Evaluating the toxicity of zinc oxide nanoparticles on the dominant bacteria in the sludge of wastewater treatment facilities

We intended to assess the toxicity and evaluate the toxicity of the ZnO nanoparticles by examining them on bacteria of wastewater sludge. The results of this study can justify the use of nanoparticles as antimicrobial agents. The stock solution of 10 g/L of these nanoparticles were diluted by the Mueller Hinton Agar culture and 5 to 6000 mg/L concentrations were created. and purified bacteria were cultivated on them. Then the percentage of growth prohibiting was determined by comparing the samples including nanoparticles and control samples. Half maximal effective concentration (EC₅₀), NOEC and the concentration with 100% growth prohibition was determined. The EC₅₀ of ZnO nanoparticles for E. Coli, Bacillus Subtilis, Staphylococcus Aureus and Pseudomonas Aeruginosa were respectively 181.7, 656.4, 93.9 and 935.8 mg/L. Staphylococcus Aureus had a high sensitivity to ZnO nanoparticles and can be used as a parameter in the biological tests for the effect of nanoparticles on bacteria. Also the ZnO nanoparticles had a high toxicity and even the least amount (at 2813 mg/L) could stop the growth of all bacteria. This nanoparticle can probably be used for hygienic and water treatment purposes and for protecting food from contamination.