Impact of chronic exposure to the ionic liquid ([C8mim] [PF6]) on intestinal physical barrier, immunological barrier and gut microbiota in common carp (Cyprinus carpio L.)

Ionic liquids (ILs) are commonly known as green solvents and have been widely used in various fields. However, the ecotoxicity of ILs in aquatic environment has received considerable attention from scientific researchers. This study investigated the toxic effects of different concentrations of 1-octyl-3-methylimidazolium hexafluorophosphate ([C8mim][PF6]) (0, 1.35, 2.70 and 5.40 mg/L) on intestinal physical barrier, immunological barrier, and intestinal microbiome in common carp on days 30 and 60. The results showed that ([C8mim] [PF6]) exposure could reduce the intestinal villus height, decrease the mRNA expression of tight junction genes (occludin, claudin-2 and zonula occludens-1), and increase the levels of D-lactic and diamine oxidase, and reduce acid phosphatase and lysozyme activities, complement 3 and 4 contents, and anti-inflammatory cytokine TGF-beta protein level, while increase pro-inflammatory cytokines TNF-alpha and IL-1 beta protein levels in common carp. Moreover, ([C8mim] [PF6]) exposure was also found to significantly reduce gut microbial diversity and alter microbial community structure in common carp. Collectively, our study highlighted that exposure to ([C8mim] [PF6]) could disrupt intestinal physical barrier, impair immunological barrier and alter intestinal microbiome in common carp, suggesting that ILs exert a negative effect on fish intestinal health status and may pose serious health risks in fish. The results of this study may be helpful to illuminate the toxicity mechanisms of the ILs on fish.