Abstract
The ubiquitous presence of microplastics and their marine ecotoxicity are major public concerns. Microplastics are ingested accidentally by the marine fauna or are taken up indirectly through the food chain. These particles can accumulate in cells and tissues and affect the normal biological functions of organisms, including their defense mechanisms. There is limited information available about the response of immune cells to microplastics; the degree of uptake by the cells, the response of different organs or the impact of environmental concentrations of microplastic are matters that remain unclear. Moreover, very little is known about the toxicity of different polymer types. This study aimed to shed light on the physical impact of small microplastics (1–5 μm) on cells from Atlantic salmon. Immune cells from intestine, blood, and head kidney were exposed to green fluorescent polyethylene microplastic (PE-MP), yellow fluorescent polystyrene microplastic (PS-MP) and both. High (50 mg/L), medium (5 mg/L), and low (0.05 mg/L) concentrations were tested for 1, 24, 48, and 72 h to study cell mortality and microplastic uptake. Quantitative data of microplastic uptake by fish immune cells were obtained for the first time by imaging flow cytometry. Salmon immune cells showed a relatively low ability to phagocytose microplastics. Less than 6% of the cells ingested the particles after 48 h of exposure to high concentrations. Cells also phagocytosed microplastics at low concentrations although at low rates (<0.1%). PE-MPs was phagocytosed by higher percentage of cells compared to PS-MPs and the former bioaccumulated in time while the latter decreased over time. However, each cell generally phagocytosed more PS-MPs particles than PE-MPs. Cells from different tissues showed different responses to the microplastic polymers. In conclusion, this study shows that immune cells of Atlantic salmon can phagocytose microplastics, and the impact is dependent on the microplastic type. PE-MPs, the most abundant polymer in the oceans and a widely used plastic in salmon aquaculture, was more easily taken up than PS-MPs. Furthermore, the study demonstrates how imaging flow cytometry can be applied in microplastics research.
Highlights
The increasing presence of microplastics (MPs) in the marine environment is of global concern
The present study shows that Atlantic salmon immune cells can phagocytose MPs, to a relatively low degree
We found that MPs can impact the immune cells of Atlantic salmon even at relatively low concentrations and that different polymers can induce distinct responses on the cells
Summary
The increasing presence of microplastics (MPs) in the marine environment is of global concern. Thermoplastic polymers are the most abundant plastic types found in the marine environment; a study conducted in 2014 found that almost half of the MPs collected in the North Atlantic ocean was polyethylene (PE) and polypropylene (PP) (Enders et al, 2015). A study carried out in 2015 found that PE accounted for 73% of the small MPs (20–999 μm) collected in the North Atlantic Subtropical Gyre, followed by PP, PVC, and PS (Ter Halle et al, 2017). Other synthetic polymers such as polyethylene terephthalate (PET)
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