Preliminary study on the determination of microplastics and the assessment of histopathological effects in mussel tissue intended for consumption.

To assess the presence of microplastics (MPs) and potential histopathological effects in Mytilus galloprovincialis farmed in an offshore facility in the Gulf of Naples. Methods. In two seasonal samplings, winter and spring, five points were identified corresponding to four perimeter rows and one central row, for a total of five samples per sampling. A portion of each sample was subjected to MPs determination and histopathological analysis. MPs extraction was performed by acid digestion of the tissues. The count was performed using scanning electron microscopy with an EDX energy dispersive detector, dividing the particles into two size classes: >10 μm and <10 μm. Histological examination was performed on samples fixed in formalin, dehydrated, embedded in paraffin and stained with haematoxylin-eosin. Observations were made using transmitted and polarised light optical microscopy at 200×–400× magnification. The digital images acquired were analysed to determine the distribution, morphology and density of the lesions in the tissue compartments. Results. The results, expressed as number of MPs/g w.w., showed a min-max range of 4660–11947 in winter and 4097–14870 in spring for particles <10 μm; for MPs >10 μm, 24–53 in winter and 35–65 in spring. Point E showed the highest concentrations in both samples: 11,947 in winter and 14,870 in spring for MPs <10 μm; 53 in winter and 65 in spring for those >10 μm. The lowest concentrations of MPs <10 μm were found at point C in winter (4661) and A in spring (4097); for MPs >10 μm, at points C (24) in winter and B (35) in spring. In all samples, histopathological analyses showed the highest number of MPs in the digestive tract lumen at point E, associated with a high number of histological alterations: thickening of the gill lamellae with epithelial dysplasia, cell degeneration, infiltration of phagocytic haemocytes, vacuolisation of epithelial cells and hepatopancreas in response to the accumulation of MPs. At points C and B, a lower quantity of MPs was observed in the tubular lumen and more limited histopathological alterations (epithelial dysplasia, haemocyte infiltrates, phagocyte activation). At the remaining points, moderate or absent quantities of MPs and minor lesions were found. Conclusions. The distribution of MPs in M. galloprovincialis intended for consumption is greater for MPs <10 μm than for those >10 μm in the central row of the farm compared to the perimeter rows, and in the spring sampling rather than in the winter sampling. This seems to imply the influence of exposure factors such as the levels of contamination of the marine area, the spatial arrangement of the rows of the farm and the season of mussel harvesting. In accordance with the literature data, the histopathological alterations observed in the cells of the digestive tract of mussels indicate the susceptibility of this tissue to exposure to MPs. Although preliminary, the results seem to indicate a possible correlation between the concentrations of MPs in mussels and the extent and severity of the histopathological alterations found in their tissues. Further investigations are necessary for the purpose of food safety assessment.