.
Conclusion: Microplastics were observed in the digestive tracts of all the examined samples of S. genie. The isolated MPs were in the form of fibers, irregular fragments and films. Black, gray, and transparent colors were evident as the dominant colors, and fiber was the dominant shape in microplastics. MPs smaller than 1 mm were the most abundant particle (92%), too. The presence of microplastics in the studied fish lead to ecological and health concerns. Therefore, it is necessary to raise public awareness and manage the entry of plastic pollutants into the marine environment.