Adsorption And Degradation Of Tetracyclines In Soil Under The Greenhouse Factors And Its Phytotoxicity Assessment

With the rapid development of intensive livestock and poultry breeding,a large number of livestock manure was used as organic fertilizer into the soil.At the same time,the antibiotics of organic fertilizer would remain in the soil,which threaten the soil environmental quality and human health.The greenhouse soils were obviously different from the open field soils,which salinization and acidification were more serious.In this research,we study the adsorption and degradation behavior of TCs in greenhouse soil and assessment of its phytotoxicity for pakchoi（brassica pekimensis）by combining analysis of batch sorption methods with the indoor simulation experiment on basis of the new HPLC method.We mainly draw the following conclusions:（1）The samples of soils were extracted with mixture of Na₂EDTA,Mcllvaine buffer solution and methanol（1:1:2,V/V/V）.The first concentration mode for samples of soils was rotary evaporation.The mobile phase used in HPLC for soil samples was methanol-0.01 mol/L dicarboxyl-acetonitril（8:76:16,V/V/V）with gradient elution,and was:0 min,8%methanol+76%0.01 mol/L dicarboxy+16%acetonitrilel;0¹2 min,15%methanol+60%0.01 mol/L dicarboxy+25%acetonitrilel;12¹7 min,8%methanol+76%0.01 mol/L dicarboxy+16%acetonitrilel;finally keep five minutes.The recovery rate of oxytetracyline（OTC）,tetracycline（TC）,chlorotetracycline（CTC）and doxycycline（DXC）in greenhouse soil was 61.80%,46.54%,48.61%and 56.60%,respectively.（2）With the increase of the initial concentration of TCs,the adsorption capacity of TCs in greenhouse soil were increased.The adsorption order was always:DXC>CTC>TC>OTC under the same concentration and environmental conditions.Compare the linear equation,Freundlich equation and Langmuir equation were better fitting to the antibiotics adsorption isotherm in greenhouse soils.There is no significant difference between them.Chicken manure,pig manure and sludge all can enhance the adsorption of TCs in greenhouse soil,and its adsorption capacity were increased with the increase of organic matter content.At the same time,the order of adsorption capacity of TCs was:pig manure>dewatered sewage sludge>chicken manure.With the environment temperature risen from 8℃to 37℃,the adsorption capacity of TCs in greenhouse soil were increased significantly,which has risen from 59.88 to 252.79.With pH value of the greenhouse soil was acidation from 6.75 to 5.40,the adsorption capacity of TCs in greenhouse soil were increased significantly.Salinization could increase the adsorption capacity of TCs in greenhouse under the salinization degree from mild salinity to severe,significantly.In severe salinization degree of greenhouse soil,Ca²⁺,K⁺,NH₄⁺,NO₃^-,Cl^-and SO₄^2-all had obvious positive effect on adsorption process.（3）The four kinds of TCs in greenhouse soil could rapidly degrade under various environmental conditions.The dynamic changes of their residues showed a rapid decline in the early stage of culture and a steady trend in the later stage.In addition,the degradation sequence of TCs in greenhouse soil was always CTC>TC>DXC>OTC.After the TCs of chicken manure,pig manure and sludge entered the greenhouse soil,the order of degradation rate of TCs was:pig manure>dewatered sewage sludge>chicken manure.In addition,the types of antibiotics,the types of organic fertilizers and the organic matter all could affect the degradation rate of TCs.When the environment temperature risen from 8℃to 37℃,the degradation ability of TCs in greenhouse soil was improved,significantly.At the same time,the degradation rate of TCs was between96.31%⁹9.70%under 37℃.With the pH value of greenhouse soil risen from 6.75 to5.40,soil acidification could reduce the degradation rate of TCs in the greenhouse soil,significantly,which decreased by 5.89%¹1.42%.With soil salinization degree of the greenhouse soil increased from mild salinization to severe,the degradation rate of TCs in greenhouse soil was significantly reduced,which decreased by 4.35%¹2.06%.（4）The degradation of TCs in greenhouse soil could be alleviated by avoiding light and sterilization.The degradation of TCs in greenhouse soil mainly depended on chemical hydrolysis,which accounted for 71.20%⁸1.14%,at the same time,microbial degradation accounted for 16.84%²5.71%,photodegradation accounted for1.20%⁴.59%.With the extension of incubation time,the chemical hydrolysis was continuously enhanced.The microbial degradation was increased first and then decreased,it maintained a certain proportion.The photodegradation generally decreased.Among the three degradation functions,the degradation sequence order of four TCs was always:CTC>TC>DXC>OTC.（5）The four kinds of TCs had no significant effect on seed germination rate of Chinese Cabbage.The TCs with concentration below 1 mg/L could promote root elongation of cabbage seeds,and the TCs with concentration more than 5 mg/L high concentration could inhibite root elongation of Pakchoi seeds.Under the same mass concentration,the inhibition effect of four kinds of TCs on the root length of Chinese cabbage showed CTC>OTC>TC>DXC.In addition,the root elongation of Chinese cabbage was more sensitive to four kinds of TCs than its germination rate.