Analysis of Inactivation of Giardia Lamblia by Chlorine

Clark, Robert M.; Read, Eleanor J.; Hoff, John C.

doi:10.1061/(asce)0733-9372(1989)115:1(80)

Cited by 37 publications

(22 citation statements)

References 7 publications

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“…As indicated previously C't values have been found to be a function of pH, temperature, disinfectant concentration and level of inactivation [7]. Therefore in this study, dividing both sides of equation 5 by C"" 1 yields:…”

Section: Effect Of Other Variablessupporting

confidence: 58%

Development ofGiardia C · tvalues for the surface water treatment rule

Clark¹,

Regli

1993

Journal of Environmental Science and Health . Part A: Environme

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As a consequence of the 1986 Amendments to the Safe Drinking Water Act (SDWA) the U.S. EPA has issued a Surface Water Treatment Rule (SWTR) for systems using surface and ground waters under the direct influence of surface water. In the Guidance Manual to the SWTR, the EPA recommends C·t values (product of disinfection concentration in milligrams per liter and disinfectant contact time in minutes) for different disinfectants to achieve required levels of inactivation for Giardia lamblia. This paper describes the procedure by which C·t values were calculated for Giardia lamblia by chlorine disinfection in the SWTR. A model has been developed which can be used to approximate the C't values that are embodied in the SWTR. It was found that C·t values increased due to higher pH, the level of inactivation required, and chlorine concentration, and were inversely related to temperature.

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Section: Effect Of Other Variablessupporting

confidence: 58%

Development ofGiardia C · tvalues for the surface water treatment rule

Clark¹,

Regli

1993

Journal of Environmental Science and Health . Part A: Environme

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“…There is a general phenomenon that occurs as pH increases, viz. the germicidal activity of chlorine decreases (Clark et al 1989). Using the formula developed by Clark et al (1989), adjustment of pH from 9 to 7 should double toxicity (based on results with Giardia, Health Canada 2004).…”

Section: Discussionmentioning

confidence: 99%

“…the germicidal activity of chlorine decreases (Clark et al 1989). Using the formula developed by Clark et al (1989), adjustment of pH from 9 to 7 should double toxicity (based on results with Giardia, Health Canada 2004). The most germicidal form of chlorine is HOCl, and above pH 7.5 less exists as this active form, while most becomes the less active form OCl -.…”

Section: Discussionmentioning

confidence: 99%

“…Furthermore, we compared our results to previous studies by evaluating Encephalitozoon cuniculi with our SYTOX staining. We also conducted assays with various chlorine concentrations in which the pH of the solution was adjusted to pH 7, as chlorine is less toxic to microorganisms at higher pH values (Clark et al 1989). Finally, we conducted an experimental exposure of zebrafish larvae to Pseudoloma neurophilia spores treated with various concentrations of chlorine to corroborate our in vitro findings.…”

Section: Introductionmentioning

confidence: 99%

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Spores of two fish microsporidia (Pseudoloma neurophilia and Glugea anomala) are highly resistant to chlorine

Ferguson¹,

Watral²,

Schwindt³

et al. 2007

Dis. Aquat. Org.

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Pseudoloma neurophilia (Microsporidia) is the most common pathogen found in zebrafish Danio rerio research facilities. The parasite is associated with marked emaciation. Zebrafish laboratories usually disinfect eggs to prevent transmission of pathogens, typically with chlorine at 25 to 50 ppm for 10 min. The ability of chlorine to kill spores of P. neurophilia and 2 other microsporidia, Glugea anomala and Encephalitozoon cuniculi, was evaluated using 2 viability stains. SYTOX ® Green was used to visualize dead spores, and live spores were identified by their ability to extrude polar tubes in Fungi-Fluor™ solution following UV exposure. Results with both stains were similar at various chlorine concentrations for P. neurophilia and G. anomala, but Fungi-Fluor was not useful for E. cuniculi, due to the much smaller spore size. Using the SYTOX stain, we found that 5 ppm chlorine for 10 min causes 100% death in spores of E. cuniculi, which was similar to findings in other studies. In contrast, the spores of P. neurophilia and G. anomala were much more resistant to chlorine, requiring >100 or 1500 ppm chlorine, respectively, to achieve > 95% spore death. Repeating chlorine exposures with spores of P. neurophilia using solutions adjusted to pH 7 increased the efficacy of 100 ppm chlorine, achieving > 99% spore inactivation. We corroborated our viability staining results with experimental exposures of zebrafish fry, achieving heavy infections in fry at 5 to 7 d postexposure in fish fed spores treated at 50 ppm (pH 9). Some fish still became infected with spores exposed to 100 ppm chlorine (pH 9.5). This study demonstrates that spores of certain fish microsporidia are highly resistant to chlorine, and indicates that the egg disinfection protocols presently used by most zebrafish research facilities will not prevent transmission of P. neurophilia to progeny.KEY WORDS: SYTOX Green · Fungi-Fluor · Pseudoloma neurophilia · Glugea anomala · Encephalitozoon cuniculi · Chlorine toxicity · Viability staining Resale or republication not permitted without written consent of the publisher

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“…These studies are included in developing the proposed general model for Ct values. Clark et al [3] described the procedure by which Ct values were calculated in the Guidance Manual for the SWTR, based on earlier work [4] utilizing the Chick-Watson theory, in which the survival rate of microorganisms is linked to a first order chemical reaction…”

Section: Introductionmentioning

confidence: 99%

Estimation of Giardia Ct Values at High pH for the Surface Water Treatment Rule

Sivaganesan

Rice

2003

Journal of Environmental Science and Health, Part A

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The U.S. Environmental Protection Agency currently recommends Ct (disinfectant concentration multiplied by the exposure time) values to achieve required levels of inactivation of Giardia lamblia cysts by different disinfectants including free chlorine. Current guidance covers inactivation levels in the pH range between 6 and 9. Subsequent to the publication of these criteria, studies on the inactivation kinetics of Giardia cysts by chlorine have been performed at pH levels greater than 9. It has been shown that the chlorine inactivation process for Giardia cysts is pH dependent. The objective of this paper is to extend the current Ct values for higher pH levels. The Chick-Watson first order kinetics model was used to develop Ct values for pH levels from 6 to 11.5. A formula is provided to calculate a 100(1 - alpha)% upper confidence bound for these values.

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Analysis of Inactivation of Giardia Lamblia by Chlorine

Cited by 37 publications

References 7 publications

Development ofGiardia C · tvalues for the surface water treatment rule

Development ofGiardia C · tvalues for the surface water treatment rule

Spores of two fish microsporidia (Pseudoloma neurophilia and Glugea anomala) are highly resistant to chlorine

Estimation of Giardia Ct Values at High pH for the Surface Water Treatment Rule

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