Toxicological impact of dietary exposure to polypropylene microplastics in Atlantic salmon (Salmo salar)

Microplastics (MPs) have been documented in farmed fish and in aquaculture feed. In this dietary exposure experiment, Atlantic salmon (63 ± 2 g) were fed standard feed spiked with five different concentrations of polypropylene (PP) MPs (dietary groups B-F) for 90 days. The nominal exposure concentrations ranged from lower than realistic (B), realistic (C-D), to higher than realistic (E-F). Py-GC/MS analysis of the feed also showed presence of PP-MPs in the control (A). Dietary groups A-D therefore reflect realistic conditions for salmon aquaculture, while the two highest groups, E and F, reflect about twice and five-fold of concentrations expected in aquaculture. After 90 days exposure, no significant differences in PP-MPs levels in liver and muscle of feeding groups A, E and F were detected by μFTIR. Dietary exposure to PP-MPs for 90 days had no effect on survival, growth, or morphology. Plasma chloride levels were increased in fish exposed to the three highest PP-MP concentrations, while plasma parameters albumin, ALP, ALT, creatinine, triglyceride, IgM and total protein were elevated in salmon exposed to the two highest concentrations. A dose-dependent increase in plasma glutathione (GSH) suggested MP-induced oxidative stress, and benchmark modelling suggested that plasma GSH was the most sensitive parameter to dietary MPs. Transcriptomic profiling pointed to responses such as oxidative stress, DNA damage, and metabolic dysregulation in salmon exposed to the highest MP concentrations. In conclusion, the study suggests that exposure to MPs might induce multiple toxicity mechanisms in Atlantic salmon, with realistic MPs concentrations affecting GSH levels.