Antimicrobial and Oxidative Activities of Different Levels of Silver-Exchanged Zeolites X and ZSM-5 and Their Ecotoxicity.

OBJECTIVES

The antimicrobial, oxidative activities, and ecotoxicity of synthesized silver-loaded zeolites (X and ZSM-5(MFI), Si-to-Al ratios 12 and 25) were studied, linking antimicrobial properties to material structure and released active silver species.

METHODS

The materials were characterized by SEM, EDX, TEM, and XRPD. All materials, with a silver content of 1-3%wt for the Ss and about 35%wt for the X-zeolites, were tested against and . Redox activity was studied in physiological (pH 7.4/37 °C) and optimal (pH 8.5/37 °C) conditions in chemiluminescent model systems. In the ecotoxicity tests, we used Results: A proportional correlation was observed between the bactericidal effect of and the silver content in the zeolites. AgX with a Si/Al ratio of ~1.23 and 35% silver showed a higher antimicrobial efficiency, particularly against Gram-negative versus Gram-positive . The concentration thresholds were as follows: AgXas had a bactericidal effect at 0.003 g/L, with an MIC at 0.0015 m/L for ; SA25-Ag, AgXcl, AgXrc had a bactericidal effect at 2.5 g/L. The bacteria were more resilient than , which showed a 90-100% lethality at Ag-zeolite concentrations of 0.00625 to 0.0125 g/L. AgXas and AgXrc demonstrated strong reactive oxygen species generation at both the physiological and optimal pH, explaining their bactericidal effects. In general, the tested materials showed an inhibition of the generated reactive oxygen species depending on the model system and conditions.

CONCLUSIONS

The silver species leached from the new materials explain their higher oxidation and bactericidal activity. While suitable for stringently controlled biological applications, their release into the environment, in concentrations higher than 0.01g/L, should be avoided.