Physicochemical transformation of ZnO and TiO2 nanoparticles in sea water and its impact on bacterial toxicity

The enormous properties of metal oxide nanoparticles make it possible to use these nanoparticles in a wide range of products. As their usage and application continue to expand, environmental health concerns have been raised. In order to understand the behavior and effect of metal oxide nanoparticles in the environment, comprehensive and comparable physicochemical and toxicological data on the environmental matrix are required. However, the behavior and effect of nanoparticles in the real environmental matrix, e.g. sea water, are still unknown. In this study, the effects of zinc oxide (ZnO) and titanium dioxide (TiO2) nanoparticles on the bacteria (gram positive-Bacillus subtilis, Staphylococcus aureus/gram-negative Escherichia coli, and Pseudomonas aeruginosa) in sea water were investigated. Furthermore, to better understand the behavior of the toxicity, surface chemistry, sedimentation, dissolution, particle size, and zeta potential of the nanoparticles dispersed in the sea water matrices were investigated using Fourier-transform infrared spectrometry (FTIR), ultraviolet–visible (UV-VIS) spectrophotometry, graphite furnace atomic absorption spectrometer (GFAAS), and dynamic light scattering (DLS), respectively. The environmental matrix had a significant influence on physicochemical behavior of the tested nanoparticles. Besides, the inhibition of tested bacteria was observed against ZnO and TiO2 nanoparticles in the presence of sea water, while there was no inhibition in the controlled condition. The results demonstrate that surface chemistry with exposure to the sea water can have a significant role on the physicochemical properties of nanoparticles and their toxicity.