Effects Of Biochar On Combined Pollution Of Heavy Metal Copper And Oxytetracycline In Soil

Tetracyclines(TCs)and copper(Cu)are the most widely used additives in livestock and poultry breeding.They are mainly used to promote animal growth,improve feed efficiency and treat diseases.TCs and Cu cannot be completely absorbed by animals,and will be excreted with feces,enter the farmland system,and accumulate in the soil to form a composite pollution.In this study,based on the investigation of the occurrence characteristics of TCs and heavy metals in the farmland applied with pig manure,oxytetracycline(OTC)and Cu were used as the research objects.Through soil culture experiments,the adsorption and degradation of OTC in soil under the synergistic effect of biochar were studied.A pot experiment was conducted to study the residual characteristics of OTC in soil-vegetable system and the effects of OTC single/OTC-Cu combined pollution on enzyme activity,soil microbial community and resistance gene abundance.By simulating the accelerated aging process of biochar in soil,the changes of surface properties of biochar before and after aging and the effects of biochar aging on the bioavailability of heavy metals in soil were studied,and the mechanism of biochar aging on the bioavailability of heavy metals was clarified.The following main test results were as follows:1.Taking the corn farmland with pig manure as the research object,seven large pig farms in the black soil area of Jilin Province were selected to study the contents of heavy metals and tetracycline antibiotics in the surrounding farmland soil,and the effect of pig manure on the soil environmental quality of cultivated land was clarified.The results showed that the average content of Cu was 1.86 times of the soil background value of Jilin Province,and the proportion of exceeding the background value was100 %,which was the highest accumulation of heavy metals in soil.The average value of ΣTCs was 1.31 mg / kg,with the highest accumulation in typical black soil.OTC accounted for the highest proportion of ΣTCs,with an average of 50.82 %,which was the most important component of TCs in the study area.2.The batch equilibrium method was used to study the adsorption kinetic characteristics of OTC in typical black soil under the synergistic effect of biochar,and the effects of soil type,pH value,ionic strength,OTC-Cu combined pollution and other factors on the adsorption thermodynamic process of OTC in soil.The pseudo-secondorder kinetic equation better fitted the adsorption kinetic process of OTC in typical black soil.The Freundlich model can better describe the thermodynamic process of OTC adsorption in soil under different influencing factors.The adsorption capacity of OTC in typical black soil was strong,and decreased with the increase of pH value and ionic strength.The combined pollution of OTC and Cu promoted the adsorption of OTC in soil.Biochar can provide more adsorption sites and promote the adsorption of OTC in soil by improving soil structure and physical and chemical properties,such as increasing organic matter,soluble organic carbon and cation exchange capacity.3.Under the synergistic effect of biochar,soil water content,ambient temperature and Cu-OTC combined pollution had significant effects on the degradation of OTC in typical black soil.When the soil water content is 60 % of the field capacity and the ambient temperature is 35 ° C,it is more conducive to the degradation of OTC in the soil.The combined pollution of Cu-OTC is not conducive to the degradation of OTC in soil.Biochar can promote the hydrolysis reaction of OTC in soil,improve the living environment of soil microorganisms,provide more space and nutrients for soil microorganisms,improve the metabolic activity of soil microorganisms,and promote the degradation of OTC in soil.4.Biochar could reduce the accumulation and transport capacity of OTC in soilvegetable system,while the combined pollution of OTC and Cu increased the residue and migration capacity of OTC in the system.The application of biochar and the combined pollution of OTC and Cu activated the activities of catalase,urease and sucrase in soil and the activities of reactive oxygen species,malondialdehyde and superoxide dismutase in Chinese cabbage.Biochar can provide carbon sources and nutrients for microorganisms,accelerate microbial reproduction,and increase soil enzyme activity.However,biochar contains a certain amount of harmful substances,which are released into the soil with the aging effect in the soil and absorbed by plants,thus having a negative impact on plant enzyme activity.5.The application of biochar reduced the abundance of microorganisms such as Proteobacteria,Gemmatimonadetes and Acidobacteria,and increased the abundance of Actinobacteria,Firmicutes and Bacteroidetes.However,under Cu-OTC combined pollution stress,the relative abundance of Proteobacteria,Acidobacteria and Gemmatimonadetes in soil increased,and the relative abundance of Actinobacteria in soil decreased.At the genus level,biochar reduced the relative abundance of Sphingomonas and increased the relative abundance of Bradyrhizobium in soil.CuOTC combined pollution stress increased the relative abundance of Sphingomonas and Gemmatirosa,and decreased the relative abundance of Bradyrhizobium,Pseudolabrys and Sphingomonas.This is mainly due to the bactericidal effect of OTC,which can kill specific microbial flora in the soil,and also provide carbon source for some microorganisms resistant to OTC to grow.Biochar changed soil nutrient levels and indirectly affected the activity of soil microbial flora.Cu can produce toxic effects on some sensitive bacteria.Three tetracycline resistance genes(tx R,tet B,tet T)and class I integron gene(intl1)were detected in the soil-vegetable system.Biochar reduced the absolute abundance of tx R and tet B genes in soil,and increased the absolute abundance of tet T and int I1 in soil.Cu-OTC combined pollution stress increased the absolute abundance of tx R gene,but decreased the gene abundance of intl1.In Chinese cabbage tissues,OTC stress increased the absolute abundance of four resistance genes.The application of biochar and Cu-OTC combined pollution stress reduced the absolute abundance of tx R gene and increased the absolute abundance of tet B,tet T and int I1 in Chinese cabbage.Biochar has a direct impact on the abundance of resistance genes by promoting the horizontal transfer of resistance genes and providing niches for certain resistant bacteria.It can also indirectly affect the abundance of resistance genes in the soilvegetable system by affecting the abundance of soil microbial flora.6.After 30 days of different artificial aging treatment of biochar in soil,the pH value decreased,the content of C element decreased,the content of O element increased,the specific surface area and porosity increased,and the pore size decreased.Fourier transform infrared spectroscopy showed that the surface functional groups of biochar changed to varying degrees after different aging treatments.It can be seen from the scanning electron microscope that the microstructure of biochar after chemical-wetting alternation(CDW)and chemical-freeze-thaw cycle(CFT)aging treatment changed significantly.Aging had a significant effect on the speciation distribution of heavy metals in biochar soil.The exchangeable content of Cd,Cu and Pb in CDW and CFT treatments increased significantly,and the residual content decreased significantly.Natural aging treatment had little effect on the speciation of heavy metals.After biochar aging,the decrease of pH value,the increase of aromatization degree and the increase of acidic oxygen-containing functional groups all lead to the increase of free heavy metal content,which improves the bioavailability of heavy metals and increases the risk of soil heavy metal pollution.