Microfiber Pollution in Commercial Fish Species

Microfiber Pollution in Commercial Fish Species: Comparison

Please note this is a comparison between Version 2 by Serena Santonicola and Version 1 by Serena Santonicola.

Microfiber pollution is a widespread threat to marine fauna, including fish edible species. These particles may be released into water from textiles during the washing process, and due to their low dimensions, the majority of microfibers cannot be blocked from wastewater treatment plants, reaching seas and oceans.

microplastics
microfiber pollution
seafood contamination
human exposure

1. Introduction

Microplastics have been defined as particles of different shapes (fragments, fibers, spheroids, granules, pellets, splinters, or beads) whose dimensions are between 0.1 μm and 5000 μm [1]. Furthermore, microplastics are classified into primary and secondary. Primary microplastics may result directly from the production of micro-sized particles for special domestic or industrial uses, while secondary microplastics may be derived from larger plastic objects by chemical or mechanical fragmentation [2]. Microplastics are highly persistent, accumulating in different marine habitats at increasing rates [3]. Among the different forms of microplastics found in the environment, several studies have shown that microparticles with fibrous shapes are predominant in the marine ecosystem [4,5,6], often accounting for more than 80% of the total items [7,8,9,10,11]. Microfibers are defined as “particles with a diameter less than 50 μm, length ranging from 1 μm to 5 mm, and length to diameter ratio greater than 100” [12]. Microfibers include both synthetic microfibers (e.g., nylon, polyester, polyolefin, and acrylic) and natural ones (e.g., cotton, flax, wool, and silk), which have been reported as the most abundant in the environment [6,12,13].

Microfiber pollution has become a global concern due to its wide diffusion not only in marine and freshwater habitats [14,15,16] but also in the air, soil, and sediments [16,17,18]. Most of the microfibers found in the oceans are released from textile industries [19]. Cotton is the most important natural fiber in the textile market and is second only to polyester, the predominant synthetic textile fiber [6]. Domestic sewers and wastewater treatment plants (WWTPs) are considered the main pathways of textile microfibers in the marine environment [5,20]. A high number of microfibers may in fact be discharged from textile garments during domestic and industrial laundering processes [20,21]. In particular, more than 600,000 fibers may be released in a usual 5 kg wash load of polyester textiles [6,22]. Other sources that may contribute to microfiber pollution are fishing nets, curtains, carpets, and mattresses. On average, while 34.8% of microfibers in the oceans are derived from the laundering of synthetic textiles, 28.3% of microfibers are released from the friction of tires [6,12,19]. Moreover, due to the global COVID-19 epidemic, the wide consumption of masks, mainly composed of fiber materials that may be further broken to form microfibers, has also increased this type of pollution [23]. Once released into the environment, microfibers may be dangerous due to the risk of ingestion by marine species that are part of the food chain.^[1]

2. Impact of Marine Microfiber Pollution on Fish Species for Human Consumption

Microfiber pollution was recognized in all major ocean basins [8,18,33] as well as within the marine trophic web [11,27,34,35,36,37,38]. In the Mediterranean Sea, microfibers released from synthetic fabrics represent about 40% (range 1.6–85.9%) of microplastics in seawater and the sea bottom, followed by fragments (mean 34.5%, range 1.6–72.7%) [11]. Most of the microfibers found in this area and in the Western Indian Ocean, North Atlantic, and South Atlantic Oceans were cellulose microfibers (79.5%) and animal microfibers (12.3%), such as wool [23]. In particular, microfibers are widely spread in estuaries and coastal waters [39], as documented in the Ebro Delta estuary in Spain [40] and in coastal waters in the Shanghai area [41], where synthetic microfibers represented 70% and 80%, respectively, of the total microplastics [42]. However, despite the fact that the majority of plastic pollution is derived from land and impacts coastal waters, recent evidence supports the hypothesis that currents may move these particles into the open ocean and to higher latitudes [8]. Regarding the vertical distribution of microfibers in seawater, the physical shape and the nature of these particles may affect their position in the water column due to the different sinking rate densities and, therefore, their availability to marine organisms [23,45].

Due to their tiny size and wide distribution, microfibers may be ingested by wild-captured pelagic and benthic fish and farmed species ^[2][3][4]. The extensive distribution of blue-colored microfibers in seawater has resulted in wide exposure in fish species due to active ingestion or indirect uptake, while transparent/clear (white and gray) microfibers may be ingested because they are mistaken for gelatinous prey [11,27]. The available information suggests that among the marine biota, crustaceans, and bivalve mollusks are also contaminated^[5][6].

Exposure to microfibers in marine organisms may cause physical damage, such as blockage in the gut, the segregation of digestive enzymes, low absorption of nutrients, disruption of the endocrine system, and disturbances in body functions, including respiration [6]. However, the effects of microfiber ingestion on marine biota could vary depending on the species and environmental conditions. Moreover, due to their large surface area and hydrophobic properties, synthetic microfibers can absorb hydrophobic pollutants and pathogenic microorganisms [48] that may enter the food chain [23]. Also the leaching of toxic additives may pose a significant threat to aquatic organisms [23,47]. Microplastic exposure in marine biota may also cause adverse consequences for biodiversity conservation, ecosystem services, and human food security (in terms of reduced food availability for the human population) [3,47,49]. Chronic exposure to microplastics may also be associated with behavioral changes and reductions in energy, growth, fecundity, and reproductive output [51,52]. However, there is a huge gap in this research field and a lack of information on the extent of this phenomenon. Few investigations have tried to examine some of these aspects, and discrepancies between laboratory and environmental conditions highlighted the need to consider the possible harmful effects related to microplastics via studies on wild-caught fish species [50].

Humans may be exposed via seafood consumption. In particular, the differences in the sizes and shapes of microfibers could influence translocation among fish tissues and consumer exposure^[7]. Mainly bivalves and small pelagic fish (e.g., sardines, anchovies, and sprats) which are usually eaten whole, could contribute to the amount of ingested microplastics by humans^[89]. However, small pelagic fish species that could be consumed whole (e.g., sardines, anchovies, and sprats) may also cause consumer exposure^[98]. However, some studies have shown the occurrence of microfibers in the gutted meat of marine organisms at levels even higher than those in viscera^[10]. Moreover, fish from point-of-sale may undergo additional contamination due to airborne fallout from clothing and machinery during processing or from packaging^[1]. Despite the fact that exposure to microplastics, including microfibers, may pose significant concerns, the required quality-controlled data to make a food safety risk assessment are lacking, and further work is needed to fully assess natural and synthetic microfiber pollution^[11].

References

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