Inactivation of Cryptosporidium parvum oocysts using medium- and low-pressure ultraviolet radiation

Effects of UV 254 irradiation on residual chlorine and DBPs in chlorination of model organic-N precursors in swimming pools

Ultraviolet (UV) irradiation is commonly applied as a secondary disinfection process in chlorinated pools. UV-based systems have been reported to yield improvements in swimming pool water and air chemistry, but to date these observations have been largely anecdotal. The objectives of this investigation were to evaluate the effects of UV irradiation on chlorination of important organic-N precursors in swimming pools. Creatinine, L-arginine, L-histidine, glycine, and urea, which comprise the majority of the organic-N in human sweat and urine, were selected as precursors for use in conducting batch experiments to examine the time-course behavior of several DBPs and residual chlorine, with and without UV(254) irradiation. In addition, water samples from two natatoria were subjected to monochromatic UV irradiation at wavelengths of 222 nm and 254 nm to evaluate changes of liquid-phase chemistry. UV(254) irradiation promoted formation and/or decay of several chlorinated N-DBPs and also increased the rate of free chlorine consumption. UV exposure resulted in loss of inorganic chloramines (e.g., NCl(3)) from solution. Dichloromethylamine (CH(3)NCl(2)) formation from creatinine was promoted by UV exposure, when free chlorine was present in solution; however, when free chlorine was depleted, CH(3)NCl(2) photodecay was observed. Dichloroacetonitrile (CNCHCl(2)) formation (from L-histidine and L-arginine) was promoted by UV(254) irradiation, as long as free chlorine was present in solution. Likewise, UV exposure was observed to amplify cyanogen chloride (CNCl) formation from chlorination of L-histidine, L-arginine, and glycine, up to the point of free chlorine depletion. The results from experiments involving UV irradiation of chlorinated swimming pool water were qualitatively consistent with the results of model experiments involving UV/chlorination of precursors in terms of the behavior of residual chlorine and DBPs measured in this study. The results indicate that UV(254) irradiation promotes several reactions that are involved in the formation and/or destruction of chlorinated N-DBPs in pool settings. Enhancement of DBP formation was consistent with a mechanism whereby a rate-limiting step in DBP formation was promoted by UV exposure. Promotion of these reactions also resulted in increases of free chlorine consumption rates.

Evolution of phytoplankton cultures after ultraviolet light treatment

Introducing invasive species in new environments through ballast water is a specific problem of contamination and has recently become one of the main concerns of Maritime Organizations. Ultraviolet-C radiation (UV-C) is a technological alternative to prevent this maritime pollution. This study addresses the effect of UV-C on different phytoplankton cultures and also the ability to recover following exposure to damage. A UV-C low-pressure lamp irradiates the cultures. The distance from the source and the thickness of the layer prevent part of the energy from reaching the culture and the disinfective process is diminished. Some cultures such as Chlorella autotrophica and Chaetoceros calcitrans can easily recover from UV-C damage. However, Phaeocystis globosa does not have this ability. C. calcitrans forms cysts and exhibits two different behaviours depending on the dose applied.

Effects of UV irradiation and UV/chlorine co-exposure on natural organic matter in water

The effects of co-exposure to ultraviolet (UV) irradiation (with either low- or medium-pressure UV lamps) and free chlorine (chloramine) at practical relevant conditions on changes in natural organic matter (NOM) properties were investigated using four waters. The changes were characterized using the specific disinfection by-product formation potential (SDBPFP), specific total organic halogen formation potential (STOXFP), differential UV absorbance (∆UVA), and size-exclusion chromatography (SEC). The results for exposure to UV irradiation alone and for samples with no exposure were also obtained. The SDBPFPs in all UV-irradiated NOM waters observed were higher than those of non-irradiated samples. UV irradiation led to increases in STOXFPs as a result of chlorination, but no changes, or only small decreases, from chloramination. UV irradiation alone led to positive ∆UVA spectra of the four NOM waters; co-exposure to UV and chlorine gave larger negative ∆UVA spectra than those obtained by chlorine exposure alone. No obvious changes in SEC results were observed for samples only irradiated with UV light; co-exposure gave no detectable changes in the abundances of small fractions for exposure to chlorine only. Both UV photooxidation and photocatalytic oxidation appear to affect the reactivity of the NOM toward subsequent chlorination, and the magnitude of the changes is generally greater for medium-pressure lamps than for low-pressure lamps. These results suggest that applying UV disinfection technology to a particular source may not always be disinfection by-product-problem-free, and the interactions between UV light, chlorine, and NOM may need to be considered.

Sequential use of ultraviolet light and chlorine for reclaimed water disinfection

Several disinfection processes of ultraviolet (UV), chlorine or UV followed by chlorine were investigated in municipal wastewater according to the inactivation of Escherichia coli, Shigella dysenteriae and toxicity formation. The UV inactivation of the tested pathogenic bacteria was not affected by the quality of water. It was found that the inactivated bacteria were obviously reactivated after one day in dark. Fluorescent light irradiation increased the bacteria repair. The increase of UV dosage could cause more damage to bacteria to inhibit bacteria self-repair. No photoreactivation was detected when the UV dose was up to 80 mJ/cm2 for E. coli DH5alpha, and 23 mJ/cm2 for S. dysenteriae. Nevertheless, sequential use of 8 mJ/cm2 of UV and low concentration of chlorine (1.5 mg/L) could effectively inhibit the photoreactivation and inactivate E. coli below the detection limits within seven days. Compared to chlorination alone, the sequential disinfection decreased the genotoxicity of treated wastewater, especially for the sample with high NH3-N concentration.

Determining UV inactivation of Toxoplasma gondii oocysts by using cell culture and a mouse bioassay

The effect of UV exposure on Toxoplasma gondii oocysts has not been completely defined for use in water disinfection. This study evaluated UV-irradiated oocysts by three assays: a SCID mouse bioassay, an in vitro T. gondii oocyst plaque (TOP) assay, and a quantitative reverse transcriptase real-time PCR (RT-qPCR) assay. The results from the animal bioassay show that 1- and 3-log(10) inactivation is achieved with 4 mJ/cm(2) UV and 10 mJ/cm(2) low-pressure UV, respectively. TOP assay results, but not RT-qPCR results, correlate well with bioassay results. In conclusion, a 3-log(10) inactivation of T. gondii oocysts is achieved by 10-mJ/cm(2) low-pressure UV, and the in vitro TOP assay is a promising alternative to the mouse bioassay.

Quantitative risk assessment of Cryptosporidium in tap water in Ireland

Cryptosporidium species are protozoan parasites associated with gastro-intestinal illness. Following a number of high profile outbreaks worldwide, it has emerged as a parasite of major public health concern. A quantitative Monte Carlo simulation model was developed to evaluate the annual risk of infection from Cryptosporidium in tap water in Ireland. The assessment considers the potential initial contamination levels in raw water, oocyst removal and decontamination events following various process stages, including coagulation/flocculation, sedimentation, filtration and disinfection. A number of scenarios were analysed to represent potential risks from public water supplies, group water schemes and private wells. Where surface water is used additional physical and chemical water treatment is important in terms of reducing the risk to consumers. The simulated annual risk of illness for immunocompetent individuals was below 1 x 10(-4) per year (as set by the US EPA) except under extreme contamination events. The risk for immunocompromised individuals was 2-3 orders of magnitude greater for the scenarios analysed. The model indicates a reduced risk of infection from tap water that has undergone microfiltration, as this treatment is more robust in the event of high contamination loads. The sensitivity analysis highlighted the importance of watershed protection and the importance of adequate coagulation/flocculation in conventional treatment. The frequency of failure of the treatment process is the most important parameter influencing human risk in conventional treatment. The model developed in this study may be useful for local authorities, government agencies and other stakeholders to evaluate the likely risk of infection given some basic input data on source water and treatment processes used.

Biofouling control in water by various UVC wavelengths and doses

UV light irradiation is being increasingly applied as a primary process for water disinfection, effectively used for inactivation of suspended (planktonic) cells. In this study, the use of UV irradiation was evaluated as a pretreatment strategy to control biofouling. The objective of this research was to elucidate the relative effectiveness of various targeted UV wavelengths and a polychromatic spectrum on bacterial inactivation and biofilm control. In a model system using Pseudomonas aeruginosa, the inactivation spectra corresponded to the DNA absorption spectra for all wavelengths between 220 and 280 nm, while wavelengths between 254 nm and 270 nm were the most effective for bacterial inactivation. Similar wavelengths of 254-260-270 nm were also more effective for biofilm control in most cases than targeted 239 and 280 nm. In addition, the prevention of biofilm formation by P. aeruginosa with a full polychromatic lamp was UV dose-dependent. It appears that biofilm control is improved when larger UV doses are given, while higher levels of inactivation are obtained when using a full polychromatic MP lamp. However, no significant differences were found between biofilms produced by bacteria that survived UV irradiation and biofilms produced by control bacteria at the same microbial counts. Moreover, the experiments showed that biofilm prevention depends on the post-treatment incubation time and nutrient availability, in addition to targeted wavelengths, UV spectrum and UV dose.

Comparison of the action spectra and relative DNA absorbance spectra of microorganisms: information important for the determination of germicidal fluence (UV dose) in an ultraviolet disinfection of water

The action spectra of Bacillus subtilis spores (ATCC6633) and Salmonella typhimurium LT2 were characterized using physical radiometry for irradiance measurements and a multiple target model to interpret the inactivation kinetics. The observed action spectrum of B. subtilis spores deviated significantly from the relative absorbance spectrum of the DNA purified from the spores, but matched quite well with the relative absorbance spectrum of decoated spores. The action spectrum of B. subtilis spores determined in this study was statistically different from those reported in previous studies. On the other hand, the action spectrum of S. typhimurium bacteria matched quite well with the relative absorbance spectrum of DNA extracted from vegetative cells, except in the region below 240nm. It is concluded that the common use of the relative DNA absorbance spectrum as a surrogate for the germicidal action spectrum can result in systematic errors when evaluating the performance of a polychromatic UV light reactors using bioassays. For example, if the weighted germicidal fluence (UV dose) calculated using the relative DNA absorbance spectrum as the germicidal weighting factor is found to be 40mJcm(-2) for a medium pressure lamp UV reactor, that calculated using the relative action spectrum of B. subtilis spores, as determined in this study, would be 66mJcm(-2).

Evaluation of five decontamination methods for filtering facepiece respirators

Concerns have been raised regarding the availability of National Institute for Occupational Safety and Health (NIOSH)-certified N95 filtering facepiece respirators (FFRs) during an influenza pandemic. One possible strategy to mitigate a respirator shortage is to reuse FFRs following a biological decontamination process to render infectious material on the FFR inactive. However, little data exist on the effects of decontamination methods on respirator integrity and performance. This study evaluated five decontamination methods [ultraviolet germicidal irradiation (UVGI), ethylene oxide, vaporized hydrogen peroxide (VHP), microwave oven irradiation, and bleach] using nine models of NIOSH-certified respirators (three models each of N95 FFRs, surgical N95 respirators, and P100 FFRs) to determine which methods should be considered for future research studies. Following treatment by each decontamination method, the FFRs were evaluated for changes in physical appearance, odor, and laboratory performance (filter aerosol penetration and filter airflow resistance). Additional experiments (dry heat laboratory oven exposures, off-gassing, and FFR hydrophobicity) were subsequently conducted to better understand material properties and possible health risks to the respirator user following decontamination. However, this study did not assess the efficiency of the decontamination methods to inactivate viable microorganisms. Microwave oven irradiation melted samples from two FFR models. The remainder of the FFR samples that had been decontaminated had expected levels of filter aerosol penetration and filter airflow resistance. The scent of bleach remained noticeable following overnight drying and low levels of chlorine gas were found to off-gas from bleach-decontaminated FFRs when rehydrated with deionized water. UVGI, ethylene oxide (EtO), and VHP were found to be the most promising decontamination methods; however, concerns remain about the throughput capabilities for EtO and VHP. Further research is needed before any specific decontamination methods can be recommended.

Effect of the radiation intensity, water turbidity and exposure time on the survival of Cryptosporidium during simulated solar disinfection of drinking water

The solar disinfection (SODIS) technique is a highly effective process that makes use of solar energy to inactivate pathogenic microorganisms in drinking water in developing countries. The pathogenic protozoan parasite Cryptosporidium parvum is often found in surface waters and is associated with waterborne outbreaks of cryptosporidiosis. In the present study, a complete multi-factorial mathematical model was used to investigate the combined effects of the intensity of solar radiation (200, 600 and 900W/m(2) in the 320nm to 10microm range), water turbidity (5, 100 and 300 NTU) and exposure time (4, 8 and 12h) on the viability and infectivity of C. parvum oocysts during simulated SODIS procedures at a constant temperature of 30 degrees C. All three factors had significant effects (p<0.05) on C. parvum survival, as did the interactions of water turbidity with radiation intensity and radiation intensity with exposure time. However, the parameter with the greatest effect was the intensity of radiation; levels > or =600W/m(2) and times of exposure between 8 and 12h were required to reduce the oocyst infectivity in water samples with different degrees of turbidity.

Evaluation of water treatment plant UV reactor efficiency against Cryptosporidium parvum oocyst infectivity in immunocompetent suckling mice

AIM

To assess the efficiency of a medium-pressure UV reactor under full-scale water treatment plant (WTP) conditions on the infectivity of Cryptosporidium parvum oocysts in an Naval Medical Research Institute (NMRI) suckling mice infectivity model.

METHODS AND RESULTS

Six/seven-day-old mice were administered orally 2-10x10(4)Cryptosporidium parvum oocysts. Compared with nonirradiated oocysts, 40 mJ cm(-2) UV irradiation of ingested oocysts resulted 7 days later in a 3.4-4.0 log10 reduction in the counts of small intestine oocysts, using a fluorescent flow cytometry assay.

CONCLUSION

Present data extend to industrial conditions previous observations of the efficiency of UV irradiation against Cryptosporidium parvum oocyst in vivo development.

SIGNIFICANCE AND IMPACT OF THE STUDY

Present results suggest that in WTP conditions, a medium-pressure UV reactor is efficient in reducing the infectivity of Cryptosporidium parvum oocysts, one of the most resistant micro-organisms present in environmental waters.

Characteristics of trihalomethane (THM) production and associated health risk assessment in swimming pool waters treated with different disinfection methods

Swimming pool water must be treated to prevent infections caused by microbial pathogens. In Korea, the most commonly used disinfection methods include the application of chlorine, ozone/chlorine, and a technique that uses electrochemically generated mixed oxidants (EGMOs). The purpose of this study was to estimate the concentrations of total trihalomethanes (TTHMs) in indoor swimming pools adopting these disinfection methods, and to examine the correlations between the concentrations of THMs and TTHMs and other factors affecting the production of THMs. We also estimated the lifetime cancer risks associated with various exposure pathways by THMs in swimming pools. Water samples were collected from 183 indoor swimming pools in Seoul, Korea, and were analyzed for concentrations of each THM, TOC, and the amount of KMnO(4) consumption. The free chlorine residual and the pH of the pool water samples were also measured. The geometric mean concentrations of TTHMs in the swimming pool waters were 32.9+/-2.4 microg/L for chlorine, 23.3+/-2.2 microg/L for ozone/chlorine, and 58.2+/-1.7 microg/L for EGMO. The concentrations of THMs differed significantly among the three treatment methods, and the correlation between THMs and TTHMs and the other factors influencing THMs varied. The lifetime cancer risk estimation showed that, while risks from oral ingestion and dermal exposure to THMs are mostly less than 10(-6), which is the negligible risk level defined by the US EPA, however swimmers can be at the greater risk from inhalation exposure (7.77x10(-4)-1.36x10(-3)).

Environmental inactivation of Cryptosporidium parvum oocysts in waste stabilization ponds

The survival of Cryptosporidium parvum oocysts in a waste stabilization pond system in northwestern Spain and the effects of sunlight and the depth and type of pond on oocyst viability were evaluated using an assay based on the exclusion or inclusion of two fluorogenic vital dyes, 4',6-diamidino-2-phenylindole (DAPI) and propidium iodide (PI). All tested factors had significant effects (P < 0.01) over time on C. parvum oocyst viability. Sunlight exposure was the most influential factor for oocyst inactivation. A 40% reduction was observed after 4 days exposure to sunlight conditions compared with dark conditions. The type of pond also caused a significant reduction in C. parvum oocyst viability (P < 0.01). Inactivation rates reflected that the facultative pond was the most aggressive environment for oocysts placed both at the surface (presence of sunlight) and at the bottom (absence of sunlight) of the pond, followed by the maturation pond and the anaerobic pond. The mean inactivation rates of oocysts in the ponds ranged from 0.0159 to 0.3025 day(-1).

Prevalence of Cryptosporidium spp. and Giardia intestinalis in swimming pools, Atlanta, Georgia

Cryptosporidium spp. and Giardia intestinalis have been found in swimming pool filter backwash during outbreaks. To determine baseline prevalence, we sampled pools not associated with outbreaks and found that of 160 sampled pools, 13 (8.1%) were positive for 1 or both parasites; 10 (6.2%) for Giardia sp., 2 (1.2%) for Cryptosporidium spp., and 1 (0.6%) for both.

Photocatalytic inactivation of Cryptosporidium parvum with TiO(2) and low-pressure ultraviolet irradiation

This study investigated the efficacy of low-pressure ultraviolet (UV) irradiation and the synergistic effect of UV/titanium dioxide (TiO(2)) photocatalysis on Cryptosporidium parvum oocyst inactivation. At UV doses of 2.7, 8.0, and 40mJ/cm(2), oocyst inactivation was 1.3, 2.6, and 3.3log(10), respectively. Reactive oxygen species (ROS) generated by longwave UV radiation (>315nm) and TiO(2) achieved less than 0.28-log inactivation. However, the synergistic effect of germicidal (254nm) UV and TiO(2) resulted in 2-log and 3-log oocyst inactivation with 4.0 and 11.0mJ/cm(2), respectively. Therefore, using TiO(2) in combination with UV reduced the dose requirement for 3-log inactivation by 56%. An approximate 1-log decrease in inactivation of oocysts was observed with nanopure water in comparison to buffered water, whereas changes in pH from 6 to 8 had little effect on the photocatalytic inactivation of oocysts in either matrix (P>0.1).

Pulsed-UV light inactivation of Cryptosporidium parvum

Cryptosporidium parvum is an organism that threatens public health in the water industry. It is critical to develop improved detection methods as well as disinfection methods for protecting against cryptosporidiosis, which is caused by C. parvum. In this study, we investigated the ability of pulsed-light irradiation at 200-900 nm to inactivate C. parvum. Absolute quantitative real-time PCR was performed with cDNA made from total RNA extracted from C. parvum oocysts or HCT-8 cells infected with C. parvum oocysts in vitro. C. parvum oocysts in 100-mL quartz flasks were positioned 20, 30, and 40 cm from the light source, and the duration of irradiation was either 5 or 60 s. The reductions in oocyst viability (4.9 log10) and infectivity (6 log10) were maximal when the C. parvum oocysts were irradiated 20 cm from the pulsed-light source for 60 s, for which the UV dose was 278 mJ/cm2. The minimum dose of pulsed-UV light required for effective reduction in C. parvum infectivity (2 log10) was 15 mJ/cm2, which was achieved by 5 s of irradiation at 30 cm from the light source. This study confirmed that short-duration pulsed-UV light is an effective disinfection measure for C. parvum.

Effects of ozone and ultraviolet radiation treatments on the infectivity of Toxoplasma gondii oocysts

Clinical toxoplasmosis in humans has been epidemiologically linked to the consumption of drinking water contaminated by Toxoplasma gondii oocysts. We evaluated killing of T. gondii oocysts after ultraviolet (UV) or ozone treatments by bioassay in mice and/or cell culture. A 4-log inactivation of the oocyst/sporozoite infectivity was obtained for UV fluences >20 mJ cm(-2). In contrast, oocysts were not inactivated by ozone with an exposure (Ct) up to 9.4 mg min l (-1) in water at 20 degrees C. In conclusion, UV treatment can be an effective disinfection method to inactivate T. gondii oocysts in drinking water, but ozone did not show promise in this research.

Pulsed-light system as a novel food decontamination technology: a review

In response to consumer preferences for high quality foods that are as close as possible to fresh products, athermal technologies are being developed to obtain products with high levels of organoleptic and nutritional quality but free of any health risks. Pulsed light is a novel technology that rapidly inactivates pathogenic and food spoilage microorganisms. It appears to constitute a good alternative or a complement to conventional thermal or chemical decontamination processes. This food preservation method involves the use of intense, short-duration pulses of broad-spectrum light. The germicidal effect appears to be due to both photochemical and photothermal effects. Several high intensity flashes of broad spectrum light pulsed per second can inactivate microbes rapidly and effectively. However, the efficacy of pulsed light may be limited by its low degree of penetration, as microorganisms are only inactivated on the surface of foods or in transparent media such as water. Examples of applications to foods are presented, including microbial inactivation and effects on food matrices.

Impact of microparticles on UV disinfection of indigenous aerobic spores

Numerous studies have shown that the efficacy of ultraviolet (UV) disinfection can be hindered by the presence of particles that can shield microorganisms. The main objective of this study was to determine to what extent natural particulate matter can shield indigenous spores of aerobic spore-forming bacteria (ASFB) from UV rays. The extent of the protective shielding was assessed by comparing the inactivation rates in three water fractions (untreated, dispersed and filtered on an 8 microm membrane) using a collimated beam apparatus with a low-pressure lamp emitting at 254 nm. Levels of inactivation were then related to the distribution and abundance of particles as measured by microflow imaging. Disinfection assays were completed on two source waters of different quality and particle content. A protocol was developed to break down particles and disperse aggregates (addition of 100mg/L of Zwittergent 3-12 and blending at 8000 rpm for 4 min). Particle size distribution (PSD) analysis confirmed a statistically significant decrease in the number of particles for diameter ranges above 5 microm following the dispersion protocol and 8 microm filtration. The fluence required to reach 1-log inactivation of ASFB spores was independent of particle concentration, while that required to reach 2-log inactivation or more was correlated with the concentration of particles larger than 8 microm (R(2)>0.61). Results suggest that natural particulate matter can protect indigenous organisms from UV radiation in waters with elevated particle content, while source water with low particle counts may not be subject to this interference.

Artificial UV-B and solar radiation reduce in vitro infectivity of the human pathogen Cryptosporidium parvum

The potential for solar ultraviolet (UV) radiation to act as a significant abiotic control of Cryptosporidium parvum oocysts in nature is unknown. Infectivity of C. parvum following exposure to artificial UV-B and natural solar radiation, with and without UV wavelengths, was tested under controlled pH and temperature conditions. Percent infectivity of exposed oocysts was determined by in vitro cell culture. Artificial UV-B exposures of 32 and 66 kJ/m2 significantly decreased oocyst infectivity by an average of 58 and 98%, respectively. Exposure of oocysts to approximately half and full intensity of full solar spectrum (all wavelengths) for a period of less than 1 day (10 h) in mid-summer reduced mean infectivity by an average of 67% and >99.99%, respectively. Exposure of the C. parvum oocysts to UV-shielded solar radiation (>404 nm) in early autumn reduced mean infectivity by 52%, while full spectrum solar radiation (exposure at all wavelengths) reduced mean infectivity by 97%. The data provide strong evidence that exposure to natural solar radiation can significantly reduce C. parvum infectivity. Direct effects of solar radiation on oocysts in nature will depend on the depth distribution of the oocysts, water transparency, mixing conditions, and perhaps other environmental factors such as temperature, pH, and stress.

Effect of sunlight on the infectivity ofCryptosporidium parvumin seawater

The prevalence of pathogenic microorganisms in seawater can result in waterborne and food borne outbreaks. This study was performed to determine the effect of sunlight and salinity on the die-off of Cryptosporidium parvum . Cryptosporidium parvum oocysts, Escherichia coli , and MS2 coliphage were seeded into tap water and seawater samples and then exposed to sunlight. The die-off of C. parvum in seawater, as measured by infectivity, was greater under sunlight (–3.08 log10) than under dark conditions (–1.31 log10). While, no significant difference was recorded in the die-off of C. parvum, under dark conditions, in tap water as compared to seawater (P < 0.05), indicating that the synergistic effect of salinity and sunlight was responsible for the enhanced die-off in seawater. The die-off of MS2 coliphage and E. coli was greater than that observed for C. parvum under all tested conditions. This indicates that these microorganisms cannot serve as indicators for the presence of C. parvum oocysts in seawaters. The results of the study suggest that C. parvum can persist as infectious oocysts for a long time in seawater and can thus pose a serious hazard by direct and indirect contact with humans.

Chlorine photolysis and subsequent OH radical production during UV treatment of chlorinated water

The photodegradation of chlorine-based disinfectants NH(2)Cl, HOCl, and OCl(-) under UV irradiation from low- (LP) and medium-pressure (MP) Hg lamps was studied. The quantum yields of aqueous chlorine and chloramine under 254 nm (LP UV) irradiation were greater than 1.2 mol Es(-1) for free chlorine in the pH range of 4-10 and 0.4 mol Es(-1) for monochloramine at pH 9. Quantum yields for MP (200-350 nm) ranged from 1.2 to 1.7 mol Es(-1) at neutral and basic pH to 3.7 mol Es(-1) at pH 4 for free chlorine, and 0.8 mol Es(-1) for monochloramine. Degradation of free chlorine was enhanced under acidic water conditions, but water quality negatively impacted the MP Hg lamp degradation of free chlorine, compared to the LP UV source. The production of hydroxyl radical via chlorine photolysis was assessed along with the rate of reaction between (*)OH and HOCl using radical scavengers (parachlorobenzoic acid and nitrobenzene) in chlorinated solutions at pH 4. The quantum yield of OH radical production from HOCl at 254 nm was found to be 1.4 mol Es(-1), while the reaction of HOCl with OH radical was measured as 8.5 x 10(4)M(-1)s(-1). NH(2)Cl was relatively stable in all irradiated solutions, with <0.3 mg L(-1) increase in nitrate following a UV dose of 1000 mJ cm(-2). For water treatment plants, no significant changes in chlorine concentration would be expected under typical pH levels and UV doses; however, the formation of (*)OH could have implications for chlorinated byproducts or decay of unwanted chemical contaminants.

Effectiveness of standard UV depuration at inactivating Cryptosporidium parvum recovered from spiked Pacific oysters (Crassostrea gigas)

When filter-feeding shellfish are consumed raw, because of their ability to concentrate and store waterborne pathogens, they are being increasingly associated with human gastroenteritis and have become recognized as important pathogen vectors. In the shellfish industry, UV depuration procedures are mandatory to reduce pathogen levels prior to human consumption. However, these guidelines are based around more susceptible fecal coliforms and Salmonella spp. and do not consider Cryptosporidium spp., which have significant resistance to environmental stresses. Thus, there is an urgent need to evaluate the efficiency of standard UV depuration against the survival of Cryptosporidium recovered from shellfish. Our study found that in industrial-scale shellfish depuration treatment tanks, standard UV treatment resulted in a 13-fold inactivation of recovered, viable C. parvum oocysts from spiked (1 x 10(6) oocysts liter (-1)) Pacific oysters. Depuration at half power also significantly reduced (P < 0.05; ninefold) the number of viable oocysts recovered from oysters. While UV treatment resulted in significant reductions of recovered viable oocysts, low numbers of viable oocysts were still recovered from oysters after depuration, making their consumption when raw a public health risk. Our study highlights the need for increased periodic monitoring programs for shellfish harvesting sites, improved depuration procedures, and revised microbial quality control parameters, including Cryptosporidium assessment, to minimize the risk of cryptosporidiosis.

A field study evaluation for mitigating biofouling with chlorine dioxide or chlorine integrated with UV disinfection

The drinking water industry is continually seeking innovative disinfection strategies to control biofouling in transmission systems. This research, conducted in collaboration with the East Bay Municipal Utility District (EBMUD) in California, compared the efficacy of chlorine dioxide (ClO2) to free chlorine (Cl2) with and without pre-treatment with low-pressure ultraviolet (UV) light for biofilm control. An additional goal was to determine disinfection by-product (DBP) formation with each disinfection strategy. Annular reactors (ARs) containing polycarbonate coupons were used to simulate EBMUD's 90-mile aqueduct that transports surface water from a source reservoir to treatment facilities. ARs were dosed with chemical disinfectants to achieve a residual of 0.2 mg/L, which is a typical value mid-way in the aqueduct. The experiment matrix included four strategies of disinfection including UV/ClO2, ClO2, UV/Cl2 and Cl2. Two ARs acted as controls and received raw water (RW) or UV-treated water. The data presented show that the UV/ClO2 combination was most effective against suspended and attached heterotrophic (heterotrophic plate count, HPC) bacteria with 3.93 log and 2.05 log reductions, respectively. ClO2 was more effective than Cl2 at removing suspended HPC bacteria and similarly effective in biofilm bacterial removal. UV light alone was not effective in controlling suspended or biofilm bacteria compared to treatment with ClO2 or Cl2. Pre-treatment with UV was more effective overall for removal of HPC bacteria than treating with corresponding chemical disinfectants only; however, it did not lower required chemical dosages. Therefore, no significant differences were observed in DBP concentrations between ARs pre-treated with UV light and ARs not pre-treated. Disinfection with ClO2 produced fewer total trihalomethanes (TTHMs) and haloacetic acids (HAAs) than chlorination but did produce low levels of chlorite. These data indicate that replacing Cl2 with ClO2 would further control microbiological re-growth and minimize TTHM and HAA formation, but may introduce other DBPs.

Comparison of levels of inactivation of two isolates of Giardia lamblia cysts by UV light

The effects of 254-nm UV irradiation on two human isolates (WB and H3) of Giardia lamblia cysts were assessed using a collimated beam protocol and a Mongolian gerbil model. The levels of infection of cysts in the gerbils were assessed based on the presence of cysts in feces and the presence and activity of trophozoites in the small intestine of inoculated gerbils. The results suggest that there were differences in the infectivities of the WB and H3 isolates, as well as in susceptibilities of the parasites to UV light. Without UV exposure, gerbils were more readily infected by isolate H3 cysts. After UV exposure of the cysts, however, the gerbils were more susceptible to isolate WB cysts.

The application of bioluminescence assay with culturing for evaluating quantitative disinfection performance

Various methods, including bioluminescence assay, were investigated regarding their suitability for quantitatively evaluating the disinfection performance. Although bioluminescence assay itself has been widely reported as a rapid, easy and suitable method for analyzing live microorganisms, the limited sensitivity of its measurement (approximately 10(3)-10(4)cells/assay vial), which is insufficient for disinfection study, requires further study. Among three methods (amplifying by enzymatic method, membrane filtration, and amplification by culturing) examined for increasing the detection sensitivity, amplification by culturing showed the best performance as Escherichia coli was employed as an indicating microorganism. Even with a short culturing time of 4h, the detection limit of E. coli measurement was successfully improved 200-fold, and the analytical results were not dependent upon the state of E. coli growth (stationary state with E. coli stock suspension vs. growth state with E. coli). In addition, the analytical integrity of bioluminescence assay with culturing was further demonstrated in comparison with spread plate method as free chlorine and UV irradiation were employed in the disinfection study.

Comparison of most probable number-PCR and most probable number-foci detection method for quantifying infectious Cryptosporidium parvum oocysts in environmental samples

Microbial contamination of public water supplies is of significant concern, as numerous outbreaks, including Cryptosporidium, have been reported worldwide. Detection and enumeration of Cryptosporidium parvum oocysts in water supplies is important for the prevention of future cryptosporidiosis outbreaks. In addition to not identifying the oocyst species, the U.S. EPA Method 1622 does not provide information on oocyst viability or infectivity. As such, current detection strategies have been coupled with in vitro culture methods to assess oocyst infectivity. In this study, a most probable number (MPN) method was coupled with PCR (MPN-PCR) to quantify the number of infectious oocysts recovered from seeded raw water concentrates. The frequency of positive MPN-PCR results decreased as the oocyst numbers decreased. Similar results were observed when MPN was coupled to the foci detection method (MPN-FDM), which was done for comparison. For both methods, infectious oocysts were not detected below 10(3) seeded oocysts and the MPN-PCR and MPN-FDM estimates for each seed dose were generally within one-log unit of directly enumerated foci of infection. MPN-PCR estimates were 0.25, 0.54, 0 and 0.66 log(10) units higher than MPN-FDM estimates for the positive control, 10(5), 10(4) and 10(3) seed doses, respectively. The results show the MPN-PCR was the better method for the detection of infectious C. parvum oocysts in environmental water samples.

Inactivation of protozoan parasites in food, water, and environmental systems

Protozoan parasites can survive under ambient and refrigerated storage conditions when associated with a range of substrates. Consequently, various treatments have been used to inactivate protozoan parasites (Giardia, Cryptosporidium, and Cyclospora) in food, water, and environmental systems. Physical treatments that affect survival or removal of protozoan parasites include freezing, heating, filtration, sedimentation, UV light, irradiation, high pressure, and ultrasound. Ozone is a more effective chemical disinfectant than chlorine or chlorine dioxide for inactivation of protozoan parasites in water systems. However, sequential inactivation treatments can optimize existing treatments through synergistic effects. Careful selection of methods to evaluate inactivation treatments is needed because many studies that have employed vital dye stains and in vitro excystation have produced underestimations of the effectiveness of these treatments.

Detection of UV-induced thymine dimers in individual Cryptosporidium parvum and Cryptosporidium hominis oocysts by immunofluorescence microscopy

To investigate the effect of UV light on Cryptosporidium parvum and Cryptosporidium hominis oocysts in vitro, we exposed intact oocysts to 4-, 10-, 20-, and 40-mJ x cm-2 doses of UV irradiation. Thymine dimers were detected by immunofluorescence microscopy using a monoclonal antibody against cyclobutyl thymine dimers (anti-TDmAb). Dimer-specific fluorescence within sporozoite nuclei was confirmed by colocalization with the nuclear fluorogen 4',6'-diamidino-2-phenylindole (DAPI). Oocyst walls were visualized using either commercial fluorescein isothiocyanate-labeled anti-Cryptosporidium oocyst antibodies (FITC-CmAb) or Texas Red-labeled anti-Cryptosporidium oocyst antibodies (TR-CmAb). The use of FITC-CmAb interfered with TD detection at doses below 40 mJ x cm-2. With the combination of anti-TDmAb, TR-CmAb, and DAPI, dimer-specific fluorescence was detected in sporozoite nuclei within oocysts exposed to 10 to 40 mJ x cm-2 of UV light. Similar results were obtained with C. hominis. C. parvum oocysts exposed to 10 to 40 mJ x cm-2 of UV light failed to infect neonatal mice, confirming that results of our anti-TD immunofluorescence assay paralleled the outcomes of our neonatal mouse infectivity assay. These results suggest that our immunofluorescence assay is suitable for detecting DNA damage in C. parvum and C. hominis oocysts induced following exposure to UV light.

Synergistic inactivation of Cryptosporidium parvum using ozone followed by monochloramine in two natural waters

The effect of sequential exposure to ozone followed by monochloramine on inactivation of Cryptosporidium parvum oocysts suspended in untreated natural surface water from two different sources was studied in bench-scale batch reactors. Animal infectivity using neonatal CD-1 mice was used to measure oocyst inactivation. A statistically significant synergistic effect on oocyst inactivation was measured in both natural water samples studied. The magnitude of the effect measured in the natural water with lower turbidity, colour, and organic carbon concentration was comparable to that previously reported for oocysts suspended in buffered de-ionized water but was reduced considerably in the natural water with higher turbidity, colour and organic carbon concentration. Synergy increased with initial pH and with the degree of ozone pre-treatment but was independent of temperature. For water treatment plants with adequate disinfectant contact times, ozone followed by monochloramine may be a practical means of achieving additional C. parvum inactivation, however, the influence of water quality characteristics should be considered.

Pulsed ultra-violet inactivation spectrum of Escherichia coli

Inactivation of Escherichia coli is examined using ultra-violet (UV) radiation from a pulsed xenon flashlamp. The light from the discharge has a broadband emission spectrum extending from the UV to the infrared region with a rich UV content. The flashlamp provides high-energy UV output using a small number of short-duration pulses (30 micros). The flashlamp is used with a monochromator to investigate the wavelength sensitivity of E. coli to inactivation by the pulsed UV light. Using 8 nm wide pulses of UV radiation, the most efficient inactivation is found to occur at around 270 nm and no inactivation is observed above 300 nm. A pyroelectric detector allows the energy dose to be determined at each wavelength, and a peak value for E. coli population reduction of 0.43 log per mJ/cm(2) is measured at 270 nm. The results are compared with the published data available for continuous UV light sources.

Effect of lot variability on ultraviolet radiation inactivation kinetics of Cryptosporidium parvum oocysts

Numerous studies have demonstrated the efficiency of ultraviolet (UV) radiation for the inactivation of oocysts of Cryptosporidium parvum. In these studies inactivation is measured as reduction in oocysts. A primary goal is to estimate the UV radiation required to achieve a high degree of inactivation. Different lots of Cryptosporidium parvum oocysts are used in these studies, and the inactivation rate may vary depending on the lot of oocysts used. The goal of this paper is to account for the error in estimating the amount of inactivation after exposure to UV radiation, and for the effect of lot variability in determining the required UV radiation. A Bayesian approach is used to simultaneously model the logistic dose-response model and the UV inactivation kinetic model. The oocysts lot variability is incorporated using a hierarchical Bayesian model. Posterior distributions using Markov Chain Monte Carlo method is used to obtain estimates and Bayesian credible interval for the required UV radiation to achieve a given inactivation level of Cryptosporidium parvum oocysts.

UV inactivation of Cryptosporidium hominis as measured in cell culture

The Cryptosporidium spp. UV disinfection studies conducted to date have used Cryptosporidium parvum oocysts. However, Cryptosporidium hominis predominates in human cryptosporidiosis infections, so there is a critical need to assess the efficacy of UV disinfection of C. hominis. This study utilized cell culture-based methods to demonstrate that C. hominis oocysts displayed similar levels of infectivity and had the same sensitivity to UV light as C. parvum. Therefore, the water industry can be confident about extrapolating C. parvum UV disinfection data to C. hominis oocysts.

The response of Cryptosporidium parvum to UV light

Ultraviolet (UV) light is being considered as a disinfectant by the water industry because it appears to be very effective for controlling potential waterborne pathogens, including Cryptosporidium parvum. However, many organisms have mechanisms such as nucleotide excision repair and photolyase enzymes for repairing UV-induced DNA damage and regaining preirradiation levels of infectivity or population density. Genes encoding UV repair proteins exist in C. parvum, so the parasite should be able to regain infectivity following exposure to UV. Nevertheless, there is an increasing body of evidence that the organism is unable to reactivate following UV irradiation. This paper describes the effective inactivation of C. parvum by UV light, identifies nucleotide excision repair genes in the C. parvum and Cryptosporidium hominis genomes and discusses the inability of UV-exposed oocysts to regain infectivity.

Irreversible UV inactivation of Cryptosporidium spp. despite the presence of UV repair genes

Ultraviolet light is being considered as a disinfectant by the water industry because it appears to be very effective for inactivating pathogens, including Cryptosporidium parvum. However, many organisms have mechanisms for repairing ultraviolet light-induced DNA damage, which may limit the utility of this disinfection technology. Inactivation of C. parvum was assessed by measuring infectivity in cells of the human ileocecal adenocarcinoma HCT-8 cell line, with an assay targeting a heat shock protein gene and using a reverse transcriptase polymerase chain reaction to detect infections. Oocysts of five different isolates displayed similar sensitivity to ultraviolet light. An average dosage of 7.6 mJ/cm2 resulted in 99.9% inactivation, providing the first evidence that multiple isolates of C. parvum are equally sensitive to ultraviolet disinfection. Irradiated oocysts were unable to regain pre-irradiation levels of infectivity, following exposure to a broad array of potential repair conditions, such as prolonged incubation, pre-infection excystation triggers, and post-ultraviolet holding periods. A combination of data-mining and sequencing was used to identify genes for all of the major components of a nucleotide excision repair complex in C. parvum and Cryptosporidium hominis. The average similarity between the two organisms for the various genes was 96.4% (range, 92-98%). Thus, while Cryptosporidum spp. may have the potential to repair ultraviolet light-induced damage, oocyst reactivation will not occur under the standard conditions used for storage and distribution of treated drinking water.

Drinking water treatment processes for removal of Cryptosporidium and Giardia

Major waterborne cryptosporidiosis and giardiasis outbreaks associated with contaminated drinking water have been linked to evidence of suboptimal treatment. Cryptosporidium parvum oocysts are particularly more resistant than Giardia lamblia cysts to removal and inactivation by conventional water treatment (coagulation, sedimentation, filtration and chlorine disinfection); therefore, extensive research has been focused on the optimization of treatment processes and application of new technologies to reduce concentrations of viable/infectious oocysts to a level that prevents disease. The majority of the data on the performance of treatment processes to remove cysts and oocysts from drinking water have been obtained from pilot-tests, with a few studies performed in full-scale conventional water treatment plants. These studies have demonstrated that protozoan cyst removal throughout all stages of the conventional treatment is largely influenced by the effectiveness of coagulation pretreatment, which along with clarification constitutes the first treatment barrier against protozoan breakthrough. Physical removal of waterborne Crytosporidium oocysts and Giardia cysts is ultimately achieved by properly functioning conventional filters, providing that effective pretreatment of the water is applied. Disinfection by chemical or physical methods is finally required to inactivate/remove the infectious life stages of these organisms. The effectiveness of conventional (chlorination) and alternative (chlorine dioxide, ozonation and ultra violet [UV] irradiation) disinfection procedures for inactivation of Cryptosporidium has been the focus of much research due to the recalcitrant nature of waterborne oocysts to disinfectants. This paper provides technical information on conventional and alternative drinking water treatment technologies for removal and inactivation of the protozoan parasites Cryptosporidium and Giardia.