Toxicity and transcriptome sequencing analyses of Daphnia magna under multi-walled carbon nanotubes (MWCNTs) stress

Due to the rapid development of the power battery industry, the potential pollution of carbon nanotubes (CNTs) has drawn great attention in recent years. In this study, the toxicity of multi-walled CNTs (MWCNTs) on antioxidant capacity, digestive capacity, and transcriptome in Daphnia magna, which is a model organism of plankton, was conducted. D. magna individuals were exposed to different concentrations (0, 0.53 mg/L, and 5.3 mg/L) of MWCNTs for 48 h. The results showed that 5.3 mg/L MWCNTs induced obvious oxidative stress reflected by significantly increased malondialdehyde content, and significantly decreased activities of superoxide dismutase, catalase, and glutathione. There were marked reductions in digestive enzyme activities, including lipase activity, trypsin activity, and amylase activity, in the 5.3 mg/L-exposed group relative to those in the control group. KEGG function annotation analysis showed that MWCNTs at both concentrations disturbed two pathways, including metabolism of xenobiotics by cytochrome P450 and the fatty acid elongation signaling pathway. However, the protein digestion and absorption pathway was disturbed in the 5.3 mg/L MWCNTs-exposed group but not in the 0.53 mg/L MWCNTs-exposed group. Overall, we deduce that oxidative damage, impairment of detoxification function, and disorders of protein metabolism and lipid metabolism are associated with CNTs toxicity on D. magna.