ZmEREB92 plays a negative role in seed germination by regulating ethylene signaling and starch mobilization in maize.

Rapid and uniform seed germination is required for modern cropping system. Thus, it is important to optimize germination performance through breeding strategies in maize, in which identification for key regulators is needed. Here, we characterized an AP2/ERF transcription factor, ZmEREB92, as a negative regulator of seed germination in maize. Enhanced germination in ereb92 mutants is contributed by elevated ethylene signaling and starch degradation. Consistently, an ethylene signaling gene ZmEIL7 and an α-amylase gene ZmAMYa2 are identified as direct targets repressed by ZmEREB92. OsERF74, the rice ortholog of ZmEREB92, shows conserved function in negatively regulating seed germination in rice. Importantly, this orthologous gene pair is likely experienced convergently selection during maize and rice domestication. Besides, mutation of ZmEREB92 and OsERF74 both lead to enhanced germination under cold condition, suggesting their regulation on seed germination might be coupled with temperature sensitivity. Collectively, our findings uncovered the ZmEREB92-mediated regulatory mechanism of seed germination in maize and provide breeding targets for maize and rice to optimize seed germination performance towards changing climates.

Synthesis of Acylhydroquinones through Visible-Light-Mediated Hydroacylation of Quinones with α-Keto Acids.

A mild and eco-friendly visible-light-induced protocol for the hydroacylation of quinones with α-keto acids has been developed. In the absence of any catalyst or additive, the decarboxylative hydroacylation proceeded smoothly under visible-light irradiation at room temperature. A wide range of quinones and α-keto acids were well-tolerated and afforded hydroacylation products up to 88% isolated yield. The reaction can be scaled up, and the induced groups are useful for further synthetic applications. Preliminarily, mechanistic studies indicated that photoactive quinones absorb visible light to facilitate the transformation.

Aerobic Denitrification Promoting by Actinomycetes Coculture: Investigating Performance, Carbon Source Metabolic Characteristic, and Raw Water Restoration.

The coculture theory that promotes denitrification relies on effectively utilizing the resources of low-efficiency denitrification microbes. Here, the strains Streptomyces sp. PYX97 and Streptomyces sp. TSJ96 were isolated and showed lower denitrification capacity when cultured individually. However, the coculture of strains PYX97 and TSJ96 enhanced nitrogen removal (removed 96.40% of total nitrogen) and organic carbon reduction (removed 92.13% of dissolved organic carbon) under aerobic conditions. Nitrogen balance analysis indicated that coculturing enhanced the efficiency of nitrate converted into gaseous nitrogen reaching 70.42%. Meanwhile, the coculturing promoted the cell metabolism capacity and carbon source metabolic activity. The coculture strains PYX97 and TSJ96 thrived in conditions of C/N = 10, alkalescence, and 150 rpm shaking speed. The coculturing reduced total nitrogen and CODMn in the raw water treatment by 83.32 and 84.21%, respectively. During this treatment, the cell metabolic activity and cell density increased in the coculture strains PYX97 and TSJ96 reactor. Moreover, the coculture strains could utilize aromatic protein and soluble microbial products during aerobic denitrification processes in raw water treatment. This study suggests that coculturing inefficient actinomycete strains could be a promising approach for treating polluted water bodies.

Older adults preferences for long-term caregivers in China: a discrete choice experiment.

OBJECTIVE: Understanding the preferences of old-age adults for their long-term caregivers can improve person-centred health care and the quality of long-term care (LTC). This study examines Chinese older adults' preferences for long-term caregivers. STUDY DESIGN: This is a cross-sectional study. METHODS: A national representative discrete choice experiment (DCE) surveyed 2031 adults aged 50-70 across 12 provinces in China. Each DCE scenario described five attributes: type of caregivers, place of LTC, contents of LTC, out-of-pocket payments, and quality of life (QoL). Preferences and the marginal willingness to pay (WTP) were derived using mixed-logit and latent class models. RESULTS: Older adults displayed higher preferences for long-term caregivers who improve their QoL, incur lower out-of-pocket payments, and provide medical LTC services at home, with the maximum WTP of $22.832 per month. QoL was rated as the most important LTC factor, followed by the place of LTC and the type of caregivers. When the level of QoL improved from poor to good, respondents would be willing to pay $18.375 per month more (95% confidence interval: 16.858 to 20.137), and the uptake rate increased by 76.47%. There was preference heterogeneity among older people with different sex, education, family size, and knowledge of LTC insurance. CONCLUSION: QoL was the most important factor in older Chinese adults' preference for caregivers. Home care and medical care from formal caregivers was preferred by older adults. We recommend training family caregivers, raising older people's awareness of LTC insurance, and guiding policymakers in developing people-oriented LTC and a multi-level LTC system.

Performance of aerobic denitrifying fungal community for promoting nitrogen reduction and its application in drinking water reservoirs.

The effect of mix-cultured aerobic denitrifying microorganisms on the water remediation has been extensively explored, but little is known about the performance of mix-cultured low efficiency fungi on denitrification. In this study, two kinds of aerobic denitrifying fungi (Trichoderma afroharzianum H1 and Aspergillus niger C1) were isolated from reservoirs, improved the capacity by mix-cultured. The results showed a difference between northern and southern reservoirs, the dominants of genera were Cystobasidium and Acremonium. The removals of total nitrogen (TN) was 12.00%, 7.53% and 69.33% in Trichoderma afroharzianum H1, Aspergillus niger C1 and mix-cultured (C1 and H1) under the denitrification medium. The contents of ATP and electron transport system activity in mix-cultured amendment were increased by 42.54% and 67.52%, 1.72 and 2.91 times, respectively. Besides, the raw water experiment indicated that TN removals were 24.05%, 12.66% and 73.42% in Trichoderma afroharzianum H1, Aspergillus niger C1 and mix-cultured. The removals of dissolved organic carbon in mix-cultured were increased 35.02% and 50.46% compared to Trichoderma afroharzianum H1 and Aspergillus niger C1. Therefore, mix-cultured of two low efficiency aerobic denitrifying fungi has been considered as a novelty perspective for mitigation of drinking water source.

ZmEREB92 interacts with ZmMYC2 to activate maize terpenoid phytoalexin biosynthesis upon Fusarium graminearum infection through jasmonic acid/ethylene signaling.

Maize (Zea mays) terpenoid phytoalexins (MTPs) induced by multiple fungi display extensive antimicrobial activities, yet how maize precisely regulates MTP accumulation upon pathogen infection remains elusive. In this study, pretreatment with jasmonic acid (JA)/ethylene (ET)-related inhibitors significantly reduced Fusarium graminearum-induced MTP accumulation and resulted in enhanced susceptibility to F. graminearum, indicating the involvement of JA/ET in MTP regulatory network. ZmEREB92 positively regulated MTP biosynthetic gene (MBG) expression by correlation analysis. Knockout of ZmEREB92 significantly compromised maize resistance to F. graminearum with delayed induction of MBGs and attenuated MTP accumulation. The activation of ZmEREB92 on MBGs is dependent on the interaction with ZmMYC2, which directly binds to MBG promoters. ZmJAZ14 interacts both with ZmEREB92 and with ZmMYC2 in a competitive manner to negatively regulate MBG expression. Altogether, our findings illustrate the regulatory mechanism for JA/ET-mediated MTP accumulation upon F. graminearum infection with the involvement of ZmEREB92, ZmMYC2, and ZmJAZ14, which provides new insights into maize disease responses.

Multi-scale Investigation of Ammonia-Oxidizing Microorganisms in Biofilters Used for Drinking Water Treatment.

Ammonia-oxidizing microorganisms (AOMs) include ammonia-oxidizing bacteria (AOB), archaea (AOA), and Nitrospira spp. sublineage II capable of complete ammonia oxidation (comammox). These organisms can affect water quality not only by oxidizing ammonia to nitrite (or nitrate) but also by cometabolically degrading trace organic contaminants. In this study, the abundance and composition of AOM communities were investigated in full-scale biofilters at 14 facilities across North America and in pilot-scale biofilters operated for 18 months at a full-scale water treatment plant. In general, the relative abundance of AOM in most full-scale biofilters and in the pilot-scale biofilters was as follows: AOB > comammox Nitrospira > AOA. The abundance of AOB in the pilot-scale biofilters increased with increasing influent ammonia concentration and decreasing temperature, whereas AOA and comammox Nitrospira exhibited no correlations with these parameters. The biofilters affected AOM abundance in the water passing through the filters via collecting and shedding but exhibited a minor influence on the composition of AOB and Nitrospira sublineage II communities in the filtrate. Overall, this study highlights the relative importance of AOB and comammox Nitrospira compared to AOA in biofilters and the influence of filter influent water quality on AOM in biofilters and their release into the filtrate.

Nitrate Protects Microorganisms and Promotes Formation of Toxic Nitrogenous Byproducts during Water Disinfection by Far-UVC Radiation.

Far-UVC radiation is an emerging tool for combating pathogenic microorganisms in water, but its vulnerability to water matrix components remains unclear. We herein report the critical impacts of nitrate during Far-UVC disinfection of water. Nitrate at environmentally relevant concentrations (0.5-10.0 mg-N L-1) significantly inhibits Escherichia coli inactivation by Far-UVC radiation at 222 nm, via prolonging the "lag phase" of inactivation and reducing the inactivation rate constants by 1.08-2.74 times, while it shows negligible impact on E. coli inactivation by UVC radiation at 254 nm. The inhibitory impact of nitrate on Far-UVC disinfection is attributed to its strong light-shielding effect. Although hydroxyl radicals and reactive nitrogen species are generated from Far-UVC photolysis of nitrate at high concentrations of 10-13 and ∼10-7 M, respectively, those radicals are unable to compensate for the light-shielding effect of nitrate on E. coli inactivation. Moreover, reactive nitrogen species lead to the formation of nitrogenous byproducts, which increase the genotoxicity of the water. The findings advance the fundamental photochemistry and radical chemistry of nitrate at 222 nm and provide useful insights to guide the operation of Far-UVC in treating nitrate-containing water.

Aerobic Denitrification Enhanced by Immobilized Slow-Released Iron/Activated Carbon Aquagel Treatment of Low C/N Micropolluted Water: Denitrification Performance, Denitrifying Bacterial Community Co-occurrence, and Implications.

The key limiting factors in the treatment of low C/N micropolluted water bodies are deficient essential electron donors for nitrogen removal processes. An iron/activated carbon aquagel (IACA) was synthesized as a slowly released inorganic electron donor to enhance aerobic denitrification performance in low C/N micropolluted water treatment. The denitrification efficiency in IACA reactors was enhanced by more than 56.72% and the highest of 94.12% was accomplished compared with those of the control reactors. Moreover, the CODMn removal efficiency improved by more than 34.32% in IACA reactors. The Illumina MiSeq sequencing consequence explained that the denitrifying bacteria with facultative denitrification, iron oxidation, and iron reduction function were located in the dominant species niches in the IACA reactors (e.g., Pseudomonas, Leptothrix, and Comamonas). The diversity and richness of the denitrifying bacterial communities were enhanced in the IACA reactors. Network analysis indicated that aerobic denitrifying bacterial consortia in IACA reactors presented a more complicated co-occurrence structure. The IACA reactors presented the potential for long-term denitrification operation. This study affords a pathway to utilize IACA, promoting aerobic denitrification during low C/N micropolluted water body treatment.

Rapid Inactivation of Fungal Spores in Drinking Water by Far-UVC Photolysis of Free Chlorine.

Effective and affordable disinfection technology is one key to achieving Sustainable Development Goal 6. In this work, we develop a process by integrating Far-UVC irradiation at 222 nm with free chlorine (UV222/chlorine) for rapid inactivation of the chlorine-resistant and opportunistic Aspergillus niger spores in drinking water. The UV222/chlorine process achieves a 5.0-log inactivation of the A. niger spores at a chlorine dosage of 3.0 mg L-1 and a UV fluence of 30 mJ cm-2 in deionized water, tap water, and surface water. The inactivation rate constant of the spores by the UV222/chlorine process is 0.55 min-1, which is 4.6-fold, 5.5-fold, and 1.8-fold, respectively, higher than those of the UV222 alone, chlorination alone, and the conventional UV254/chlorine process under comparable conditions. The more efficient inactivation by the UV222/chlorine process is mainly attributed to the enhanced generation of reactive chlorine species (e.g., 6.7 × 10-15 M of Cl•) instead of hydroxyl radicals from UV222 photolysis of chlorine, which is verified through both experiments and a kinetic model. We further demonstrate that UV222 photolysis damages the membrane integrity and benefits the penetration of chlorine and radicals into cells for inactivation. The merits of the UV222/chlorine process over the UV254/chlorine process also include the more effective inhibition of the photoreactivation of the spores after disinfection and the lower formation of chlorinated disinfection byproducts and toxicity.

Structuring healthcare advance directives: Evidence from Chinese end-of-life cancer patients' treatment preferences.

BACKGROUND: Patients' treatment decisions may be influenced by the ways in which treatment options are presented. There is little evidence on how patients with advanced cancer choose preferences for advance directives (ADs) in China. Informed by behavioural economics, we assess whether end-of-life (EOL) cancer patients held deep-seated preferences for their health care and whether default options and order effects influenced their decision-making. METHODS: We collected data on 179 advanced cancer patients who were randomly assigned to complete one of the four types of ADs: comfort-oriented care (CC) AD (comfort default AD); a life extension (LE)-oriented care option (LE default AD); CC (standard CC AD) and LE-oriented (standard LE AD). Analysis of variance test was used. RESULTS: In terms of the general goal of care, 32.6% of patients in the comfort default AD group retained the comfort-oriented choice, twice as many as in the standard CC group without default options. Order effect was significant in only two individual-specific palliative care choices. Most patients (65.9%) appointed their children to make EOL care decisions, but patients choosing the CC goal were twice as likely to ask their family members to adhere to their choices than patients who chose the LE goal. CONCLUSION: Patients with advanced cancer did not hold deep-seated preferences for EOL care. Default options shaped decisions between CC and LE-oriented care. Order effect only shaped decisions in some specific treatment targets. The structure of ADs matters and influence different treatment outcomes, including the role of palliative care. PATIENT OR PUBLIC CONTRIBUTION: Between August and November 2018, from 640 cancer hospital medical records fitting the selection criteria at a 3A level hospital in Shandong Province, we randomly selected 188 terminal EOL advanced cancer patients using a random generator programme to ensure all eligible patients had an equal chance of selection. Each respondent completes one of the four AD surveys. While respondents might require support in making their healthcare choices, they were informed about the purpose of our research study, and that their survey choices would not affect their actual treatment plan. Patients who did not agree to participate were not surveyed.

Public acceptability and its determinants of unit pricing for municipal solid waste disposal: Evidence from a household survey in Beijing.

Unit pricing for domestic waste, or pay-as-you-throw (PAYT), affords a promising policy option for waste classification and reduction at source. As an emerging economy, China intends to adopt the sophisticated instrument of unit pricing. The public attitude to this policy is of high relevance for its actual implementation. For the first time in China, this paper quantitatively examined the acceptability of the policy among urban residents by randomly delivering 632 questionnaires by taking Beijing, a megacity expected to introduce the practice, as an example. Based on the ordered logit model, determinants of acceptability were empirically tested including intrinsic, external and demographic factors. The results show that the acceptability rate of PAYT in Beijing is less than half, with the proportion of firm support reaching only 42.6%. The respectively low acceptability rate indicates substantial compliance costs, due to intensive resistance to policy implementation and more resources to be invested to promote acceptability. Empirical analysis further indicates that (1) regarding demographic features, aged or less educated residents tend to accept unit pricing, (2) as for intrinsic factors, a friendly environmental attitude, deeper understanding of charging policy and better social perception can significantly improve the public acceptability of the policy, and (3) in terms of external factors, better property services and transparent funding mechanisms play significant roles in enhancing public acceptability. These findings are further confirmed by replacing the dependent variable with either the willingness to pay for household waste disposal or the acceptability of the operated sewage treatment fee. The status of residents' preference for specific pricing methods is further investigated with underlying reasons being revealed. For developing regions with an urgent demand for waste reduction, it is proposed to install unit pricing in time to avoid possible growing social acceptability costs. Specific measures are proposed including changes in intrinsic factors, paying attention to focus groups, and building social consensus for unit pricing.

High-Entropy Spinel Ferrites with Broadband Wave Absorption Synthesized by Simple Solid-Phase Reaction.

In this work, high-entropy (HE) spinel ferrites of (FeCoNiCrM)xOy (M = Zn, Cu, and Mn) (named as HEO-Zn, HEO-Cu, and HEO-Mn, respectively) were synthesized by a simple solid-phase reaction. The as-prepared ferrite powders possess a uniform distribution of chemical components and homogeneous three-dimensional (3D) porous structures, which have a pore size ranging from tens to hundreds of nanometers. All three HE spinel ferrites exhibited ultrahigh structural thermostability at high temperatures even up to 800 °C. What is more, these spinel ferrites showed considerable minimum reflection loss (RLmin) and significantly enhanced effective absorption bandwidth (EAB). The RLmin and EAB values of HEO-Zn and HEO-Mn are about -27.8 dB at 15.7 GHz, 6.8 GHz, and -25.5 dB at 12.9 GHz, 6.9 GHz, with the matched thickness of 8.6 and 9.8 mm, respectively. Especially, the RLmin of HEO-Cu is -27.3 dB at 13.3 GHz with a matched thickness of 9.1 mm, and the EAB reaches about 7.5 GHz (10.5-18.0 GHz), which covers almost the whole X-band range. The superior absorbing properties are mainly attributed to the dielectric energy loss involving interface polarization and dipolar polarization, the magnetic energy loss referring to eddy current and natural resonance loss, and the specific functions of 3D porous structure, indicating a potential application prospect of the HE spinel ferrites as EM absorbing materials.

NirS-type denitrifying bacteria in aerobic water layers of two drinking water reservoirs: Insights into the abundance, community diversity and co-existence model.

The nirS-type denitrifying bacterial community is the main drivers of the nitrogen loss process in drinking water reservoir ecosystems. The temporal patterns in nirS gene abundance and nirS-type denitrifying bacterial community harbored in aerobic water layers of drinking water reservoirs have not been studied well. In this study, quantitative polymerase chain reaction (qPCR) and Illumina Miseq sequencing were employed to explore the nirS gene abundance and denitrifying bacterial community structure in two drinking water reservoirs. The overall results showed that the water quality parameters in two reservoirs had obvious differences. The qPCR results suggested that nirS gene abundance ranged from (2.61 ± 0.12) × 105 to (3.68 ± 0.16) × 105 copies/mL and (3.01 ± 0.12) × 105 to (5.36 ± 0.31) × 105 copies/mL in Jinpen and Lijiahe reservoirs, respectively. The sequencing results revealed that Paracoccus sp., Azoarcus sp., Dechloromonas sp. and Thauera sp. were the dominant genera observed. At species level, Cupriavidus necator, Dechloromonas sp. R-28400, Paracoccus denitrificans and Pseudomonas stutzeri accounted for more proportions in two reservoirs. More importantly, the co-occurrence network analysis demonstrated that Paracoccus sp. R-24615 and Staphylococcus sp. N23 were the keystone species observed in Jinpen and Lijiahe reservoirs, respectively. Redundancy analysis indicated that water quality (particularly turbidity, water temperature, pH and Chlorophyll a) and sampling time had significant influence on the nirS-type denitrifying bacterial community in both reservoirs. These results will shed new lights on exploring the dynamics of nirS-type denitrifying bacteria in aerobic water layers of drinking water reservoirs.

Temporal patterns of algae in different urban lakes and their correlations with environmental variables in Xi'an, China.

Urban lakes were critical in aquatic ecology environments, but how environmental factors affected the distribution and change characteristics of algal communities in urban lakes of Xi'an city was not clearly. Here, we investigated the algal community structure of six urban lakes in Xi'an and evaluated the effects of water quality parameters on algae. The results indicated that the significant differences on physicochemical parameters existed in different urban lakes. The maximum concentration of total phosphorus in urban lakes was (0.18 ± 0.01) mg/L and there was a phenomenon of phosphorus limitation. In addition, 51 genera of algae were identified and Chlorella sp. was the dominant algal species, which was affiliated with Chlorophyta. Network analysis elucidated that each lake had a unique algal community network and the positive correlation was dominant in the interaction between algae species, illustrating that mature microbial communities existed or occupied similar niches. Redundancy analysis illustrated that environmental factors explained 47.35% variance of algal species-water quality correlation collectively, indicating that water quality conditions had a significant influence on the temporal variations of algae. Structural equation model further verified that algal community structure was directly or indirectly regulated by different water quality conditions. Our study shows that temporal patterns of algal communities can reveal the dynamics and interactions of different urban ecosystem types, providing a theoretical basis for assessing eutrophication levels and for water quality management.

Metal-Organic Framework Supported Copper Photoredox Catalysts for Iminyl Radical-Mediated Reactions.

Visible-light copper photocatalysis has recently emerged as a viable technology for building sustainable synthetic processes. To broaden the applications of phosphine-ligated copper(I) complexes, we describe herein an effective metal-organic framework (MOF)-supported copper(I) photocatalyst for multiple iminyl radical-mediated reactions. Due to site isolation, the heterogenized copper photosensitizer has a significantly higher catalytic activity than its homogeneous counterpart. Using a hydroxamic acid linker to immobilize copper species on MOF supports affords the heterogeneous catalysts with high recyclability. The post-synthetic modification sequence on MOF surfaces allows for the preparation of previously unavailable monomeric copper species. Our findings highlight the potential of using MOF-based heterogeneous catalytic systems to address fundamental challenges in the development of synthetic methodologies and mechanistic investigations of transition-metal photoredox catalysis.

Strategies for targeting the P2Y12 receptor in the central nervous system.

The purinergic 2Y type 12 receptor (P2Y12R) is a well-known biological target for anti-thrombotic drugs due to its role in platelet aggregation and blood clotting. While the importance of the P2Y12R in the periphery has been known for decades, much less is known about its expression and roles in the central nervous system (CNS), where it is expressed exclusively on microglia - the first responders to brain insults and neurodegeneration. Several seminal studies have shown that P2Y12 is a robust, translatable biomarker for anti-inflammatory and neuroprotective microglial phenotypes in models of degenerative diseases such as multiple sclerosis and Alzheimer's disease. An enduring problem for studying this receptor in vivo, however, is the lack of selective, high-affinity small molecule ligands that can bypass the blood-brain barrier and accumulate in the CNS. In this Digest, we discuss previous attempts by researchers to target the P2Y12R in the CNS and opine on strategies that may be employed to design and assess the suitability of novel P2Y12 ligands for this purpose going forward.

Iron-Activated Carbon Systems to Enhance Aboriginal Aerobic Denitrifying Bacterial Consortium for Improved Treatment of Micro-Polluted Reservoir Water: Performances, Mechanisms, and Implications.

Although many source waterbodies face nitrogen pollution problems, the lack of organic electron donors causes difficulties when aerobic denitrifying bacteria are used to treat micro-polluted water. Different forms of iron with granular activated carbon (AC) as carriers were used to stimulate aboriginal microorganisms for the purification of micro-polluted source water. Compared with the iron-absent AC system, targeted pollutants were significantly removed (75.76% for nitrate nitrogen, 95.90% for total phosphorus, and 80.59% for chemical oxygen demand) in the sponge-iron-modified AC system, which indicated that iron promoted the physical and chemical removal of pollutants. In addition, high-throughput sequencing showed that bacterial distribution and interaction were changed by ion dosage, which was beneficial for pollutant transformation and reduction. Microbial functions, such as pollutant removal and expression of functional enzymes that were responsible for the transformation of nitrate nitrogen to ammonia, were highly efficient in iron-applied systems. This study provides an innovative strategy to strengthen in situ remediation of micro-pollution in waterbodies.

Field study of early implementation of UV sources and their relative effectiveness for public health and safety.

The emergence of COVID-19 and its corresponding public health burden has prompted industries to rapidly implement traditional and novel control strategies to mitigate the likelihood of SARS-CoV-2 transmission, generating a surge of interest and application of ultraviolet germicidal irradiation (UVGI) sources as disinfection systems. With this increased attention the need to evaluate the efficacy and safety of these types of devices is paramount. A field study of the early implementation of UVGI devices was conducted at the Space Needle located in Seattle, Washington. Six devices were evaluated, including four low-pressure (LP) mercury-vapor lamp devices for air and surface sanitation not designed for human exposure and two krypton chloride (KrCl*) excimer lamp devices to be operated on and around humans. Emission spectra and ultraviolet (UV) irradiance at different locations from the UV devices were measured and germicidal effectiveness against SARS-CoV-2 was estimated. The human safety of KrCl* excimer devices was also evaluated based on measured irradiance and estimated exposure durations. Our results show all LP devices emitted UV radiation primarily at 254 nm as expected. Both KrCl* excimers emitted far UVC irradiation at 222 nm as advertised but also emitted at longer, more hazardous wavelengths (228 to 262 nm). All LP devices emitted strong UVC irradiance, which was estimated to achieve three log reduction of SARS-CoV-2 within 10 sec of exposure at reasonable working distances. KrCl* excimers, however, emitted much lower irradiance than needed for effective disinfection of SARS-CoV-2 (>90% inactivation) within the typical exposure times. UV fluence from KrCl* excimer devices for employees was below the American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Values (TLVs) under the reported device usage and work shifts. However, photosensitive individuals, human susceptibility, or exposure to multiple UV sources throughout a worker's day, were not accounted for in this study. Caution should be used when determining the acceptability of UV exposure to workers in this occupational setting and future work should focus on UVGI sources in public settings.

UV Inactivation of SARS-CoV-2 across the UVC Spectrum: KrCl* Excimer, Mercury-Vapor, and Light-Emitting-Diode (LED) Sources.

Effective disinfection technology to combat severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can help reduce viral transmission during the ongoing COVID-19 global pandemic and in the future. UV devices emitting UVC irradiation (200 to 280 nm) have proven to be effective for virus disinfection, but limited information is available for SARS-CoV-2 due to the safety requirements of testing, which is limited to biosafety level 3 (BSL3) laboratories. In this study, inactivation of SARS-CoV-2 in thin-film buffered aqueous solution (pH 7.4) was determined across UVC irradiation wavelengths of 222 to 282 nm from krypton chloride (KrCl*) excimers, a low-pressure mercury-vapor lamp, and two UVC light-emitting diodes. Our results show that all tested UVC devices can effectively inactivate SARS-CoV-2, among which the KrCl* excimer had the best disinfection performance (i.e., highest inactivation rate). The inactivation rate constants of SARS-CoV-2 across wavelengths are similar to those for murine hepatitis virus (MHV) from our previous investigation, suggesting that MHV can serve as a reliable surrogate of SARS-CoV-2 with a lower BSL requirement (BSL2) during UV disinfection tests. This study provides fundamental information on UVC's action on SARS-CoV-2 and guidance for achieving reliable disinfection performance with UVC devices. IMPORTANCE UV light is an effective tool to help stem the spread of respiratory viruses and protect public health in commercial, public, transportation, and health care settings. For effective use of UV, there is a need to determine the efficiency of different UV wavelengths in killing pathogens, specifically SARS-CoV-2, to support efforts to control the ongoing COVID-19 global pandemic and future coronavirus-caused respiratory virus pandemics. We found that SARS-CoV-2 can be inactivated effectively using a broad range of UVC wavelengths, and 222 nm provided the best disinfection performance. Interestingly, 222-nm irradiation has been found to be safe for human exposure up to thresholds that are beyond those effective for inactivating viruses. Therefore, applying UV light from KrCl* excimers in public spaces can effectively help reduce viral aerosol or surface-based transmissions.