The Study On Environmental Behavior Of Tetracycline Antibiotics In Soils

The tetracycline antibiotics （TCs） used in Poultry and Animal Aqua-Culture with the animalfeces resided in the soil, which caused the soil pollution and posed a potentially high risk for theecological environment and the safety of agricultural products. Currently, many countries hadcarried out survey of residues of TCs in environmental samples, but their transformationbehavior in the environment have rarely been reported. In this paper, with the solid phaseextraction （SPE） and high-performance liquid chromatography （HPLC）/liquidchromatographmass spectrometer （LC-MS）technology study the dynamics, the thermodynamicadsorption, soil column migration, degradation and its impact factors of OTC, TC and CTC,which were the most widely used, in soil. This study was provided available data and parametersto set a more complete model to predict environmental concentration of TCs and evaluation theirenvironmental risk. The results were as follows:Oxytetracycline（OTC）, tetracycline（TC）, chlortetracycline（CTC） were the most common TCsin the soil, a SPE-HPLC/LC-MS method was set up for the confirmed identification andquantitation of the three antibiotics in soil samples. Foucus on the optimization of the pH ofmobile phase and pre-treatment method including analyzing the influence of the extractioneluent, solid phase extraction eluent, extraction time and times, on the three typical antibioticstesting in soil. The results showed that the detection limits for OTC、TC and CTC in soil withHPLC were0.19,0.16and0.26mg/kg, the average recoveries were in the range of85.5%⁹2.8%, showed that this method in practical testing is feasible. The detection limits forOTC、TC and CTC in soil with LC-MS were0.89、0.56and1.17μg/kg, the average recoverieswere in the range of87.4%⁹5.7%. That is, the reproducibility and recovery of LC-MS werehigher and better than HPLC, but also more accurately for analysing complex matrix and tracesamples.Static equilibrium experiments were used to investigate the adsorption and desorption ofantibiotic tetracyclines in paddy soil. Results showed that TCs can be quickly reached adsorptionequilibrium in red soil, they reached up to98.2%of their adsorption capacity in30min.Elovich equation can well describe the process of the TCs adsorption kinetics equation, thecorrelation coefficient R²>0.82. all adsorption and desorption isotherms could be best describedby the Freundlich model, and the correlation coefficients, R²>0.99, the Freundlich constants,K_f,for TCs are between58.73and69.63,belong to a moderate adsorption level, which indicatedthat soil had relatively strong adsorption to TCs and the poorly migration of TCs in soil.Theempirical constants,1/n, for TCs are between1.09and1.20, that means, the adsorption curves are “S” shape. In addition, the results showed that the adsorption of TCs increased with theincreased of the content of organic matter, clay, oxide, and the pH of solution from4to9, whenpH was6, the adsorption of TCs was maximum.To simulate the transport of tetracycline antibiotics （TCs）, column experiments were used tosurvey the impact factors in the processes of TCs transport, such as the soil types, the watervolume, the pH of leaching water and pesticide application rates. The results indicated that TCsaccumulated mainly at the topsoil of the soil column after leaching. The content of TCsdecreased sharply with the increase of depth in the soil columns, and the depth of migration ofTCs in the soil could be ranked the order of most to least effective as follows: latosolic red soil>red soil> black soil. The TCs content in the same depth increased with increasing the volume ofsolution, and decreased with increasing the pH of solution. The TCs content distribution andleaching depth in the soil was positively correlated with the pesticide application rates.When theleaching solution contains a certain amount of TCs, the depth of TCs transport in the soilincreased significantly.In this paper, using L₉（3⁴） orthogonal experiments to investigate the impact factors, of TCsdegradation in soil, such as the Soil moisture, pH, the initialization content of TCs and theintension of illumination. The results indicated that the effect of each factor to OTC and TCfollowed the order of initialization contents> the intension of illumination> soil moisture> pH,however, to TC, the order was initialization contents> soil moisture> the intension ofillumination> pH. The rate of degradation of TCs in different types of soil followed the order ofred soil>paddy soil> black soil, for the same soil, the rate of degradation followed the order ofCTC>TC>OTC. Light was the main degradation factors to TCs in the soil, the degradationhalf-life of the TCs in the dark treatment conditions is about twice than the light treatmentconditions. The impact of microorganisms on the degradation of TCs is relatively small, sterilesoil degradation half-life of degradation half-life than the end of sterilization3to7days long, andTCs two degradation process in the soils could be well described with a dynamic equationC=C₀e^-Kt, with their correlation coefficients of above0.91.