Alexander Cabaj

UV inactivation, liquid-holding recovery, and photoreactivation of Escherichia coli O157 and other pathogenic Escherichia coli strains in water.

Drinking water, water used in food production and for irrigation, water for fish farming, waste water, surface water, and recreational water have been recently recognized as a vector for the transmission of pathogenic Escherichia coli, especially serotype O157:H7. We investigated the UV (253.7 nm) inactivation behavior and the capability of dark repair (liquid-holding recovery) and photoreactivation of seven pathogenic (including three enterohemorrhagic E. coli) strains and one nonpathogenic strain of E. coli (ATCC 11229) with respect to the use of UV light for water disinfection purposes. Because most bacteria and yeast are known to be able to repair UV damage in their nucleic acids, repair mechanisms have to be considered to ensure safe water disinfection. We found a wide divergence in the UV susceptibility within the strains tested. A 6-log reduction of bacteria that fulfills the requirement for safe water disinfection was reached for the very most susceptible strain O157:H7 (CCUG 29199) at a UV fluence of 12 J/m2, whereas for the most resistant strain, O25:K98:NM, a UV fluence of about 125 J/m2 was needed. Except for one strain (O50:H7) liquid-holding recovery did not play an important role in recovery after UV irradiation. By contrast, all strains, particularly strains O25:K98:NM, O78:K80:H12, and O157:H7 (CCUG 29193), demonstrated photorepair ability. For a 6-log reduction of these strains, a UV fluence (253.7 nm) up to 300 J/m2 is required. The results reveal that the minimum fluence of 400 J/m2 demanded in the Austrian standard for water disinfection is sufficient to inactivate pathogenic E. coli. A fluence of 160 J/m2 (recommendation in Norway) or 250 J/m2 (recommendation in Switzerland) cannot be regarded as safe in that respect.

Calicivirus Inactivation by Nonionizing (253.7-Nanometer-Wavelength [UV]) and Ionizing (Gamma) Radiation

ABSTRACT Noroviruses (previously Norwalk-like viruses) are the most common viral agents associated with food- and waterborne outbreaks of gastroenteritis. In the absence of culture methods for noroviruses, animal caliciviruses were used as model viruses to study inactivation by nonionizing (253.7-nm-wavelength [UV]) and ionizing (gamma) radiation. Here, we studied the respiratory feline calicivirus (FeCV) and the presumed enteric canine calicivirus (CaCV) and compared them with the well-studied bacteriophage MS2. When UV irradiation was used, a 3-log10 reduction was observed at a fluence of 120 J/m2 in the FeCV suspension and at a fluence of 200 J/m2 for CaCV; for the more resistant phage MS2 there was a 3-log10 reduction at a fluence of 650 J/m2. Few or no differences were observed between levels of UV inactivation in high- and low-protein-content virus stocks. In contrast, ionizing radiation could readily inactivate MS2 in water, and there was a 3-log10 reduction at a dose of 100 Gy, although this did not occur when the phage was diluted in high-protein-content stocks of CaCV or FeCV. The low-protein-content stocks showed 3-log10 reductions at a dose of 500 Gy for FeCV and at a dose of 300 for CaCV. The inactivation rates for both caliciviruses with ionizing and nonionizing radiation were comparable but different from the inactivation rates for MS2. Although most FeCV and CaCV characteristics, such as overall particle and genome size and structure, are similar, the capsid sequences differ significantly, making it difficult to predict human norovirus inactivation. Adequate management of UV and gamma radiation processes for virus inactivation should limit public health risks.

Inactivation of bacteriophages in water by means of non-ionizing (uv-253.7 nm) and ionizing (gamma) radiation: a comparative approach

Thc inactivation behaviour of the bacteriophages PHI X 174 (ssDNA virus). MS2 (ssRNA virus) and B40-8 (dsDNA) toward non-ionizing (UV-253.7 nm) as well as to ionizing radiation (gamma radiation) was studied in order to evaluate their potential as viral indicators for water disinfection by irradiation. Previous findings of the high UV-253.7 nm resistance of MS2 were confirmed whereas an unexpected high sensitivity to gamma radiation compared to the two other phages was found. On the other hand, PHI X 174 revealed an enhanced UV sensitivity but a high resistance to ionizing radiation. B40-8 had an intermediate position between the other two bacteriophages relative to both types of radiation. As expected, the data of E. coli reconfirmed the unreliability of fecal indicator bacteria for the purpose of predicting responses of viruses to water treatment. In UV disinfection the influence of water matrix may be adequately controlled by considering the UV (253.7 nm) absorption of the water whereas so far no such parameter has existed for the influence of the water quality on ionizing irradiation with respect to the scavenger concentration.

Biodosimetry : Model calculations for u.v. water disinfection devices with regard to dose distributions

Abstract The increasing importance of disinfection of drinking water by u.v. radiation makes it necessary to determine the u.v. dose which is applied to the water by u.v.-disinfection plants. In Austria a minimum microbicidal dose of 400 Jm −2 at a wavelength of 253.7 nm is demanded for drinking water, the control of it shall be assured by type testing. A method was developed in using calibrated spores of Bacillus subtilis as biodosimeter which are added to the inflowing water, and after determination of their survival rate in the plant one can deduce the applied dose from it. This procedure is unproblematic as long as all microorganisms receive the same dose on their way through the reactor. But in some cases, and probably this is the normal case, not all microorganisms receive the same dose. It follows that a dose distribution will exist among the test organisms which have passed through the reactor. The dose (reduction-equivalent dose or RED) which is deduced from the survival rate of the microorganisms passing flow-through systems for u.v.-disinfection of wastewater or drinking water in general is different from the arithmetic mean of the dose distribution. The RED depends on the special form of the dose distribution and on the specific shape of the survival curve of the test organisms. The broader the dose distribution and the higher the u.v.-susceptibility of the microorganisms, the lower is the measured RED. But if the survival curve of the microorganisms used would have a shoulder ( D s > D m ), and the dose distribution would overlap with the shoulder the RED may increase. We investigated by calculations and by experiments the influences on the test results obtained by this method.

Genotoxic response of Austrian groundwater samples treated under standardized UV (254 nm)—disinfection conditions in a combination of three different bioassays

Ground water samples from different geographic areas in Austria, with different amounts of natural and anthropogenic organic compounds were treated with a standardized low pressure UV (254 nm)-irradiation laboratory flow-through system (UV fluence: 800 J/m2). The genotoxic activities of the water samples before and after the UV disinfection were investigated using a combination of three different bioassays which complement each other with regard to their sensitivity detecting different genotoxins. The test battery comprises the Salmonella/microsome assay (Ames test with TA98. TA 100 and TA 102, with and without S9 mix) and two micronucleus tests with the plant Tradescantia (clone #4430) and with primary rat hepatocytes. Overall, the tested Austrian groundwater samples used for human consumption caused only weak genotoxic activities compared to drinking water samples reported from other countries under similar experimental conditions. With the exception of one weak positive result in the Ames test (only in strain TA98 without S9 mix) with an induction factor of 1.9) all samples after UV disinfection were devoid of additional mutagenic and clastogenic activities compared to the samples before UV disinfection.

Facial solar UV exposure of Austrian farmers during occupation.

Optoelectronic personal UV‐meters were used to monitor the occupational facial solar erythemally effective exposure of 12 Austrian full‐time farmers with high temporal resolution. To ensure high quality measurements several quality assurance procedures were applied, like calibration with respect to solar elevation and total ozone column. From April to October the test persons carried the UV‐meters on the forehead during working hours. A digital diary (activity, location, weather, photoprotective measures) was completed on an hourly basis. Our field test produced 1427 complete daily records (measurement and diary). The total exposures showed high variability (77 –757 standard erythema dose [SED]) which correlates with the number of working days and even stronger with the little numbers of days with high exposure (>10 SED). Risk factors for high exposures were: mixed‐culture farms with aggravated working conditions, low degree of automation of working processes, inadequate operating logistics (summarized as manual work outdoor), driving machines without cabins, and female gender. UV exposure of female farmers was approximately twice as high as that of men: Women received 15% of ambient radiation while men got 8%. Avoiding daily exposure >10 SED could reduce exposure down to 40% and the risk in developing skin cancer by a factor of 40.

Measurement of UV radiation using suspensions of microorganisms.

The measurement of solar UV radiation is usually performed using physical devices like photodiodes or photomultipliers or with chemical substances (actinometry). The application of biological material such as microorganisms for this purpose has gained increasing importance in the last few years. The microorganisms may be dried and spread on a flat surface or they may be in aqueous suspensions contained in UV-transparent vessels. If the measurements are done on flat surfaces, the irradiance weighted by the action spectrum of the dried microorganism used is the result of the measurement. If aqueous suspensions of microorganisms are used, contained for instance in spherical vessels, the fluence weighted by the action spectrum of the microorganisms in the aqueous suspension is the result. A problem of this method of measurement can be that inside the vessel the distribution of UV radiation is usually not homogeneous, causing distributions of fluences among the irradiated microorganisms, which may result in variation of the results depending on the mixing characteristics of the suspension during irradiation.

Bacteriophages as viral indicators for radiation processing of water: a chemical approach.

Inactivation of the bacteriophages PHI X 174 (somatic coliphage), MS2 (F-specific coliphage) and B40-8 (phage infecting Bacteroides fragilis) suspended in tap water was studied applying gamma and electron beam irradiation as well. PHI X 174 phage was found to be a suitable viral indicator for water disinfection by means of ionizing radiation. The nutrient broths introduced simultaneously with the bacteriophages into the water when it is spiked with the phages for the experiments did not significantly change the scavenging capacity of the water matrix. No dose rate effect was observed with MS2 and B40-8 phages but PHI X 174 phage showed a clear dose rate effect. It was found that in water MS2 phage is significantly more sensitive to ionizing radiation than Escherichia coli.

Effect of Work-Related Ultraviolet Exposure and Ophthalmic Changes in Austrian Farmers: The SVB-UV Study

Background: Epidemiological screening to examine possible ultraviolet-induced ocular changes and pathologies in Austrian farmers. Methods: The study was performed on behalf of the Austrian farmer insurance (Sozialversicherungsanstalt der Bauern). Randomly selected farmers and office workers as controls, both at the age of 35–55 years, underwent ophthalmic screening examinations. All subjects underwent complete ophthalmic examinations by slit lamp examination and Schirmer’s test 1. A survey, regarding per- sonal habits in the sun, was also conducted. Results: Three hundred and ninety-two subjects underwent ophthalmic examinations of whom 297 were farmers and 95 were controls. Due to the survey, 89.7% of the farmers claimed to protect themselves from the sun during work. From these subjects, 83.7% wear a head protection, 71.0% wear sunglasses, and 54.4% usually work in the shade. There were significant differences in lid (p = 0.021) and conjunctival pathologies (p < 0.0001) between farmers and controls. Conclusion: Austrian farmers are at a higher risk for developing lid and conjunctival tumours which require treatment at some point. We believe that the study group was too young to show significant differences within the lens and the posterior pole. A 5-year follow-up is planned.

Disinfection of Drinking Water by UV Irradiation: Basic Principles - Specific Requirements - International Implementations

The quality control of UV drinking water disinfection has made an enormous progress in the last decade. The better understanding of the process and the higher quality assurance of the UV disinfection plants has increased the acceptance of UV drinking water disinfection. Three UV water disinfection standards were internationally developed by the USEPA, the German Association for Gas and Water and the Austrian Standards Institute. The quality assurance of safe UV water disinfection is based on 3 main prerequisites: the knowledge of the UV resistance of health related microorganisms transmittable by water, to set a sufficient high UV fluence, the careful evaluation of commercial UV plants and the control of the UV irradiation process during practical application by means of defined alarm points and a calibrated UV sensor, which allows checks against official specifications. Here we describe the basic principles of the validation of UV drinking water systems and point out the specific differences between the three international UV disinfection standards with regard to validation.