Effects Of Biochar On Availability And Form Transformation Of Tetracycline Antibiotics In Soil

With the rapid development of aquaculture industry and the pharmaceutical industry,the antibiotics entered into the environment are increasing,and in which tetracycline antibiotics are the main pollutants.Research shows that the tetracycline antibiotic residues in soils can transfer by food chain and cumulate risk,which resulting into serious harm to human health and the environment.Because of its advantages of economy,safety and high efficiency,biochar has received increasing attention in recent years.Research on the enhancement of adsorption for tetracycline antibiotics in soils has made many advances by biochar,but the key problems affecting the biochar on tetracycline antibiotic availability and the form transformation between tetracycline antibiotics during the aging process are still not clear,which urgently need to study.This paper studied the preparation of modified walnut shell-based biochar and its properties for adsorption of oxytetracycline,tetracycline and chlortetracycline as the representative of the tetracycline antibiotics;add biochar into soils,and explore the enhance role of biochar for adsorption of tetracycline antibiotics and the effects on availability of tetracycline antibiotics in soils;and carry out soil aging test to investigate the effect of biochar on form transformation of tetracycline antibiotics during the aging process.The main results are as follows:(1)With the modified agents of a series of concentrations of KOH,H3PO4 and ZnCl2,walnut shells as raw materials were used to prepare walnut shell-based biochar.The prepared biochar was characterized and a preferable biochar was chosen for the adsorption of tetracycline antibiotics.The results showed that when each initial concentration was 20 mg·L-1,the biochar dosage was 0.010g,and the reaction reached equilibrium at 24 h,adsorption efficiencies of oxytetracycline,tetracycline and chlortetracycline were 97.56%,91.14%and 96.01%,respectively,and adsorption strength order was:oxytetracycline>tetracycline>chlortetracycline.The kinetics of adsorption belongs to the pseudo-second-order kinetic equation,and the adsorption equilibrium was similar to Langmuir isothermal model.In addition,thermodynamic data can determine that the adsorption was an exothermic reaction.(2)When biochar was added to the yellow brown soils,the adsorption of tetracycline antibiotics in soils can be enhanced.In the adsorption kinetics experiment,when the mass of soils was 1 g,the adsorption efficiency of test group containing 1%biochar was faster than the one of control group without biochar.At adsorption equilibrium,adsorption amount of test group at equilibrium were 1.18,1.14 and 1.15 times of the control group,and the order of adsorption ability was:oxytetracycline>chlortetracycline>tetracycline.The reaction belongs to the pseudo-second-order kinetic equation,and the adsorption equilibrium obeyed to Langmuir isothermal equation with all the regression coefficients R2 greater than 0.99.Besides,adding the biochar can greatly enhance the adsorption of tetracycline antibiotics,and effectively reduce the availability of tetracycline antibiotics in soils.(3)When biochar content was 1%,and the concentrations of oxytetracycline in the yellow brown soils were 10,20,and 50 mg·kg-1,with the increase of aging time,the part of desorbable oxytetracycline can be gradually transformed into bound oxytetracycline.And with the increase of the initial concentration of oxytetracycline,the transformational bound content increases gradually,but the proportion gradually reduces.When biochar contents were 0%,1%and 2%,with the increase of biochar content,the adsorption of oxytetracycline on soil samples enhanced,which to a certain extent reduced the desorption of adsorbed oxytetracycline.At the same time,the extractable content of oxytetracycline also could be decreased resulting into lower availability.For the three tetracycline antibiotics,oxytetracycline,tetracycline and chlortetracycline,the order of transformation rate of the antibiotic from the extractable into bound was:oxytetracycline>tetracycline>chlortetracycline.