Impact of Micro- and Nanoplastics on Aquaculture and its Products
Aquatic animals of commercial or non-commercial use unintentionally ingest micro- and nanoplastics, which are dumped into oceans and inland waters. These plastic fragments along with the adsorbed chemicals pose a threat to food safety of aquaculture products and fishery itself . Plastics contaminate aquatic environments either by direct runoff or by degradation of macro- or meso-plastic debris. Direct release results from industrial wastes, untreated sewage and fishing gears. Out of 25 most important aquatic species, microplastics have been found in 12 genera and, thus, have a global impact on marine fisheries . They therefore pose an extreme food-safety concern, as some of the micro- and nanoplastic components along with the additives and adsorbed polymers are carcinogenic in nature. These micro- and nanoplastics are capable of causing negative effects like alteration in lipid metabolism, physical damage, cytotoxicity and change in behavior in fishes. Ingestion of micro- and nanoplastics blocks the digestive system , which may cause either starvation or satiation in fishes. It also slows down the digestive process in aquatic animals. As per the study conducted by Mazurais et al., under laboratory conditions, the mortality rate of young fishes feeding on microplastics was found to be significantly higher when compared to the control . Mechanical injuries and ulceration are also caused by microplastics with sharp edges. In another study by Pedia et al., fishes fed with microplastics under laboratory conditions showed alteration in histopathology of the distal intestine like detachment of mucosal epithelium form lamina propria, swelling and shortening of villi, increase in the number of goblet cells, vacuolation of enterocytes, loss of regular structure of serosa, widened lamina propria and hyperplasia of goblet cells .
Micro- and nanoplastics often enter the fish circulatory system. Nanoplastics are capable of changing fish metabolism through alteration of the triglycerides-to-cholesterol ratio in blood serum and through distribution of cholesterol between liver and muscle . Downregulation of amino acids and upregulation of fatty acids was also observed upon exposure of fishes to micro- and nanoparticles . They also reported necrosis, accumulation of lipid droplets and infiltration upon exposure of zebrafish liver to microplastics. In another study by Rochman et al., it was concluded that exposure of fish liver to microplastics shows signs of fatty vacuolation, necrosis, stress and glycogen depletion .