Size- and Time-Dependent Impacts of Polyvinyl Chloride Microplastics on Turbot (Scophthalmus maximus L.): Intestinal Tolerance, Hepatic Injury, and Intestinal Microbiota Dysbiosis

L.) at 3 and 9 weeks of exposure. Three diets were formulated: a control diet with no microplastics, a diet containing 2% micrometer-sized plastics (MPs), and a diet containing 2% nanoplastics (NPs), with four replicates (40 fish/tank, 12 tanks total). The results showed that MPs and NPs had no significant effects on the growth performance of turbot. Analyses of intestinal histology and gene expression (intestinal barrier-related and antioxidant-related genes) indicated that the turbot intestine exhibited a certain degree of tolerance and adaptability to MPs and NPs exposure. Observations of liver histology and analyses of gene expression (inflammatory cytokines, apoptosis-related, and antioxidant-related genes) revealed that the liver damage induced by microplastics in turbot exhibited obvious size-dependent and time-cumulative effects, with NPs exerting a stronger impact. Compared with MPs, long-term exposure to NPs can induce obvious intestinal microbiota dysbiosis in turbot. In summary, particle size and exposure duration are important factors regulating the impacts of PVC microplastics on the intestinal and hepatic health of turbot.