Toxicity Mechanism Of Nanoparticles In Aniline-Degrading Bacteria

With the rapid development of nanotechnology, engineered nanoparticles (ENPs) were used gradually in the chemical industry, energy and medical areas. However, the usage, transport and disposal of ENPs inevitably result in their release into the wastewater treatment plant (WWTP), evoke adverse effects to bacteria, and then pose unexpected impacts to WWTP. Aniline is an important chemical raw material which is widely used in printing and dyeing industry, but it is also a kind of serious environmental pollutants harming to human health, which is under strict control in the industrial drainage. The microorganisms, expecially for aniline-degrading bacteria (ADB) play a vital role in aniline degradation in the wastewater treatment system. In this study, the ADB was chosen as the test bacteria. The aim was to investigate the toxicity of ZnO nanoparticles (ZnO ENPs) and titanium dioxide nanoparticles (TiO2 ENPs) to ADB and the related toxic mechanism. The results were present as follows:(1) Due to the small size, ZnO ENPs may lead to much more contact with the bacteria and induce potentially toxic effcts. Compared to ZnO ENPs in ultra-pure water, Zeta potential increased when ZnO ENPs added in simulated aniline medium (SAM), resulting in a better stability in simulated aniline medium. The concentration of PO43- and aniline had effect on the dissolution of ZnO ENPs, and the concentration of PO43- had more serious influence.(2) ZnO ENPs could significantly inhibit the growth of ADB, and after 12 h exposure,10 and 50 mg/L ZnO ENPs still had significant toxic effect to ADB. Furthermore, ZnO ENPs had obvious inhibitory effect on the degradation of aniline and the two-plus oxygen enzyme activity.(3) SEM and CLSM analysis demonstrated ZnO ENPs destroy the cell membrane integrity, further research could be found that cell membranes damage induced the increase of cell membrane liquidity of ADB, and a significant change of membrane fatty acid composition. TEM analysis demonstrated ZnO ENPs could entry into the bacteria. ZnO ENPs induced a large number of ROS, which subsequently increased the content of protein carbonyl and 8-OHdG significantly, finally caused proteins and DNA damage.(4) Compared with ZnO ENPs, TiO2 ENPs had a larger particle size. Zeta potential of TiO2 ENPs decreased after addingwhen in SAM, and TiO2 ENPs tended to be more aggregated. Thus TiO2 ENPs were hard to contact with bacteria or enter into the cells, which may decrease the toxic effects.(5) TiO2 ENPs had no effect on ADB. In this experiment, TiO2 ENPs were rutile, had a lower photocatalytic activity and lower toxicity under no light conditions. The results in this study showed that, TiO2 ENPs had no significant effect on ADB growth and aniline degradation, and did not enter into and damage the cells. There was no accumulation of ROS, or proteins and DNA damage in bacteria with exposure of TiO2 ENPs.