Thomas Haider

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.

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.

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.

Clastogenic effects of radiofrequency radiations on chromosomes of Tradescantia

The clastogenicity of electromagnetic fields (EMF) has so far been studied only under laboratory conditions. We used the Tradescantia-micronucleus (Trad-MCN) bioassay in an in situ experiment to find out whether short-wave electromagnetic fields used for broadcasting (10-21 MHz) may show genotoxic effects. Plant cuttings bearing young flower buds were exposed (30 h) on both sides of a slewable curtain antenna (300/500 kW, 40-170 V/m) and 15 m (90 V/m) and 30 m (70 V/m) distant from a vertical cage antenna (100 kW) as well as at the neighbors living near the broadcasting station (200 m, 1-3 V/m). The exposure at both sides of the slewable curtain antenna was performed simultaneously within cages, one of the Faraday type shielding the field and one non-shielding mesh cage. Laboratory controls were maintained for comparison. Higher MCN frequencies than in laboratory controls were found for all exposure sites in the immediate vicinity of the antennae, where the exposure standards of the electric field strength of the International Radiation Protection Association (IRPA) were exceeded. The results at all exposure sites except one were statistically significant. Since the parallel exposure in a non-shielding and a shielding cage also revealed significant differences in MCN frequencies (the latter showing no significant differences from laboratory controls), the clastogenic effects are clearly attributable to the short-wave radiation from the antennae.

Lead in drinking water of Vienna in comparison to other European countries and accordance with recent guidelines.

Due to the decrease of lead intake via inhalation route, the oral route, particularly from drinking water in cities with lead installations, gains relative importance. In two surveys a total of 288 objects were investigated and 1768 samples were analysed. The first series with 51 objects using a field experimental approach systematically investigated the effects of daytime, floor and flushing. Because only objects built before 1945 and suspected of lead plumbing were chosen, the first series approaches worst case conditions. The second series investigating 237 randomly chosen objects stratified according to time of consumption should allow inferences about the present situation in Viennese households. Each sampling procedure comprised one sample without flushing and three further samples with flushing of 1 l, 3 l and 10 l, respectively. Statistically significant decreases occurred between these flushing conditions. The sampling data of the upper floors showed significantly higher lead contents compared to the lower floors, which indicates that house installations are the main causes of lead contamination in Viennese drinking water. In comparison to other European countries the percentage of samples exceeding the guideline levels (50 micrograms/l as current value and 10 micrograms/l as target value) was lower.

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.

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.

What Means “Dose” in UV-Disinfection with Medium Pressure Lamps?

Abstract The “dose” in UV-disinfection plants for water, which are equipped with (nearly monochromatic) low pressure mercury lamps is already well defined as Reduction Equivalent Fluence (REF). For plants with medium pressure mercury lamps, which emit polychromatic UV-radiation, several definitions of “dose” are possible. We measured the spectral sensitivity of spores of Bacillus subtilis ATCC 6633 and compared results gained by calculations using these spectral functions with results from irradiation with a medium pressure lamp. The measurements and calculations showed good agreement.

Microflora in External Auditory Canals of Recreational Scuba-Divers and Swimmers Related to the Tropical Waterflora of a Coral Island

Recent studies described the acute diffuse external otitis frequently observed in recreational scuba-divers and swimmers in the tropics. In this study the microflora of the external auditory canal of 90 persons was determined. Additionally, a group of 17 persons was examined before, during and at the end of a two weeks vacation on a tropical coral island as well as three months after. Further, samples from sea, lagoon water and the water supplies used for the showers were microbiologically examined. 14 different and fecultatively pathogenic microorganisms were isolated from the external auditory canals. We found a temporary colonization with those microorganisms during the two weeks. Above all Pseudomonas aeruginosa was predominant during and at the end of the vacation especially in children. Before the vacation and three months after P. aeruginosa could not be found. The samples of sea and lagoon waters did not seem to be noticeably polluted, whereas the samples of the water supply were extremely contaminated with Pseudomonas aeruginosa . It was concluded that besides indirect factors such as tropical climate and intensive exposition to water, the insufficient treatment of the water from the supply could also be a reason for the temporary microbiological colonization of the external auditory canal.