Residual Character And Bioremediation Of Bensulfuron Methyl In Agricultural Fields

Bensulfuron methyl is one of the most widely used sulfonylurea herbicides in rice and wheat fields.In order to better control weeds,a variety of herbicides are mixed in agricultural fields.Bensulfuron methyl is not easy to volatilize or photolysis,which has small mobility,strong stability and long half-life.If the herbicide is continuously used in farmland for a long time,it is easy to cause herbicide residue pollution in farmland.The herbicide residues in the soil will be absorbed by crops.The value of bensulfuron methyl residue was 0.486 mg·kg^-1detected in vegetables from agricultural fields by Nasir,et al.The residual herbicides will be harmful to sensitive crops.For the treatment of herbicide residue pollution in the ecological environment,bioremediation is the focus.Bioremediation includes phytoremediation and microbial remediation.From the existing technology,as it is known that the bioremediation technology includes microbial degradation,which is safe and high efficient,without secondary pollution or residue.Therefore microbial degradation gradually become an important method to control organic pollution.Compared with the environmental bacteria isolated from the polluted soil,sludge or sewage and other special environment.The plant-endophytic symbiosis has more potential application value in the control of herbicide pollution.Residue characteristics of bensulfuron methyl and butachlor in rice and wheat fields in two agricultural planting districts were investigated.Because bensulfuron methyl degrades more slowly,an endophytic bacterium that can efficiently degrade bensulfuron methyl was isolated from the plants polluted by bensulfuron methyl,and its optimal growth conditions were explored.The main research results are as follows:In order to investigate the residual status of butachlor and bensulfuron methyl in agricultural fields from Nanjing,samples of soils and crops were collected according to the“Technical specification for soil environmental”（HJ/T 166—2004）on June 1 and November 3,2019.The residue of butachlor and bensulfuron methyl in the samples were analyzed by high performance liquid chromatography（HPLC–UV）.The residue and degradation dynamics of the herbicides were performed under the simulated conditions in the laboratory.Butachlor was detected in most paddy soils,bensulfuron methyl was detected in most paddy soils and wheat field soils.The results showed that butachlor and bensulfuron methyl were detected in agricultural fields of 10 sampling sites,they were not detected in crop samples.Butachlor could be detected in 12 soil samples and bensulfuron methyl could be detected in 14 soil samples.The detection rate of butachlor and bensulfuron methyl were 54.55%and 63.64%,the highest values of butachlor and bensulfuron methyl residue were 1.578 mg·kg^-1 and 0.102 mg·kg^-1.The average residual concentration of butachlor was higher than that of bensulfuron methyl in paddy soils,while the average residual concentration of bensulfuron methyl was higher than that of butachlor from different districts in wheat field soils.The average residual concentration of butachlor and bensulfuron methyl from Jiangning District were 0.226 mg·kg^-1 and 0.006 mg·kg^-1 higher than that from Liuhe District in all agricultural field soils.The average residual concentration of butachlor were 0.299 and 0.035 mg·kg^-1 higher than that of bensulfuron methyl in all agricultural field soils from Jiangning and Liuhe Districts.Moreover,the residual herbicides were more likely to stay in the soil with lower organic quality and higher p H value.Bensulfuron methyl residue were negatively correlated with soil organic quality,positively correlated with p H value.Butachlor residue was negatively correlated with soil organic quality,were not correlated with p H value under acidic condition.The degradation of bensulfuron methyl and butachlor were followed the first-order kinetic equation under the simulated conditions in the laboratory,their half-lives were 7.94 d and 13.08 d,their dissipation rate were 0.087 d^-1 and 0.053 d^-1.Although the dosage of butachlor was higher than that of bensulfuron methyl in agricultural soils,it’s degrade more quickly.The amount of butachlor applied is too high in some agricultural fields,it is necessary to enhance the control in agrochemical markets.An endophytic strain BQ1 was isolated and purified by dilution coating method from the well growing plant samples（Hemarthria,etc.）collected from the sewage outfall of a pesticide factory in Nanjing,in China’s eastern Jiangsu province.The bacterial morphology,physiological and biochemical properties and 16S rRNA gene sequence homology analysis of BQ1 were analyzed showed that strain BQ1 was identified as Microbacterium sp.High performance liquid chromatography（HPLC）was used to detect concentration of bensulfuron methyl in culture medium(10～100 mg·L^-1)inoculated with functional strain BQ1.The effect of p H,temperature,salt concentration,liquid volume,inoculum volume and additional nutrients was investigated on the growth and degradation ability of bensulfuron methyl inoculated with functional Microbacterium sp.BQ1.The optimum pH value for the growth of Microbacterium sp.BQ1 was 7.2.When the pH value was lower than 7.2 or higher than 7.2,the number of strain BQ1 and the degradation rate of bensulfuron methyl decreased.When the salt content was lower than or higher than 5 g·L^-1,the number of Microbacterium sp.BQ1 and the degradation rate of bensulfuron methyl decreased with the increase or decrease of salt content.Therefore,the optimum salt content for the growth of strain BQ1 was 5 g·L^-1.The growth of Microbacterium sp.BQ1 was inhibited and the degradation rate of bensulfuron methyl was decreased with the increase of medium volume.The addition of appropriate nutrients（glucose and yeast extract）could promote the growth of Microbacterium sp.BQ1 and the degradation efficiency of bensulfuron methyl.When the glucose content was 100 mg·L^-1 and the yeast extract content was 50 mg·L^-1,the growth of Microbacterium sp.BQ1 was inhibited The amount of Microbacterium sp.BQ1 and the degradation rate of bensulfuron methyl reached the maximum.Antibiotic resistance marker technology was used to mark Microbacterium sp.BQ1chloramphenicol and tetracycline hydrochloride were selected as screening antibiotics.Microbacterium sp.BQ1 was colonized into wheat and soybean by seed soaking.The results showed that the functional strain Microbacterium sp.BQ1 could be well colonized in wheat and soybean tissues.Under the condition of bensulfuron methyl pollution,the number of Microbacterium sp.The number of colonization in roots was significantly higher than that in stems and leaves.The colonization of strain Microbacterium sp.BQ1 significantly increased the growth rate of wheat by 26.0%（4 d）and 39.3%（8 d）,and the growth rate of soybean by 4.8%（4 d and 8 d）compared with control group.The accumulation of bensulfuron methyl concentration of bensulfuron methyl decreased by45.9%（4 d）and 59.6%（8 d）in wheat roots,decreased by 15.6%（4 d）and 27.5%（8 d）in wheat leaves colonized by Microbacterium sp.BQ1 compared with control group.The accumulation of bensulfuron methyl concentration of bensulfuron methyl decreased by 45.4%（4 d）and 38.6%（8 d）in soybean roots,decreased by 37.0%（4 d）and 26.4%（8 d）in soybean leaves colonized by Microbacterium sp.BQ1 compared with control group.The removal rate of bensulfuron methyl decreased by 12.6%（4 d）10.5%（8 d）in wheat Hogland nutritive medium colonized by Microbacterium sp.BQ1 compared with control group.The removal rate of bensulfuron methyl decreased by 10.6%（4 d）9.0%（8 d）in soybean Hogland nutritive medium colonized by Microbacterium sp.BQ1 compared with control group.The removal rate of bensulfuron methyl in Hoagland nutrient solution in the colonization group was significantly higher than that in the control group,and the reduction rate of bensulfuron methyl increased steadily with time.The results showed that Microbacterium sp.BQ1 can significantly reduce the residue of bensulfuron methyl in agricultural crops and environment.