Combined effects of cadmium and nanoplastics on oxidative stress, histopathology, and intestinal microbiota in largemouth bass (Micropterus salmoides)

As a momentous emerging contaminant, nanoplastics (NPs) can pose as vectors for other environmental pollutants, leading to their migration, spreading throughout ecosystems and converting their toxicity. However, research on the combined effects of NPs and cadmium (Cd) on aquatic animals is still in its infancy, especially freshwater carnivore fish. Therefore, we investigated the combined effects of NPs and Cd in water on growth performance, oxidative stress, histopathology, and intestinal microbiota in juvenile Micropterus salmoides (initial weight: 14.67 ± 0.08 g). Analyses were done on control group (unexposed to NPs or Cd), 10 μg/L Cd group, 100 μg/L NPs group, and 10 μg/L Cd + 100 μg/L NPs group for 19 days, and fish were sampled on day 7 and 19. Our analyses revealed that the combined exposure to NPs and Cd significantly reduced feed intake after 7-day exposure and caused poor growth after 19-day exposure (P < 0.05). Combined exposure to NPs and Cd markedly triggered oxidative stress and oxidative damage in liver. After 7-day exposure, two-way ANOVA showed a significant interaction between Cd and NPs for SOD, CAT, GSH and MDA. After 19-day exposure, two-way ANOVA showed a significant interaction between Cd and NPs for MDA. Histological abnormalities in gills, livers, and intestines were observed after exposure to Cd and NPs, alone or in combined. Furthermore, combined exposure damaged the liver ultrastructure and caused intestinal microbiota dysbiosis. Overall, by combining physiological and 16S rRNA sequencing analysis, a better understanding of the potential risks posed by nanoplastic and heavy metal pollution in freshwater carnivores has been obtained. The toxicity of co-exposure to NPs and Cd is higher than that of NPs and Cd alone.