Combined Toxic Effects Of Nanoscale Zero-valent Iron And Tetrachlorobiphenyl On Earthworm Eisenia Fetida

Nanoscale zero-valent iron(nZVI) has been widely used in remediation of contaminated sites,polychlorinated biphenyls(PCBs)are one of the main persistent organic toxic pollutants in e-waste dismantling contaminated sites.The combined toxicity effect and mechanism of engineering remediation materials and persistent toxic substances on functional organisms in the site need to be further studied.In this thesis,nZVI and 3,3',4,4'-tetrachlorobiphenyl(PCB77)were chosen as the tested pollutants,the typical soil animal Eisenia fetida as a model organism,and the temperature controlled soil exposure experiment based on orthogonal design was conducted to study the toxic effects of single and combined exposure of nZVI and PCB77 at individual,tissue and molecular levels on earthworms and the enrichment of pollutants in earthworms.The main findings are present as follows:(1)Eisenia fetida had bioaccumulation effects on nZVI and PCB77.During the28-day exposure period,the enrichment of iron in earthworm was concentration dependent(7.89-16.34 mg/kg),the enrichment of PCB77 increased gradually with the extension of exposure time and reached the peak on the 14 th day(13.86-96.73 mg/kg).nZVI promoted the enrichment of PCB77 in earthworms,the coexistence of 10 g/kg nZVI and 1 mg/kg PCB77 significantly increased the content of PCB77 in earthworms,which was 169.64% higher than that without nZVI.At the same time,nZVI promoted the degradation of PCB77 in soil,and the effect was related to the dosage of nZVI.(2)The combined exposure of nZVI and PCB77 produced synergistic toxic effects on Eisenia fetida.The coexistence of PCB77 and nZVI significantly inhibited the growth and reproduction of earthworm,the highest inhibition rates were 16.32%and 93.16,respectively.TEM images of earthworm epidermis showed that the upper epidermis of earthworm was damaged and the cuticle was disordered after exposure to nZVI and PCB77 for 28 days.The apoptosis data of coelomocytes of earthworms further showed that the coexposure of nZVI and PCB77 had a synergistic effect on the cell apoptosis of earthworms.PCB77 and nZVI at corresponding high levels(10 mg/kg and 10 g/kg)synergistically induced both oxidative stress and lipid peroxidation in earthworms,which were manifested in earthworms with reactive oxygen species(ROS).Lipid peroxidation product malondialdehyde(MDA)content increased significantly and antioxidant enzymes superoxide dismutase(SOD)and catalase(CAT)activities in the early and mid-term exposure(2-14 days)significantly increased and was suppressed in the late exposure period(28 days).According to Pearson correlation analysis,the weight of earthworms and ROS could be used as sensitive response indexes for the combined toxicity of PCB77 and nZVI(R ? 0.784,p < 0.05).(3)Combined exposure of nZVI and PCB77 interfered with the metabolism of Eisenia fetida.A total of 102 metabolites were detected in earthworms exposed to PCB77 and nZVI,among which lipids and organic acids accounted for 34.69% and26.53 of the total metabolites,respectively.13,25 and 36 differential metabolites compared with the control were screened in the earthworms exposed to 10 mg/kg PCB77,10 g/kg nZVI,and the combined 10 mg/kg PCB77 & 10 g/kg nZVI,respectively.The enrichment analysis of metabolic pathway showed that the amino acid metabolism in earthworms was significantly promoted after exposure to 10 mg/kg PCB77,and the tricarboxylic acid(TCA)cycle and energy metabolism of earthworms were disturbed when exposed to 10 g/kg nZVI.The metabolic disturbance of earthworm exposed to 10 mg/kg PCB77 and 10 g/kg nZVI was more significant than that of single exposure,the TCA cycle,aerobic respiration and the normal glutamate metabolism of earthworms were impeded.