Immunological responses, oxidative stress, and histopathological effects of nanoplastics on commercially relevant mussel species: A review

Nanoplastics (NPs, <1000 nm) are considered emerging contaminants with the ability to cross biological barriers and accumulate in tissues and organs of aquatic organisms. In the past decade, bivalves have been used to monitor the in vitro and in vivo effects of micro-nanoplastics exposure on normal homeostasis in immune cells, larval stages and adults. However, the study of the effects of NPs on mussels is still scarce and focuses on a few farmed species. Here we aim to comprehensively review the physiological and pathological effects associated with exposure to NPs on commercially important mussels, using an in-depth literature evaluation. Our analysis show that exposure to NPs adversely affect different mussel species, by altering relevant metabolism- and growth-related physiological rates (filtration, absorption, respiration and clearance rates). The accumulation of NPs elicit inflammatory responses, recruiting and altering in vivo the number of cellular subtypes of hemocytes that, in vitro, endure changes in lysosomal function, enhanced synthesis of nitric oxide synthase (NOs) and acid phosphatase (AcP), changes in the phagocytic activity, cell and mitochondrial membrane instability, cell viability and apoptosis. NPs exposure also elicits the synthesis of oxidative stress mediators, which may lead to DNA damage. During the developmental stages, the accumulation of NPs may induce histopathological alterations in the gills, gonads, and digestive tubes, producing malformations of the veliger larvae, developmental delays and decreased mineralization, among others effects. Here we also briefly highlight some of the shortcomings that should be taken into account to improve the analysis of the physiological disturbances of NPs exposure in mussels.