Study On The Mechanism Of U(?) Bioaccumulation And Its Biological Effects

The radionuclide uranium U(?)was one of the key nuclides throughout the nuclear industry system.With the continuous development of nuclear energy,the production of radionuclide uranium is increasing.Uranium-containing nuclear waste was inevitably released into the environment,causing direct and potential hazards to the ecosystem and even threatening human health.The hazards of radionuclide uranium mainly include the radiation generated during the decay process and the toxicity of heavy metals.In recent years,microbial enrichment has been widely used in actual environmental pollution and restoration,and has significant advantages.In this paper,the resistant microorganisms isolated from radionuclide-contaminated soil were used as adsorbents to enrich uranium remaining in water,and the mechanism of the interaction between uranium and microorganisms was studied.The biological effects of Candida utilis under uranium stress were also investigated.This paper mainly includes the following three parts:The first part mainly studies the separation of the filamentous fungus Absidiacorymbifera from the contaminated soil by nuclear waste.Firstly,the uranium enrichment was studied by using A.corymbifera,including the effects of microbial concentration,temperature.pH and ionic strength on U(?)enrichment.Then,SEM,FTIR and XPS were used to analyze the changes before and after microbial enrichment.The isotherm experimental data fit is consistent with the Langmuir model,and the kinetic experimental data fits to the second-order kinetic model.In addition,at pH 6.0,the maximum enrichment of uranium by A.corymbifera can reach 46.5 mg/g.The study showed that A.corymbifera can be used as a potential microbial adsorbent to remove radionuclides such as U(?).The second part mainly evaluates the ability of the resistant bacteria B.amyloliquefaciens to enrich U(?).B.amyloliquefaciens was isolated and screened from the contaminated soil by nuclear waste.At the same time,the effects of bacterial concentration,adsorption time,pH and ionic strength on bioaccumulation were also studied.The experimental data was consistent with the Langmuir model and the second-order kinetic model.According to the Langmuir fitting results,the ability of B.amyloliquefaciensto enrich uranium reached 179.5 mg/g at pH 6.0.According to the thermodynamic calculation results,?Go,?Ho and ?So were-6.3359 kJ/mol,14.20 kJ/mol,67.19 J/mol K-',respectively.This study shows that B.amyloliquefaciens can be used as an ideal biosorbent for removing radionuclides of uranium.The third part mainly studies the interaction between Candida utilis and U(?),and also studies the effects of enrichment time,pH and ionic strength on bioaccumulation.At the same time,SEM,TEM?FTIR and XPS were used to characterize the changes before and after enrichment of C.utilis.The enrichment kinetics was consistent with the second-order kinetic model and the enrichment equilibrium was reached in 3.5 hours.According to the Langmuir model,the maximum enriched uranium was 41.15 mg/g(wet cells)at pH 5.0.According to the thermodynamic calculation results.?Go,?Ho and ?So were-3.556 kJ/mol,7.17 kJ/mol,34.41 J/mol K-1,respectively.Since Candida utilis can produce GSH,it can better improve the binding ability of C..utilis and radionuclide U(?).Secondly,the effects of different concentrations of U(?)on the growth and reproduction of Candida utilis were studied.The concentration changes of intracellular hydrogen peroxide and malondialdehyde(MDA)were also determined.The radionuclide U(?)inhibited the growth of C.utilis and leaded to an increase in reactive oxidative species(ROS).In addition,the concentration of total superoxide dismutase(T-SOD)and glutathione(GSH)in C.utilis cells was measured,indicating that radionuclide U(?)can promote intracellular antioxidant enzymes and antibiotics.The amount of oxidized small molecules was increased.The above studies showed that C.utilis can be used as an ideal adsorbent for removing radionuclide uranium from water.In addition,these results have certain reference value for evaluating the toxicity of radionuclides U(?)and the antioxidation of C.utilis.