| As one of the most important metal nanoparticles(MNPs),Cu-based MNPs(Cu-MNPs)are widely used in catalysts,semiconductor materials,photovoltaic cells,antifouling coatings and conductive inks due to their excellent electrical,photocatalytic and antibacterial properties.Global Cu-MNPs production is estimated to be about 570 t/y in 2014 and will reach 1600 t/y in 2025.The synthesis,use and disposal of Cu-MNPs will inevitably lead to their release into the environment and bring potential ecological risks.Due to the high specific surface area and high reactivity,Cu-MNPs interact with environmental factors after being released into the environment,thereby affecting their microstructure and physicochemical properties,which determine their fate and potential toxicity in the environment.Bacteria play important roles in geochemical cycling and plant nutrient uptake and utilization,which are essential for ecosystem function and stability.Therefore,it is crucial to study the biochemical transformation of Cu-MNPs in the environment and clarify the bacterial toxicity of Cu-MNPs and their transformation products.To solve this problem,two Cu-MNPs,the traditional CuO NPs and the new hybrid copper phosphate nanoflowers(HNFs),were selected in this paper to study the biochemical transformation of the two Cu-MNPs,and systematically evaluate the bacterial toxicity of the two Cu-MNPs and the transformation products.The specific research and results are as follows:(1)The transformation of CuO NPs by soluble phosphate(Pi)and the changes of the properties and bacterial toxicity of the transformed CuO NPs were clarified.Pi can induce the phosphorylation of CuO NPs to form a core-shell structure of NPs.The decrease of pH enhances the phosphorylation of CuO NPs and changes the type of products.Some products change from Cu3(PO4)2·3H2O toCu4H(PO4)3·3H2O,and exist in the form of blocky films.Combined with HRTEM,ICP-MS,FT-IR and XPS,it was found that CuO NPs was mainly transformed by ligand exchange and dissolution-reprecipitation.After phosphorylation,the surface potential of NPs was reversed,and its aggregation and sedimentation performance became worse,which made it more stable in aqueous solution and showed stronger acute bacterial toxicity.(2)The biotransformation process and mechanism of HNFs under Pseudomonas aeruginosa were revealed.Scan electron microscopy shows that the conversion of HNFs starts mainly from the internal erosion of the nanoplate,followed by the collapse of the flower-like structure to generate smaller particle size NPs and finally complete conversion to ions.About 50%of the product copper ion is adsorbed on the surface or inside the cell by bacteria,and the remaining ions remain in the solution,while Pi is almost completely absorbed and utilized by bacteria.The fluorescence intensity and pH changes of bacterial metabolites indicated that the transformation of HNFs involves both complexation and acidification.Metabolic analysis showed that fumaric acid,valine,leucine and other small organic acids and amino acids played an important role in transformation and detoxification.(3)The toxicity of HNFs against Pseudomonas aeruginosa was evaluated from a life cycle perspective.HNFs showed low bacterial toxicity,whereas its transformation products(MNPs and copper ions)were significantly toxic to Pseudomonas aeruginosa in planktic and biofilm states.Analysis of extracellular polymers(EPSs),membrane permeability and intracellular ROS revealed that the transformation products reduced cellular metabolic activity,increased bacterial membrane permeability by 42%and increased intracellular ROS levels by 68%,resulting in higher bacterial toxicity.The results of this study provide an important theoretical basis for ecological risk assessment of HNFs and CuO NPs,and contribute to the development of targeted applications and reasonable design of future nanomaterials,which is of great significance for the green and sustainable development of nanotechnology. |
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