Influence of multi-walled carbon nanotubes on the toxicity of ZnO nanoparticles in the intestinal histopathology, apoptosis, and microbial community of common carp

In recent years, carbon nanotubes (CNTs) have gained tremendous attention due to their widespread application. Previous research indicated that carbon nanomaterials can affect the toxicity of some pollutants. In this study, we investigated the influence of multi-walled CNTs (MWCNTs) on the toxicity of ZnO nanoparticles (ZnONPs) in the intestine of common carp (Cyprinus carpio). After four-week exposure, histopathological observation and TUNEL assay showed concentration ratio-dependent intestinal lesions and apoptosis, with the most severe in the HSCZnONPs group (50 mg L-1 ZnONPs and 2.5 mg L-1 MWCNTs), less severe in the ZnONPs group (50 mg L-1 ZnONPs) and the least in the LSC-ZnONPs group (50 mg L-1 ZnONPs and 0.25 mg L-1 MWCNTs). Furthermore, ICP-OES indicated that intercellular zinc accumulation was significantly decreased by the presence of the MWCNTs, which suggested the varied contribution of ZnONPs to intestine injury in different groups. Moreover, 16 s rDNA sequencing revealed that ZnONPs alone and in combination with MWCNTs significantly altered the microbial community diversity and composition of the gut microbiota compared with controls. In addition, the predominant phylum, class, order, family, and genus were significantly different among these groups. In conclusion, the influence of MWCNTs on the toxicity of ZnONPs was related to the concentration and concentration ratio of the mixture.