Study On The Effect Of Black Soil DOM On The Toxicity Of Nano Copper Oxide To Escherichia Coli And Its Mechanism

In recent years,nanomaterials have attracted much attention due to their wide applications in many fields,such as medicine,bioengineering,electronics industry,environmental industry,energy and environmental conservation.Nanometer copper oxide(nano-CuO)is one of the most widely used nanomaterials.However,nano-CuO also has toxic effects on organisms due to its small particle size,surface effect and ability to dissolve metal ions.When nano-CuO in production and application enters the water and soil environment,it will affect the living creatures and thus pose a potential threat to the ecological environment system.Soil dissolved organic matter(DOM)can provide energy and nutrients for microorganisms in the soil,it affects the content of elements and components in the soil,and also can change the quality of soil environment.At the same time,DOM is considered as the first protective barrier of soil microorganisms,which is because the main components of DOM,such as humic acid and protein,can combine with pollutants,and can directly affect the environmental behavior of pollutants,such as migration and transformation.The toxic effect of nano-CuO on Escherichia coli was studied by measuring the morphology and bacteriostatic rate of Escherichia coli.DOM was selected to alleviate the toxicity of nano-CuO to Escherichia coli,and the changes of fluorescence component content and fluorescence intensity in DOM under different concentrations of nano-CuO were obtained by means of three-dimensional fluorescence spectrum,synchronous fluorescence spectrum,two-dimensional fluorescence spectrum and two-dimensional infrared spectrum.According to the fitting of synchronous fluorescence data,the binding sites are calculated,and the quenching mode is judged to reveal the binding mechanism of DOM and nano-CuO,so as to reduce the toxicity of nano-CuO to Escherichia coli.The main contents and conclusions of this study are divided into the following three aspects.(1)The toxic effect of nano-CuO on Escherichia coli was studied.Firstly,nano-CuO was characterized by transmission electron microscopy(TEM),particle size distribution,ultraviolet-visible absorption spectrum(UV-Vis),sedimentation and solubility under different conditions.The results show that the nano-CuO diameter is mainly distributed at 60-70 nm,the absorption peak of copper oxide transition appears at 270 nm.The toxic effects of nano-CuO on Escherichia coli were observed by scanning electron microscopy(SEM)and TEM.It was found that nano-CuO caused the Eschericia coli to lose its regular shape.The surface of Eschericia coli was broken.At the same time,nano-CuO could enter into the interior of Eschericia coli,resulting in the damage and lysis of cell membrane.The higher the concentration of nano-CuO,the higher the degree of cracking.The inhibition rate of nano-CuO on Escherichia coli increased with the increase of concentration and time.The inhibition rates of 10 mg/L,20 mg/L and 50 mg/L nano-CuO on Escherichia coli were 92%,94%and 96%respectively at 6 h,which indicated that nano-CuO had obvious inhibition on Escherichia coli.(2)In the experiment of DOM alleviating the toxic effect of nano-CuO on Escherichia coli,the toxic effect of nano-CuO on Escherichia coli was measured in the presence of DOM.The effects of DOM,nano-CuO and Escherichia coli were compared by SEM and TEM.At the same time,the antibacterial rate of nano-CuO to Eschericia coli in the presence of DOM was tested.The results showed that DOM itself had no effect on the surface and internal structure of Eschericia coli.In the presence of DOM,nano-CuO still destroys the surface and internal structure of Escherichia coli,and nano-CuO enters into the cell and causes cell lysis.However,compared with the same concentration of nano-CuO,the degree of surface destruction and lysis is decreased.In terms of growth inhibition,at the same time and concentration of nano-CuO,the growth inhibition of Eschericia coli with DOM was lower than that of Eschericia coli without DOM.(3)In order to explore the combination characteristics of DOM and nano-CuO,three-dimensional fluorescence spectrum,synchronous fluorescence spectrum,two-dimensional fluorescence spectrum and two-dimensional infrared spectrum were used to characterize and analyze the interaction mechanism between DOM and different concentrations of nano-CuO.The results of three-dimensional fluorescence spectrum show that the main components of DOM are protein,fulvic acid and humic acid,and the three components have strong binding ability with nano-CuO.The synchronous fluorescence spectrum showed that humic acid was the main component of DOM in soil.When the concentration of nano-CuO increased gradually,the fluorescence intensity of DOM decreased.The quenching constants Kq of protein and humic acid were 1.8 × 1011L/mol/S and 3.5×1011 L/mol/S respectively,which indicated that the quenching process was static.By fitting the binding sites,we found that humic acid and protein have a kind of binding sites.The results of two-dimensional fluorescence spectrum show that humic acid is prior to protein in binding nano-CuO.The two-dimensional infrared spectra showed that the order of the structural changes of nano-CuO and DOM was OH ? C-O<C-H<amide I C-O<polysaccharide C-O<COO-.The 2D-hetero results show that the fluorescence of protein-like components changes after humic like substances(aromatic functional groups in humic-like substances>carboxylic groups in protein-like structures>inorganics related functional groups).