Evidence integration on health damage for humidifier disinfectant exposure and legal presumption of causation.

OBJECTIVES: Inhalation exposure to humidifier disinfectants has resulted to various types of health damages in Korea. To determine the epidemiological correlation necessary for presuming the legal causation, we aimed to develop a method to synthesize the entire evidence. METHODS: Epidemiological and toxicological studies are systematically reviewed. Target health problems are selected by criteria such as frequent complaints of claimants. Relevant epidemiologic studies are reviewed and the risk of bias and confidence level of the total evidence are evaluated. Toxicological literature reviews are conducted on three lines of evidence including hazard information, animal studies, and mechanistic studies, considering the source-to-exposure-to-outcome continuum. The confidence level of the body of evidence is then translated into the toxicological evidence levels for the causality between humidifier disinfectant exposure and health effects. Finally, the levels of epidemiological and toxicological evidence are synthesized. RESULTS: Under the Special Act revised in 2020, if the history of exposure and the disease occurred/worsened after exposure were approved, and the epidemiological correlation between the exposure and disease was verified, the legal causation is presumed unless the company proves the evidence against it. The epidemiological correlation can be verified through epidemiological investigations, health monitoring, cohort investigations and/or toxicological studies. It is not simply as statistical association as understood in judicial precedents, but a general causation established by the evidence as a whole, i.e., through weight-of-the-evidence approach. CONCLUSIONS: The weight-of-the-evidence approach differs from the conclusive single study approach and this systematic evidence integration can be used in presumption of causation.

Ambient air pollution and the risk of neurological diseases in residential areas near multi-purposed industrial complexes of korea: A population-based cohort study.

Emerging evidence suggest that long-term exposure to air pollution may induce adverse effects on the central nervous system. However, no study explored the associations in large industrial complex (IC) areas which are one of the major contributors to air pollution. Therefore, we aimed to investigate the pollution status and the association between residential proximity and incidence of neurological diseases near two major ICs characterized as multi-purposed ICs in Korea. A retrospective cohort of residents near the ICs was constructed using Korea's health insurance data and monitored from 2008 to 2019. Emission amounts of the ICs and the air pollution status in the nearby (exposed) and remote (control) area were evaluated using data from national regulatory networks, and hazard ratios (HRs) and 95% confidence intervals (CIs) for neurological diseases of the exposed group compared to the control group were calculated using Cox proportional regression models. Overall, the complexes emitted large amounts of VOCs, CO, NOx, and PM10, and annual levels of ambient PM (2.5, 10), gaseous substances (NO2, SO2), VOCs and PAHs were higher in the exposed area compared to the control and/or the national average. The risk of inflammatory disease of the CNS (G00-09) and extrapyramidal and movement disorders (G20-26) were higher in the exposed area with a HR (95% CI) of 1.36 (1.10-1.68) and 1.33 (1.27-1.39) respectively. Among the subclasses, other extrapyramidal and movement disorders (G25) and epilepsy (G40) were associated with higher risks in the exposed area (HR (95%CI): 1.11 (1.04-1.18), 1.08 (1.00-1.16)) after adjusting for potential confounders. These results suggest that people living near ICs are more likely to be exposed to higher air pollution levels and have higher risks of developing several neurological disorders. However, further epidemiological studies in these industrial areas supplemented with other indicators of environmental exposure and control of other diverse factors are warranted.

Evaluation of residual level and distribution characteristics of organochlorine pesticides in agricultural soils in South Korea.

In this study, we evaluated the residual levels and distribution characteristics of 10 organochlorine pesticides (OCPs) in the soil of agricultural lands (paddy field, vegetable field, and orchard, n = 150) nationwide. As a result of the investigation, 3-10 types of OCPs were detected in combination in 144 locations (96%) of the total 150 locations. Among those OCPs, dichlorodiphenyltrichloroethane (DDT) and endosulfan were detected in high amounts. The geometric mean concentrations of DDT and endosulfan were ∑DDT 0.31 ng g-1 (ND-2187.18 ng g-1) and ∑endosulfan 0.33 ng g-1 (ND-312.68 ng g-1), respectively. OCP concentrations were generally higher in orchards than in other agricultural fields due to a large amount of pesticides used. DDT in two orchards was detected at 2187.18 ng g-1 and 1061.78 ng g-1, exceeding the levels stated in the Canadian DDT Soil Quality Guidance (SQG, 700 ng g-1). The result of applying the isomer ratio to evaluate the recent or past use of DDT, endosulfan, and hexachlorocyclohexane (HCH), which had a high detection rate, showed that it could be attributable to historical usage. DDT and HCH showed statistically similar residual distribution patterns; however, endosulfan did not show a clear correlation with DDT and HCH due to the effect of its recent use. Thus, the results of evaluation of OCP residual levels and distribution characteristics can be used for the soil management policy of OCPs in agricultural lands in Korea.

Development of diagnostic systems for wide range and highly sensitive detection of two waterborne hepatitis viruses from groundwater using the conventional reverse transcription nested PCR assay.

Waterborne epidemics of human hepatitis virus A and E (HAV and HEV) have been reported worldwide. Molecular biology techniques, such as reverse transcription polymerase chain reaction (RT-PCR), have been widely used to detect the two hepatitis viruses. However, comparative studies of various types of samples are needed, and different environmental factors, including the low copy pathogens, presence of PCR inhibitors in the sample, unknown non-specific reaction with template, and sequence diversity leading to new variants in viruses, should be considered. In addition, standard positive material is required to determine the accuracy of the PCR and should be able to distinguish between false and real positives. In this study, we developed RT-PCR primer sets and optimised standard templates for HAV and HEV detection to address the above concerns associated with test sensitivity and possible PCR inhibition. Finally, previously reported diagnostic methods of HAV and HEV were compared and an applicability test using groundwater was performed. The nested RT-PCR developed in this study is expected to contribute to assess water safety by monitoring HAV and HEV in non-disinfected water, like groundwater.

Characterization of urinary cotinine concentrations among non-smoking adults in smoking and smoke-free homes in the Korean national environmental health survey (KoNEHS) cycle 3 (2015-2017).

BACKGROUND: Although many indoor public places have implemented smoke-free regulations, private homes have remained sources of tobacco smoke pollutants. This study examined differences in urinary cotinine concentrations in the Korean non-smoking adult population between living in smoking and smoke-free homes, and the relationship of urinary cotinine concentrations with socio-demographic factors in smoke-free homes. METHODS: Samples from 2575 non-smoking adults (≥19 years old) in the Korean National Environmental Health Survey cycle 3 (2015-2017), a representative Korean study, were used. Smoking and smoke-free homes were defined based on whether there were smokers at homes. Weighted linear regression models were used to determine urinary cotinine concentrations and identify factors associated with urinary cotinine. RESULTS: The geometric mean of urinary cotinine concentrations for non-smoking adults living in smoking homes was 2.1 µg/L (95% confidence interval [CI] = 1.8-2.4), which was significantly higher than the mean of 1.3 µg/L (95% CI = 1.2-1.4) for those living in smoke-free homes. Urinary cotinine concentrations were different significantly by home smoking status in most socio-demographic subgroups. Data from smoke-free home showed urinary cotinine concentration in adults was significantly higher in those who lived in homes with ventilation duration < 30 min/day, those who spent more time indoors at home, those who spent less time outdoors, and those who worked in non-manual or manual occupations. CONCLUSIONS: The urinary cotinine concentration in Korean non-smoking adults living in smoking homes was higher than that in adults living in smoke-free homes. Even in smoke-free homes, home-related factors, such as ventilation duration and time spent indoors, were associated with urinary cotinine concentration. Further study is warranted to examine potential sources of tobacco smoke pollution in smoke-free homes.

Determination of pharmaceuticals in solid samples in municipal wastewater treatment plants by online SPE LC-MS/MS using QuEChERS extraction.

In this study, a pretreatment method based on the QuEChERS method has been applied for simultaneously extracting 27 residual pharmaceuticals from wastewater solids. The extracted compounds have been analyzed using online solid-phase extraction (SPE) coupled to liquid chromatography with tandem mass spectrometry (LC-MS/MS). A recovery test was conducted according to the absorbent type, and buffers were added in the sample extraction step. The highest recovery efficiency could be observed when Na2SO4 was used as an absorbent and Na2EDTA was injected during the extraction process; the recovery efficiencies of the proposed method for the target compounds ranged from 61.3 to 137.2%, and the repeatability was 6.8%. These recovery and repeatability data showed that the proposed method could reliably analyze the 27 target residual pharmaceuticals. The concentrations of the target compounds were all below the limits of quantification: 830 ng g-1 for the target compounds in suspended solids, 2353 ng g-1 in activated sludge, and 1929 ng g-1 in waste sludge. The analytical method established in this study can be applied to quantify residual pharmaceuticals in solid samples and to investigate their behaviors in a municipal wastewater treatment plant.

Spatial variation of pharmaceuticals in the unit processes of full-scale municipal wastewater treatment plants in Korea.

Several reports have elucidated the removal of pharmaceutical residues in municipal wastewater treatment plants (WWTPs). However, there remains a need to determine the spatial distribution of pharmaceuticals in the unit processes of full-scale municipal WWTPs. Herein, spatial variations of fifteen pharmaceuticals in the unit processes of four full-scale municipal WWTPs were assessed by analyzing both solid and liquid samples. Furthermore, different pathways of each pharmaceutical such as biodegradation, adsorption, deconjugation, and electrostatic interaction were investigated. Pharmaceutical mass loading were measured at various points for the different unit process and evaluated using liquid chromatography-tandem mass spectrometry. The average mass loading of acetaminophen and caffeine decreased tremendously in the first biological treatment process regardless of the process configuration. In contrast, a temporary increase was observed in the mass loading of ibuprofen in the anaerobic and/or anoxic processes, which was presumably caused by deconjugation. Additionally, the adverse effect of coagulation on ibuprofen removal was validated. The major removal mechanism for the selected antibiotics, except for sulfamethoxazole, was the adsorption by biosolids due to electrostatic interaction. Subsequently, a drastic decrease was observed in their mass loadings in the solid-liquid separation process of the WWTPs. The membrane bioreactor (MBR) shows excellent capability for mitigation of pharmaceuticals in municipal wastewater because it comprises a high concentration of biosolids that act as adsorbents. The evaluation of the spatial variations of the selected pharmaceuticals in different unit processes provides valuable information on their behavior and removal mechanisms.

Distribution and Removal of Pharmaceuticals in Liquid and Solid Phases in the Unit Processes of Sewage Treatment Plants.

In this study, we analyzed 27 pharmaceuticals in liquid and solid phase samples collected from the unit processes of four different sewage treatment plants (STPs) to evaluate their distribution and behavior of the pharmaceuticals. The examination of the relative distributions of various categories of pharmaceuticals in the influent showed that non-steroidal anti-inflammatory drugs (NSAIDs) were the most dominant. While the relative distribution of antibiotics in the influent was not high (i.e., 3%-5%), it increased to 14%-30% in the effluent. In the four STPs, the mass load of the target pharmaceuticals was reduced by 88%-95% mainly in the biological treatment process, whereas the ratio of pharmaceuticals in waste sludge to those in the influent (w/w) was only 2%. In all the STPs, the removal efficiencies for the stimulant caffeine, NSAIDs (acetaminophen, naproxen, and acetylsalicylic acid), and the antibiotic cefradine were high; they were removed mainly by biological processes. Certain compounds, such as the NSAID ketoprofen, contrast agent iopromide, lipid regulator gemfibrozil, and antibiotic sulfamethoxazole, showed varying removal efficiencies depending on the contribution of biodegradation and sludge sorption. In addition, a quantitative meta-analysis was performed to compare the pharmaceutical removal efficiencies of the biological treatment processes in the four STPs, which were a membrane bioreactor (MBR) process, sequencing batch reactor (SBR) process, anaerobic-anoxic-oxic (A2O) process, and moving-bed biofilm reactor (MBBR) process. Among the biological processes, the removal efficiency was in the order of MBR > SBR > A2O > MBBR. Among the tertiary treatment processes investigated, powdered activated carbon showed the highest removal efficiency of 18%-63% for gemfibrozil, ibuprofen, ketoprofen, atenolol, cimetidine, and trimethoprim.

National Reconnaissance Survey of Microplastics in Municipal Wastewater Treatment Plants in Korea.

Large quantities of microplastics are thought to be emitted to freshwater environments via wastewater treatment plants (WWTPs). To evaluate the occurrence of microplastics in Korean WWTPs, a nationwide study was conducted for the first time in 50 representative WWTPs with large treatment capacities. Grab sampling and laboratory filtration were used for influents, whereas in situ filtration using a custom-made sampling device was used for effluents. The filtrates were pretreated using wet peroxidation and density separation prior to the identification of microplastics with a dissection microscope and Fourier-transform infrared spectroscopy. Pooled analyses of the microplastics revealed that they were predominantly fragment-shaped, and thermoplastics and synthetic fibers were the dominant microplastic materials in WWTPs. The concentration ranged from 10 to 470 L-1 in influents and 0.004 to 0.51 L-1 in effluents. The removal efficiency of microplastics during wastewater treatment was calculated to be 98.7-99.99% in 31 WWTPs. Additionally, WWTPs using advanced phosphorus removal processes exhibited higher removal efficiency than those not implementing such processes. Power-law distribution was successful in describing microplastic particle sizes down to 100 µm, although it was not applicable for smaller particles. This comprehensive monitoring study provides information on the current level and characteristics of microplastics in WWTPs in Korea.

Prevalence of human Norovirus by genotype in contaminated groundwater in Korea over the last decade (2007-2016).

This study investigated the occurrence of human Norovirus (HuNoV) by genotype in 1,486 groundwater samples collected from 843 groundwater wells suspected of contamination during 2007-2016, in South Korea. We identified and genotyped 186 HuNoV sequences in 178 HuNoV-positive samples using the RIVM-NoroNet norovirus genotyping tool (NGT) and phylogenetic tree analysis based on RIVM-NoroNet reference sequences. HuNoV GII was more prevalent than GI. The major genotypes detected were HuNoV GII.4 (43.0%), GII.22 (15.6%), GI.5 (10.2%), and GI.1 (8.6%); several genotypes accounted for < 5.0% of all HuNoVs, including GII.17, GI.6, GI.4, GII.6, GI.8, GII.3, GII.13, GI.3, GI.7, GI.2, GI.9, GII.1, GII.8, and GII.10. The prevalence of HuNoVs and number of genotypes detected has drastically decreased over the last decade. HuNoV GII.17, the emerging genotype worldwide including Europe and Asia, appeared in Korean groundwater from 2010, dominated in 2013-2014, and continued to be observed. HuNoV GII.4, the major type occurred last decade from Korean groundwater except 2013-2014, continued to be detected and prevalent similar to HuNoV GII.17 in 2016.

Nocardioides suum sp. nov. isolated from the air environment in an indoor pig farm.

A bacterial strain PBT33-2T was isolated from the air environment in an indoor pig farm. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain PBT33-2T belonged to the genus Nocardioides in the phylum Actinobacteria, and was most closely related to Nocardioides daphnia D287T in a maximum-likelihood and neighbor-joining phylogenetic trees. Strain PBT33-2T shared 95.3% sequence identity with N. daphnia D287T. However, the highest sequence similarity was shown with N. sediminis MSL-01T (96.0%). It had less than 96.0% sequence identities with other type species of the genus Nocardioides. Strain PBT-33-2T grew at 15-45°C (optimum 20-35°C), pH 5.0-11.0 (optimum pH 7.0) and 0-4.0% (w/v) NaCl (optimum 0%). The major fatty acid and quinone were iso-C16:0 and MK-8, and the DNA G+C content of strain PBT33-2T was 69.3 mol%. On the basis of poly-phasic results, strain PBT33-2T represents a novel species of the genus Nocardioides, for which the name Nocardioides suum sp. nov. is proposed. Its type strain is PBT33-2T (=KCTC 39558T =DSM 102833T).

Associations between malaria and local and global climate variability in five regions in Papua New Guinea.

BACKGROUND: Malaria is a significant public health issue in Papua New Guinea (PNG) as the burden is among the highest in Asia and the Pacific region. Though PNG's vulnerability to climate change and sensitivity of malaria mosquitoes to weather are well-documented, there are few in-depth epidemiological studies conducted on the potential impacts of climate on malaria incidence in the country. METHODS: This study explored what and how local weather and global climate variability impact on malaria incidence in five regions of PNG. Time series methods were applied to evaluate the associations of malaria incidence with weather and climate factors, respectively. Local weather factors including precipitation and temperature and global climate phenomena such as El Niño-Southern Oscillation (ENSO), the ENSO Modoki, the Southern Annular Mode, and the Indian Ocean Dipole were considered in analyses. RESULTS: The results showed that malaria incidence was associated with local weather factors in most regions but at the different lag times and in directions. Meanwhile, there were trends in associations with global climate factors by geographical locations of study sites. CONCLUSIONS: Overall heterogeneous associations suggest the importance of location-specific approaches in PNG not only for further investigations but also public health interventions in repose to the potential impacts arising from climate change.

Tracking Mallards (Anas platyrhynchos) with GPS Satellite Transmitters Along Their Migration Route Through Northeast Asia.

In this study, Global Positioning System satellite transmitters were attached to three mallards (Anas platyrhynchos) wintering in South Korea to track their migration routes, stopover sites, breeding sites, and migration patterns. We successfully tracked only one mallard (no. 108917) from November 15, 2011, to November 29, 2013, and determined separate migration routes in two cases of spring migration and one case of fall migration. The mallard repeatedly migrated to the same final destination, even though the travel path varied. We identified six stopover sites: Hunhe River, Liaohe River, Yinma River, Yalu River, Songjeon Bay, and Dahuofang Reservoir in China and South Korea. The wintering sites of two migration cases were discovered to be identical (Gokgyo River in Asan, South Korea). The terminal sites, which were presumed to be breeding grounds, were the same in both cases (Hinggan League in Inner Mongolia Autonomous Region, China). On the basis of the migration routes identified in this study, we suggest that future efforts to control highly pathogenic avian influenza (HPAI) should not only include avian influenza surveillance but also implement flyway-based strategies, with regard to all countries affected by potential HPAI outbreaks.

Prevalence of avian influenza virus in wild birds before and after the HPAI H5N8 outbreak in 2014 in South Korea.

Since 2003, highly pathogenic avian influenza (HPAI) virus outbreaks have occurred five times in Korea, with four HPAI H5N1 outbreaks and one HPAI H5N8 outbreak. Migratory birds have been suggested to be the first source of HPAI in Korea. Here, we surveyed migratory wild birds for the presence of AI and compared regional AI prevalence in wild birds from September 2012 to April 2014 for birds having migratory pathways in South Korea. Finally, we investigated the prevalence of AI in migratory birds before and after HPAI H5N8 outbreaks. Overall, we captured 1617 migratory wild birds, while 18,817 feces samples and 74 dead birds were collected from major wild bird habitats. A total of 21 HPAI viruses were isolated from dead birds, and 86 low pathogenic AI (LPAI) viruses were isolated from captured birds and from feces samples. Spatiotemporal distribution analysis revealed that AI viruses were spread southward until December, but tended to shift north after January, consistent with the movement of migratory birds in South Korea. Furthermore, we found that LPAI virus prevalences within wild birds were notably higher in 2013-2014 than the previous prevalence during the northward migration season. The data from our study demonstrate the importance of the surveillance of AI in wild birds. Future studies including in-depth genetic analysis in combination with evaluation of the movement and ecology of migratory birds might help us to bridge the gaps in our knowledge and better explain, predict, and ultimately prevent future HPAI outbreaks.

Pathogens in water deer (Hydropotes inermis) in South Korea, 2010-12.

Water deer (Hydropotes inermis) are among the most common wildlife to approach farmhouses and livestock barns in Korea. We collected 305 water deer from Gangwon (n=168), South Chungcheong (n=89), and Gyeongsang (n=48) provinces in 2010-12 and used PCR and serologic tests to screen the deer for pathogens. In 2010, tests for bovine viral diarrhea virus (BVDV), rotavirus, and Brucella abortus were positive in 8% (5/60), 2% (1/60), and 59% (33/56) of the animals, respectively. In 2010, the water deer were negative for foot-and-mouth disease virus, coronaviruses, and Mycobacterium bovis. All samples collected in 2011 and 2012 were negative for all pathogens analyzed. These results suggest that at least two of the investigated pathogens, BVDV and B. abortus, circulate among water deer in South Korea.

Study on Fe(VI) species as a disinfectant: quantitative evaluation and modeling for inactivating Escherichia coli.

Ferrate (Fe(VI)) has high potentials as a multi-purpose water treatment chemical acting as an oxidant, coagulant, and disinfectant, but little detail has been reported concerning its biocidal ability. In this study, the inactivation efficiencies of three Fe(VI) species (H(x)FeO(4)(x-2), x=0, 1, 2) are quantified using Escherichia coli as a model microorganism. E. coli inactivation by Fe(VI) was performed in solutions buffered with 25 mM phosphate in the pH range of 5.6-8.2 and at 25 degrees C. Kinetics of E. coli inactivation were successfully fitted to the Modified Delayed Chick-Watson model in the tested pH range, indicating that log inactivation level of E. coli is linearly proportional to exposure amount of E. coli to Fe(VI). The rate constant of E. coli inactivation by Fe(VI) (k(obs)) that was obtained from the linear regression increased non-linearly from 0.33 to 6.25 l(mg min)(-1) with decreasing pH from 8.2 to 5.6. From the measured pH dependency of k(obs) and the known acidity constants of Fe(VI) species (pK(a), H(2)FeO(4)=3.50 and pK(a), HFeO(4)(-)=7.23), HFeO(4)(-) and H(2)FeO(4) were found to be 3 and 265 times as effective as FeO(4)(2-) in E. coli inactivation, respectively.

Outbreaks of gastroenteritis that occurred during school excursions in Korea were associated with several waterborne strains of norovirus.

In May 2004, 97 of 309 (31%) and 97 of 207 (47%) school students from geographically distant areas were affected by acute gastroenteritis during excursions to neighboring hotels. The two hotels were 300 m apart, on Jeju Island, South Korea. Several strains of norovirus, including both genogroup I and genogroup II viruses, were identified in stool samples from the students and food handlers and in groundwater from the hotels. Of these several strains of norovirus, the nucleotide sequences for one strain were identical for samples from the students, food handlers, and groundwater.

Enhanced disinfection efficiency of mechanically mixed oxidants with free chlorine.

To the best of our knowledge, this study is the first investigation to be performed into the potential benefits of mechanically mixed disinfectants in controlling bacterial inactivation. The purpose of this study was to evaluate the disinfection efficiency of mechanically mixed oxidants with identical oxidant concentrations, which were made by adding small amounts of subsidiary oxidants, namely ozone (O3), chlorine dioxide (ClO2), hydrogen peroxide (H2O2) and chlorite (ClO2(-)), to free available chlorine (Cl2), using Bacillus subtilis spores as the indicator microorganisms. The mechanically mixed oxidants containing Cl2/O3, Cl2/ClO2 and Cl2/ClO2(-) showed enhanced efficiencies (of up to 52%) in comparison with Cl2 alone, whereas no significant difference was observed between the mixed oxidant, Cl2/H2O2, and Cl2 alone. This enhanced disinfection efficiency can be explained by the synergistic effect of the mixed oxidant itself and the effect of intermediates such as ClO2(-)/ClO2, which are generated from the reaction between an excess of Cl2 and a small amount of O3/ClO2(-). Overall, this study suggests that mechanically mixed oxidants incorporating excess chlorine can constitute a new and moderately efficient method of disinfection.

Different inactivation behaviors of MS-2 phage and Escherichia coli in TiO2 photocatalytic disinfection.

Despite a wealth of experimental evidence concerning the efficacy of the biocidal action associated with the TiO(2) photocatalytic reaction, our understanding of the photochemical mechanism of this particular biocidal action remains largely unclear. It is generally accepted that the hydroxyl radical (.OH), which is generated on the surface of UV-illuminated TiO(2), plays the main role. However, our understanding of the exact mode of action of the hydroxyl radical in killing microorganisms is far from complete, and some studies report that other reactive oxygen species (ROS) (H(2)O(2) and O(2).(-), etc.) also play significant roles. In particular, whether hydroxyl radicals remain bound to the surface or diffuse into the solution bulk is under active debate. In order to examine the exact mode of action of ROS in inactivating the microorganism, we tested and compared the levels of photocatalytic inactivation of MS-2 phage and Escherichia coli as representative species of viruses and bacteria, respectively. To compare photocatalytic microbial inactivation with the photocatalytic chemical degradation reaction, para-chlorobenzoic acid, which rapidly reacts with a hydroxyl radical with a diffusion-limited rate, was used as a probe compound. Two different hydroxyl radical scavengers, tert-butanol and methanol, and an activator of the bulk phase hydroxyl radical generation, Fe(2+), were used to investigate their effects on the photocatalytic mode of action of the hydroxyl radical in inactivating the microorganism. The results show that the biocidal modes of action of ROS are very different depending on the specific microorganism involved, although the reason for this is not clear. It seems that MS-2 phage is inactivated mainly by the free hydroxyl radical in the solution bulk but that E. coli is inactivated by both the free and the surface-bound hydroxyl radicals. E. coli might also be inactivated by other ROS, such as O(2).(-) and H(2)O(2), according to the present results.

Linear correlation between inactivation of E. coli and OH radical concentration in TiO2 photocatalytic disinfection.

The biocidal action of the TiO2 photocatalyst has been now well recognized from massive experimental evidences, which demonstrates that the photocatalytic disinfection process could be technically feasible. However, the understanding on the photochemical mechanism of the biocidal action largely remains unclear. In particular, the identity of main acting photooxidants and their roles in the mechanism of killing microorganisms is under active investigation. It is generally accepted that reactive oxygen species (ROS) and OH radicals play the role. The aim of this study is to determine how the OH radical, acting either independently or in collaboration with other ROS, is quantitatively related to the inactivation of E. coli. The steady-state concentrations of OH radicals ([*OH]ss) in UV-illuminated TiO2 suspensions could be quantified from the measured photocatalytic degradation rates of p-chlorobenzoic acid (a probe compound) and its literature bimolecular rate constant with OH radicals. The results demonstrated an excellent linear correlation between [*OH]ss and the rates of E. coli inactivation, which indicates that the OH radical is the primary oxidant species responsible for inactivating E. coli in the UV/TiO2 process. The CT value of OH radical for achieving 2 log E. coli inactivation was initially found to be 0.8x10(-5) mg min/l, as predicted by the delayed Chick-Watson model. Although the primary role of OH radicals in photocatalytic disinfection processes has been frequently assumed, this is the first quantitative demonstration that the concentration of OH radicals and the biocidal activity is linearly correlated.