Pepper mild mottle virus intended for use as a process indicator for drinking water treatment: Present forms and quantitative relations to norovirus and rotavirus in surface water.

Pepper mild mottle virus (PMMoV) has been proposed as a potential indicator of human enteric viruses in environmental water and for viral removal during drinking water treatment. To investigate the occurrence and present forms of PMMoV and quantitative relations to norovirus GII and rotavirus A (RVA) in surface waters, 147 source water samples were collected from 21 drinking water treatment plants (DWTPs) in Japan between January 2018 and January 2021, and the concentrations of viruses in suspended and dissolved fractions were measured using real-time RT-PCR. PMMoV was detected in 81-100 % of samples in each sample month and observed concentrations ranged from 3.0 to 7.0 log10 copies/L. The concentrations of PMMoV were higher in dissolved fraction compared to suspended fractions, while different partitioning was observed for NoV GII depending on seasons. The concentrations of PMMoV were basically higher than those of norovirus GII (1.9-5.3 log10 copies/L) and RVA (1.9-6.6 log10 copies/L), while in 18 samples, RVA presented higher concentrations than PMMoV. Partial regions of VP7, VP4, and VP6 of the RVA in the 18 samples were amplified using nested PCR, and the genotypes were determined using an amplicon-based next-generation sequencing approach. We found that these source water samples included not only human RVA but also various animal RVA and high genetic diversity due to the existence of animal RVA was associated with a higher RVA concentration than PMMoV. Our findings suggest that PMMoV can be used as an indicator of norovirus GII and human RVA in drinking water sources and that the indicator performance should be evaluated by comparing to zoonotic viruses as well as human viruses.

Temporal variations of human and animal Rotavirus A genotypes in surface water used for drinking water production.

Rotavirus is a major cause of gastroenteritis among infants and children. In this study, nested PCR assays were developed to amplify partial regions of the VP7, VP4, and VP6 genes of Rotavirus A (RVA) for amplicon-based Illumina MiSeq sequencing to investigate RVA genotypes in environmental water samples. Eight sets of inner primers were first designed and screened for use in the nested PCR assays, and four sets of them could produce amplicons. Six sets of outer primers were then designed and combined with the four sets of inner primers that worked. The assays were evaluated for sensitivity using raw water samples collected from one drinking water treatment plant between April 2019 and March 2020 (Sample Set 1; N = 12) and seven DWTPs between 2018 and 2020 (Sample Set 2; N = 18). In total, 43 amplicons from Set 1 were sequenced and diverse sequences from human, porcine, bovine, equine, and feline RVA were observed. Human G8, G3, and G2 genotypes were obtained, with G8 predominant (relative abundance, 36-87%) in samples taken during the rotavirus epidemic season between April and June. Porcine G5, G11, and G4, and bovine G10 and G6 genotypes were also detected. VP4 sequence analysis revealed that the human P[8] genotype was present throughout the year, whereas P[4] and P[9] were present only in the epidemic season. The vaccine strains P[5] and P[8] (RotaTeq®) were also detected. Our approach enables the identification of prevalent human and animal RVA genotypes and their host species that potentially caused fecal contamination in water sources.

Metal leaching test of commercially available faucets in the Japanese market in 2016-2020.

In this study, metal leaching was investigated in commercially available faucets in Japan to clarify their compliance to Japanese regulations. We purchased 37 faucets from the market and analyzed the leaching of cadmium, mercury, selenium, lead (Pb), arsenic, hexavalent chromium, boron, zinc (Zn), copper, manganese, and nickel. The leaching tests were performed with and without a conditioning treatment, that simulated approximately 1-month intermittent use of faucets on weekdays, and the results were compared to estimate the changes in metal leaching during the use of faucets. The results revealed that metal leaching from most of the faucets complied with Japanese regulations. However, the levels of Pb leaching from several faucets produced by certain manufacturers exceeded the Japanese standard. The conditioning treatment was generally effective in reducing metal leaching. However, the reductions in Pb and Zn leaching tended to be lower than those of the other metals. Nickel is not legally regulated in Japan; although the number of cases where nickel concentration in leachate exceeded the water quality management target value was greater, such cases were limited to faucets primarily made of copper alloys. We believe that these results will be helpful to improve the public health associated with metal leaching from faucets.

The water temperature changes the effect of pH on copper toxicity to the green microalgae Raphidocelis subcapitata.

Rising temperature enhances the algal growth, which in turn increases the water pH. Ecotoxicity studies have suggested that copper becomes more toxic to microalgae species by increasing the temperature (within 20-30 °C) and pH. In this study, the joined effect of pH and temperature on copper toxicity to the microalgae Raphidocelis subcapitata was investigated using acclimated cells. Algal growth and toxicity tests were conducted using the medium recommended by the Organisation for Economic Co-operation and Development (OECD medium) at pH 6, 7, and 8 units from 15 to 30 °C, spaced by 3 °C. The specific growth rate of R. subcapitata increased by raising the pH and temperature, attributed to the higher membrane permeability and metabolism. The ecotoxicity tests showed that temperature changes the effect of pH on copper toxicity. Copper became less toxic when rising the temperature from 15 to 18 °C and from 6 to 8 pH-unit, suggesting that high pH controls copper bioavailability and toxicity. In contrast, from 21 to 30 °C, the effect of copper was not significantly altered by temperature, but it became more toxic at high pH. Results of this study warn about the higher risk of copper in cold seasons rather than warm conditions.

Temperature affects growth, geosmin/2-methylisoborneol production, and gene expression in two cyanobacterial species.

Cyanobacterial blooms accompanied by taste and odor (T&O) compounds affect the recreational function and safe use of drinking water. Geosmin and 2-methylisoborneol (2-MIB) are the most common T&O compounds. In this study, we investigated the effect of temperature on geosmin and 2-MIB production in Dolichospermum smithii and Pseudanabaena foetida var. intermedia. More specifically, transcription of one geosmin synthase gene (geoA) and two 2-MIB synthase genes (mtf and mtc) was explored. Of the three temperatures (15, 25, and 35 °C) tested, the maximum Chl-a content was determined at 25 °C in both D. smithii and P. foetida var. intermedia. The maximum total geosmin concentration (19.82 µg/L) produced by D. smithii was detected at 25 °C. The total 2-MIB concentration (82.5 µg/L) produced by P. foetida var. intermedia was the highest at 35 °C. Besides, the lowest Chl-a content and minimum geosmin/2-MIB concentration were observed at 15 °C. There was a good positive correlation between geosmin/2-MIB concentration and Chl-a content. The expression levels of the geoA, mtf, and mtc genes at 15 °C were significantly higher than those at 25 and 35 °C. The transcription of the mtf and mtc genes in P. foetida var. intermedia was higher at 35 °C than at 25 °C. The results highlight unfavorable temperature can increase the potential of geosmin/2-MIB synthesis from the gene expression level in cyanobacteria. This study could provide basic knowledge of geosmin/2-MIB production by cyanobacteria for better understanding and management of T&O problems in drinking water.

Recovery of Nucleic Acids of Enteric Viruses and Host-Specific Bacteroidales from Groundwater by Using an Adsorption-Direct Extraction Method.

In this study, the adsorption-elution method was modified to concentrate viral particles in water samples and investigate the contamination of groundwater with norovirus genogroup II (NoV GII), rotavirus A (RVA), and Pepper mild mottle virus (PMMoV). The mean recovery rate of a murine norovirus strain, which was inoculated into groundwater samples collected from a deep well, was the highest (39%) when the viral RNA was directly extracted from the membrane instead of eluting the adsorbed viral particles. This adsorption-direct extraction method was applied to groundwater samples (20 liters) collected from deep wells used for the public drinking water supply (n = 22) and private wells (n = 9). RVA (85 copies/liter) and NoV GII (35 copies/liter) were detected in water samples from a deep well and a private well, respectively. PMMoV was detected in 95% and 89% of water samples from deep wells and private wells, respectively, at concentrations of up to 990 copies/liter. The modified method was also used to extract bacterial DNA from the membrane (recovery rate of inoculated Escherichia coli K-12 was 22%). The Bacteroidales genetic markers specific to ruminants (BacR) and pigs (Pig2Bac) were detected in samples from a deep well and a private well, respectively. The modified virus concentration method has important implications for the management of microbiological safety in the groundwater supply. IMPORTANCE We investigated the presence of enteric viruses and bacterial genetic markers to determine fecal contamination in groundwater samples from deep wells used for the public drinking water supply and private wells in Japan. Groundwater is often subjected to chlorination; malfunctions in chlorine treatment result in waterborne disease outbreaks. The modified method successfully concentrated both viruses and bacteria in 20-liter groundwater samples. Norovirus genogroup II (GII), rotavirus A, Pepper mild mottle virus, and Bacteroidales genetic markers specific to ruminants and pigs were detected. Frequent flooding caused by increased incidences of extreme rainfall events promotes the infiltration of surface runoff containing livestock wastes and untreated wastewater into wells, possibly increasing groundwater contamination risk. The practical and efficient method developed in this study will enable waterworks and the environmental health departments of municipal/prefectural governments to monitor water quality. Additionally, the modified method will contribute to improving the microbiological safety of groundwater.

Effects of elevated nitrogen on the growth and geosmin productivity of Dolichospermum smithii.

Geosmin is one of the most common earthy-musty odor compounds, which is mainly produced by cyanobacteria in surface water. Nitrogen (N) is an important factor affecting the growth of cyanobacteria and its secondary metabolites production due to the eutrophication. In this study, we compared the effects of elevated N on the growth and geosmin productivity of Dolichospermum smithii NIES-824 (synonym Anabaena smithii NIES-824), aiming to better understand the mechanisms involved and give an important and fundamental knowledge to solve off-flavor problem. Results show that elevated N concentration promoted more chlorophyll a (Chl-a) production, whereas the geosmin synthesis decreased, revealing a possible competitive correlation between the Chl-a concentration and geosmin production of D. smithii NIES-824. The majority of geosmin (> 90%) was retained intracellularly during the 28 days of cultivation. The qRT-PCR analysis demonstrates that the expression level of the geosmin synthase gene (geoA) was constitutive and decreased at the higher N concentration during the exponential growth phase of cyanobacterial cells. Furthermore, the decrease of geoA expression during the decline phase suggested that geoA transcription was closely related to cell activity and isoprenoid productivity.

Exploration of an odorous aldehydes and ketones produced by Uroglena americana using high resolution mass spectrometry, GC-Olfactometry, and multivariate analysis.

Off-flavor events in tap water have been reported from various regions of Japan. Fishy smell is the second most common off-flavor in Japan and Uroglena americana (U. americana) is known to be a major contributor to the smell. However, the causative compound of the smell it produces still remains unrevealed to the best of our knowledge. In this study, an exploration of odorous aldehydes and ketones originating from U. americana was performed with a view to discovering a possible candidate substance of causative compounds. Environmental samples containing U. americana colony and cultured media with U. americana were analyzed with two high resolution mass spectrometers, one of them is coupled with liquid chromatography (LC-HRMS), and the other is with gas chromatography and a sniffing port (GC-O-HRMS). Multivariate analyses (MVA) were utilized to explore a compound that is likely to be odorous aldehydes or ketones with a reduced time of exploration. A combination of LC-HRMS and MVA resulted in the selection of one candidate substance and its formula was determined to be C13H20O3 on the basis of its accurate mass and natural isotopic pattern. The candidate substance underwent GC-O-HRMS analyses and milk-like smell was detected at around its retention time. Although the detected smell was different from fishy smell, it is expected that the fishy smell is caused by multiple compounds to which the candidate substance belongs. First generation product ion spectra of the candidate substance suggested that it contains a hydroxyl group, a cyclohexene ring, and a ketone moiety.

Detection of Norovirus and Rotavirus Present in Suspended and Dissolved Forms in Drinking Water Sources.

We investigated the present forms of genogroup II norovirus and group A rotavirus in surface water used for drinking water production. River water samples (N = 15) collected at a drinking water treatment plant (DWTP) monthly from June 2017 to August 2018 were fractioned by filtration through 10- and 0.45-µm-pore-size membranes, and viruses present in suspended and dissolved forms were quantitatively detected. Norovirus GII was present in > 10-µm- and 0.45-10-µm-suspended and dissolved forms with detection rates of 33%, 60%, and 87%, respectively. Rotavirus A was detected more frequently than norovirus GII in each form (> 10 µm suspended, 73%; 0.45-10 µm suspended, 93%; dissolved, 100%). We also analyzed surface water samples from 21 DWTPs all over Japan in non-epidemic and epidemic seasons of gastroenteritis. Norovirus GII was detected in 48% and 81% of samples with the concentrations of up to 4.1 and 5.3 log10 copies/L in dissolved form in non-epidemic and epidemic seasons, respectively, and GII.4 Sydney 2012 was predominant genotype followed by GII.2. Rotavirus A was detected in 95% and 86% of samples with the maximum concentrations of 5.5 and 6.3 log10 copies/L in dissolved form in respective seasons. Concentration of norovirus GII was similar in 0.45-10-µm suspended and dissolved forms, while there was a significant difference for rotavirus A (P < 0.01, pared t test), indicating that rotavirus A was less associated with suspended solids in the surface water samples compared to norovirus GII. Our observations provide important implications for understanding of viral behavior in environmental waters.

Occurrence and fate of endotoxin activity at drinking water purification plants and healthcare facilities in Japan.

Occurrence of residual endotoxin activity (ET) in dialysis water and also tap water as its source is a matter of great concern to medical professionals conducting dialysis therapy at healthcare facilities (HCFs). The present study was performed to determine the occurrence and fate of the ET at selected Japanese drinking water purification plants and HCFs between 2014 and 2016. Chemical coagulation and sedimentation, rapid sand filtration, and membrane filtration were highly effective to decrease both ET dissolved in water (free-ET) and ET bound to cells/particles (bound-ET). Moderate decreases in bound-ET and limited decreases in free-ET were observed by chlorination and ozonation. Bacterial activated carbon filtration was a major cause of significant increases in endotoxin activity during the course of drinking water purification process. Levels of residual ET in water supplied to HCFs were strongly affected by their source waters and the configurations of water purification processes served. Microbial regrowth on the premises, from water tanks to faucets at HCFs could also contribute to ET increases in tap water.

Removal of haloacetamides and their precursors at water purification plants applying ozone/biological activated carbon treatment.

Haloacetamides (HAcAms) are nitrogenous disinfection byproducts in drinking water. The profiles of six HAcAms and their formation potentials (FPs) upon chlorination at water purification plant 1 (WPP-1) in September 2016 and at WPP-2 in September 2016 and January 2017 were investigated. HAcAms were removed effectively when they were formed via intermediate chlorination during water purification processes. Removal of total HAcAm-FPs ranged from 50% to 75%. Coagulation/flocculation/sand filtration showed the highest removal of total HAcAm-FPs. As for individual HAcAms, while chlorinated acetamide-FPs were removed, brominated acetamide-FPs, particularly 2,2-dibromoacetamide, remained. The bromine incorporation factors increased during all water purification processes except ozonation and the ozone/hydrogen peroxide process for diHAcAms (2,2-dichloroacetamide, 2-bromo-2-chloroacetamide, and 2,2-dibromoacetamide). The trends in relationships between DOM indices (fractions of dissolved organic matter, ultraviolet absorbance at 260 nm, and fluorescence intensities representing humic-like and tryptophan-like compounds) and total HAcAm-FPs during ozonation and ozone/hydrogen peroxide process were different from those during other processes.

Formation of 2,6-dichloro-1,4-benzoquinone from aromatic compounds after chlorination.

Halobenzoquinones are a group of disinfection byproducts formed by chlorination of certain substances in water. However, to date, the identities of halobenzoquinone precursors remain unknown. In this study, the formation of 2,6-dichloro-1,4-benzoquinone (DCBQ), a typical halobenzoquinone, from 31 aromatic compounds was investigated after 60 min of chlorination. DCBQ was formed from 21 compounds at molar formation yields ranging from 0.0008% to 4.9%. Phenol and chlorinated phenols served as DCBQ precursors, as reported previously. Notably, DCBQ was also formed from para-substituted phenolic compounds. Compounds with alkyl and carboxyl groups as para-substituents led to relatively higher molar formation yields of DCBQ. Moreover, p-quinone-4-chloroimide, 2,6-dichloroquinone-4-chloroimide (2,6-DCQC), and para-substituted aromatic amines (e.g., aniline and N-methyl aniline) served as DCBQ precursors upon chlorination. It was deduced that DCBQ was formed from the para-substituted aromatic amines via 3,5-dichloroquinone-4-chloroimide, a structural isomer of 2,6-DCQC. These results suggested that DCBQ was formed by chlorination of natural organic matter containing para-substituted phenolic species and para-substituted aromatic amines, despite the absence of phenol in water.

Occurrence and formation of haloacetamides from chlorination at water purification plants across Japan.

The occurrence of six haloacetamides (HAcAms), which are a group of emerging nitrogenous disinfection byproducts, was investigated in drinking water across Japan in September 2015 and February 2016. At least one of the six HAcAms were found in all of the drinking water samples and their total concentrations ranged from 0.3 to 3.8 µg/L. The detection frequencies and concentrations of 2,2-dichloroacetamide (DCAcAm) and 2-bromo-2-chloroacetamide (BCAcAm) were the largest among the targeted HAcAm species. The total HAcAm concentrations in the raw water after chlorination ranged from 0.8 to 11 µg/L. The bromine incorporation factors (BIFs) of the targeted dihalogenated HAcAms (di-HAcAms) (DCAcAm, BCAcAm, and 2,2-dibromoacetamide) in the drinking water samples correlated well with those in the raw water after chlorination. The total HAcAm concentrations and the BIF of the di-HAcAms in the raw water after chlorination correlated with trihalomethane concentrations. HAcAm concentrations after chlorination increased with chlorination time. While the formation of di-HAcAms after chlorination was higher at higher pH, that of 2,2,2-trichloroacetamide remained unaffected by pH.

Community analysis of picocyanobacteria in an oligotrophic lake by cloning 16S rRNA gene and 16S rRNA gene amplicon sequencing.

In this study, the picocyanobacterial species composition of Lake Miyagase was examined by analyzing the 16S rRNA gene in a clone library and by amplicon sequencing using a benchtop next-generation sequencer. Five separate samples were analyzed from different days over a ten-month period. In the picocyanobacterial lineage, 9 and 12 OTUs were identified from a clone library and by amplicon sequencing, respectively. Both analyses suggested that a picocyanobacterium related to Synechococcus sp. MW6B4 was dominant in Lake Miyagase. Our findings suggest that 16S rRNA gene amplicon sequencing enables detailed evaluation of picocyanobacteria composition. One OTU identified was found to be a novel cluster that does not group with any of the known freshwater picocyanobacteria.

Determination of a N-Nitrosodimethylamine Precursor in Water Using Ultra-high Performance Liquid Chromatography-Tandem Mass Spectrometry.

1,1,5,5-Tetramethylcarbohydrazide (TMCH) is the main precursor of N-nitrosodimethylamine upon ozonation in the Yodo River basin, Japan. This study was performed to develop an analytical method for TMCH using solid-phase extraction with ultra-high performance liquid chromatography-tandem mass spectrometry. TMCH is hydrophilic and a tertiary amine derivative, so Oasis(®) MCX cartridges were used as solid-phase cartridges. The recoveries of TMCH in tap and river waters as well as secondary effluent from a sewage treatment plant ranged from 75 to 94%. The limit of quantification of TMCH was 4 ng L(-1). The source of TMCH in the Yodo River basin was found to be effluent from one sewage treatment plant. The concentrations were < 4 ng L(-1) in raw water from water purification plants in regions other than the Yodo River basin, indicating that TMCH was used specifically in the basin.

Occurrence of selected pharmaceuticals at drinking water purification plants in Japan and implications for human health.

The present study was performed to determine the occurrence of 64 pharmaceuticals and metabolites in source water and finished water at 6 drinking water purification plants and 2 industrial water purification plants across Japan. The analytical methods employed were sample concentration using solid-phase extraction cartridges and instrumental analysis by liquid chromatography with tandem mass spectrometry (LC-MS/MS), liquid chromatography with mass spectrometry (LC/MS), or trimethylsilyl derivatization followed by gas chromatography with mass spectrometry (GC/MS). Thirty-seven of the 64 target substances were detected in the source water samples. The maximum concentrations in the source water were mostly below 50 ng/L except for 13 substances. In particular, residual concentrations of iopamidol (contrast agent) exceeded 1000 ng/L at most facilities. Most of the residual pharmaceuticals and metabolites in the source water samples were removed in the course of conventional and/or advanced drinking water treatments, except for 7 pharmaceuticals and 1 metabolite, i.e., amantadine, carbamazepine, diclofenac, epinastine, fenofibrate, ibuprofen, iopamidol, and oseltamivir acid. The removal ratios of the advanced water treatment processes including ozonation and granular activated carbon filtration were typically much higher than those of the conventional treatment processes. The margins of exposure estimated by the ratio of daily minimum therapeutic dose to daily intake via drinking water were substantial, and therefore the pharmacological and physiological impacts of ingesting those residual substances via drinking water would be negligible.

Identification of a new N-nitrosodimethylamine precursor in sewage containing industrial effluents.

N-Nitrosodimethylamine (NDMA), a potential human carcinogen, is known to be a disinfection byproduct of chloramination and ozonation. NDMA is formed during ozonation at water purification plants in the Yodo River basin, a major drinking water source in western Japan. An NDMA precursor, 1,1,5,5-tetramethylcarbohydrazide (TMCH) was identified in sewage containing industrial effluents via ultrahigh performance liquid chromatography-tandem mass spectrometry, and ultrahigh performance liquid chromatography-time-of-flight mass spectrometry, as well as nuclear magnetic resonance spectroscopy. The mean of the NDMA molar formation yield of TMCH upon ozonation in four water matrices was 140%. TMCH removal was low during biological treatment processes at a sewage treatment plant. The mean TMCH contribution to total NDMA precursors upon ozonation of the primary, secondary, and final effluents of the sewage treatment plant in January and February of 2014 was 43-72%, 51-72%, and 42-60%, respectively, while the contributions of 4,4'-hexamethylenebis(1,1-dimethylsemicarbazide) and 1,1,1',1'-tetramethyl-4,4'-(methylene-di-p-phenylene)disemicarbazide, two other known NDMA precursors, were limited to 0.6% and 6.9%, respectively. Thus, TMCH was identified as the primary precursor yielding NDMA upon ozonation in the Yodo River basin.

Quantitative detection of human enteric adenoviruses in river water by microfluidic digital polymerase chain reaction.

We describe an assay for simple and accurate quantification of human enteric adenoviruses (EAdVs) in water samples using a recently developed quantification method named microfluidic digital polymerase chain reaction (dPCR). The assay is based on automatic distribution of reaction mixture into a large number of nanolitre-volume reaction chambers and absolute copy number quantification from the number of chambers containing amplification products on the basis of Poisson statistics. This assay allows absolute quantification of target genes without the use of standard DNA. Concentrations of EAdVs in Japanese river water samples were successfully quantified by the developed dPCR assay. The EAdVs were detected in seven of the 10 samples (1 L each), and the concentration ranged from 420 to 2,700 copies/L. The quantified values closely resemble those by most probable number (MPN)-PCR and real-time PCR when standard DNA was validated by dPCR whereas they varied substantially when the standard was not validated. Accuracy and sensitivity of the dPCR was higher than those of real-time PCR and MPN-PCR. To our knowledge, this is the first study that has successfully quantified enteric viruses in river water using dPCR. This method will contribute to better understanding of existence of viruses in water.

Formaldehyde formation from tertiary amine derivatives during chlorination.

In May 2012, formaldehyde (FA) precursor contamination in the Tone River Basin led to the suspension of water supply to approximately 360,000 homes, which affected approximately 870,000 people in the Tokyo Metropolitan Area. The discharge of industrial effluents containing hexamethylenetetramine (HMT), a tertiary amine and FA precursor, without proper treatment resulted in the formation of FA during chlorination at water purification plants. Tertiary amines are known to be the precursors of aldehydes upon chlorination. In this study, FA formation from 29 separate amine derivatives during chlorination was investigated to determine any other potential causes of this water quality accident. The FA formation yield also included FA formation by the autolysis of the target compounds as well as the chlorination of the autolysis products. The FA molar formation yield of HMT was the highest after 24h of chlorination (440%). Among the various tertiary amine derivatives containing N-methyl groups, tertiary amines and hydrazines were found to be strong FA precursors because the FA molar formation yields per N-methyl group ranged from 25% to 45% (with a mean of 38%) and from 35% to 45% (with a mean of 41%), respectively. Guanidines and sulfamides containing N-methyl groups were also FA precursors but they exhibited lower FA molar formation yields per N-methyl group. The FA molar formation yields of the remaining compounds were <4%. The FA formation yield of HMT was extremely high even on a per weight basis (95 wt.%). The FA weight formation yields of some tertiary amines and hydrazines were greater than 20 wt.%.

[Current situation and problems associated with inactivation of microorganisms in water using copper].

OBJECTIVES: The current situation and problems associated with inactivation of microorganisms in water using copper were elucidated. METHODS: A literature review was conducted regarding the history and mechanisms of inactivation technology using copper, the variety of microorganisms shown to be inactivated by these methods in previous experiments, and the efficacy of such technologies for the inactivation of microorganisms in water. RESULTS: The use of copper for inactivation of microorganisms has a long history. Although the use of copper was discontinued temporarily owing to the advent of antibiotics in the 1930s, the occurrence of antibiotic-resistant bacteria has resulted in the need for different approaches to control pathogenic microorganisms. One such alternative is the use of copper. Although the mechanisms underlying the efficacy of copper inactivation technology have not yet been elucidated in detail, it has been suggested that pathogenic bacteria are inactivated due to the toxicity of copper ions and strong oxidation effects of reactive oxygen species. Copper inactivation technology is effective against many pathogenic microorganisms that pose a risk to public health, such as Legionella pneumophila, Salmonella enterica, and Mycobacterium tuberculosis. In recent years, copper inactivation technology has been used in various water-related devices, especially water supply pipes in buildings. Previous studies have demonstrated that microorganisms can be sufficiently inactivated by copper even at concentrations below that specified in the Water Quality Standard for Drinking Water. However, some previous studies have indicated that the inactivation effect of copper is short-lived. Therefore, the development of techniques to maintain a long-term inactivation effect is a key concern. In addition, it has been reported that the use of copper pipes triggers chlorine decay and results in the formation of chlorine disinfection byproducts. Hence, further studies should aim at assessing the risks and benefits associated with the use of copper. CONCLUSION: Although the practical issues regarding copper inactivation technology are persistent, this method has been demonstrated to be efficacious. Therefore, this technology could be expected to be used in many devices such as water supply systems in hospitals in the near future.