Detection Of Ecotoxicity In Microbial Remediation Of Petroleum Contaminated Soil

The use of petroleum and its byproducts has expanded substantially as the national economy has grown rapidly.Petroleum hydrocarbons leak owing to irregular operation or accident reasons during the production,processing,storage,transportation,and use of petroleum,resulting in significant soil petroleum contamination.Petroleum contamination impacts soil’s physical,chemical,and biological processes,as well as crop cell metabolism and yield.It can also enter the human body through respiration,skin contact and dietary intake,affecting human health.Therefore,the remediation of petroleum contaminated soil is becoming more and more important.The problem of small number and insufficient activity of microorganisms with petroleum hydrocarbon degradation ability leads to low natural degradation ability.Bioaugmentation and biological stimulation can effectively improve petroleum hydrocarbon degradation rate.Therefore,in this study,the immobilized bacteria was prepared by fermentation of the flora with good degradation screened in the early stage of the laboratory,and the microbial remediation experiment was carried out on the petroleum contaminated soil near the abandoned oil well.The higher plant toxicity test,earthworm toxicity test,enzyme activity test and luminescent bacteria toxicity test were used to detect the ecological toxicity of soil in different restoration periods.High-throughput sequencing technology was used to analyze the changes of bacterial diversity and its correlation with environmental factors during soil remediation,which provided theoretical support for microbial remediation technology.The main findings are as follows:（1）After 42 days of remediation,the content of petroleum hydrocarbons(C₁₀-C₄₀)in Group A decreased from 1.66 g/kg to 1.00 g/kg,and the degradation rate reached40.64%.The content of petroleum hydrocarbons(C₁₀-C₄₀)in Group B decreased from4.00 g/kg to 1.94 g/kg,and the degradation rate reached 51.56%.The microbial agent can effectively degrade petroleum hydrocarbon pollutants in soil.The microbial remediation process through microbial remediation has good remediation effect.（2）The germination rate index of wheat seeds did not indicate the changes of soil toxicity in this study.The growth and development indexes of wheat seedlings（plant height,aboveground fresh weight,root fresh weight）indicated that the soil ecological toxicity of 7 d and 14 d was strong.In the whole remediation process,the soil of Group A and Group B inhibited the photosynthetic pigment content of wheat,the chlorophyll a content and carotenoid content decreased to the lowest on the 21^st day of remediation.The 7 d and 14 d survival rates of earthworms in the two groups of soils gradually decreased during the soil remediation process,and then gradually increased.The survival rate at the end of the remediation was higher than that at the beginning of the remediation.The survival rate of earthworms in Group B decreased to the lowest on the 21^st day of remediation.The relative luminosity of luminescent bacteria in dichloromethane（DCM）/dimethyl sulfoxide（DMSO）extracts of the two groups of soils was the lowest on day 21.Catalase activity was significantly negatively correlated with petroleum hydrocarbon content（P<0.01）,which could better indicate the change of petroleum hydrocarbon content in soil.In the process of microbial remediation,the toxicity of petroleum contaminated soil increased in the early and middle stages,and decreased in the later stage.The photosynthetic pigment content index in the higher plant toxicity test,the survival rate index in the earthworm toxicity test and the DCM/DMSO extraction liquid phase in the luminescent bacteria toxicity test showed good consistency with the luminescence index.Earthworm avoidance response showed higher sensitivity than survival rate test.（3）The relative abundance of dominant bacteria in the contaminated soil was significantly higher than that before repair（P<0.05）.The dominant bacteria changed fromMycobacterium,norank＿f＿＿no-rank＿o＿＿norank＿c＿＿J-G30-KF-CM66,norank＿f＿＿norank＿o＿＿norank＿c＿＿PAUC43f＿marine＿benthic＿group,norank＿f＿＿norank＿o＿＿Actinomarinales,Bacillus to Proteus,Bacillus,Salinimicrobium,norank＿f＿＿norank＿o＿＿SBR1031,Mycobacterium.The number of soil microbial species and community richness dropped progressively over the remediation process,while microbial remediation of petroleum polluted soil improved soil bacterial community diversity.Compared with the early and middle stages of remediation,the differential species with higher relative abundance in the soil at the late stage of remediation were bacteria that degraded refractory macromolecules such as aromatic hydrocarbons,polycyclic aromatic hydrocarbons and long-chain fatty acids.Microbial enhanced remediation stimulates the enhancement of functions such as degradation of organic pollutants,carbohydrate metabolism and energy metabolism.The changes of soil microbial community structure were related to environmental factors.In this study,the species distribution of prtroleum contaminated remediation soil was greatly affected by environmental factors TPH,EC,AN and TP（P<0.05）.