The Toxicity Of Green Synthesized Graphene And Iron Nanoparticles To Microorganisms

The green synthesis of nanoparticles using plant extracts have attracted much attention due to its eco-friendly route,simple operation,low cost and can realize large-scale production.Despite graphene and nanoscale zero-valent iron(nZVI)are considered to be a promising material in many fields due to its unique physical and chemical properties.However,their behavior in the environment,especially the toxicity of graphene and nZVI to the ecosystem is still unclear.The objective of this study was to investigate the toxic effect of commercial nanomaterials and green synthetic nanomaterials(graphene and nZVI)on the growth of Acidithiobacillus ferrooxidans and Burkholderia vietnamiensis C09V at different initial concentration.The main results are described as follows:Firstly,the toxic effects of commercial graphene and green synthetic graphene on Acidithiobacillus ferrooxidans were investigated.In the concentration range from 1 mg/L to 50 mg/L,the results showed that the decreasing in concentrations of commercial graphene markedly inhibited the growth of Acidithiobacillus ferrooxidans and hence the toxicity increased.In addition,1 mg/L of commercial graphene significantly inhibited the pH and oxidation-reduction potential(ORP)of Acidithiobacillus ferrooxidans.The bioleaching of heavy metals from sewage using Acidithiobacillus ferrooxidans were be further investigated,the results showed that the removal rate of Cu and Zn were largely inhibited at 1 mg/L commercial graphene.In the contrary,the toxic effect of green synthesis of graphene(EL-rGO)on Acidithiobacillus ferrooxidans was dose-dependent,which showed that the biomass decreases with the dose increase.50 mg/L of EL-rGO significantly inhibited the pH and oxidation-reduction potential(ORP)of Acidithiobacillus ferrooxidans,and the removal rate of Cu and Zn were largely inhibited as well.Secondly,the toxic effects of commercial nZVI and green synthetic nZVI on the growth of Burkholderia vietnamiensis C09V were investigated.The result of OD600 and crystal violet removal efficiency of Burkholderia vietnamiensis C09V showed that the increasing in concentrations of nZVI markedly inhibited the growth of Burkholderia vietnamiensis C09V and hence the toxicity increased.100 mg/L of commercial nZVI has no significant effect on the growth and the removal efficiency of Burkholderia vietnamiensis C09V.Similarly,the toxic effect of EL-nZVI on Burkholderia vietnamiensis C09V was enhanced with the increasing dose.Interestingly,100 mg/L of EL-nZVI had a slightly beneficial impact on the growth of cell,including biomass and removal efficiency of crystal violet.Furthermore,the fluorescence microscope confirmed that increasing in concentrations of nZVI significantly inhibited the growth of Burkholderia vietnamiensis C09V.Finally,various analysis techniques,including Fourier transform infrared spectroscopy(FTIR),scanning electron microscopy(SEM),lactate dehydrogenase(LDH)release rate and superoxide dismutase(SOD)activity,were conducted.The results showed that the toxic effect of commercial graphene was physical damage,and the damage of cell membrane by direct contact of the bacteria with the sharp edges of the graphene.In addition,the toxic mechanisms of nZVI(commercial nZVI and EL-nZVI)were physical and oxidative damage,where the nutrition channel were blocked by the high concentration of nZVI covering the surface of the bacteria,including a large number of reactive oxygen production by reacting with the intracellular molecular oxygen to inhibit the growth of cell ultimately.Furthermore,compared with the same dose of commercial nanomaterials,green synthesis of graphene and nZVI provided good biocompatibility.Low concentration of green synthetic nanomaterials promoted the growth of microorganisms.The high concentration of green synthetic nanomaterials was less toxic to microorganisms because of its surface-coated organic functional groups.This study provides a basis for evaluation of ecotoxicity of graphene and nZVI.