Mechanistic aspects of adenovirus serotype 2 inactivation with free chlorine

Bacterial inactivation processes in water disinfection - mechanistic aspects of primary and secondary oxidants - A critical review

Water disinfection during drinking water production is one of the most important processes to ensure safe drinking water, which is gaining even more importance due to the increasing impact of climate change. With specific reaction partners, chemical oxidants can form secondary oxidants, which can cause additional damage to bacteria. Cases in point are chlorine dioxide which forms free available chlorine (e.g., in the reaction with phenol) and ozone which can form hydroxyl radicals (e.g., during the reaction with natural organic matter). The present work reviews the complex interplay of all these reactive species which can occur in disinfection processes and their potential to affect disinfection processes. A quantitative overview of their disinfection strength based on inactivation kinetics and typical exposures is provided. By unifying the current data for different oxidants it was observable that cultivated wild strains (e.g., from wastewater treatment plants) are in general more resistant towards chemical oxidants compared to lab-cultivated strains from the same bacterium. Furthermore, it could be shown that for selective strains chlorine dioxide is the strongest disinfectant (highest maximum inactivation), however as a broadband disinfectant ozone showed the highest strength (highest average inactivation). Details in inactivation mechanisms regarding possible target structures and reaction mechanisms are provided. Thereby the formation of secondary oxidants and their role in inactivation of pathogens is decently discussed. Eventually, possible defense responses of bacteria and additional effects which can occur in vivo are discussed.

Persistence of endogenous RNA biomarkers of SARS-CoV-2 and PMMoV in raw wastewater: Impact of temperature and implications for wastewater-based epidemiology

Understanding the persistence of SARS-CoV-2 biomarkers in wastewater should guide wastewater-based epidemiology users in selecting best RNA biomarkers for reliable detection of the virus during current and future waves of the pandemic. In the present study, the persistence of endogenous SARS-CoV-2 were assessed during one month for six different RNA biomarkers and for the pepper mild mottle virus (PMMoV) at three different temperatures (4, 12 and 20 °C) in one wastewater sample. All SARS-CoV-2 RNA biomarkers were consistently detected during 6 days at 4° and differences in signal persistence among RNA biomarkers were mostly observed at 20 °C with N biomarkers being globally more persistent than RdRP, E and ORF1ab ones. SARS-CoV-2 signal persistence further decreased in a temperature dependent manner. At 12 and 20 °C, RNA biomarker losses of 1-log10 occurred on average after 6 and 4 days, and led to a complete signal loss after 13 and 6 days, respectively. Besides the effect of temperature, SARS-CoV-2 RNA signals were more persistent in the particulate phase compared to the aqueous one. Finally, PMMoV RNA signal was highly persistent in both phases and significantly differed from that of SARS-CoV-2 biomarkers. We further provide a detailed overview of the latest literature on SARS-CoV-2 and PMMoV decay rates in sewage matrices.

Chloride Enhances DNA Reactivity with Chlorine under Conditions Relevant to Water Treatment

Free available chlorine (FAC) is widely used to inactivate viruses by oxidizing viral components, including genomes. It is commonly assumed that hypochlorous acid (HOCl) is the chlorinating agent responsible for virus inactivation; however, recent studies have underscored that minor constituents of FAC existing in equilibrium with HOCl, such as molecular chlorine (Cl₂), can influence FAC reactivity toward select organic compounds. This study measures the FAC reaction kinetics with dsDNA and ssDNA extracted from representative bacteriophages (T3 and ϕX174) in samples augmented with chloride. Herein, chloride enhances FAC reactivity toward dsDNA and, to a lesser extent, toward ssDNA, especially at pH < 7.5. The enhanced reactivity can be attributed to the formation of Cl₂. Second-order rate constants were determined for reactions of ssDNA and dsDNA with HOCl and Cl₂. DNA chlorination kinetics followed the reactivity-selectivity principle, where the more-reactive nucleophilic species (ssDNA, ∼100× more reactive than dsDNA) reacted less selectively with electrophilic FAC species. The addition of chloride was also shown to enhance the inactivation of bacteriophage T3 (dsDNA genome) by FAC but did not enhance the inactivation of bacteriophage ϕX174 (ssDNA genome). Overall, the results suggest that Cl₂ is an important chlorinating agent of nucleic acids and viruses.

Wastewater-Based Epidemiology: Detection of SARS-CoV-2 RNA in Different Stages of Domestic Wastewater Treatment in Santa Fe, Argentina

The COVID-19 pandemic affected human life at every level. In this study, we analyzed genetic markers (N and ORF1ab, RNA genes) of SARS-CoV-2 in domestic wastewaters (DWW) in San Justo City (Santa Fe, Argentina), using reverse transcription-quantitative real-time PCR. Out of the 30 analyzed samples, 30% were positive for SARS-CoV-2 RNA. Of the total positive samples, 77% correspond to untreated DWW, 23% to pre-chlorination, and no SARS-CoV-2 RNA was registered at the post-chlorination sampling site. The viral loads of N and OFR1ab genes decreased significantly along the treatment process, and the increase in the number of viral copies of the N gene could anticipate, by 6 days, the number of clinical cases in the population. The concentration of chlorine recommended by the WHO (≥ 0.5 mg L-1 after at least 30 min of contact time at pH 8.0) successfully removed SARS-CoV-2 RNA from DWW. The efficiency of wastewater-based epidemiology (WBE) confirms the need to control and increase DWW treatment systems on a regional and global scale. This work could contribute to building a network for WBE to monitor SARS-CoV-2 in wastewaters during the pandemic waves and the epidemic remission phase.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s11270-022-05772-w.

Reactivity of Viral Nucleic Acids with Chlorine and the Impact of Virus Encapsidation

Free chlorine disinfection is widely applied to inactivate viruses by reacting with their biomolecules, which include nucleic acids, proteins, and lipids. Knowing the reactivities of viral genomes with free chlorine and the protection that encapsidation provides would ultimately help predict virus susceptibility to the disinfectant. The relative reactivities of different viral genome types and the impact of viral higher order structure with free chlorine are poorly characterized. Here, we studied the reactivity of viral genomes representing four genome types from virus particles with diverse structures, namely, (+)ssRNA (MS2), dsRNA (φ6), ssDNA (φX174), and dsDNA (T3) with free chlorine. We compared the reactivities of these viral nucleic acids when they were suspended in phosphate buffer solutions (naked forms) and when they were in the native virus particles (encapsidated forms). The reactivities of nucleic acids were tracked by polymerase chain reaction (PCR)-based assays. The naked dsDNA of T3 was the least reactive with free chlorine, with an average second order rate constant normalized by the number of bases in the measured regions (in M^-1 s^-1 b^-1) that was 34×, 65×, and 189× lower than those of the dsRNA of φ6, ssRNA of MS2, and ssDNA of φX174, respectively. Moreover, different regions in the ssRNA genome of MS2 and the dsRNA genome of φ6 exhibited statistically different reaction kinetics. The genomes within virus particles reacted slower than the naked genomes overall, but the extent of these differences varied among the four viruses. The results on viral nucleic acid reactivity help explain different susceptibilities of viruses to inactivation by free chlorine and also provide a valuable comparison of the susceptibilities of different nucleic acids to oxidants.

Monitoring of new coronavirus (SARS-CoV-2): Origin, transmission, and food preservation methods

Unfortunately, there is limited research on coronavirus survival of food products and also food processing. The knowledge of the physical and chemical characteristics of coronaviruses mostly comes from the study of SARS-CoV and MERS-CoV physical (i.e., thermal processing, chilling and freezing, microwave irradiation, ultraviolet light, gamma irradiation, high hydrostatic pressure) and chemical (acidification and use of common disinfectants in the food industry like chlorinated derivatives and ozone) are means which could be used to inactive the coronaviruses or reduce the infection. These methods can be applied individually or in combination to act better performance. Thermal processing is one of the most effective methods for inactive coronavirus. Heating at 75°C (15-60 min) and 65°C (1 min) was the best temperature for inactive SARS-CoV and MERS virus, respectively. Among irradiation methods (microwave, UV, and gamma), the most effective one is UVC rays. Moreover, the use of disinfectant like chlorinated derivatives is appropriate way to disinfect food product surfaces.

Novelty impact statement

This review provided updated information on effective strategies for inactive coronavirus that can be used in the food industry. SARS-CoV-2 as a new pandemic coronavirus was initiated from contaminated foods and can be transmitted by close contact, aerosols, and food surfaces. Food preservation (physical and chemical) methods could decrease SARS-CoV-2. Probably, heating and UVC are the most effective approach to inactive SARS-CoV-2. Despite the findings of coronavirus inactivation which were here discussed, much research is still needed for the development of new approaches to overcome the coronavirus.

Aerobic Conditions and Endogenous Reactive Oxygen Species Reduce the Production of Infectious MS2 Phage by Escherichia coli

Most of the defective/non-infectious enteric phages and viruses that end up in wastewater originate in human feces. Some of the causes of this high level of inactivity at the host stage are unknown. There is a significant gap between how enteric phages are environmentally transmitted and how we might design molecular tools that would only detect infectious ones. Thus, there is a need to explain the low proportion of infectious viral particles once replicated. By analyzing lysis plaque content, we were able to confirm that, under aerobic conditions, Escherichia coli produce low numbers of infectious MS2 phages (I) than the total number of phages indicated by the genome copies (G) with an I/G ratio of around 2%. Anaerobic conditions of replication and ROS inhibition increase the I/G ratio to 8 and 25%, respectively. These data cannot only be explained by variations in the total numbers of MS2 phages produced or in the metabolism of E. coli. We therefore suggest that oxidative damage impacts the molecular replication and assembly of MS2 phages.

Mechanism and efficacy of virus inactivation by a microplasma UV lamp generating monochromatic UV irradiation at 222 nm

This study evaluated the potential of a microplasma UV lamp as an alternative UV source to the current mercury-based (Hg-based) UV lamp for water disinfection. We developed a set of PCR-based molecular assays (long-range qPCR, DNase, and binding assay) to quantify the adenovirus genome, capsid, and fiber damage with a wide detection range (10^0.5-10^6.5 PFU/mL). We used these molecular assays to characterize adenovirus (AdV) inactivation kinetics by microplasma UV that produced monochromatic UV at 222 nm. We found that the inactivation rate constant (0.142 cm²/mJ) due to microplasma UV was 4.4 times higher than that of low-pressure Hg UV (0.032 cm²/mJ). This high efficacy was attributed to monochromatic UV wavelength at 222 nm damaging the AdV capsid protein. The results of these molecular assays also proved that microplasma UV and medium-pressure Hg UV with a bandpass filter at 223 nm (MPUV_223nm) have a similar influence on AdV (p>0.05). We then estimated the relative energy efficiency of MPUV and microplasma UV to LPUV for 4 log reduction of the viruses. We found that the microplasma UV resulted in higher inactivation rate constants for viruses than the current Hg-based UV. Consequently, microplasma UV could be more energy efficient than low-pressure Hg UV for water disinfection if the wall-plug efficiency of the microplasma UV lamp improved to 8.4% (currently 1.5%). Therefore, the microplasma UV lamp is a promising option for water disinfection.

Coronaviruses in wastewater processes: Source, fate and potential risks

The last 17 years have seen three major outbreaks caused by coronaviruses, with the latest outbreak, COVID-19, declared a pandemic by the World Health Organization. The frequency of these outbreaks, their mortality and associated disruption to normal life calls for concerted efforts to understand their occurrence and fate in different environments. There is an increased interest in the occurrence of coronaviruses in wastewater from the perspective of wastewater-based epidemiology. However, there is no comprehensive review of the knowledge on coronavirus occurrence, fate and potential transmission in wastewater. This paper, provides a review of the literature on the occurrence of coronaviruses in wastewater treatment processes. We discuss the presence of viral RNA in feces as a result of diarrhoea caused by gastrointestinal infections. We also reviewed the literature on the presence, survival and potential removal of coronaviruses in common wastewater treatment processes. The detection of infectious viral particles in feces of patients raises questions on the potential risks of infection for people exposed to untreated sewage/wastewater. We, therefore, highlighted the potential risk of infection with coronaviruses for workers in wastewater treatment plants and the public that may be exposed through faulty plumbing or burst sewer networks. The mortalities and morbidities associated with the current COVID-19 pandemic warrants a much more focused research on the role of environments, such as wastewater and surface water, in disease transmission. The current wealth of knowledge on coronaviruses in wastewater based on the reviewed literature is scant and therefore calls for further studies.

Structural Organizations of Qβ and MS2 Phages Affect Capsid Protein Modifications by Oxidants Hypochlorous Acid and Peroxynitrite

Pathogenic enteric viruses and bacteriophages such as Qβ and MS2 are transmitted through the fecal-oral route. However, oxidants such as peroxynitrite (ONOOH) and hypochlorous acid (HClO) can prevent new infection by inactivating infectious viruses. Their virucidal effect is well recognized, and yet predicting the effects of oxidants on viruses is currently impossible because the detailed mechanisms of viral inactivation remain unclear. Our data show that ONOOH and HClO cross-linked the capsid proteins and RNA genomes of Qβ and MS2 phages. Consistently, the capsids appeared intact by transmission electron microscopy (TEM) even when 99% of the phages were inactivated by oxidation. Moreover, a precise molecular study of the capsid proteins shows that ONOOH and HClO preferentially targeted capsid protein regions containing the oxidant-sensitive amino acid C, Y, or W. Interestingly, the interaction of these amino acids was a crucial parameter defining whether they would be modified by the addition of O, Cl, or NO₂ or whether it induced the loss of the protein region detected by mass spectrometry, together suggesting potential sites for cross-link formation. Together, these data show that HClO and ONOOH consistently target oxidant-sensitive amino acids regardless of the structural organization of Qβ and MS2, even though the phenotypes change as a function of the interaction with adjacent proteins/RNA. These data also indicate a potential novel mechanism of viral inactivation in which cross-linking may impair infectivity.

The impact of chlorine and heat on the infectivity and physicochemical properties of bacteriophage MS2

Enteric viruses and bacteriophages are exposed to various inactivating factors outside their host, and among them chlorine and heat are the most commonly used sanitizer in water industry and treatment in the food industry, respectively. Using MS2 phages as models for enteric viruses, we investigated the impact of free chlorine and heat on their physicochemical properties. Free chlorine was first evaluated alone. No increase in either capsid permeability or hydrophobicity was observed. The negative surface charge slightly increased suggesting molecular changes in the capsid. However, a weakening of the capsid by chlorine was suggested by differential scanning fluorimetry. This phenomenon was confirmed when chlorination was followed by a heat treatment. Indeed, an increase in the inactivation of MS2 phages and the permeability of their capsids to RNases was observed. More interestingly, an increase in the expression of hydrophobic domains at the phage surface was observed, but only for phages remaining infectious. The chlorine-caused weakening of the capsid suggested that, for an optimal use, the oxidant should be followed by heat. The increased permeability to RNases and the expression of hydrophobic domains may contribute to the development or improvement of molecular methods specific for infectious enteric viruses.

Specific Interactions between Human Norovirus and Environmental Matrices: Effects on the Virus Ecology

Human norovirus is the major cause of non-bacterial epidemic gastroenteritis. Human norovirus binds to environmental solids via specific and non-specific interactions, and several specific receptors for human norovirus have been reported. Among them, histo-blood group antigens (HBGA) are the most studied specific receptor. Studies have identified the presence of HBGA-like substances in the extracellular polymeric substances (EPS) and lipopolysaccharides (LPS) of human enteric bacteria present in aquatic environments, gastrointestinal cells, gills, and palps of shellfish, and cell walls, leaves, and veins of lettuce. These HBGA-like substances also interact with human norovirus in a genotype-dependent manner. Specific interactions between human norovirus and environmental matrices can affect norovirus removal, infectivity, inactivation, persistence, and circulation. This review summarizes the current knowledge and future directions related to the specific interactions between human norovirus and HBGA-like substances in environmental matrices and their possible effects on the fate and circulation of human norovirus.

Analogies and differences among bacterial and viral disinfection by the photo-Fenton process at neutral pH: a mini review

Over the last years, the photo-Fenton process has been established as an effective, green alternative to chemical disinfection of waters and wastewaters. Microorganisms' inactivation is the latest success story in the application of this process at near-neutral pH, albeit without clearly elucidated inactivation mechanisms. In this review, the main pathways of the combined photo-Fenton process against the most frequent pathogen models (Escherichia coli for bacteria and MS2 bacteriophage for viruses) are analyzed. Firstly, the action of solar light is described and the specific inactivation mechanisms in bacteria (internal photo-Fenton) and viruses (genome damage) are presented. The contribution of the external pathways due to the potential presence of organic matter in generating reactive oxygen species (ROS) and their effects on microorganism inactivation are discussed. Afterwards, the effects of the gradual addition of Fe and H₂O₂ are assessed and the differences among bacterial and viral inactivation are highlighted. As a final step, the simultaneous addition of both reagents induces the photo-Fenton in the bulk, focusing on the differences induced by the homogeneous or heterogeneous fraction of the process and the variation among the two respective targets. This work exploits the accumulated evidence on the mechanisms of bacterial inactivation and the scarce ones towards viral targets, aiming to bridge this knowledge gap and make possible the further application of the photo-Fenton process in the field of water/wastewater treatment.

Adenovirus Replication Cycle Disruption from Exposure to Polychromatic Ultraviolet Irradiation

Polychromatic ultraviolet (UV) light with bandwidth of 20 nm and peak emission centered at 224, 254, or 280 nm (UV₂₂₄, UV₂₅₄, and UV₂₈₀, respectively) were used to inactivate human adenovirus type 2 (HAdV-2). Quantitative polymerase chain reaction (qPCR) and reverse transcriptase qPCR assays were used to elucidate the step in the HAdV-2 replication cycle that was disrupted after UV exposure. UV treatment at any of the wavelengths analyzed did not inhibit association of HAdV-2 to the host cells even after exposure to a fluence (UV dose) that would produce a virus inactivation efficiency, measured by plaque assay, greater than 99.99%. In contrast, UV irradiation at all three peak emissions disrupted early E1A gene transcription and viral DNA replication, but different mechanisms appeared to be dominating such disruptions. UV₂₂₄ seemed to have little effect on the integrity of the viral genome but produced a structural transformation of the viral capsid that may inhibit the delivery of viral genome into the host cell nucleus. On the other hand, UV₂₅₄ and UV₂₈₀ did not affect the integrity of the viral capsid, but the mutations they produced on the viral genome might cause the inhibition of the early gene transcription and DNA replication after the viral genome successfully translocated into the host cell nucleus.

Efficacy of Neutral Electrolyzed Water for Inactivation of Human Norovirus

Human norovirus (NoV) is the leading cause of acute gastroenteritis worldwide. Persistence on surfaces and resistance to many conventional disinfectants contribute to widespread transmission of norovirus. We examined the efficacy of neutral electrolyzed water (NEW; pH 7) for inactivation of human NoV GII.4 Sydney in suspension (ASTM method 1052-11) and on stainless steel surfaces (ASTM method 1053-11) with and without an additional soil load. The impact of the disinfectant on viral capsid was assessed using reverse transcriptase quantitative PCR (RT-qPCR; with an RNase pretreatment), SDS-PAGE, transmission electron microscopy, and a histo-blood group antigen (HBGA) receptor-binding assay. These studies were done in parallel with those using Tulane virus (TuV), a cultivable human NoV surrogate. Neutral electrolyzed water at 250 ppm free available chlorine produced a 4.8- and 0.4-log10 reduction in NoV genome copy number after 1 min in suspension and on stainless steel, respectively. Increasing the contact time on surfaces to 5, 10, 15, and 30 min reduced human NoV genomic copies by 0.5, 1.6, 2.4, and 5.0 log10 and TuV infectious titers by 2.4, 3.0, 3.8, and 4.1 log10 PFU, respectively. Increased soil load effectively eliminated antiviral efficacy regardless of testing method and virus. Exposure to NEW induced a near complete loss of receptor binding (5 ppm, 30 s), degradation of VP1 major capsid protein (250 ppm, 5 min), and increased virus particle aggregation (150 ppm, 30 min). Neutral electrolyzed water at 250 ppm shows promise as an antinoroviral disinfectant when used on precleaned stainless steel surfaces.IMPORTANCE Norovirus is the leading cause of acute viral gastroenteritis worldwide. Transmission occurs by fecal-oral or vomitus-oral routes. The persistence of norovirus on contaminated environmental surfaces exacerbates its spread, as does its resistance to many conventional disinfectants. The purpose of this research was to evaluate the antinoroviral efficacy of neutral electrolyzed water (NEW), a novel chlorine-based disinfectant that can be used at reduced concentrations, making it more environmentally friendly and less corrosive than bleach. An industrial-scale electrochemical activation device capable of producing relatively stable electrolyzed water at a wide pH range was used in this study. Experiments showed that 250 ppm NEW effectively eliminated (defined as a 5-log10 reduction) human norovirus GII.4 Sydney (epidemic strain) on clean stainless steel surfaces after a 30-min exposure. Supporting studies showed that, like bleach, NEW causes inactivation by disrupting the virus capsid. This product shows promise as a bleach alternative with antinoroviral efficacy.

The Effect of Heat and Free Chlorine Treatments on the Surface Properties of Murine Norovirus

Heat and free chlorine are among the most efficient and commonly used treatments to inactivate enteric viruses, but their global inactivation mechanisms have not been elucidated yet. These treatments have been shown to affect at least the capsid proteins of viruses and thus may affect the surface properties (i.e. electrostatic charge and hydrophobicity) of such particles. Our aim was to study the effects of heat and free chlorine on surface properties for a murine norovirus chosen as surrogate for human norovirus. No changes in the surface properties were observed with our methods for murine norovirus exposed to free chlorine. Only the heat treatment led to major changes in the surface properties of the virus with the expression of hydrophobic domains at the surface of the particles after exposure to a temperature of 55 °C. No modification of the expression of hydrophobic domains occurred after exposure to 60 °C, and the low hydrophobic state exhibited by infectious and inactivated particles after exposure to 60 °C appeared to be irreversible for inactivated particles only, which may provide a means to discriminate infectious from inactivated murine noroviruses. When exposed to a temperature of 72 °C or to free chlorine at a concentration of 50 mg/L, the genome became available for RNases.

Quantitative reverse transcription PCR to determine the inactivation of Human Rotavirus by chlorine

Human rotaviruses (HRVs) are the major cause of acute diarrhea in infants and young children. Here, a real-time reverse transcription polymerase chain reaction assay targeting the rotaviral VP4 gene (VP4-RT-qPCR) was established to evaluate the inactivation of HRV upon chlorine disinfection, based on a previous report that damage to the 1227-2354bp region of the VP4 gene was associated with eliminated HRV infectivity by chlorine. In this study, inactivation of HRV by 0.6mg/L free chlorine was assessed in phosphate buffered saline (PBS; pH 7.2), and tap and river water samples, using both TCID₅₀ and RT-qPCR (VP2- and VP4-RT-qPCR) assays, respectively. Among the samples tested, the VP2-RT-qPCR method did not show significant inactivation after chlorine disinfection; however, the reduction in VP4-RT-qPCR signal was correlated with decreased HRV infectivity. Moreover, the higher sensitivity of the VP4-RT-qPCR assay allowed for assessment of chlorine HRV inactivation at longer exposure times compared with the conventional TCID₅₀ assay. Collectively, these results indicated that the VP4-RT-qPCR assay is a rapid, sensitive, and reliable tool to detect infectious HRV following chlorine inactivation, and highlights the potential for further development of qPCR/RT-qPCR assays to provide information regarding viral infectivity from drinking water plants.

Analysis of Hydroxyl Radicals and Inactivation Mechanisms of Bacteriophage MS2 in Response to a Simultaneous Application of UV and Chlorine

The simultaneous application of UV and chlorine (expressed as UV/Cl₂) as a water treatment method may be a good disinfection option for UV-resistant microorganisms, such as human adenoviruses (HAdVs). In this study, we developed two approaches using UV/Cl₂: one to quantitate the OH• radicals based on the degradation of the probe compound para-chlorobenzoic acid (pCBA) and the other to use bacteriophage MS2 to understand the virus inactivation mechanisms in response to UV, chlorine and UV/Cl₂ disinfection using reverse-transcription quantitative polymerase chain reaction (RT-qPCR), attachment and genome penetration assays. The results revealed that OH• radicals were produced at a concentration of 2.70 × 10^-14 M in the UV/Cl₂ treatment with a practical chlorine dose of 1 mg/L and with a minimum UV₂₅₄ fluence of approximately 10 mJ/cm², whereas UV or chlorine alone did not produce OH• radicals. In the UV/Cl₂ treatment, synergistic effects on viral genome damage were observed, but were not directly due to OH• radicals. The ability of MS2 to penetrate the genome of the host bacteria was impaired, but its ability to attach to the host was not affected by the treatment. We concluded that the major cause of virus inactivation in response to UV/Cl₂ was the damage to the viral genome caused by combination actions of chlorine species and OH• radicals.

Tracking Human Adenovirus Inactivation by Gamma Radiation under Different Environmental Conditions

Adenovirus is the most prevalent enteric virus in waters worldwide due to its environmental stability, which leads to public health concerns. Mitigation strategies are therefore required. The aim of this study was to assess the inactivation of human adenovirus type 5 (HAdV-5) by gamma radiation in aqueous environments. Various substrates with different organic loads, including domestic wastewater, were inoculated with HAdV-5 either individually or in a viral pool (with murine norovirus type 1 [MNV-1]) and were irradiated in a Cobalt-60 irradiator at several gamma radiation doses (0.9 to 10.8 kGy). The infectivity of viral particles, before and after irradiation, was tested by plaque assay using A549 cells. D10 values (dose required to inactivate 90% of a population or the dose of irradiation needed to produce a 1 log10 reduction in the population) were estimated for each substrate based on virus infectivity inactivation exponential kinetics. The capability of two detection methods, nested PCR and enzyme-linked immunosorbent assay (ELISA), to track inactivated viral particles was also assessed. After irradiation at 3.5 kGy, a reduction of the HAdV-5 titer of 4 log PFU/ml on substrates with lower organic loads was obtained, but in highly organic matrixes, the virus titer reduction was only 1 log PFU/ml. The D10 values of HAdV-5 in high organic substrates were significantly higher than in water suspensions. The obtained results point out some discrepancies between nested PCR, ELISA, and plaque assay on the assessments of HAdV-5 inactivation. These results suggest that the inactivation of HAdV-5 by gamma radiation, in aqueous environments, is significantly affected by substrate composition. This study highlights the virucidal potential of gamma radiation that may be used as a disinfection treatment for sustainable water supplies.

IMPORTANCE

Human adenovirus (HAdV) is the most prevalent of the enteric viruses in environmental waters worldwide. The purposes of this study are to provide new insights on the inactivation of enteric virus by gamma irradiation and to introduce new concepts and reinforce the benefits and utility of radiation technologies as disinfection processes. This may be an effective tool to guarantee the reduction of viral pathogens and to contribute to public health and sustainable water supplies.

Technical aspects of using human adenovirus as a viral water quality indicator

Despite dramatic improvements in water treatment technologies in developed countries, waterborne viruses are still associated with many of cases of illness each year. These illnesses include gastroenteritis, meningitis, encephalitis, and respiratory infections. Importantly, outbreaks of viral disease from waters deemed compliant from bacterial indicator testing still occur, which highlights the need to monitor the virological quality of water. Human adenoviruses are often used as a viral indicator of water quality (faecal contamination), as this pathogen has high UV-resistance and is prevalent in untreated domestic wastewater all year round, unlike enteroviruses and noroviruses that are often only detected in certain seasons. Standard methods for recovering and measuring adenovirus numbers in water are lacking, and there are many variations in published methods. Since viral numbers are likely under-estimated when optimal methods are not used, a comprehensive review of these methods is both timely and important. This review critically evaluates how estimates of adenovirus numbers in water are impacted by technical manipulations, such as during adenovirus concentration and detection (including culturing and polymerase-chain reaction). An understanding of the implications of these issues is fundamental to obtaining reliable estimation of adenovirus numbers in water. Reliable estimation of HAdV numbers is critical to enable improved monitoring of the efficacy of water treatment processes, accurate quantitative microbial risk assessment, and to ensure microbiological safety of water.

Human and animal enteric virus in groundwater from deep wells, and recreational and network water

This study was designed to assess the presence of human adenovirus (HAdV), rotavirus-A (RVA), hepatitis A virus (HAV), and porcine circovirus-2 (PCV2) in groundwater from deep wells, and recreational and network waters. The water samples were collected and concentrated and the virus genomes were assessed and quantified by quantitative PCR (qPCR). Infectious HAdV was evaluated in groundwater and network water samples by integrated cell culture using transcribed messenger RNA (mRNA) (ICC-RT-qPCR). In recreational water samples, HAdV was detected in 100 % (6/6), HAV in 66.6 % (4/6), and RVA in 66.6 % (4/6). In network water, HAdV was detected in 100 % (6/6) of the samples (these 83 % contained infectious HAdV), although HAV and RVA were not detected and PCV2 was not evaluated. In groundwater from deep wells, during rainy period, HAdV and RVA were detected in 80 % (4/5) of the samples, and HAV and PCV2 were not detected; however, during dry period, HAdV and RVA were detected in 60 % (3/5), HAV in only one sample, and PCV2 in 60 % (4/5). In groundwater, all samples contained infectious HAdV. PCV2 presence in groundwater is indicative of contamination caused by swine manure in Concórdia, Santa Catarina, Brazil. The disinfection of human and animal wastes is urgent, since they can contaminate surface and groundwater, being a potential threat for public and animal health.

Degradation of Amino Acids and Structure in Model Proteins and Bacteriophage MS2 by Chlorine, Bromine, and Ozone

Proteins are important targets of chemical disinfectants. To improve the understanding of disinfectant-protein reactions, this study characterized the disinfectant:protein molar ratios at which 50% degradation of oxidizable amino acids (i.e., Met, Tyr, Trp, His, Lys) and structure were observed during HOCl, HOBr, and O3 treatment of three well-characterized model proteins and bacteriophage MS2. A critical question is the extent to which the targeting of amino acids is driven by their disinfectant rate constants rather than their geometrical arrangement. Across the model proteins and bacteriophage MS2 (coat protein), differing widely in structure, methionine was preferentially targeted, forming predominantly methionine sulfoxide. This targeting concurs with its high disinfectant rate constants and supports its hypothesized role as a sacrificial antioxidant. Despite higher HOCl and HOBr rate constants with histidine and lysine than for tyrosine, tyrosine generally was degraded in preference to histidine, and to a lesser extent, lysine. These results concur with the prevalence of geometrical motifs featuring histidines or lysines near tyrosines, facilitating histidine and lysine regeneration upon Cl[+1] transfer from their chloramines to tyrosines. Lysine nitrile formation occurred at or above oxidant doses where 3,5-dihalotyrosine products began to degrade. For O3, which lacks a similar oxidant transfer pathway, histidine, tyrosine, and lysine degradation followed their relative O3 rate constants. Except for its low reactivity with lysine, the O3 doses required to degrade amino acids were as low as or lower than for HOCl or HOBr, indicating its oxidative efficiency. Loss of structure did not correlate with loss of particular amino acids, suggesting the need to characterize the oxidation of specific geometric motifs to understand structural degradation.

The Impact of Capsid Proteins on Virus Removal and Inactivation During Water Treatment Processes

This study examined the effect of the amino acid composition of protein capsids on virus inactivation using ultraviolet (UV) irradiation and titanium dioxide photocatalysis, and physical removal via enhanced coagulation using ferric chloride. Although genomic damage is likely more extensive than protein damage for viruses treated using UV, proteins are still substantially degraded. All amino acids demonstrated significant correlations with UV susceptibility. The hydroxyl radicals produced during photocatalysis are considered nonspecific, but they likely cause greater overall damage to virus capsid proteins relative to the genome. Oxidizing chemicals, including hydroxyl radicals, preferentially degrade amino acids over nucleotides, and the amino acid tyrosine appears to strongly influence virus inactivation. Capsid composition did not correlate strongly to virus removal during physicochemical treatment, nor did virus size. Isoelectric point may play a role in virus removal, but additional factors are likely to contribute.

Solar Disinfection of Viruses in Polyethylene Terephthalate Bottles

Solar disinfection (SODIS) of drinking water in polyethylene terephthalate (PET) bottles is a simple, efficient point-of-use technique for the inactivation of many bacterial pathogens. In contrast, the efficiency of SODIS against viruses is not well known. In this work, we studied the inactivation of bacteriophages (MS2 and ϕX174) and human viruses (echovirus 11 and adenovirus type 2) by SODIS. We conducted experiments in PET bottles exposed to (simulated) sunlight at different temperatures (15, 22, 26, and 40°C) and in water sources of diverse compositions and origins (India and Switzerland). Good inactivation of MS2 (>6-log inactivation after exposure to a total fluence of 1.34 kJ/cm(2)) was achieved in Swiss tap water at 22°C, while less-efficient inactivation was observed in Indian waters and for echovirus (1.5-log inactivation at the same fluence). The DNA viruses studied, ϕX174 and adenovirus, were resistant to SODIS, and the inactivation observed was equivalent to that occurring in the dark. High temperatures enhanced MS2 inactivation substantially; at 40°C, 3-log inactivation was achieved in Swiss tap water after exposure to a fluence of only 0.18 kJ/cm(2). Overall, our findings demonstrate that SODIS may reduce the load of single-stranded RNA (ssRNA) viruses, such as echoviruses, particularly at high temperatures and in photoreactive matrices. In contrast, complementary measures may be needed to ensure efficient inactivation during SODIS of DNA viruses resistant to oxidation.

Leveraging the Mechanism of Oxidative Decay for Adenylate Kinase to Design Structural and Functional Resistances

Characterization of the mechanisms underlying hypohalous acid (i.e., hypochlorous acid or hypobromous acid) degradation of proteins is important for understanding how the immune system deactivates pathogens during infections and damages human tissues during inflammatory diseases. Proteins are particularly important hypohalous acid reaction targets in pathogens and in host tissues, as evidenced by the detection of chlorinated and brominated oxidizable residues. While a significant amount of work has been conducted for reactions of hypohalous acids with a range of individual amino acids and small peptides, the assessment of oxidative decay in full-length proteins has lagged in comparison. The most rigorous test of our understanding of oxidative decay of proteins is the rational redesign of proteins with conferred resistances to the decay of structure and function. Toward this end, in this study, we experimentally determined a putative mechanism of oxidative decay using adenylate kinase as the model system. In turn, we leveraged this mechanism to rationally design new proteins and experimentally test each system for oxidative resistance to loss of structure and function. From our extensive assessment of secondary structure, protein hydrodynamics, and enzyme activity upon hypochlorous acid or hypobromous acid challenge, we have identified two key strategies for conferring structural and functional resistance, namely, the design of proteins (adenylate kinase enzymes) that are resistant to oxidation requires complementary consideration of protein stability and the modification (elimination) of certain oxidizable residues proximal to catalytic sites.

Sequential and Simultaneous Applications of UV and Chlorine for Adenovirus Inactivation

Adenoviruses are water-borne human pathogens with high resistance to UV disinfection. Combination of UV treatment and chlorination could be an effective approach to deal with adenoviruses. In this study, human adenovirus 5 (HAdV-5) was challenged in a bench-scale experiment by separate applications of UV or chlorine and by combined applications of UV and chlorine in either a sequential or simultaneous manner. The treated samples were then propagated in human lung carcinoma epithelial cells to quantify the log inactivation of HAdV-5. When the processes were separate, a fluence of 100 mJ/cm(2) and a CT value of 0.02 mg min/L were required to achieve 2 log inactivation of HAdV-5 by UV disinfection and chlorination, respectively. Interestingly, synergistic effects on the HAdV-5 inactivation rates were found in the sequential process of chlorine followed by UV (Cl2-UV) (p < 0.05, ANCOVA) in comparison to the separate processes or the simultaneous application of UV/Cl2. This implies that a pretreatment with chlorine may increase the sensitivity of the virus to the subsequent UV disinfection. In conclusion, this study suggests that the combined application of UV and chlorine could be an effective measure against adenoviruses as a multi-barrier approach in water disinfection.

Solar and temperature treatments affect the ability of human rotavirus wa to bind to host cells and synthesize viral RNA

Rotavirus, the leading cause of diarrheal diseases in children under the age of five, is often resistant to conventional wastewater treatment and thus can remain infectious once released into the aquatic environment. Solar and heat treatments can inactivate rotavirus, but it is unknown how these treatments inactivate the virus on a molecular level. To answer this question, our approach was to correlate rotavirus inactivation with the inhibition of portions of the virus life cycle as a means to identify the mechanisms of solar or heat inactivation. Specifically, the integrity of the rotavirus NSP3 gene, virus-host cell interaction, and viral RNA synthesis were examined after heat (57°C) or solar treatment of rotavirus. Only the inhibition of viral RNA synthesis positively correlated with a loss of rotavirus infectivity; 57°C treatment of rotavirus resulted in a decrease of rotavirus RNA synthesis at the same rate as rotavirus infectivity. These data suggest that heat treatment neutralized rotaviruses primarily by targeting viral transcription functions. In contrast, when using solar disinfection, the decrease in RNA synthesis was responsible for approximately one-half of the decrease in infectivity, suggesting that other mechanisms, including posttranslational, contribute to inactivation. Nevertheless, both solar and heat inactivation of rotaviruses disrupted viral RNA synthesis as a mechanism for inactivation.

Analysis of the viral replication cycle of adenovirus serotype 2 after inactivation by free chlorine

Free chlorine is effective at inactivating a wide range of waterborne viral pathogens including human adenovirus (HAdV), but the mechanisms by which free chlorine inactivates HAdV and other human viruses remain to be elucidated. Such advances in fundamental knowledge are key for development of new disinfection technologies and novel sensors to detect infectious viruses in drinking water. We developed and tested a quantitative assay to analyze several steps in the HAdV replication cycle upon increasing free chlorine exposure. We used quantitative polymerase chain reaction (qPCR) to detect HAdV genomic DNA as a means to quantify attachment and genome replication of untreated and treated virions. Also, we used quantitative reverse-transcription PCR (RT-qPCR) to quantify the transcription of E1A (first early protein) and hexon mRNA. We compared these replication cycle events to virus inactivation kinetics to determine what stage of the virus replication cycle was inhibited as a function of free chlorine exposure. We observed that adenovirus inactivated at levels up to 99.99% by free chlorine still attached to host cells; however, viral DNA synthesis and early E1A and late hexon gene transcription were inhibited. We conclude that free chlorine exposure interferes with a replication cycle event occurring postbinding but prior to early viral protein synthesis.

Recombinant adenovirus as a model to evaluate the efficiency of free chlorine disinfection in filtered water samples

BACKGROUND

In Brazil, ordinance no. 2,914/2011 of the Ministry of Health requires the absence of total coliforms and Escherichia coli (E. coli) in treated water. However it is essential that water treatment is effective against all pathogens. Disinfection in Water Treatment Plants (WTP) is commonly performed with chlorine.

METHODS

The recombinant adenovirus (rAdV), which expresses green fluorescent protein (GFP) when cultivated in HEK 293A cells, was chosen as a model to evaluate the efficiency of chlorine for human adenovirus (HAdV) inactivation in filtered water samples from two WTPs: Lagoa do Peri (pH 6.9) and Morro dos Quadros (pH 6.5). Buffered demand free (BDF) water (pH 6.9 and 8.0) was used as control. The samples were previously submitted to physicochemical characterization, and bacteriological analysis. Two free chlorine concentrations and two temperatures were assayed for all samples (0.2 mg/L, 0.5 mg/L, and 15°C, and 20°C). Fluorescence microscopy (FM) was used to check viral infectivity in vitro and qPCR as a molecular method to determine viral genome copies. Real treated water samples from the WTP (at the output of WTP and the distribution network) were also evaluated for total coliforms, E. coli and HAdV.

RESULTS

The time required to inactivate 4log₁₀ of rAdV was less than 1 min, when analyzed by FM, except for BDF pH 8.0 (up to 2.5 min for 4log₁₀). The pH had a significant influence on the efficiency of disinfection. The qPCR assay was not able to provide information regarding rAdV inactivation. The data were modeled (Chick-Watson), and the observed Ct values were comparable with the values reported in the literature and smaller than the values recommended by the EPA. In the treated water samples, HAdV was detected in the distribution network of the WTP Morro dos Quadros (2.75 × 10(3) PFU/L).

CONCLUSION

The Chick-Watson model proved to have adjusted well to the experimental conditions used, and it was possible to prove that the adenoviruses were rapidly inactivated in the surface water treated with chlorine and that the recombinant adenovirus expressing GFP is a good model for this evaluation.

Inactivation of internalized and surface contaminated enteric viruses in green onions

With increasing outbreaks of gastroenteritis associated with produce, it is important to assess interventions to reduce the risk of illness. UV, ozone and high pressure are non-thermal processing technologies that have potential to inactivate human pathogens on produce and allow the retention of fresh-like organoleptic properties. The objective of this study was to determine if UV, ozone, and high pressure are effective technologies compared to traditional chlorine spray on green onions to reduce enteric viral pathogens and to determine the effect of location of the virus (surface or internalized) on the efficacy of these processes. Mature green onion plants were inoculated with murine norovirus (MNV), hepatitis A virus (HAV) and human adenovirus type 41 (Ad41) either on the surface through spot inoculation or through inoculating contaminated hydroponic solution allowing for uptake of the virus into the internal tissues. Inoculated green onions were treated with UV (240 mJ s/cm(2)), ozone (6.25 ppm for 10 min), pressure (500 MPa, for 5 min at 20°C), or sprayed with calcium hypochlorite (150 ppm, 4°C). Viral inactivation was determined by comparing treated and untreated inoculated plants using cell culture infectivity assays. Processing treatments were observed to greatly affect viral inactivation. Viral inactivation for all three viruses was greatest after pressure treatment and the lowest inactivation was observed after chlorine and UV treatment. Both surface inoculated viruses and viruses internalized in green onions were inactivated to some extent by these post-harvest processing treatments. These results suggest that ozone and high pressure processes aimed to reduce the level of microbial contamination of produce have the ability to inactivate viruses if they become localized in the interior portions of produce.

Development of a quantitative immunocapture real-time PCR assay for detecting structurally intact adenoviral particles in water

Development of rapid, sensitive and specific methods for detection of infectious enteric viruses in water is challenging but crucial for gaining reliable information for risk assessment. An immunocapture real-time PCR (IC-qPCR) was designed to detect jointly the two major viral particle components, i.e. the capsid protein and the viral genome. Targeting both constituents helps circumventing the technical limits of cell culture approaches and the inability of PCR based methods to predict the infectious status. Two waterborne pathogenic virus models, human adenovirus types 2 and 41, were chosen for this study. IC-qPCR showed a detection limit of 10MPNCU/reaction with a dynamic range from 10(2) to 10(6)MPNCU/reaction. Sensitivity was thus 100-fold higher compared to ELISA-based capture employing the same anti-hexon antibodies. After optimisation, application on environmental water samples was validated, and specificity towards the targeted virus types was obtained through the qPCR step. Heat-treated pure samples as well as surface water samples brought evidence that this method achieves detection of encapsidated viral genomes while excluding free viral genome amplification. As a consequence, adenovirus concentrations estimated by IC-qPCR were below those calculated by direct qPCR. The results demonstrate that the IC-qPCR method is a sensitive and rapid tool for detecting, in a single-tube assay, structurally intact and thus potentially infectious viral particles in environmental samples.

Effects of chlorine and chlorine dioxide on human rotavirus infectivity and genome stability

Despite the health risks posed by waterborne human rotavirus (HRV), little information is available concerning the effectiveness of chlorine or chlorine dioxide (ClO2), two common disinfectants of public water sources, against HRV and their effects on its genome remain poorly understood. This study investigated the effects of chlorine and ClO2 on purified HRV by using cell culture and RT-PCR to assess virus infectivity and genetic integrity, respectively. The disinfection efficacy of ClO2 was found to be higher than that of chlorine. According to the efficiency factor Hom model, Ct value (mg/L min) ranges required for a 4-log reduction of HRV at 20 °C by chlorine and ClO2 were 5.55-5.59 and 1.21-2.47 mg/L min, respectively. Detection of the 11 HRV genome segments revealed that damage to the 1227-2354 bp of the VP4 gene was associated with the disappearance of viral infectivity by chlorine. However, no complete accordance between culturing and RT-PCR assays was observed after treatment of HRV with ClO2. These results collectively indicate that the current practice of chlorine disinfection may be inadequate to manage the risk of waterborne HRV infection, and offer the potential to monitor the infectivity of HRV adapting PCR-based protocols in chlorine disinfection.

Virus inactivation mechanisms: impact of disinfectants on virus function and structural integrity

Oxidative processes are often harnessed as tools for pathogen disinfection. Although the pathways responsible for bacterial inactivation with various biocides are fairly well understood, virus inactivation mechanisms are often contradictory or equivocal. In this study, we provide a quantitative analysis of the total damage incurred by a model virus (bacteriophage MS2) upon inactivation induced by five common virucidal agents (heat, UV, hypochlorous acid, singlet oxygen, and chlorine dioxide). Each treatment targets one or more virus functions to achieve inactivation: UV, singlet oxygen, and hypochlorous acid treatments generally render the genome nonreplicable, whereas chlorine dioxide and heat inhibit host-cell recognition/binding. Using a combination of quantitative analytical tools, we identified unique patterns of molecular level modifications in the virus proteins or genome that lead to the inhibition of these functions and eventually inactivation. UV and chlorine treatments, for example, cause site-specific capsid protein backbone cleavage that inhibits viral genome injection into the host cell. Combined, these results will aid in developing better methods for combating waterborne and foodborne viral pathogens and further our understanding of the adaptive changes viruses undergo in response to natural and anthropogenic stressors.

Comparative inactivation of murine norovirus, human adenovirus, and human JC polyomavirus by chlorine in seawater

Viruses excreted by humans affect the commercial and recreational use of coastal water. Shellfish produced in contaminated waters have been linked to many episodes and outbreaks of viral gastroenteritis, as well as other food-borne diseases worldwide. The risk can be reduced by appropriate treatment following harvesting and by depuration. The kinetics of inactivation of murine norovirus 1 and human adenovirus 2 in natural and artificial seawater by free available chlorine was studied by quantifying genomic copies (GC) using quantitative PCR and infectious viral particles (PFU). Human JC polyomavirus Mad4 kinetics were evaluated by quantitative PCR. DNase or RNase were used to eliminate free genomes and assess potential viral infectivity when molecular detection was performed. At 30 min of assay, human adenovirus 2 showed 2.6- and 2.7-log(10) GC reductions and a 2.3- and 2.4-log(10) PFU reductions in natural and artificial seawater, respectively, and infectious viral particles were still observed at the end of the assay. When DNase was used prior to the nucleic acid extraction the kinetic of inactivation obtained by quantitative PCR was statistically equivalent to the one observed by infectivity assays. For murine norovirus 1, 2.5, and 3.5-log(10) GC reductions were observed in natural and artificial seawater, respectively, while no viruses remained infectious after 30 min of contact with chlorine. Regarding JC polyomavirus Mad4, 1.5- and 1.1-log(10) GC reductions were observed after 30 min of contact time. No infectivity assays were conducted for this virus. The results obtained provide data that might be applicable to seawater used in shellfish depuration.

UV radiation induces genome-mediated, site-specific cleavage in viral proteins

Much research has been dedicated to understanding the molecular basis of UV damage to biomolecules, yet many questions remain regarding the specific pathways involved. Here we describe a genome-mediated mechanism that causes site-specific virus protein cleavage upon UV irradiation. Bacteriophage MS2 was disinfected with 254 nm UV, and protein damage was characterized with ESI- and MALDI-based FT-ICR, Orbitrap, and TOF mass spectroscopy. Top-down mass spectrometry of the products identified the backbone cleavage site as Cys46-Ser47 in the virus capsid protein, a location of viral genome-protein interaction. The presence of viral RNA was essential to inducing backbone cleavage. The similar bacteriophage GA did not exhibit site-specific protein cleavage. Based on the major protein fragments identified by accurate mass analysis, a cleavage mechanism is proposed by radical formation. The mechanism involves initial oxidation of the Cys46 side chain followed by hydrogen atom abstraction from Ser47 C(α). Computational protein QM/MM studies confirmed the initial steps of the radical mechanism. Collectively, this study describes a rare incidence of genome-induced protein cleavage without the addition of sensitizers.

Virus disinfection mechanisms: the role of virus composition, structure, and function

Drinking waters are treated for enteric virus via a number of disinfection techniques including chemical oxidants, irradiation, and heat, however the inactivation mechanisms during disinfection remain elusive. Owing to the fact that a number of significant waterborne virus strains are not readily culturable in vitro at this time (e.g. norovirus, hepatitis A), the susceptibility of these viruses to disinfection is largely unknown. An in-depth understanding of the mechanisms involved in virus inactivation would aid in predicting the susceptibility of non-culturable virus strains to disinfection and would foster the development of improved disinfection methods. Recent technological advances in virology research have provided a wealth of information on enteric virus compositions, structures, and biological functions. This knowledge will allow for physical/chemical descriptions of virus inactivation and thus further our understanding of virus disinfection to the most basic mechanistic level.

Trisodium phosphate for foodborne virus reduction on produce

Human noroviruses (NoVs) are recognized as the major cause of acute nonbacterial foodborne gastroenteritis outbreaks in both developed and developing countries. They are resistant to most chemical inactivation processes, and can survive in the environment for long periods. The aim of this research was to apply trisodium phosphate (TSP) on spiked produce (lettuce and peppers) for the reduction of foodborne NoV surrogates, feline calicivirus (FCV-F9), and murine norovirus (MNV-1). Washed and dried lettuce (3 × 3 cm²) and Jalapeno peppers (25-30 g/pepper) were spiked with FCV-F9 and MNV-1 at titers of ∼7 log₁₀ plaque forming unit (PFU)/mL or ∼5 log₁₀ PFU/mL and dried aseptically in a biosafety hood for 5 min. Samples were treated with 2% TSP, 5% TSP, 200 mg/L sodium hypochlorite, or water for 15 or 30 sec. Treatments were immediately neutralized with cell culture media containing 10% fetal bovine serum, and viruses were recovered and evaluated using standardized plaque assays. No significant differences between the two contact times on viral reduction was observed (p > 0.05). All three chemicals reduced FCV-F9 titers at ∼5 log₁₀ PFU/mL to undetectable levels, but MNV-1 at ∼5 log₁₀ PFU/mL was decreased by ∼2-3 log₁₀ PFU/mL with 200 mg/L sodium hypochlorite and 2% TSP, and to undetectable levels by 5% TSP. FCV-F9 at ∼7 log₁₀ PFU/mL was reduced by >5 log₁₀ PFU/mL with 2% TSP, in comparison to 200 mg/L sodium hypochlorite that showed ≤ 1.4 log₁₀ PFU/mL reduction. MNV-1 at ∼7 log₁₀ PFU/mL was decreased by ∼2-3.4 log₁₀ PFU/mL with 2% TSP; and by <1.3 log₁₀ PFU/mL with 200 mg/L sodium hypochlorite. FCV-F9 and MNV-1 at ∼7 log₁₀ PFU/mL were reduced to undetectable levels by 5% TSP. Treatments by 5% TSP for 30 sec did not result in any statistically significant color changes of the tested produce. TSP at 5% appears suitable as an alternative treatment to chlorine washes for NoV reduction on produce, without any noticeable visual quality changes.