Effects Of Biochars On The Dissipation Of Antibiotics In Soil

Multiple antibiotics were frequently detected in soil,then we investigated sixteen typical antibiotics including tetracyclines?TCs?,sulfonamides?SAs?,and quinolones?QLs?.Corn cob?CC?,corn straw?CS?and walnut shell?WS?were used to produce biochars at 250?,400? and 600?,respectively.The above nine kinds of biochar were applied to the soil at 1%weight to weight.In the sterilized soil,the effects of biochar on the abiotic dissipation of antibiotics were investigated by measuring the total level and fraction of the antibiotics?water-soluble,exchangeable,loosely bound,and tightly bound?,combined with changes of soil properties;In the unsterilized soil,the effects of biochar on the microbial degradation of antibiotics were investigated by measuring the total level and fraction of antibiotics,combined with soil properties,bacterial community structure and nutrient elements.The results were as follows:In sterilized soil without biochars,the abiotic dissipation rates of antibiotics were generally tetracyclines?TCs?>sulfonamides?SAs?>quinolones?QLs?.The dissipation trend of TCs?except for oxytetracycline?and QLs?except for ofloxacin?was just opposite to the order of their log K_ow,indicating that hydrophobic adsorption played the key role in their abiotic dissipation.For SAs,sulfadiazine and sulfachinoxalin had the highest and lowest abiotic dissipation rates,respectively.QLs and TCs were dominant as the tightly bound fractions,while the bound fractions of SAs were depended on molecular structures.In biochar-treated soils,biochars produced at 250?generally had the positive effect on the abiotic dissipation of antibiotics.The effect sizes of biochars produced at 400?and 600?for the abiotic dissipation of antibiotics depended on both biochar types and antibiotic molecular structures.Biochars had the strongest impacts on bound fractions of SAs,followed by TCs,while had little influence on QLs.Biochars generally decreased apparent distribution coefficients of antibiotics in soil,indicating the increase of potential risk after biochar addition.In unsterilized soil,biochars generally played a negative role in bacterial abundance,while had little impact on the bacterial diversity in the soil studied.The clustering results indicated that the response of bacteria at genus level to biochars significantly depends on biochar feedstocks rather than pyrolysis temperatures.Regarding antibiotics,the biodegradation rates of tetracyclines?TCs?were lower than those of sulfonamides?SAs?and quinolones?QLs?,which was most likely due to the larger relative molecular weight and more ring-structures of TCs than those of SAs and QLs.Biochars enhanced or inhibited the biodegradation of antibiotics depending on both biochar types and antibiotic moleculars.The impact degrees of biochars on antibiotic biodegradation rates varied as TCs>QLs>SAs.Generally,the significantly negative correlations between biodegradation rates of most antibiotics and tightly bound fractions of antibiotics were observed,indicating that just the tightly bound fractions can not be utilized by microorganisms.Considering the linking bacterial taxonomic composition to biodegradation of antibiotics,Steroidobacter belonging to the phylum of Proteobacteria had significantly positive correlations with the biodegradation of all SAs studied?p<0.05?,indicating that Steroidobacter had high biodegradation ability to SAs.Additionally,significantly positive correlations between specific genera?Iamia,Parviterribacter,and Gaiella?belonging to the phylum of Actinobacteria and biodegradation of specific individual SAs could also be observed?p<0.05?.There was no significantly positive correlation between bacterial genera and the biodegradation rates of QLs?except for enrofloxacin?and TCs,which might due to that various microorganisms involved in their biodegradation.All in all,nine different biochars were used to systematically study the dissipation of antibiotics in soil.The potential mechanism of biochar influencing the abiotic dissipation of antibiotics in soil was discussed.The biochar at 250?could effectively promote the antibiotic dissipation rate in soil.Also the mechanism how biochar affect the biodegradation efficiency of antibiotics in soil was clarified,and Steroidobacter was identified as the key microorganism to promote the biodegradation of sulfonamide?SAs?in soil.These results make certain theoretical and practical significance for using biochar to control antibiotic pollution in soil and predicting the impact of biochar on the environmental behavior of antibiotics in soil.