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Microplastic pollution monitoring in rainbow trout farms of Fars and Kohgiluyeh and Boyer-Ahmad Provinces
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Arya Vazirzadeh *1   , Issa Askarinia1 |
| 1- Department of Natural Resources and Environmental Engineering, School of Agriculture, Shiraz University, Shiraz, Iran |
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Abstract: (22 Views) |
Introduction
Microplastic (MP) pollution in aquatic environments has become a major environmental concern due to its widespread distribution and detrimental effects on aquatic organisms. Microplastics can accumulate and biomagnify throughout aquatic food webs, posing substantial ecological risks and raising concerns about potential threats to human health through the consumption of contaminated aquatic products. In fish, MPs may cause direct physical damage by accumulating in the gastrointestinal tract, inducing false satiety, and injuring the gills and other tissues. Moreover, MPs can act as carriers of chemical contaminants that adsorb onto their surfaces during production or transport in aquatic environments. Once ingested, these toxic compounds may be released within the fish, adversely affecting physiological functions, including endocrine regulation and immune responses (Vazirzadeh et al., 2025).
Methodology
To investigate MP accumulation in rainbow trout (Oncorhynchus mykiss), six fish were collected from each of eight selected trout farms in Fars and Kohgiluyeh and Boyer-Ahmad provinces at each sampling event over a two-year period. Microplastics were examined in the entire gastrointestinal tract, gills, and a 5-g muscle sample collected from the dorsal musculature above the lateral line. In addition, samples of incoming water (500 mL) and commercial feed (50 g) were collected to assess potential sources of MP contamination (Gündoğdu et al., 2021). To remove organic matter, tissue samples were digested with 10% KOH at a tissue-to-solution ratio of 1:10 (v/v) (Devries et al., 2015). Following a 14-day digestion period, the digested samples were sequentially filtered through stainless-steel sieves and 60-µm paper filters using vacuum filtration to isolate MP particles. The isolated particles were initially characterized according to their shape, color, and size using a stereomicroscope. Polymer composition was subsequently identified by Raman spectroscopy (Gündoğdu et al., 2021).
Results
The gastrointestinal tract contained the highest total number of MPs regardless of particle size or shape. However, when MP abundance was normalized to tissue weight, the gills exhibited the highest concentration. Fibers were the predominant particle shape in all examined tissues, accounting for 47.98%, 87.62%, and 57.14% of the MPs detected in the gastrointestinal tract, gills, and muscle, respectively.
The dominant particle size in the gastrointestinal tract exceeded 1000 µm, whereas particles measuring 100–250 µm were most common in the gills and muscle tissue. Significant differences in MP contamination were observed between the two provinces, with farm water from Fars Province containing lower MP levels than that from Kohgiluyeh and Boyer-Ahmad Province. In feed samples collected from the eight farms, fragments were the dominant particle shape (57.14%), with most particles ranging from 500 to 1000 µm. Moreover, Feed from farms in Fars Province contained higher MP contamination than feed from farms in Kohgiluyeh and Boyer-Ahmad Province. Raman spectroscopy revealed a diverse range of polymer types, predominantly polyurethane, polyamide, polyether, polystyrene, polyolefins, and polyhalogenated polymers. Among these, polyamides were the most abundant polymers detected across all examined tissues.
Discussion and conclusion
The present study investigated the occurrence, distribution, and characteristics of microplastics in different tissues of rainbow trout -as the cold-species with the highest production rate in Iran- and examined potential sources of contamination in aquaculture farms. In Kohgiluyeh and Boyer-Ahmad Province, the highest mean microplastic abundance per gram of tissue was detected in the gills, approximately twice that observed in the gills of fish from Fars Province. Microplastic concentrations in the incoming water of farms in Kohgiluyeh and Boyer-Ahmad were also higher than those in Fars, suggesting that the greater microplastic load in the incoming water may partly explain the higher accumulation in the gills. In contrast, microplastic abundance per gram of muscle was significantly higher in fish from Fars Province, where the feed also contained significantly more microplastics than feed from Kohgiluyeh and Boyer-Ahmad. This pattern suggests that feed may contribute to microplastic transfer to muscle tissue, although further studies are required to confirm this relationship. In line with present study, Shayana et al. (2022) examined microplastics in the gastrointestinal tract, gills, and muscle of 56 fish belonging to Selar crumenophthalmus and Decapterus macarellus from the Maldives. The mean abundance was 4.6 particles per fish, with gills showing the highest abundance. Microplastics were mainly fragments (57.5%), fibers (41.5%), and films (1%), and polyethylene (PE) and polypropylene (PP) were the dominant polymers. In the present study, although the highest absolute number of microplastics was detected in the gastrointestinal tract, gills showed the highest abundance after normalization by tissue weight. This may be related to the continuous direct exposure of gills to the surrounding water and their large surface area, which increases the probability of microplastic retention. The predominance of microplastics in the gastrointestinal tract was also consistent with previous studies. Microplastics may enter fish through direct ingestion or unintentionally with food and can cause intestinal obstruction and physical damage, histopathological alterations, behavioral changes, and disturbances in lipid metabolism (Jovanovic, 2017). In the present study, fiber-shaped particles were the most abundant. Atamanalp et al. (2021) similarly reported the highest microplastic abundance in the gastrointestinal tract (40%) of two commercially important fish species from the Black Sea, followed by the gills. Most particles were fibrous (51%), black (49%), and 50–200 μm in size. Microplastics may enter aquaculture systems through incoming water, feed, and secondary generation caused by abrasion and wear of farm equipment and materials (Vazirzadeh et al., 2025). Feed may represent an important pathway because fishmeal can contain considerable amounts of microplastics. Thiele et al. (2021) reported 0.72 microplastic particles per fish and 123.9 ± 16.5 particles per kg of fishmeal, with fibers and polyethylene among the dominant components. Thus, part of the microplastics detected in the present study may have originated from feed ingredients, although source-tracking studies are needed to determine the relative contribution of feed and water. Raman spectroscopy revealed a diverse range of polymers in the present study, predominantly polyurethane, polyamide, polyether, polystyrene, polyolefin, and polyhalofin. Similarly, Keshavarzifard et al. (2021) identified polyethylene terephthalate (46%), polypropylene (27%), and polystyrene (27%) as the dominant polymers in white shrimp (Metapenaeus affinis) from the Persian Gulf. The diversity of polymers detected in the present study suggests multiple potential sources, including urban and industrial wastewater and plastic waste. Plastic debris can undergo physical degradation, producing smaller particles that may subsequently enter aquatic environments and, ultimately, aquaculture systems. Interestingly, larger fish (>750 g) contained fewer MPs per unit of muscle tissue (one particle per 203 g of muscle) than smaller fish weighing 250–500 g (one particle per 55 g of muscle). This finding may be associated with faster somatic growth in larger fish, together with reduced exposure to incoming water, which was identified as the primary source of MP contamination. During a one-year production cycle, approximately 315,360 L of water enters a farm for every kg of rainbow trout produced. Based on the measured MP concentrations in incoming water, this volume introduces an estimated 197,100 MP particles into trout farms in the two studied provinces. Overall, the findings indicate that microplastic contamination in rainbow trout farms is likely associated with multiple pathways, particularly incoming water and feed. The differences observed among provinces and tissues highlight the need for improved monitoring and source-control strategies to reduce microplastic exposure in aquaculture systems. In conclusion, the findings demonstrate that farmed rainbow trout from Fars and Kohgiluyeh and Boyer-Ahmad provinces are exposed to considerable MP contamination. Nevertheless, most MPs accumulated in non-edible tissues, particularly the gastrointestinal tract and gills, suggesting that the potential risk to consumers through the consumption of fish muscle is relatively low.
Conflict of interest
The authors declare no conflict of interest.
Acknowledgments
The authors gratefully acknowledge the Vice Chancellery for Research of Shiraz University for providing partial financial support for this study. The authors also sincerely thank the owners and staff of the selected trout farms for their valuable cooperation throughout the study and their assistance with sample collection.
Keywords: Microplastics, Rainbow trout, Fars, Kohgiluyeh and Boyer-Ahmad, gastrointestinal tract, gills, flesh |
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| Keywords: Microplastics, Rainbow trout, Fars, Kohgiluyeh and Boyer-Ahmad, gastrointestinal tract, Gills, Flesh |
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Full-Text [PDF 821 kb]
(9 Downloads)
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Type of Study: Research |
Subject:
آلودگي محيطهاي آبي
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