In this study, we investigated biological effects associated with ingestion of polystyrene (PS) microplastic (MPs) in fish. We examined whether ingestion of contaminated PS MPs (100–400 μm) results in chemical stress in rainbow trout (Oncorhynchus mykiss) liver and we explored whether this exposure can affect the oxidative stability of the fillet during ice storage. Juvenile rainbow trout were fed for 4 weeks with four different experimental diets: control (1) and feeds containing virgin PS MPs (2) or PS MPs exposed to sewage (3) or harbor (4) effluent. A suite of ecotoxicological biomarkers for oxidative stress and xenobiotic-related pathways was investigated in the hepatic tissue, and included gene expression analyses and enzymatic measurements. The potential impact of MPs exposure on fillet quality was investigated in a storage trial where lipid hydroperoxides, loss of redness and development of rancid odor were assessed as indications of lipid peroxidation. Although, chemical analysis of PS MPs revealed that particles sorb environmental contaminants (e.g., PAHs, nonylphenol and alcohol ethoxylates and others), the ingestion of relatively high doses of these PS MPs did not induce adverse hepatic stress in fish liver. Apart from small effect on redness loss in fillets of fish exposed to PS MPs, the ingestion of these particles did not affect lipid peroxidation or rancid odor development, thus did not affect fillet’s quality.

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Ingestion has been proposed as a prominent exposure route for plastic debris in aquatic organisms, including fish. While the consequences of ingestion of large plastic litter are mostly understood, the impacts resulting from ingestion of microplastics (MPs) are largely unknown. We designed a study that aimed to assess impacts of MPs on fish intestinal physiology and examined integrity of extrinsic, physical and immunological barriers. Rainbow trout were exposed to polystyrene (PS) MPs (100–400 μm) via feed for a period of 4 weeks. Fish were fed four types of diets: control, diets containing virgin PS particles, or particles exposed to two different environmental matrices (sewage or harbor effluent). Extrinsic barrier disturbance in intestinal tissue was evaluated via histology. The paracellular permeability toward ions and molecules was examined using Ussing chambers and mRNA expression analysis of tight junction proteins. Active transport was monitored as transepithelial potential difference, short-circuits current and uptake rate of amino acid 3H-lysine. Immune status parameters were measured through mRNA expression level of cytokines, lysozyme activity, and hematological analysis of immune cells. We could not show that PS MPs induced inflammatory responses or acted as physical or chemical hazards upon ingestion. No measurable effects were exerted on fish intestinal permeability, active transport or electrophysiology.

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