Nanomaterial-enabled photothermal-based solar water disinfection processes: Fundamentals, recent advances, and mechanisms

The pathogenic microorganisms in water pose a great threat to human health. Photothermal and photothermocatalytic disinfection using nanomaterials (NPs) has offered a promising and effective strategy to address the challenges in solar water disinfection (SODIS), especially in the point-of-use operations. This review aims at providing comprehensive and state-of-the-art knowledge of photothermal-based disinfection by NPs. The fundamentals and principles of photothermal-based disinfection were first introduced. Then, recent advances in developing photothermal/photothermocatalytic catalysts were systematically summarized. The light-to-heat conversion and disinfection performance of a large variety of photothermal materials were presented. Given the complicated mechanisms of photothermal-based disinfection, the attacks from reactive oxygen species and heat, the destruction of bacterial cells, and the antibacterial effects of released metal ions were highlighted. Finally, future challenges and opportunities associated with the development of cost-effective photothermal/photothermocatalytic disinfection systems were outlined. This review will provide guidance in designing future NPs and inspire more research efforts from environmental nano-communities to move towards practical water disinfection operations.

Toxic effects of substituted p-benzoquinones and hydroquinones in in vitro bioassays are altered by reactions with the cell assay medium

Substituted para-benzoquinones and hydroquinones are ubiquitous transformation products that arise during oxidative water treatment of phenolic precursors, for example through ozonation or chlorination. The benzoquinone structural motive is associated with mutagenicity and carcinogenicity, and also with induction of the oxidative stress response through the Nrf2 pathway. For either endpoint, toxicological data for differently substituted compounds are scarce. In this study, oxidative stress response, as indicated by the AREc32 in vitro bioassay, was induced by differently substituted para-benzoquinones, but also by the corresponding hydroquinones. Bioassays that indicate defense against genotoxicity (p53RE-bla) and DNA repair activity (UmuC) were not activated by these compounds. Stability tests conducted under incubation conditions, but in the absence of cell lines, showed that tested para-benzoquinones reacted rapidly with constituents of the incubation medium. Compounds were abated already in phosphate buffer, but even faster in biological media, with reactions attributed to amino- and thiol-groups of peptides, proteins, and free amino acids. The products of these reactions were often the corresponding substituted hydroquinones. Conversely, differently substituted hydroquinones were quantitatively oxidized to p-benzoquinones over the course of the incubation. The observed induction of the oxidative stress response was attributed to hydroquinones that are presumably oxidized to benzoquinones inside the cells. Despite the instability of the tested compounds in the incubation medium, the AREc32 in vitro bioassay could be used as an unspecific sum parameter to detect para-benzoquinones and hydroquinones in oxidatively treated waters.

Synthesis and In Vitro Biological Evaluation of Psoralen-Linked Fullerenes

Photodynamic therapy (PDT) is a widely used medicinal treatment for the cancer therapy that utilizes the combination of a photosensitizer (PS) and light irradiation. In this study, we synthesized two novel C₆₀ fullerene derivatives, compounds 1 and 2, with a psoralen moiety that can covalently bind to DNA molecules via cross-linking to pyrimidine under photoirradiation. Along with several fullerene derivatives, the biological properties of several novel compounds have been evaluated. Compounds 1 and 2, which have been shown to induce the production of hydroxyl radicals using several ROS detecting reagents, induced DNA strand breaks with relatively weak activities in the in vitro detection system using a supercoiled plasmid. However, the psoralen-bound fullerene with carboxyl groups (2) only showed genotoxicity in the genotoxicity assay system of the umu test. Compound 2 was also seen to have cytotoxic activities in several cancer cell lines at higher doses compared to water-soluble fullerenes.

A comparison of genotoxicity change in reclaimed wastewater from different disinfection processes

Effluents before disinfection from four wastewater reclamation plants were treated with chlorine (Cl₂), ozone (O₃), chlorine dioxide (ClO₂), medium-pressure ultraviolet (MPUV) and four different combinations of the above, to evaluate the effect of disinfection processes on the genotoxicity removal by the SOS/umu test. Results showed that the genotoxicity increased after MPUV irradiation (10-100 mJ/cm²), but declined when adopting other disinfection processes. The effectiveness of genotoxicity reduction by five chemical disinfectants was identified as: O₃ > pre-ozonation with Cl₂ ≈ ClO₂ > combination of ClO₂ and Cl₂ > Cl₂. The sequential combination of MPUV, Cl₂ and O₃ reduced the genotoxicity to a level similar to the source water. The influence of differential disinfection process varied on iodinated wastewater, which is closely related to the competitive reactions between disinfectants, iodine and dissolved organic matters. The removal of genotoxic pollutants and the formation of genotoxic disinfection by-products are the two major factors that lead to the change in genotoxicity during disinfection.

Development and progress for three decades in umu test systems

Umu test have been widely used to predict the detection and assessment of DNA- damaging chemicals in environmental genotoxicity field for three decades. This test system is more useful with respect to simplicity, sensitivity, rapidity, and reproducibility. A review of the literature on the development of the umu test is presented in this article. The contents of this article are included a description of numerous data using the umu test. This test have been fully evaluated and used in many directions. Different genetically engineered umu systems introducing bacterial and rat or human drug metabolizing enzymes into the umu tester strains, have been successfully established and are considered as useful tools for genotoxicity assays to study the mechanisms of biotransformation in chemical carcinogenesis. Actually, we developed that two types of bacterial metabolizing enzymes and 4 types of rat and human metabolizing enzyme DNAs are expressed in these strains such as nitroreductase and O-acetyltransferase, cytochrome P450, N-acetyltransferases, sulfotransferases, and glutathione S-transferases, respectively. Due to increasing numbers of minute environmental samples and new pharmaceuticals, a high-throughput umu test system using Salmonella typhimurium TA1535/pSK1002, NM2009, and NM3009 strains provides a useful for these genotoxicity screening. I also briefly describe the first attempts to incorporate such umu tester strain into photo-genotoxicity test.