Risk Assessment On Combined Effects Of Neonicotinoids Residues Mixtures In Vegetables

The pesticide residue is the main problem for the safe production of vegetables.The combined pollution and joint toxicity of a variety of pesticides residue in a vegetable has brought new challenges to agricultural safety.Pesticides called neonicotinoids are widely used but have potential risks to environments.This study is dedicated to exploring the compound residual adsorption and degradation behavior of three major neonicotinoid pesticides The combined toxic effects of three new nicotine pesticides were determined by cytotoxic methods.The study can provide fundamental data for assessing the risk of pesticide pollution and setting residue limits of various pesticides.(1)The residue detection methods of the neonicotinoids,including imidacloprid,acetamiprid,and thiamethoxam in vegetables were established based on modern chromatography and mass spectrometry.The acetonitrile was extracted by vortexing The purification process was QuEChERS methods(a purification tube containing 150 mg of anhydrous magnesium sulfate,25 mg of PSA,7.5 mg of GCB),and finally determined by UPLC-PDA.In different vegetables(brassica chinensis,cabbage,cucumber,tomato,celery and cowpea),the recovery rates of imidacloprid were between 93.7 and 108.3%,the coefficients of variation were between 0.8 and 7.6%,and the limits of quantitative were 0.1 mg·kg-1.The recovery rates range of imidacloprid and thiamethoxam were 98.3~102.0%,94.3~96.1%,the coefficients of variation were 1.5~6.4%,1.7~9.0%,respectively,the limits of quantitative were 0.1 mg·kg-1.This method is fast,sensitive,and accurate,which met the analytical standards of imidacloprid,acetamiprid,and thiamethoxam residues in vegetables.(2)The adsorption behavior of imidacloprid was studied in dynamically monitored method by the liquid pesticide immersion using brassica chinensis,cabbage,cucumber,tomato,celery and cowpea.The results showed that the adsorption concentration of imidacloprid in six kinds of vegetables increased gradually and reached the peak at 30h~36h.However,the adsorption rates were obvious different,and there was a significant difference in residue at the same time between different vegetables.The adsorption capacities were sorted as follows: cabbage> brassica chinensis > celery> cucumber> tomato> cowpea.The adsorption behavior of imidacloprid in vegetables obey pseudo-first order kinetics model and the correlation coefficient are more than 0.9.The theoretical residue at the peak is close to the actual residue.(3)With the mixing of the same action mechanism pesticides in leafy vegetables by pesticide immersion.The residues of imidacloprid,acetamiprid and thiamethoxam in three neonicotinoids after mixed application were detected timely by indoor liquid immersion and field pesticide spraying way,respectively.The compound pollution kinetics of the same mechanism of pesticide and its influence between each other were analysis.The results showed that the residues of three neonicotinoids from the indoor experiment in brassica chinensis were increased and reached the peak at 24~48 h,and then the residues were slowly reduced and tended to stable.By analyzing the residues concentration-time relationship,it suggested that the adsorption behaviors were more consistent with the pseudo-second order kinetics model and the correlation coefficient R2 are more than 0.9.There was mixed pollution between the three neonicotinoids.Although the mixed application increased the adsorption rate of neonicotinoids in brassica chinensis,but the final residues of individual neonicotinoids showed a consistent effect,thus the mixed application reduced the residues total amount of individual neonicotinoid.The degradation process of three neonicotinoids in compound pollution obey first order kinetics model and the correlation coefficient are more than 0.9.The half-life periods are between 2.8691 and 6.7374 d.The degradation half-life period of single neonicotinoid with the mixed application was longer than that with separated application,and the degradation rate slow down.Therefore,the mixed application may increase the safety risk of individual neonicotinoids residues in agricultural products.(4)The in vitro cell method was used to study the combined toxicity of three neonicotinoids(imidacloprid,acetamiprid and thiamethoxam)to five kinds of cells(Marc-145 ? Vero ? ST ? SK-N-SH ? Sf-9).The three neonicotinoids in different concentration to stimulate five kinds of cells.The IC50 of four animal cells with imidacloprid was greater than 0.5 g·L-1,the IC50 of Sf-9 was 0.021 g·L-1.The IC50 of SK-N-SH and ST with acetamiprid were greater than 2.0 g·L-1,the IC50 of Vero,SK-N-SH,and Sf-9 were 1.958?0.769?0.004 g·L-1,respectively.The IC50 of Marc-145?Vero?ST?SK-N-SH?Sf-9 with thiamethoxam were 0.515?0.555?0.647?0.502?0.002 g·L-1,respectively.After analysis the combined toxic effects with CompuSyn software,the SK-N-SH has a synergistic effect with Vero under the mixed attack in the same toxic with the IC50 of acetamiprid and thiamethoxam.Under the mixed attack in the same,there was synergies by the mixed application of acetamiprid and thiamethoxam in SK-N-SH cell at low concentrations,and antagonism at high concentrations.There were synergies by the mixed application of acetamiprid and thiamethoxam and the mixed application of three neonicotinoids.However,the mixed application will increase the human security risks,people should avoid contact with the mixed neonicotinoids.There was antagonism by the mixed application of imidacloprid and acetamiprid in Sf-9.There were synergies at low concentrations and antagonism at high concentrations in other mixed ways,thus mixed application can be used to increase the insecticidal efficiency.The toxicity threshold of the combination of three neonicotinoids was calculated by the benchmark dose effect model.The toxicity threshold of the neonicotinoids combination was lower than the single neonicotinoid,thus the mixed neonicotinoids may raise the risk.(5)Using the field residual data and cell data,using the margin of exposure to assess exposure risk assessment of harmful compounds.Under the conditions of 5 times the recommended dose of applied neonicotinoids(imidacloprid,acetamiprid and thiamethoxam were 840?720 ?600 g·hm-2),based on the consumption datas of vegetables of all ages and sexes(per capita intake is 3.259 kg/person/d),mixed neonicotinoids are at a low risk level according to the joint toxicity threshold of SK-N-SH,margin of exposure was greater than 100,three kinds of neonicotinoids mixed use wouldn't cause harm to the people of different age and sex possibly.