Synergistic Bacterial Stress Results from Exposure to Nano-Ag and Nano-TiO₂ Mixtures under Light in Environmental Media

Abstract

Due to their widespread use and subsequent release, engineered nanomaterials (ENMs) will create complex mixtures and emergent systems in the natural environment where their chemical interactions may cause toxic stress to microorganisms. We previously showed that under dark conditions n-TiO attenuated bacterial stress caused by low concentrations of n-Ag (<20 μg L) due to Ag adsorption, yet, since both n-Ag and n-TiO are photoactive, their photochemistries may play a key role in their interactions. In this work, we study the chemical interactions of n-Ag and n-TiO mixtures in a natural aqueous medium under simulated solar irradiation to investigate photoinduced stress. Using ATP levels and cell membrane integrity as probes, we observe that n-Ag and n-TiO together exert synergistic toxic stress in Escherichia coli. We find increased production of hydrogen peroxide by the n-Ag/n-TiO mixture, revealing that the enhanced photocatalytic activity and production of ROS likely contribute to the stress response observed. Based on STEM-EDS evidence, we propose that a new composite Ag/TiO nanomaterial forms under these conditions and explains the synergistic effects of the ENM mixture. Overall, this work reveals that environmental transformations of ENM mixtures under irradiation can enhance biological stress beyond that of individual components.

A Review on Synthesis, Applications, Toxicity, Risk Assessment and Limitations of Plant Extracts Synthesized Silver Nanoparticles

“…Leaching of AgNPs from commercial products and deliberate release of AgNPs into contaminated and wastewater are the main sources of AgNPs entry into the environment [183]. According to the various reports published in recent years, parameters such as ionic strength, composition of natural organic matter, pH, aggregation, stability, light and temperature conditions greatly influence the AgNPs toxicity as well as their fate in the natural environment [184,185]. Presence of AgNPs in the natural environment will affect the lower trophic levels first, i.e., microbes.…”

Environmental context determines the impact of titanium oxide and silver nanoparticles on the functioning of intertidal microalgal biofilms

“…TiO 2 -NPs can reduce Ag-NP toxicity towards bacteria in dark conditions, but increase the toxicity in the light. 105 The interaction also seems to be dependent on light quality and cycle, 49 but also on salinity, as chloride (Cl − ) concentration in seawater limits the availability of Ag + ions. 21 NPs also interact with other types of pollutants: the disruption of membranes by TiO 2 -NPs can facilitate the entry of other pollutants, such as heavy metals, in the cells, therefore increasing their toxicity.…”

“…Environmental conditions will influence how NPs aggregate and sink onto the sediment. 5,6,18,94,105 In sediments as well as in the water, chemical parameters such as sulphide content will affect toxicity. 88 Furthermore, TiO 2 -NPs are photoactive compounds, which means that the levels and wavelength range of light will influence their toxicity.…”

Natural Soil Clays from a Phaeozem to Synthesize a Nanocomposite with Exhausted Coffee Grounds and Ag- and TiO₂-Nanoparticles for Water, Air, or Soil Decontamination

“…It was found that Ag-NP/TiO 2 -NP/Phaeozem-soil-NP/ exhausted coffee-ground has functional inhibition and bacterium suppression. Other authors presented ZOI = 25 mm for the composite of Ag deposited into TiO 2 -NP [20], or a ZOI of 4 mm for the composite Ag collected on MMT for S. aureus and is not able for inhibition of E. coli [21]. The effect that hydrophilic OH groups are created on illuminated via UV light irradiation TiO 2 surface is well known [22].…”