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The objective of this study was to understand toxicity of mixture of nanoparticles (NPs) (ZnO and TiO2) and their ions to Escherichia coli.Results indicated the decrease in percentage growth of E.coli with the increase in concentration of NPs both in single and mixture setups.Even a small concentration of 1 mg/L was observed to be significantly toxic to E.coli in binary mixture setup (exposure concentration:1 mg/L ZnO and 1 mg/L TiO2;21.15％ decrease in plate count concentration with respect to control).Exposure of E.colito mixture of NPs at 1000 mg/L (i.e.,1000 mg/L ZnO and 1000 mg/L TiO2) resulted in 99.63％ decrease in plate count concentration with respect to control.Toxic effects of ions to E.coliwere found to be lesser than their corresponding NPs.The percentage growth reduction was found to be 36％ for binary mixture of zinc and titanium ions at the highest concentration (i.e.,803.0 mg/L Zn and 593.3 mg/L Ti where ion concentrations are equal to the Zn ions present in 1000 mg/L ZnO NP solution and Ti+4 ions present in 1000 mg/L TiO2 NP solution).Nature of mixture toxicity of the two NPs to E.coliwas found to be antagonistic.The alkaline phosphatase (Alp) assay indicated that the maximum damage was observed when E.coliwas exposed to 1000 mg/L of mixture of NPs.This study tries to fill the knowledge gap on information of toxicity of mixture of NPs to bacteria which has not been reported earlier.