Dietary Risk Assessment Of Epoxiconazole And Kresomix-methyl On Rice And The Adsorption Of Epoxiconazole In Biochar

In order to understand the residual degradation behavior of 250 g/L kresoxim-methyl and epoxiconazole suspnding agent on rice,understand their environmental impact,scientifically and comprehensively assess their dietary risk,and explore the remediation and treatment of water contaminated by epoxiconazole with reproductive toxicity and potential carcinogenicity.In this paper,a method for simultaneous analysis and determination of kresoxim-methyl and epoxiconazole residues in rice samples was established by means of gas chromatography with the aid of the experimental study of recovery.Based on that,through field experiments in accordance with GAP specifications,the residue digestion of kresoxim-methyl and epoxiconazole in brown rice,rice husk and rice straw was studied after the application of 250 g/L kresoxim-methyl and epoxiconazole suspnding agent in 12representative regions of China.This not only provided data support for the dietary risk assessment of brown rice,but also guided 250 g/L kresoxim-methyl and epoxiconazole.The scientific use of 250 g/L kresoxim-methyl and epoxiconazole suspnding agent and its related preparations in rice provides an important basis.Afterwards,the adsorption of epoxiconazole in water by five biochar materials was studied by batch adsorption equilibrium method.The details are as follows:（1）A method for simultaneous determination of epoxiconazole and ethermycin residues in rice samples was established,which met the technical requirements of pesticide residues analysis and detection in China.（2）The digestion of epoxiconazole and kresoxim-methyl in brown rice and rice husk conforms to the first-order chemical kinetics equation(C_t=C_0·e^-kt),and epoxiconazole and kresoxim-methyl are easily digested in brown rice and husk,which is hard to cause residual pollution.（3）250 g/L kresoxim-methyl and epoxiconazole suspnding agent was applied twice in12 representative areas of China according to 187.5 g a.i/ha（with an interval of 7 days）.At28 days after the final application,the residues of epoxiconazole in brown rice were lower than the MRL value of 0.50 mg/kg established in China;the residues of kresoxim-methyl in brown rice were all less than 0.10 mg/kg.（4）The estimated daily intakes of epoxiconazole and kresoxim-methyl were 0.13 mg and 0.27 mg,accounting for 10.3%and 1.1%of the daily allowable intake,respectively.This indicated that the residues of epoxiconazole and kresoxim-methyl did not pose unacceptable risks to the health of the general population.Suggestions for rational use are as follows:250 g/L kresoxim-methyl and epoxiconazole suspnding agent agent is used twice on rice with 187.5 g a.i/ha（50 g/mu）,with an interval of 7 days and a safe interval of 28 days.（5）Five kinds of biochars showed concentration effect on the adsorption of epoxiconazole in water,and the adsorption capacity increased with the increase of initial concentration.The adsorption capacity of five kinds of biochar to epoxiconazole in water decreased at pH 3-7,reached the lowest value at pH 7,and then increased gradually with the increase of pH value,then reached the maximum value at pH=9 and remained basically unchanged.The amount of epoxiconazole adsorbed by five kinds of biochar increased with the increase of temperature from 10 to 40℃,indicating that the adsorption of epoxiconazole on biochar in water was an endothermic process.The results of dosage test showed that when the dosage of coconut shell biochar,sawdust-coal biochar and bamboo biochar increased from 0.05 g/L to 0.50 g/L,the adsorption capacity increased significantly,and reached the maximum at 0.50 g/L;while when the dosage of rice straw biochar and rice husk biochar increased from 0.05 g/L to 2.00g/L,the adsorption capacity increased significantly,and reached the maximum at 2.00 g/L.The crystal structure of coconut shell biochar,sawdust-coal biochar and bamboo biochar is stable by X-ray diffraction characteristics of five kinds of biochar tested,which indicates that the carbonization is sufficient and the adsorption effect is better.Fourier transform infrared spectroscopy characterization showed that hydrogen bonding and charge transfer occurred mainly in the process of adsorption of epoxiconazole by five kinds of biochar.Among them,coconut shell biochar,sawdust-coal biochar and bamboo biochar with better adsorption effect mainly undergo charge transfer,while rice straw biochar and rice husk biochar with poorer adsorption effect mainly undergo hydrogen bonding.Scanning electron microscopy and specific surface analyzer characterization showed that rough,porous biochar surface meant larger specific surface area,pore volume,pore area and smaller pore diameter,and had better adsorption effect.Taken togather,the adsorption effect of coconut shell biochar,sawdust-coal biochar and bamboo biochar on epoxiconazole in water is good and stable,which is suitable for the treatment of pollution caused by the use and residue of epoxiconazole in water.