Effects of medium-term exposure to a high concentration of polystyrene nanoplastics in Chilean mussels (Mytilus chilensis)

In the present study, the alterations associated with 28 days exposure to high concentrations of polystyrene nanoplastics (PS-NPs) in Chilean mussel adults, Mytilus chilensis were assessed by evaluating histopathological alterations in gills, digestive gland and gonad, and changes in transcripts related to immune and antioxidant responses, cell and tissue repair, and iron storage in gills and digestive gland. After 2-days of exposure, a significant upregulation in the expression of genes associated with antioxidant defense (cat, sod1), immune response (def), and cellular repair (hsp70, hsp90, mt) was observed in the gills. After 28 days of exposure, a significant downregulation was detected in genes associated with iron storage (fer), as well as hsp90 and def. In digestive gland, an upregulation of sod1, mt, mytA and pgrp was observed at 2 days of exposure and a significant downregulation of mytA at 28 days of exposure to NPs-PS. These results suggest that a response of the antioxidant system generated by a possible oxidative stress was induced to the initial exposure of the contaminant. At the histopathological level, in general no changes were observed with respect to the control, however, an increase in hemocytic infiltrations, empty epithelium, dilation and desquamation in gills was observed, which can alter the correct transport of oxygen and nutrients of the mussels. The gills stand out as the main tissue affected by PS-NPs exposure. An accumulation of PS-NPs was mainly found in gills and digestive gland, and to lesser extent in gonads. Overall, the present results indicate a mild effect of high concentrations of PS-NPs in the defensive and antioxidant responses of Chilean mussels at medium-long-term.