Exposure to low-density polyethylene microplastic particles: presence in Mytilus edulis tissues and pseudofeces

The presence of microplastics in the marine environment is an emerging concern for marine life. This study investigated the presence of low-density polyethylene (LDPE) particles (20-25 μm) in the gills, intestinal lumen, digestive diverticula and pseudofeces of blue mussels (Mytilus edulis) following exposure, using histological procedures and two different staining and microscopy approaches. Mussels were exposed to microplastics at three concentrations (0 mg/L, 0.1mg/L and 5 mg/L) and two different concentrations of algae (0.7 mg/L and 2 mg/L) during 4 days and 56 days. A reference group not exposed to microplastics or algae was also included. Following exposure, tissues were dissected and embedded in paraffin, and histological sections were dyed using two different staining methods; Hematoxylin-Erythrosine-Saffron (HES) and Nile Red (NR). The HES-stained sections were examined using polarized light microscopy, and the NR sections were exposed to fluorescent light of wavelength 470nm, using a FITC (fluorescein isothiocyanat) filter. LDPE particles were easily detected in M. edulis tissues by the use of these procedures. The number of plastic particles in tissues was not affected by exposure time or algae concentration. The LDPE concentration in the exposure medium and matrix (gills, intestinal lumen, digestive gland, pseudofeces) had significant effects on the number of plastic particles observed. The largest number of particles were observed in the intestinal lumen, followed by in pseudofeces. Few particles were found in the digestive gland. These observations suggest that microplastics of this size and polymer type are not to a great extent translocated from the digestive system to other tissues, and that blue mussels are able to reject and discard unknown or unwanted particles as pseudofeces