An end to the controversy over the microscopic detection and effects of pristine microplastics in fish organs

Abstract

The aquatic environment and the associated fish assemblages are being exposed to an increasing amount of microplastics. Despite the high number of publications on the presence of microplastics in fish, little is known about their uptake, translocation and accumulation within fish organs. Experimental studies on the detection and effects of pristine microplastics in fish have shown controversial and ambiguous results, respectively. Here, we conducted two experiments to detect and assess the impacts of dietary exposure of Danio rerio to different types of pristine microplastics. Our results show that D. rerio recognizes plastic particles as inedible materials but ingests them when mixed with food or fish oil. Accidental ingestion occurs in fish exposed to relatively small (1-5 µm) microplastic particles without associated food or fish oil. Additionally, D. rerio effectively eliminated pristine microplastics 24 h after ingestion; however, retention time was associated with increasing particle size and the intake of additional meals. Clinical signs, such as anorexia and lethargy, are present in fish fed relatively large microplastics (120-220 µm). The ingestion of microplastics does not induce any histopathological changes. To the best of our knowledge, we are able, for the first time, to fully demonstrate the uptake and translocation of plastic microbeads using confocal microscopy. Our results question the findings of previous studies on the detection and effects of pristine microplastics in fish and state that inaccurate interpretations of the histological findings regarding microplastics in fish organs is a prevalent flaw in the current scientific literature. The ever-growing production of plastics 1,2 and their relatively short lifespan 3 , combined with indiscriminate waste-disposal practices and accidental releases 1 , have led to the accumulation of plastics in aquatic environments worldwide 4-9. This situation is especially worrisome due to their long degradation time 2 and potential to be ingested by aquatic organisms 3. In water, plastics undergo weathering 10 through photolytic, mechanical and biological degradation 11,12. Under these circumstances, larger plastics degrade into smaller fragments 12 , i.e., microplastics (MPs) (< 5 mm) 13. Another source of MPs in aquatic environments is micro-sized particles intentionally manufactured for use in domestic products (e.g., cosmetics and clothing) and industrial products (media blasting and industrial feedstock) 11,12 , which are directly introduced into the environment by human activity 10. MPs can display a variety of shapes, sizes and colours 12. In aquatic systems, the predominant shapes of MPs are fibres 14-18 , fragments 6,7,19,20 and microbeads 21. The small size and ubiquity of MPs 22 makes them easily available to aquatic fauna, which are prone to ingest them by confusion with food, accidental ingestion or by transfer through the food chain 23,24. Several studies have documented the ingestion of plastic and MP particles in aquatic species (invertebrat...

Microplastics affected black soldier fly (Hermetiaillucens) pupation and short chain fatty acids

“…The impacts of MP exposure have been extensively studied in aquatic animals (e.g. Barboza et al., 2018; De Sales‐Ribeiro et al., 2020; Karami et al., 2016; Romano et al, 2020), and sometimes with contrasting findings. This could be due to differences in MP type and concentration.…”

Micro and Nano Plastics Distribution in Fish as Model Organisms: Histopathology, Blood Response and Bioaccumulation in Different Organs

“…Virgin microplastics are not causing imminent harm to fish after dietary exposure in S. aurata [150] and O. mykiss [28], and did not present evident tissue damage in Barbodes gonionotus exposed to PVC fragments (0.2, 0.5 and 1.0 mg/L) for 96 h [159]. Little is known about their uptake, translocation, and accumulation within fish organs [23]. MP/NPs showed that oxidative stress and its responding pathways, including inflammatory responses, could play the role of key events [132].…”

“…Based on the histological analysis, significant changes in the MPs-treated gut tissues were observed: epithelial and villi damage has been described in zebrafish [154,171,172] as bowel wall thinning, cracking of villi, epithelial damage with splitting of enterocytes and increased volume of mucus [30,137]. In contrast, De Sales-Ribeiro et al [23] argue that the ingestion of microplastics does not induce any histopathological changes in zebrafish.…”

“…Upregulation of intestinal Cytochrome P450 gene (cyp1a) was shown by Mak et al [69] in adult zebrafish. In zebrafish, Limonta et al [138] reported transcriptomic and histological alterations on the mucosal epithelium of zebrafish although it recognizes plastic particles as inedible materials but ingests them when mixed with food or for accidental ingestion due to small particles (1-5 µm) [23]. Fluorescent MPs were observed in the villi, in the apical surface of the enterocytes, in the lamina propria and very frequently inside the goblet cells.…”

“…Secondary micro plastics, on the contrary, originate from the degradation of larger-sized plastic products once exposed to the marine environment with regular or irregular shape [21]. They are derived from abrasion, mechanical wear as a wave action, photo oxidation and biological degradation of small pieces of plastic [22,23]. MP/NPs, once released into the environment do not degrade and therefore accumulate in aquatic organisms entering the food chain until they are ingested by humans through food.…”