Application of chlorine dioxide and its disinfection mechanism.

Chlorine dioxide (ClO2) is a strong oxidizing agent and an efficient disinfectant. Due to its broad-spectrum bactericidal properties, good inactivation effect on the vast majority of bacteria and pathogenic microorganisms, low resistance to drugs, and low generation of halogenated by-products, chlorine dioxide is widely used in fields such as water purification, food safety, medical and public health, and living environment. This review introduced the properties and application status of chlorine dioxide, compared the action mode, advantages and disadvantages of various disinfectants. The mechanism of chlorine dioxide inactivating bacteria, fungi and viruses were reviewed. The lethal target of chlorine dioxide to bacteria and fungi is to destroy the structure of cell membrane, change the permeability of cell membrane, and make intracellular substances flow out, leading to their death. The lethal targets for viruses are the destruction of viral protein capsids and the degradation of RNA fragments. The purpose of this review is to provide more scientific guidance for the application of chlorine dioxide disinfectants.

Investigating the impact of chlorine dioxide in shrimp-rearing water on the stomach microbiome, gill transcriptome, and infection-related mortality in shrimp.

AIMS: This study aimed to assess the effects of chlorine dioxide (ClO2) in water on whiteleg shrimp Penaeus vannamei, evaluating its impact on the stomach microbiota, gill transcriptome, and pathogens. METHODS AND RESULTS: ClO2 was added to the aquarium tanks containing the shrimp. The application of ClO2 to rearing water was lethal to shrimp at concentrations above 1.2 ppm. On the other hand, most of the shrimp survived at 1.0 ppm of ClO2. Microbiome analysis showed that ClO2 administration at 1.0 ppm significantly reduced the α-diversity of bacterial community composition in the shrimp stomach, and this condition persisted for at least 7 days. Transcriptome analysis of shrimp gill revealed that ClO2 treatment caused massive change of the gene expression profile, including stress response genes. However, after 7 days of the treatment, the gene expression profile was similar to that of shrimp in the untreated control group, suggesting a recovery to the normal state. This 1.0-ppm ClO2 significantly reduced shrimp mortality in artificial challenges with an acute hepatopancreatic necrosis disease-causing Vibrio parahaemolyticus and white spot syndrome virus, which were added to rearing water. CONCLUSIONS: The use of ClO2 at appropriate concentrations effectively eliminates a significant portion of the bacteria in the shrimp stomach and pathogens in the water. The results of this study provide fundamental knowledge on the disinfection of pathogens in water using ClO2 and the creation of semi germ-free shrimp, which has significantly decreased microbiome in the stomach.

The toxicity of chlorine dioxide to clownfish and its bactericidal capability to pathogenic strains of vibrio spp.

Global ornamental fish transportation ranging from hours to days can produce multiple stress factors impact fish health and cause mortality. Clownfish, particularly Amphiprion ocellaris, are among the most traded saltwater ornamental fish. Vibrio includes several pathogenic strains that affect aquatic animals. Consequently, prophylactic treatment of the water or fish is recommended. In this study, six Vibrio strains including V. alginolyticus, V. parahaemolyticus and V. harveyi isolated from sick A. ocellaris and one V. harveyi strain from a sick East Asian fourfinger threadfin (Eleutheronema rhadinum) were tested for their sensitivity to a popular disinfectant, chlorine dioxide (ClO2). The results showed that 0.25 ppm ClO2 effectively suppressed five of the seven tested Vibrio strains for 24 h; however, 0.1 ppm ClO2 is safer for A. ocellaris. Meanwhile, ClO2 2.5 ppm reduced the bacterial counts to below 3.3 × 105 CFU/mL for 24 hours. The LC50 of ClO2 for A. ocellaris was 0.87 ppm at 10 min and 0.72 ppm at 24 h post treatment. Mild changes in water quality, including dissolved oxygen (DO), temperature and pH, were recorded during the trial. More research is necessary to understand the sensitivity of various aquatic animal pathogens to ClO2 and its toxicity to different aquatic animals.

Amoebicidal effect of chlorine dioxide gas against pathogenic Naegleria fowleri and Acanthamoeba polyphaga.

The pathogenic free-living amoebae, Naegleria fowleri and Acanthamoeba polyphaga, are found in freshwater, soil, and unchlorinated or minimally chlorinated swimming pools. N. fowleri and A. polyphaga are becoming problematic as water leisure activities and drinking water are sources of infection. Chlorine dioxide (ClO2) gas is a potent disinfectant that is relatively harmless to humans at the concentration used for disinfection. In this study, we examined the amoebicidal effects of ClO2 gas on N. fowleri and A. polyphaga. These amoebae were exposed to ClO2 gas from a ready-to-use product (0.36 ppmv/h) for 12, 24, 36, and 48 h. Microscopic examination showed that the viability of N. fowleri and A. polyphaga was effectively inhibited by treatment with ClO2 gas in a time-dependent manner. The growth of N. fowleri and A. polyphaga exposed to ClO2 gas for 36 h was completely inhibited. In both cases, the mRNA levels of their respective actin genes were significantly reduced following treatment with ClO2 gas. ClO2 gas has an amoebicidal effect on N. fowleri and A. polyphaga. Therefore, ClO2 gas has been proposed as an effective agent for the prevention and control of pathogenic free-living amoeba contamination.

Oral mouthwashes for asymptomatic to mildly symptomatic adults with COVID-19 and salivary viral load: a randomized, placebo-controlled, open-label clinical trial.

BACKGROUND: Recent randomized clinical trials suggest that the effect of using cetylpyridinium chloride (CPC) mouthwashes on the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) viral load in COVID-19 patients has been inconsistent. Additionally, no clinical study has investigated the effectiveness of on-demand aqueous chlorine dioxide mouthwash against COVID-19. METHODS: We performed a randomized, placebo-controlled, open-label clinical trial to assess for any effects of using mouthwash on the salivary SARS-CoV-2 viral load among asymptomatic to mildly symptomatic adult COVID-19-positive patients. Patients were randomized to receive either 20 mL of 0.05% CPC, 10 mL of 0.01% on-demand aqueous chlorine dioxide, or 20 mL of placebo mouthwash (purified water) in a 1:1:1 ratio. The primary endpoint was the cycle threshold (Ct) values employed for SARS-CoV-2 salivary viral load estimation. We used linear mixed-effects models to assess for any effect of the mouthwashes on SARS-CoV-2 salivary viral load. RESULTS: Of a total of 96 eligible participants enrolled from November 7, 2022, to January 19, 2023, 90 were accepted for the primary analysis. The use of 0.05% CPC mouthwash was not shown to be superior to placebo in change from baseline salivary Ct value at 30 min (difference vs. placebo, 0.640; 95% confidence interval [CI], -1.425 to 2.706; P = 0.543); 2 h (difference vs. placebo, 1.158; 95% CI, -0.797 to 3.112; P = 0.246); 4 h (difference vs. placebo, 1.283; 95% CI, -0.719 to 3.285; P = 0.209); 10 h (difference vs. placebo, 0.304; 95% CI, -1.777 to 2.385; P = 0.775); or 24 h (difference vs. placebo, 0.782; 95% CI, -1.195 to 2.759; P = 0.438). The use of 0.01% on-demand aqueous chlorine dioxide mouthwash was also not shown to be superior to placebo in change from baseline salivary Ct value at 30 min (difference vs. placebo, 0.905; 95% CI, -1.079 to 2.888; P = 0.371); 2 h (difference vs. placebo, 0.709; 95% CI, -1.275 to 2.693; P = 0.483); 4 h (difference vs. placebo, 0.220; 95% CI, -1.787 to 2.226; P = 0.830); 10 h (difference vs. placebo, 0.198; 95% CI, -1.901 to 2.296; P = 0.854); or 24 h (difference vs. placebo, 0.784; 95% CI, -1.236 to 2.804; P = 0.447). CONCLUSIONS: In asymptomatic to mildly symptomatic adults with COVID-19, compared to placebo, the use of 0.05% CPC and 0.01% on-demand aqueous chlorine dioxide mouthwash did not lead to a significant reduction in SARS-CoV-2 salivary viral load. Future studies of the efficacy of CPC and on-demand aqueous chlorine dioxide mouthwash on the viral viability of SARS-CoV-2 should be conducted using different specimen types and in multiple populations and settings.

Study on the disinfection effect of chlorine dioxide disinfectant (ClO2) on dental unit waterlines and its in vitro safety evaluation.

BACKGROUND: Ensuring the safety of dental unit waterlines (DUWLs) has become a pivotal issue in dental care practices, focusing on the health implications for both patients and healthcare providers. The inherent structure and usage conditions of DUWLs contribute to the risk of biofilm formation and bacterial growth, highlighting the need for effective disinfection solutions.The quest for a disinfection method that is both safe for clinical use and effective against pathogens such as Staphylococcus aureus and Escherichia coli in DUWLs underscores the urgency of this research. MATERIALS: Chlorine dioxide disinfectants at concentrations of 5, 20, and 80 mg/L were used to treat biofilms of S. aureus and E. coli cultured in DUWLs. The disinfection effectiveness was assessed through bacterial counts and culturing. Simultaneously, human skin fibroblast cells were treated with the disinfectant to observe changes in cell morphology and cytotoxicity. Additionally, the study included corrosion tests on various metals (carbon steel, brass, stainless steel, aluminum, etc.). RESULTS: Experimental results showed that chlorine dioxide disinfectants at concentrations of 20 mg/L and 80 mg/L significantly reduced the bacterial count of S. aureus and E. coli, indicating effective disinfection. In terms of cytotoxicity, higher concentrations were more harmful to cellular safety, but even at 80 mg/L, the cytotoxicity of chlorine dioxide remained within controllable limits. Corrosion tests revealed that chlorine dioxide disinfectants had a certain corrosive effect on carbon steel and brass, and the degree of corrosion increased with the concentration of the disinfectant. CONCLUSION: After thorough research, we recommend using chlorine dioxide disinfectant at a concentration of 20 mg/L for significantly reducing bacterial biofilms in dental unit waterlines (DUWLs). This concentration also ensures satisfactory cell safety and metal corrosion resistance.

Revealing the Generation of High-Valent Cobalt Species and Chlorine Dioxide in the Co3O4-Activated Chlorite Process: Insight into the Proton Enhancement Effect.

A Co3O4-activated chlorite (Co3O4/chlorite) process was developed to enable the simultaneous generation of high-valent cobalt species [Co(IV)] and ClO2 for efficient oxidation of organic contaminants. The formation of Co(IV) in the Co3O4/chlorite process was demonstrated through phenylmethyl sulfoxide (PMSO) probe and 18O-isotope-labeling tests. Both experiments and theoretical calculations revealed that chlorite activation involved oxygen atom transfer (OAT) during Co(IV) formation and proton-coupled electron transfer (PCET) in the Co(IV)-mediated ClO2 generation. Protons not only promoted the generation of Co(IV) and ClO2 by lowering the energy barrier but also strengthened the resistance of the Co3O4/chlorite process to coexisting anions, which we termed a proton enhancement effect. Although both Co(IV) and ClO2 exhibited direct oxidation of contaminants, their contributions varied with pH changes. When pH increased from 3 to 5, the deprotonation of contaminants facilitated the electrophilic attack of ClO2, while as pH increased from 5 to 8, Co(IV) gradually became the main contributor to contaminant degradation owing to its higher stability than ClO2. Moreover, ClO2- was transformed into nontoxic Cl- rather than ClO3- after the reaction, thus greatly reducing possible environmental risks. This work described a Co(IV)-involved chlorite activation process for efficient removal of organic contaminants, and a proton enhancement mechanism was revealed.

Purified Chlorine Dioxide as an Alternative to Chlorine Disinfection to Minimize Chlorate Formation During Postharvest Produce Washing.

The washwater used to wash produce within postharvest washing facilities frequently contains high chlorine concentrations to prevent pathogen cross-contamination. To address concerns regarding the formation and uptake of chlorate (ClO3-) into produce, this study evaluated whether switching to chlorine dioxide (ClO2) could reduce chlorate concentrations within the produce. Because ClO2 exhibits lower disinfectant demand than chlorine, substantially lower concentrations can be applied. However, ClO3- can form through several pathways, particularly by reactions between ClO2 and the chlorine used to generate ClO2 via reaction with chlorite (ClO2-) or chlorine that forms when ClO2 reacts with produce. This study demonstrates that purging ClO2 from the chlorine and ClO2- mixture used for its generation through a trap containing ClO2- can scavenge chlorine, substantially reducing ClO3- concentrations in ClO2 stock solutions. Addition of low concentrations of ammonia to the produce washwater further reduced ClO3- formation by binding the chlorine produced by ClO2 reactions with produce as inactive chloramines without scavenging ClO2. While chlorate concentrations in lettuce, kale, and broccoli exceeded regulatory guidelines during treatment with chlorine, ClO3- concentrations were below regulatory guidelines for each of these vegetables when treated with ClO2 together with these two purification measures. Switching to purified ClO2 also reduced the concentrations of lipid-bound oleic acid chlorohydrins and protein-bound chlorotyrosines, which are exemplars of halogenated byproducts formed from disinfectant reactions with biomolecules within produce.

Reaction Mechanisms of Chlorine Dioxide with Phenolic Compounds─Influence of Different Substituents on Stoichiometric Ratios and Intrinsic Formation of Free Available Chlorine.

Chlorine dioxide (ClO2) is an oxidant applied in water treatment processes that is very effective for disinfection and abatement of inorganic and organic pollutants. Thereby phenol is the most important reaction partner of ClO2 in reactions of natural organic matter (NOM) and in pollutant degradation. It was previously reported that with specific reaction partners (e.g., phenol), free available chlorine (FAC) could form as another byproduct next to chlorite (ClO2-). This study investigates the impact of different functional groups attached to the aromatic ring of phenol on the formation of inorganic byproducts (i.e., FAC, ClO2-, chloride, and chlorate) and the overall reaction mechanism. The majority of the investigated compounds reacted with a 2:1 stoichiometry and formed 50% ClO2- and 50% FAC, regardless of the position and kind of the groups attached to the aromatic ring. The only functional groups strongly influencing the FAC formation in the ClO2 reaction with phenols were hydroxyl- and amino-substituents in ortho- and para-positions, causing 100% ClO2- and 0% FAC formation. Additionally, this class of compounds showed a pH-dependent stoichiometric ratio due to pH-dependent autoxidation. Overall, FAC is an important secondary oxidant in ClO2 based treatment processes. Synergetic effects in pollutant control and disinfection might be observable; however, the formation of halogenated byproducts needs to be considered as well.

Antimicrobial efficiency of chlorine dioxide and its potential use as anti-SARS-CoV-2 agent: mechanisms of action and interactions with gut microbiota.

Chlorine dioxide (ClO2) is a disinfectant gas with strong antifungal, antibacterial, and antiviral activities. Applied on hard, non-porous surfaces as an aqueous solution or gas, the ClO2 exerts antimicrobial activity through its interaction and destabilization of cell membrane proteins, as well as through DNA/RNA oxidation, triggering cell death. As for viruses, the ClO2 promotes protein denaturalization mechanisms, preventing the union between the human cells and the viral envelope. Currently, ClO2 has been pointed out as a potential anti-SARS-CoV-2 clinical treatment for use in humans with the ability to oxidize the cysteine residues in the spike protein of SARS-CoV-2, inhibiting the subsequent binding with the Angiotensin-converting enzyme type 2 receptor, located in the alveolar cells. Orally administered ClO2 reaches the gut tract and exacerbates the symptoms of COVID-19, generating a dysbiosis with gut inflammation and diarrhea as side effects, and once absorbed, produces toxic effects including methemoglobinemia and hemoglobinuria, which can trigger respiratory diseases. These effects are dose-dependent and may not be entirely consistent between individuals since the gut microbiota composition is highly heterogeneous. However, to support the use of ClO2 as an anti-SARS-CoV-2 agent, further studies focused on its effectiveness and safety both in healthy and immunocompromised individuals, are needed.

The effectiveness of chlorine dioxide gas in portable personal disinfectants to inhibit bacterial growth.

Disinfectants, especially air disinfectants, are necessary to prevent the potential spread of pathogens (bacteria and viruses) in the pandemic era and minimize the spread of pathogens. Some of the commercial disinfectant products that are often used generally contain chlorine dioxide (ClO2) gas. This study tested the effectiveness of two different commercial disinfectants, a liquid stick disinfectant and a powder disinfection card, to carry out the disinfection of pathogenic bacteria in the environment. These two disinfectants were used as a medium for releasing chlorine dioxide gas which has a much stronger bactericidal effect. In the form of liquid stick, ClO2 is more effective in the disinfection process rather than in the form of powder. The effectiveness of the liquid disinfectant in inhibiting the growth of pathogenic bacteria is influenced by the temperature and the area of the open space covered. Considering that the release from both disinfectants used is very small (0.002 ppmv/h), it takes a small area to ensure that the disinfection process runs effectively.

Antimicrobial efficacy of sodium hypochlorite and hyper-pure chlorine dioxide in the depth of dentin tubules in vitro.

OBJECTIVES: The study aimed to compare the antibacterial effect of a novel disinfectant, hyper-pure chlorine dioxide (hClO2) to sodium hypochlorite (NaOCl) in various depths of dentin tubules. MATERIALS AND METHODS: The distal root of the extracted lower molars was infected artificially with Enterococcus faecalis. The control group was rinsed with saline, and the test groups were irrigated with either 5% NaOCl or 0.12% hClO2. The longitudinally split teeth were stained by viability stain. The coronal third of the root was scanned with a confocal laser scanning microscope. The fluorescent intensities were measured, and the percentage of dead bacteria was calculated at depths up to 950 µm along the dentin tubules. The effect of penetration depth, irrigants, and their interaction on antimicrobial efficacy was determined by the linear mixed model. RESULTS: The percentage of dead bacteria was higher both in the NaOCl (45.1 ± 2.3%, p < 0.01) and in the hClO2 (44.6 ± 3.8%, p < 0.01) irrigant groups compared to saline (23 ± 4.5%); however, there was no difference between them. The percentage of killed bacteria was not correlated with the depths in any group (p = 0.633). CONCLUSIONS: Our results suggest that the functional penetration depth of NaOCl is at least 2-3 times more than published to date. There is no difference in disinfection effectiveness along the dentin tubules between NaOCl and hClO2 until at least the measured 950 µm. However, both were only able to eradicate the intratubular bacteria partially. CLINICAL RELEVANCE: Hyper-pure ClO2 could be used as an alternative or final adjuvant irrigant in endodontic treatment.

Reaction of Chlorine Dioxide with Saturated Nitrogen-Containing Heterocycles and Comparison with the Micropollutant Behavior in a Real Water Matrix.

Chlorine dioxide (ClO2) is a very selective oxidant that reacts with electron-rich moieties such as activated amines and thus can degrade specific N-containing micropollutants. N-containing heterocycles (NCHs) are among the most frequent moieties of pharmaceuticals. In this study, the reactions of ClO2 with ritalinic acid and cetirizine, two abundant micropollutants, and model compounds representing their NCH moiety were investigated. The pH-dependent apparent reaction rates of all NCHs with ClO2 were measured and modeled. This model showed that neutral amines are the most important species having reaction rates between 800 and 3200 M-1 s-1, while cationic amines are not reactive. Ritalinic acid, cetirizine, and their representative model compounds showed a high stoichiometric ratio of ≈5 moles ClO2 consumption per degraded ritalinic acid and ≈4 moles ClO2 consumption per degraded cetirizine, respectively. Investigation of chlorine-containing byproducts of ClO2 showed that all investigated NCHs mostly react by electron transfer and form above 80% chlorite. The reactions of the model compounds were well comparable with cetirizine and ritalinic acid, indicating that the model compounds indeed represented the reaction centers of cetirizine and ritalinic acid. Using the calculated apparent reaction rate constants, micropollutant degradation during ClO2 treatment of surface water was predicted for ritalinic acid and cetirizine with -8 to -15% and 13 to -22% error, respectively. The results indicate that in ClO2-based treatment, piperidine-containing micropollutants such as ritalinic acid can be considered not degradable, while piperazine-containing compounds such as cetirizine can be moderately degraded. This shows that NCH model compounds could be used to predict micropollutant degradation.

Photolysis of Chlorine Dioxide under UVA Irradiation: Radical Formation, Application in Treating Micropollutants, Formation of Disinfection Byproducts, and Toxicity under Scenarios Relevant to Potable Reuse and Drinking Water.

Conversion of potable reuse water utilities and drinking water utilities from a low-pressure UV/H2O2 (LPUV/H2O2) advanced oxidation process (AOP) to alternative AOPs in which oxidants can effectively absorb photons and rapidly generate radicals has attracted great interest. Herein, we propose a novel UVA/ClO2 AOP for different water treatment scenarios because of reduced photon absorption by the background matrix and high molar absorptivity for ClO2 at UVA wavelengths. While the photolysis of ClO2 produces •Cl + O2 or •ClO + O(3P) via distinct product channels, we determined the parameters needed to accurately model the loss of oxidants and the formation of byproducts and combined a kinetic model with experimental data to determine quantum yields (Φ). Modeling incorporating the optimized Φ simultaneously predicted oxidant loss and the formation of major products -HOCl, Cl-, and ClO3-. We also systematically investigated the removal of three contaminants exhibiting different radical reactivities, the formation of 35 regulated and unregulated halogenated disinfection byproducts (DBPs), DBP-associated toxicity, and N-acetylcysteine thiol reactivity in synthetic or authentic RO permeates/surface waters treated by different AOPs. The kinetic model developed in this study was used to optimize operating conditions to control undesired products and improve contaminant removal efficiency. The results indicate that UVA/ClO2 can outperform LPUV/H2O2 in terms of electrical energy per order of contaminant degradation, disinfection byproduct formation, and toxicity indices.

Time-effectiveness and convenience of transvaginal ultrasound probe disinfection using ultraviolet vs chlorine dioxide multistep wipe system: prospective survey study.

OBJECTIVES: To compare the efficiency, ease of use and user satisfaction of two methods of transvaginal ultrasound probe high-level disinfection: ultraviolet-C radiation (UV-C) and a chlorine dioxide multistep wipe system. METHODS: This was a prospective survey study. UV-C units were introduced into a busy early pregnancy assessment service and compared with a multiwipe system for disinfection. Before seeing each patient, healthcare professionals (HCPs) measured with a stopwatch the time taken to complete a cycle of disinfection using either UV-C or chlorine dioxide multistep wipes and responded to a quick-response (QR) code-linked survey. Additional essential tasks that could be completed before seeing the next patient during probe disinfection were also documented. Using another QR code-linked survey, data on ease of use, satisfaction with the system used and preferred system were collected. The ease of use and satisfaction with the system were rated on a 0 to 10 Likert scale (0 poor, 10 excellent). A free-text section for comments was then completed. RESULTS: Disinfection using UV-C (n = 331) was 60% faster than the chlorine dioxide multiwipe system (n = 332) (101 vs 250 s; P < 0.0001). A greater number of tasks were completed during probe disinfection when using UV-C, saving a further 74 s per patient (P < 0.0001). The HCPs using UV-C (n = 71) reported greater ease of use (median Likert score, 10 vs 3; P < 0.0001) and satisfaction (median Likert score, 10 vs 2; P < 0.0001) compared with those using the multiwipe system (n = 43). HCPs reported that the chlorine dioxide system was time-consuming and environmentally unfriendly, while the UV-C system was efficient and easy to use. Overall, 98% of the HCPs preferred using the UV-C system. CONCLUSIONS: UV-C technology is more time-efficient and allows more essential tasks to be completed during disinfection. For a 4-h ultrasound list of 15 patients, the use of UV-C would save 55 min 45 s. HCPs found UV-C preferable and easier to use. © 2021 International Society of Ultrasound in Obstetrics and Gynecology.

Imaging and plate counting to quantify the effect of an antimicrobial: A case study of a photo-activated chlorine dioxide treatment.

AIM: To assess removal versus kill efficacies of antimicrobial treatments against thick biofilms with statistical confidence. METHODS AND RESULTS: A photo-activated chlorine dioxide treatment (Photo ClO2 ) was tested in two independent experiments against thick (>100 µm) Pseudomonas aeruginosa biofilms. Kill efficacy was assessed by viable plate counts. Removal efficacy was assessed by 3D confocal scanning laser microscope imaging (CSLM). Biovolumes were calculated using an image analysis approach that models the penetration limitation of the laser into thick biofilms using Beer's Law. Error bars are provided that account for the spatial correlation of the biofilm's surface. The responsiveness of the biovolumes and plate counts to the increasing contact time of Photo ClO2 were quite different, with a massive 7 log reduction in viable cells (95% confidence interval [CI]: 6.2, 7.9) but a more moderate 73% reduction in biovolume (95% CI: [60%, 100%]). Results are leveraged to quantitatively assess candidate CSLM experimental designs of thick biofilms. CONCLUSIONS: Photo ClO2 kills biofilm bacteria but only partially removes the biofilm from the surface. To maximize statistical confidence in assessing removal, imaging experiments should use fewer pixels in each z-slice, and more importantly, at least two independent experiments even if there is only a single field of view in each experiment. SIGNIFICANCE AND IMPACT OF STUDY: There is limited penetration depth when collecting 3D confocal images of thick biofilms. Removal can be assessed by optimally fitting Beer's Law to all of the intensities in a 3D image and by accounting for the spatial correlation of the biofilm's surface. For thick biofilms, other image analysis approaches are biased or do not provide error bars. We generate unbiased estimates of removal and assess candidate CSLM experimental designs of thick biofilms with different pixilations, numbers of fields of view and number of experiments using the included design tool.

Chlorine dioxide: An exception that proves the rules of localized chemical bonding.

We employ natural bond orbital and natural resonance theory tools to analyze the enigmatic properties of the C2v-symmetric isomer of chlorine dioxide radical (ClO2), whose many challenges to Pauling-type localized bonding concepts were recognized by Linus Pauling himself. Although spin-contamination is minimal in this species, ClO2 exhibits an unusually strong form of "different Lewis structures for different spins" bonding pattern, intrinsically outside the framework of "maximal pairing" concepts. We show how the novel spin-unpaired donor-acceptor interactions lead to weakened bonding in the supramolecular domain of polyradical (ClO2)n homoclusters and aqueous ClO2(H2O)n heteroclusters. Despite feeble binding energies and large inter-radical separations, the polyradical clusters are found to maintain coherent spin patterns in each cluster component, attesting to the quantal donor-acceptor nature of their interactions and the cooperative and anticooperative couplings that govern intra- and intermolecular spin distributions in such spin-clusters.

Acute respiratory distress after exposure to chlorine dioxide-based disinfectant.

A hospital cleaner developed acute respiratory distress after working with a chlorine dioxide-based disinfectant. The content of chlorine dioxide in the product is below the limit that would require the product to be labelled as hazardous to health, but we show with a simple estimation that the relevant threshold limit values for chlorine dioxide in the working atmosphere may be exceeded under normal use of the product. This may have implications for risk assessment of the use of such chlorine dioxide-based disinfectants and may warrant stricter regulations for labelling these products.

Effects of the Preferential Oxidation of Phenolic Lignin Using Chlorine Dioxide on Pulp Bleaching Efficiency.

Chlorine dioxide is widely used for pulp bleaching because of its high delignification selectivity. However, efficient and clean chlorine dioxide bleaching is limited by the complexity of the lignin structure. Herein, the oxidation reactions of phenolic (vanillyl alcohol) and non-phenolic (veratryl alcohol) lignin model species were modulated using chlorine dioxide. The effects of chlorine dioxide concentration, reaction temperature, and reaction time on the consumption rate of the model species were also investigated. The optimal consumption rate for the phenolic species was obtained at a chlorine dioxide concentration of 30 mmol·L-1, a reaction temperature of 40 °C, and a reaction time of 10 min, resulting in the consumption of 96.3% of vanillyl alcohol. Its consumption remained essentially unchanged compared with that of traditional chlorine dioxide oxidation. However, the consumption rate of veratryl alcohol was significantly reduced from 78.0% to 17.3%. Additionally, the production of chlorobenzene via the chlorine dioxide oxidation of veratryl alcohol was inhibited. The structural changes in lignin before and after different treatments were analyzed. The overall structure of lignin remained stable during the optimization of the chlorine dioxide oxidation treatment. The signal intensities of several phenolic units were reduced. The effects of the selective oxidation of lignin by chlorine dioxide on the pulp properties were analyzed. Pulp viscosity significantly increased owing to the preferential oxidation of phenolic lignin by chlorine dioxide. The pollution load of bleached effluent was considerably reduced at similar pulp brightness levels. This study provides a new approach to chlorine dioxide bleaching. An efficient and clean bleaching process of the pulp was developed.

Chlorine Dioxide: Friend or Foe for Cell Biomolecules? A Chemical Approach.

This review examines the role of chlorine dioxide (ClO2) on inorganic compounds and cell biomolecules. As a disinfectant also present in drinking water, ClO2 helps to destroy bacteria, viruses, and some parasites. The Environmental Protection Agency EPA regulates the maximum concentration of chlorine dioxide in drinking water to be no more than 0.8 ppm. In any case, human consumption must be strictly regulated since, given its highly reactive nature, it can react with and oxidize many of the inorganic compounds found in natural waters. Simultaneously, chlorine dioxide reacts with natural organic matter in water, including humic and fulvic acids, forming oxidized organic compounds such as aldehydes and carboxylic acids, and rapidly oxidizes phenolic compounds, amines, amino acids, peptides, and proteins, as well as the nicotinamide adenine dinucleotide NADH, responsible for electron and proton exchange and energy production in all cells. The influence of ClO2 on biomolecules is derived from its interference with redox processes, modifying the electrochemical balances in mitochondrial and cell membranes. This discourages its use on an individual basis and without specialized monitoring by health professionals.