Toxic Effects Of Polychlorinated Biphenyls To The Growth Of Earthworm Eisenia Fetida

It is urgent to develop low cost in situ bioremediation technology for site remediation of toxic persistent organic pollutants.In recent years,the discovery that the earthworm,as a contaminated in-situ remediation soil animal,can both absorb and degrade toxic persistent organic pollutants and promote soil fertility has attracted the attention of the research community.However,there are a certain biological tolerance to organic pollutants,and responses of its individual and cellular biochemical indexes change with the change of organic pollution concentration for soil fauna.Therefore,it is necessary to explore the time-dose-responses of earthworm to toxic persistent organic polychlorinated biphenyls(PCBs)with different chlorination status to reveal the sensitive biochemical indicators and the molecular mechanism.The laboratory temperature controlled exposure method was used,Eisenia fetida was taken as the subject,and the representative pollutants of persistent organic pollutants PCB28(Tri-PCB),PCB52(Tetra-PCB)and PCB101(Penta-PCB)were selected,comparing the toxic effect of earthworm under the condition of single and mixed pollutants(1:1:1),different dose exposure concentration(mg/kg)and exposure time(0-28d).GC-MS was used to detect PCBs accumulation,enzyme activity was detected by enzyme reaction method,epidermal damage was observed by transmission electron microscopy(TEM),cell activity was measured by flow cytometry,and the toxic mechanism was analyzed by metabolomics.The results are present as follows:(1)There was a significant correlation between the growth of Eisenia fetida and chlorination status of PCB,and there were differences in concentration,time and mixed state.When Eisenia fetida exposed to 1 and 10 mg/kg single PCB,the growth inhibition rate increased with the increase of chlorination number and time,the higher the concentration,the higher the inhibition rate within 28 days of exposure,namely PCB101>52>28.The growth inhibition ratio of compound PCBs exposure was higher than that of single PCBs exposure,and the maximum inhibition ratio was 24.39±0.07%.Transmission electron microscopy(TEM)morphological evidence also proved that the degree of damage to the epidermis of Eisenia fetida was aggravated with the increase of exposure time,and the damage between the different chlorination status was?₃-PCBs>PCB101>PCB52>PCB28.(2)The biochemical indexes of Eisenia fetida were sensitive to PCBs.The results of the enzyme system showed that the activity of SOD,CAT and the content of GSH increased first and then decreased within 28 days,and the activity was the highest at 14days.The degree of change under 10 mg/kg exposure is greater than 1 mg/kg,and the degree of oxidative damage of PCB28 and PCB52 is weaker than that of PCB101.The enzyme with the most obvious activity change is SOD.Cellulase activity in the digestive system of Eisenia fetida was increased within 28 days after PCBs exposure.PCB28 had the most obvious promoting effect on enzyme activity.Protease activity tends to decrease after PCBs exposure.The higher the concentration,the higher the integrated biomarker response,and the total index of the compound exposure group was greater than that of the single exposure group,which had a synergistic effect on the toxicity of Eisenia fetida.(3)Metabolites of Eisenia fetida were related to the accumulation of PCBs,showing differences in carbohydrate metabolism,protein metabolism and lipid metabolism.After 28 days of single PCB exposure,the maximum enrichment in earthworm was PCB28,with the absorption reaching 85.88 mg/kg.After the compound PCBs exposure,the enrichment percentage of PCB101 with the highest log K_ow value increased from 26.57%to 30.16%.Exposured to 10 mg/kg PCBs,the metabolites with significant differences in Eisenia fetida were selected and analyzed by T test and cluster analysis,and the KEGG enrichment pathway was analyzed.The results shows that significant enrichment of carbohydrate metabolism including starch and sucrose metabolism and the tricarboxylic acid cycle,protein metabolism including glycine,serine and threonine metabolism,alanine,aspartic acid and glutamic acid metabolism and glutathione metabolism,and lipid metabolism including steroids and fatty acid biosynthesis.PCB28 exposure enhanced the metabolism of carbohydrate metabolism,and slightly affected protein metabolism.PCB52 had a weaker promoting effect on carbohydrate metabolism of earthworm and a stronger effect on protein metabolism than PCB28.PCB101 not only affected protein metabolism,but also inhibited lipid metabolism.Compound PCBs exposure showed the strongest metabolic toxicity,with carbohydrate metabolism,protein metabolism and lipid metabolism all significantly affected.