Determination Of Tetracyclines In Fertilizer And Their Degradation In Soil And Accumulation By Crop

Antibiotics residues in fertilizer have attracted wide attention among domestic and foreign researchers.Oxytetracycline,tetracycline,chlortetracycline,and doxycycline are four tetracyclines widely consumed in livestock and poultry breeding.Overuse of antibiotics will contaminate ecological environment,affect the growth of plants and animals,and damage human health.Recent studies of tetracyclines mainly focus on the determination methods,while literatures about fate in farmland and remediation of contaminated soil are relatively scant.In this study,a simultaneous determination of tetracyclines based on High-Performance Liquid Chromatography coupled with UV detector?HPLC-UV?was established,and an ultrasound-assisted extraction method for tetracyclines in manure was optimized using response surface methodology.Degradation of tetracyclines in soil,uptake in crops,and control effect of biochar was also studied.The main research findings are:?1?The chromatographic conditions for simultaneous detection of tetracyclines based on HPLC-UV include:SPP C₁8 column at 30? with wavelength of 355 nm;acetonitrile,0.01 mol/L oxalic acid,and methanol as the mobile phase and pumped at a rate of 1.0 mL/min using gradient program.Good linearity was obtained for four tetracyclines in the concentration range of 0.1?20?g/mL,and limit of detections in a range of 0.03-0.05?g/mL.?2?The extraction solution was a mixture of McIlvaine buffer,0.1mol/L Na2EDTA solution and methanol?1:1:2,v/v/v,pH was adjusted to 7.15?.Tetracyclines were extracted in an ultrasonic bath for 10 min at 40? with 20,10 and 10 mL of extraction buffer each time.The recoveries of oxytetracycline,tetracycline,chlortetracycline and doxycycline were 92.42%,87.85%,81.89%and 84.46%,respectively.Relative standard deviations were 2.94%,3.88%,4.06%and 2.37%,respectively.?3?The degradation of oxytetracycline,tetracycline,chlortetracycline and doxycycline in soil matched first order loss equation?R²>0.86?,with respective degradation rates constant as 0.0047,0.0053,0.0052 and 0.0039 h-1,and respective half-lives as 6.14,5.45,5.55 and 7.41 days.?4?Lettuce?Lactuca sativa?was confirmed to absorbed tetracyclines,and the migration in soil-lettuce system could be explained by two-compartment model.The maximum concentrations in lettuce of oxytetracycline,tetracycline,chlortetracycline and doxycycline were 13.53?0.099 SW₀?,10.70?0.077 SW₀?,4.57?0.028 SW₀?and 13.50?0.080 SW₀?mg/kg dry weight,reached at 4.57,2.88,3.03 and 4.54 days after transplant,respectively,where SW₀ was the initial concentration of antibiotics in soil.The accumulation of chlortetracycline in lettuce was relatively less,while chlortetracycline and tetracycline were relatively faster.?5?The adsorption of tetracyclines to soil and biochar was nonlinear.Both Freundlich and Langmuir model were fitted to the measured data,with R² in the range of 0.815?0.994,and 0.898?0.994,respectively.By amending with biochar,the adsorptive capacities of oxytetracycline to soil increased from 2210.00mg/kg to 2920.06mg/kg,tetracycline from 2678.54mg/kg to 5069.32mg/kg,chlortetracycline from 2522.73mg/kg to 2778.99mg/kg,and doxycycline from 2372.64mg/kg to 2624.51mg/kg.?6?After adding biochar to soil,the uptake of oxytetracycline,tetracycline,chlortetracycline and doxycycline in lettuce decreased by 34.33%,34.76%,48.67%and 40.67%,respectively,indicating the control effect of biochar to reduce the absorption of tetracyclines in lettuce.