Study On Toxicity Of SWCNTs And Phenanthrene To Pacific Oyster And The Defense Mechanism Involved

With the wide application of carbon nanotubes,the ecological and health risks of carbon nanotubes have attracted more and more attention.In this study,Crassostrea gigas,a typical benthic marine organism,was used as the test organism to study the toxic effects of single-walled carbon nanotubes(SWCNTs)exposure and the oyster's defense mechanism,by measured the contents ofmakindialdehyde(MDA),total superoxide dismutase(SOD),catalase(CAT),the relative expression of cat,hsp70,aox,caspase-3,caspase-7 and p-gp in gill and digestive gland of C.gigas.Then the toxic effects of combined exposure and sequential exposure of SWCNTs and phenanthrene(PHE)were also discussed in order to provide scientific basis for marine ecological risk assessment of single-walled carbon nanotubes(SWCNTs).The following results were obtained:(1)In the single exposure experiment,0.1-10 mg/L SWCNTs had no significant toxic effect on C.gigas at 48 hours(P>0.05).However,exposure for 96 hours significantly increased MDA content in gill and digestive gland of C.gigas(P ? 0.05),SOD and CAT activity also showed a significant dose-dependent increase(P ? 0.05),and the expression of cat,hsp70,aox,caspase-7 and p-gp increased significantly(P ? 0.05).At the same time,Tariquidar,a P-gp protein inhibitor,induced a significant increase in MDA content in C.gigas(P?0.05),suggesting that Multi-xenobiotic Resistance Mechanism exogenous substances plays a crucial role in the defense of SWCNTs.(2)Compared with single exposure,when the concentration of PHE reached 10 ug/L,the combined toxicity of 0.1 mg/L SWCNTs and PHE showed stronger oxidative stress,resulting in significant increase of MDA content and antioxidant enzyme activity in gills and digestive glands of C.gigas,and the relative expression ofantioxidant genes(cat,aox,etc.)and caspase-3(P ? 0.05).The expression of p-gp protein gene was significantly up-regulated(P?0.05),indicating that the defense system of C.gigas still actively responded to the toxic effects of exposure under the exposure dose in this study.(3)In the sequential exposure experiments of SWCNTs at 0.1 mg/L and PHE,the MDA content,antioxidant enzyme activity and caspase-3 relative expression in gill and digestive gland of C.gigas increased significantly with the increase of PHE exposure concentration(P?0.05),showing that the toxic effect was higher than that of combined exposure.When the concentration of PHE reached 10 ug/L,there was no significant difference in the activity of antioxidant enzymes and the expression of antioxidant genes between exposed groups at different concentrations(P>0.05).However,the expression of p-gp was up-regulated in a dose-dependent manner at the exposure dose,indicating that C.gigas was still actively clearing the exogenous contaminants into the body.In conclusion,SWCNTs exposure under current experimental conditions can cause a a certain degree of oxidative darage to the gill and digestive gland of C.gigas.The antioxidant system and Multi-xenobiotic Resistance Mechanism exogenous substances in C.gigas play an important role in the defense of SWCNTs.At the same time,the combined exposure of SWCNTs and PHE can produce more toxic effects than the single exposure,and there are some differences in the toxic effects ofdifferent combined exposure modes,which are manifested in the fect that the toxic effects of sequential exposure are higher than that of combined exposure.