Residue Detection And Risk Assessment Of Four Herbicides On Rice In Chongqing

Rice(Oryza sativa L.)is an important grain in China.The quality and safety of rice are highly related to human health and national strategies.Herbicides play important roles in assuring paddy production and quality.However,weed resistance increased gradually for long-term use of herbicides in paddy fields.The Farmers increased herbicides dosage is inevitable in order to obtain the same control efficiency.Such phenomenon poses potential threats to the quality and safety of rice,environment and human health.Thus,it is of great significance to monitor and evaluate the residue levels of herbicides and risk assessment after high dosage application in paddy fields.Pyrazosulfuron-ethyl,bensulfuron-methyl,acetochlor and butachlor are extensively used herbicides in paddy fields in consideration of good selectivity,high efficiency and low toxicity for controlling annual and perennial broadleaf weeds.At present,few studies focus on the evaluation of residue levels and risk assessment of pyrazosulfuron-ethyl,bensulfuron-methyl,acetochlor and butachlor in rice fields after high dosage application.Therefore,field experiments of the four herbicides in rice fields were conducted in Chongqing.The dissipation dynamics in soil and water,final residue in husked rice and rice hull,and risk assessment of the four herbicides in paddy fields after high dosage application at Good Agricultural Practices condition were investigated.Such results clarified residue levels and risk assessment of the four herbicides on rice after extensive application,as well as provided scientific guidance on the proper and safe application of rice herbicides in paddy fields and assured the rice safety.The main results are as following:(1)QuEchERS coupled with-high performance liquid chromatography-tandem mass spectrometry analytical methods for the determination of pyrazosulfuron-ethyl and bensulfuron-methyl,and QuEchERS coupled with-gas chromatography-tandem mass spectrometry analytical methods for the determination of acetochlor and butachlor in rice soil,husked rice and rice hull were developed.Pyrazosulfuron-ethyl,bensulfuron-methyl,acetochlor and butachlor residue in rice soil,husked rice and rice hull were extracted with QuEChERS method.Pyrazosulfuron-ethyl and bensulfuron-methyl were determined by HPLC-MS/MS coupled with positive ion mode of multi-reaction monitoring.And the mobile phase and ion detection conditions of pyrazosulfuron-ethyl and bensulfuron-methyl were optimized.Acetochlor and butachlor were determined by GC-MS with selected ion monitoring mode.And the oven temperature program and ion detection conditions of acetochlor and butachlor were optimized.Then,external standard method was used for quantification of the four herbicides and the performance of developed method was validated.The average recoveries of the four herbicides in all matrices in the range of 78.9%~108.0% with relative standard deviation less than 15%.The limit of detection ranged from 0.04~1.0 ng and the limit of quantification ranged from 0.01~0.1 mg/kg.The results indicated the developed method was simple,quick,strong specificity and sensitivity,and qualified in determining pyrazosulfuron-ethyl,bensulfuron-methyl,acetochlor and butachlor residue in rice soil,husked rice and rice hull.(2)Field experiments were conducted in Chongqing municipality.Pyrazosulfuron-ethyl,bensulfuron-methyl,acetochlor and butachlor were sprayed one time at the recommended dosage and double of the recommended dosage in the rice tillering stage.The dissipation dynamics of the four herbicides in soil and water,and final residue in husked rice and rice hull were investigated.The results showed all the dissipation processes of the four herbicides in soil followed the first-order kinetic reaction.When the paddy environments were treated with the recommended dosage,the dissipation half-lives of pyrazosulfuron-ethyl,bensulfuron-methyl,acetochlor and butachlor in soil were 3.5~13.6 d.When the paddy environments were treated with the double of the recommended dosage,the dissipation half-lives of the four herbicides in soil were 4.0~17.8 d.Therefore,pyrazosulfuron-ethyl,bensulfuron-methyl,acetochlor and butachlor are easily degraded.The four herbicides degraded fast in water with over 95% of the initial residues dissipated within the first 5 days.The residues of pyrazosulfuron-ethyl,bensulfuron-methyl,acetochlor and butachlor were not detectable in husked rice and rice hull.The results implied that pyrazosulfuron-ethyl,bensulfuron-methyl,acetochlor and butachlor were safe on rice under the recommended dosage and double of the recommended dosage at GAP condition.(3)The risk assessment of pyrazosulfuron-ethyl,bensulfuron-methyl,acetochlor and butachlor on rice were investigated via risk assessment method with the supervised trial median residue at GAP condition,dietary structure data,maximum residue limit and acceptable daily intake.After long-term dietary intake,the risk quotient values of pyrazosulfuron-ethyl,bensulfuron-methyl,acetochlor and butachlor in various crowds in Chongqing were far less than 1 and the consumer protection level values were greater than 1.Therefore,both the risk quotient and consumer protection level of the four herbicides were within the safe range specified by national regulation.Such results indicated that if the four herbicides were applied in the paddy environments under GAP condition in Chongqing,then they will not cause chronic dietary risk.