Effects Of Biochar Application On The Migratory Behaviour Of Sulfonamide Antibiotics In The Calcareous Purpule Soil

Purple soil is the main farming soil in southwest and biochar is widely applied in the soil pollution control as a kind of new environmental protection materials.Batch experiments,column experiments and field experiments were carried out to study the effects of biochar application on the migratory behaviour of three typical sulfonamide antibiotics(Sulfadiazine,Sulfamethazine and Sulfamethoxazole)in a sloping cropland purple soil that is distributed abundantly in Sichuan hilly area.Biochar was applied at tares of 0,39.75 t/hm2(1%BC)and 198.75t/hm2(5%BC)to the soil and went through a half-year dry-wet alternate aging process(from May to November).The main conclusions of this study are as follows:(1)The adsorption capacity of three sulfonamides in the different treatments followed the order of SD>SMZ>SM2;As compared to the control treatment,addition of fresh biochar to the soils enhanced adsorption of SD,SM2 and SMZ,among which the improvement for SM2 was significant(P<0.05,but such effect became less obvious after the ageing process.As for the desorption process,the value of Freundlich coefficient Kf of three sulfonamides followed the order of SD>SMZ>SM2,indicating that SD has the highest adsorption capacity and lowest desorption capacity with SM2 being the opposite.The hysteresis coefficient(H)of three sulfonamides followed the order of SD<SMZ<SM2,which is consistent with the trend of the Freundlich coefficient n.It suggested that SM2 desorbed the fastest from the purple soil due to lowest appetency,while SM2 behaved the opposite.(2)Macropore was found in the columns with or without 1%BC and the former was more prosperous than the latter;Pollutants can enter into the groundwater environment through macropore in the form of-preferential flow,but the addition of biochar improved the structure the pore in the soil and reduced the macropore,which reduced the possibility of groundwater pollution by preferential flow through soil.(3)The concentration of dissolved organic matter(DOM)is inversely with ion concentration which leached from the soil along with the leaching time;Biochar may change the physical and chemical properties of the soil and then affect the kinds of the dissolved organic matter(DOM)in the leachate due to the fact that the addition of biochar may reduce the leaching of DOM from the soil,which is of great significant in keeping the soil fertility.(4)The transportion of three sulfonamides in the surface runoff varied with the different biochar treatment:A large amount of sulfonamides were released along with the surface runoff in the plot without any biochar amendment due to the fact that the ability of resisting heavy rain in purple soil sloping cropland is poor;In the plot of plough layer amended with 1%biochar,the outflow of three sulfonamides reduced at the beginning of the rainfall and the effect was obvious,then three sulfonamides released gradually with the process of rainfall event;The effect of holding back three sulfonamides in the surface runoff in plot of 5%biochar wall and trench was the best and the concentration of three sulfonamides was far less then the concentration in control and 1%biochar plot.(5)Sloping cropland determined that contaminants were easier to transport from the upper slop to the lower slop,which led to the phenomenon that the concentration of three sulfonamides did not decline directly in all depth in the soil of the whole rainfall events but increase and then decline.The phenomenon above in the plot of plough layer amended with 1%biochar was more obvious than the control.In the plot 5%biochar wall,when three sulfonamides transported to a certain depeth along with the rain,they would go across the biochar wall by lateral transfer and transfer upward through the solute diffusion and soil capillarity.