Bioremediation Of Soils Contaminated By Atrazine Or Nicosulfuron

Nicotine/Atrazine(atrazine and nicosulfuron-methyl)is widely used as an important herbicide in agricultural production.Due to incorrect use or excessive application,atrazine and nicosulfuron remain in the soil,rivers and other environments,causing serious phytotoxicity to crops from time to time.In addition,the residues of atrazine and nicosulfuron contaminated pose a serious threat to human health and ecological security.Therefore,the efficient and rapid removal of atrazine and nicosulfuron residues in the soil has became an urgent problem that needs to be solved.Bioaugmentation remediation and biostimulation remediation are two common remediation methods for non-point source pollution of organic pollutants.In this study,the atrazine-degrading strain Paenarthrobacter sp.strain AT-5,preserved in the laboratory,was used for bioaugmentation remediation of atrazine-contaminated soil,to study the effects of degrading bacteria on the atrazine residues in the soil,and to investigate the colonization and survival of degrading bacteria in the soil and its influence on the structure of soil microbial community.Since the high-efficiency degrading strains of nicosulfuron have not been isolated and screened,this study adopted biostimulation remediation technology,selecting rice bran,earthworm manure,and sodium acetate as exogenous additives to bioremediate nicosulfuron-contaminated soil and to study different external sources.The effect of source additives on the removal of nicosulfuron residues,and the effects of different additives on soil microbial community structure were investigated.This research will provide the theoretical basis and technical support for the bioremediation of atrazine and nicosulfuron soil residues.1.Bioaugmentation of atrazine-contaminated soilThe degrading bacterial agent AT-5 was added to atrazine-contaminated soil(residual concentration of 5 mg/kg dry soil)by mixing soil at an inoculum of 10~7 CFU/g dry soil for bioaugmentation remediation.The results showed that the control group added 5 mg/kg atrazine to the soil,the atrazine residual concentration was 3.36 mg/kg at 14 days,while the soil samples inoculated with the degrading bacterial agent AT-5 showed that the residual concentration of atrazine was lower than 1 mg/kg at 3 days,and it was not detected at 14days.At the same time,the key atrazine degrading enzyme gene(trz N)in strain AT-5 was absolutely quantified by the method of fluorescence quantitative PCR to investigate the colonisation of strain AT-5 in soil.The results showed that in the treatment group with medicine and bacteria,the number of viable bacteria of strain AT-5 in the soil gradually decreased with the passage of time,and the number of strain AT-5 dropped to 6.20×10~6CFU/g dry soil at 7 days.The number of strain AT-5 remained basically unchanged.High-throughput sequencing was used to further study the dynamic change process of the bacterial community structure in soil.The results showed that the bioaugmentation remediation of strain AT-5 had an impact on the richness and diversity of the bacterial community in the soil and would reduce the richness and diversity of the microbial community.Compared with the control group,the application of atrazine had no significant effect on the diversity and richness of the microbial community in the soil.The addition of strain AT-5 will promote the growth of bacteria belonging to the genera Paenarthrobacter and Pseudarthrobacter,while also inhibiting the growth of bacteria belonging to the genera Nocardioides.2.Biostimulation of nicosulfuron-contaminated soilRice bran,vermicompost(10%dry soil mass)and sodium acetate(2.05 g/kg dry soil)were added to the residual soil of nicosulfuron(1 mg/kg dry soil)by mixing soil,and the degradation effect of nicosulfuron in soil was determined.The results showed that the addition of rice bran could not promote the degradation of nicosulfuron in the soil compared with the dosing treatment group,and vermicompost had a slight promotion effect on the degradation of nicosulfuron in the soil.Sodium acetate could quickly and effectively promote the removal of nicosulfuron in the soil,but with the consumption of sodium acetate,the residual concentration of nicosulfuron in the soil was basically maintained at about 0.5 mg/kg after 14 days.High-throughput sequencing was used to study the dynamic change process of the microbial community structure in soil samples.The results showed that,compared with the control group,the application of nicosulfuron had no significant effect on the diversity and richness of the microbial community in the soil.Adding rice bran and vermicompost significantly affected microbial community structure,reduced community richness and diversity,and promoted or inhibited the growth of bacteria in many genera.The addition of sodium acetate has no significant effect on the structure of the soil microbial community,and over time,it will stimulate the growth of bacteria of Pseudarthrobacter and other genera.