Available Chlorine Concentration Research Articles

The shelf-life of sodium hypochlorite irrigating solutions.

Sodium hypochlorite (bleach) solutions are widely used as irrigants in endodontics. Their tendency to deteriorate is worsened by environmental influences which could cause loss of available chlorine content. This study measured the loss of available chlorine concentration in a range of sodium hypochlorite solutions under conditions which mimic clinical usage and storage. Domestic bleach, both undiluted and diluted with demineralised water or hard water, was tested, along with Milton, for initial concentration of available chlorine, and then retested after varying periods and modes of storage to measure loss of chlorine concentration. The types of storage were: (1) in closed plastic bottles which were opened daily and agitated; (2) in open plastic bottles; (3) in syringes exposed to sunlight; (4) in syringes kept in the dark; (5) in open stainless steel bowls; (6) in closed stainless steel bowls; and (7) when heated to 50 degrees C. Not all solutions were tested under all storage conditions. Of the solutions opened daily, undiluted domestic bleach was the most stable and Milton was the least stable. Initially, diluted bleach left open deteriorated rapidly but deterioration slowed with time. Solutions in syringes exposed to sunlight showed the most rapid loss of chlorine content. Heated bleach lost nearly 5 per cent of its strength in six hours. Diluted bleach surprisingly, increased its chlorine concentration in open bowls probably due to evaporation of water. Dilution of bleach with hard tap water did not significantly affect shelf-life. Preloading of diluted bleach into syringes appears to be a sound technique if the syringes are stored away from light. This study reinforces the need for sodium hypochlorite to be stored in closed opaque containers. Constant opening of containers appears to cause greater loss in chlorine concentration of diluted bleach solutions, perhaps because a lower concentration of sodium hydroxide allows the pH to drop more rapidly.

Stability and bactericidal activity of chlorine solutions.

To determine the stability of sodium hypochlorite (diluted household bleach) when stored for 30 days in various types of containers and to determine the efficacy of low concentrations of free available chlorine to inactivate test bacteria. Laboratory-based study. Solutions of standard household bleach were prepared using tap water or sterile distilled water at dilutions of 1:100, 1:50, and 1:5. Chlorine concentrations were measured, and then the solutions were placed into five polyethylene containers and left at room temperature (20 degrees C) under various conditions (translucent containers with light exposure and with or without air; brown opaque container without light or air exposure). Samples for chlorine and pH determinations were taken at time 0 and on days 7, 14, 21, 30, and 40. Bactericidal activity of chlorine solutions was assessed using the Association of Official Analytical Chemists Use-Dilution Method. Test bacteria included Pseudomonas aeruginosa, Staphylococcus aureus, and Salmonella choleraesuis. Chlorine concentrations at 30 days varied from the 40% to 50% range for 1:50 or 1:100 dilutions stored in containers other than closed brown containers to 83% to 85% for the 1:5 dilution stored in closed but non-opaque containers to 97% to 100% for 1:50 or 1:5 solutions stored in closed brown containers. The lowest concentration of sodium hypochlorite solution that reliably inactivated all the test organisms was 100 ppm. These data suggest that chlorine solutions do not need to be prepared fresh daily, as is recommended currently, and the lowest concentration of chlorine that reliably inactivates S aureus, S choleraesuis, and P aeruginosa is 100 ppm.

Stability and Bactericidal Activity of Chlorine Solutions

To determine the stability of sodium hypochlorite (diluted household bleach) when stored for 30 days in various types of containers and to determine the efficacy of low concentrations of free available chlorine to inactivate test bacteria.Laboratory-based study. Solutions of standard household bleach were prepared using tap water or sterile distilled water at dilutions of 1:100, 1:50, and 1:5. Chlorine concentrations were measured, and then the solutions were placed into five polyethylene containers and left at room temperature (20 degrees C) under various conditions (translucent containers with light exposure and with or without air; brown opaque container without light or air exposure). Samples for chlorine and pH determinations were taken at time 0 and on days 7, 14, 21, 30, and 40. Bactericidal activity of chlorine solutions was assessed using the Association of Official Analytical Chemists Use-Dilution Method. Test bacteria included Pseudomonas aeruginosa, Staphylococcus aureus, and Salmonella choleraesuis.Chlorine concentrations at 30 days varied from the 40% to 50% range for 1:50 or 1:100 dilutions stored in containers other than closed brown containers to 83% to 85% for the 1:5 dilution stored in closed but non-opaque containers to 97% to 100% for 1:50 or 1:5 solutions stored in closed brown containers. The lowest concentration of sodium hypochlorite solution that reliably inactivated all the test organisms was 100 ppm.These data suggest that chlorine solutions do not need to be prepared fresh daily, as is recommended currently, and the lowest concentration of chlorine that reliably inactivates S aureus, S choleraesuis, and P aeruginosa is 100 ppm.

Inactivation of HIV-1 by chemical disinfectants: sodium hypochlorite

The efficacy of sodium hypochlorite was assessed against human immunodeficiency virus type 1 suspended in low (8% v/v) or high (80% v/v) concentrations of serum or in a high (80%) concentration of blood. In the presence of 8% serum, 100 p.p.m. available chlorine in the disinfectant test mixture inactivated 3.75 log TCID50 HIV/ml within 30 s. When the test mixture contained 80% serum, 500 p.p.m. available chlorine inactivated more than 4 log TCID50 HIV/ml in 1-2 min. Lower concentrations of available chlorine were unable to inactivate the virus completely. In the presence of 80% blood, 1000 p.p.m. available chlorine in the disinfectant test mixture was unable to inactivate 3.75 log TCID50 HIV/ml, although 2500 p.p.m. available chlorine was able to inactivate at least 1.5 log TCID50 HIV/ml. In all test mixtures, the chlorine rapidly became combined and thus less active. Our results emphasise the importance of cleaning prior to disinfection with sodium hypochlorite since it may prove to be ineffective in the presence of high levels of organic matter. In cases where prior cleaning is impossible, care must be taken to use the higher recommended concentration (a minimum of 10,000 p.p.m. available chlorine).

Effectiveness of Commercial Germicide Products Against the Ropy Slime-Producing Lactic Acid Bacteria

The effectiveness of certain commercial germicides against ropy slime-producing lactic acid bacteria was studied using the 5-5-5-suspension test and a tray test which simulated surface disinfection conditions in actual use. The rate of the destruction of the bacteria was lower in the tray test, and the bacteria seemed to be more resistant to the germicides on a steel surface than in vitro. The sanitizer products proved to be more effective than the detergent-sanitizer products. Quaternary ammonium products and an acid sanitizer with hydrogen peroxide were more effective than products containing chlorine compounds and polyhexamethylene biguanide chloride. The effectiveness of hypochlorite products appeared to be dependent on the concentration of available chlorine. The resistance of the ropy slime-producing bacteria may prove problematic if ineffective germicides are used. The use of detergent sanitizers and low-concentration hypochlorite products is not recommended.

Efficacies of selected disinfectants against Mycobacterium tuberculosis

The activities of 10 formulations as mycobactericidal agents in Mycobacterium tuberculosis-contaminated suspensions (suspension test) and stainless steel surfaces (carrier test) were investigated with sputum as the organic load. The quaternary ammonium compound, chlorhexidine gluconate, and an iodophor were ineffective in all tests. Ethanol (70%) was effective against M. tuberculosis only in suspension in the absence of sputum. Povidone-iodine was not as efficacious when the test organism was dried on a surface as it was in suspension, and its activity was further reduced in the presence of sputum. Sodium hypochlorite required a higher concentration of available chlorine to achieve an effective level of disinfection than did sodium dichloroisocyanurate. Phenol (5%) was effective under all test conditions, producing at least a 4-log10 reduction in CFU. The undiluted glutaraldehyde-phenate solution was effective against M. tuberculosis and a second test organism, Mycobacterium smegmatis, even in the presence of dried sputum, whereas the diluted solution (1:16) was only effective against M. smegmatis in the suspension test. A solution of 2% glutaraldehyde was effective against M. tuberculosis. This investigation presents tuberculocidal efficacy data generated by methods simulating actual practices of routine disinfection.

Inactivation of Listeria Monocytogenes by Chlorine

Cells of Listeria monocytogenes strain Scott-A were harvested from cultures, washed, and then treated with a solution of sodium hypochlorite at 25°C and pH 7. The cells were more resistant to chlorine when they were (a) harvested from a 24-rather than 48-h-old culture, (b) grown in tryptose broth rather than on a slant of tryptose agar, and (c) washed and suspended using a 20 rather than 0.312mM phosphate buffer solution. Cells of L. monocytogenes were exposed for 30 s-4 h to sodium hypochlorite solutions that contained 0.5–10 ppm available chlorine. Generally, the number of survivors decreased rapidly during the first 30 s followed by a slower decrease during the rest of the exposure time. The initial count of L. monocytogenes in the suspension (1 × 108–3.2 × 108/ml) decreased 0.49 to 6.4 orders of magnitude during the first 30 s of exposure to the chlorine solutions. The effect of the presence of organic substances on the strength of hypochlorite solutions was studied. Presence of 0.05 or 0.1% peptone caused a large and rapid loss of available chlorine. Glucose or lactose (up to 1%) had almost no effect on the concentration of available chlorine.

Effect of potassium iodide concentration on measurement of combined available chlorine.

In the chlorination of miscellaneous nitrogenous compounds contained in water, N-chloro compounds are formed from amine or imine in the compounds. Although the chlorine in N-chloro compounds has property of combined available chlorine, reactivity of each N-chloro compound is different each other. In the fractional determination of available chlorines by the N, N-diethyl-p-phenylene diamine (DPD) method or amperometric titration etc. different amounts of potassium iodide are added to differentiate each class of N-chloro compound. The velocity of color reaction of DPD depends mainly on the concentration of residual available chlorine. Consequently, the color development can be approximated by a first-order reaction. From the recorded curve of color development at 550 nm, periods to reach 85% and 95% value of the maximum absorbance are measured respectively. The rate constants of the first-order reaction K are calculated from these values. The rate constants increase in proportion to KI concentrations, and all experimental data points are essentially on a straight line. The time required to finish DPD color development and reciprocal of KI concentration are also correlated. In the case of added 30 μM KI, the DPD color development is completed within a period from 19 to 38 s, except chloropiperazine (over 80 s). The relationship between rate constant K and pKa of each N-compound has a good correlation.

A survey of Legionella pneumophila in water in 12 Canadian cities

A survey of 12 cities across Canada was conducted in order to determine the prevalence of Legionella species in potable water and cooling tower water within buildings. Legionellae were detected in 11.9% of the samples overall: 6.7% from potable water sources and 28.9% from cooling tower water. The maximum concentration of the organism was 45,000 l −1 in one shower-water sample by culture methods. A significant difference in the isolation rate of Legionella pneumophila among cities was observed. The organism was isolated from waters at a temperature of 15–41°C and was most frequently isolated in the 20–29°C range. The concentration of free and total available chlorine in the water was not associated with legionellae recovery except that the organisms were never recovered when the free available chlorine residual exceeded 7.5 mg l −1. Although L. pneumophila were in low concentrations or absent in most samples, the isolated organisms were usually serogroups 1 or 6, the same serogroups that are most often implicated in legionellosis cases in Canada.

Immunological and biophysical alteration of hepatitis B virus antigens by sodium hypochlorite disinfection.

Sodium hypochlorite (NaOCl) was examined as an effective disinfectant in hepatitis laboratories. Concentrations of NaOCl containing 5,600 ppm (5,600 microgram/ml) of available chlorine were found to be effective in destroying the antigenicity of hepatitis B surface antigen (HBsAg) in virion-rich plasma after an exposure time of 1 min or more. In the treatment of protein-deficient solutions containing HBsAg, smaller concentrations of available chlorine (less than 500 pm) are equally effective. Neither 17-to 25-nm HBsAg particles nor 45-nm virion particles could be detected by electron microscopy after treatment. chemical interaction of protein and NaOCl was confirmed by isoelectrofocusing of 125I-labeled HBsAg. More than 90% of the labeled material was found at pH 3.0 or lower, indicating complete antigen oxidation. Labeled HBsAg was reduced in density from 1.21 g/cm3 in CsCl to approximately 1.07 g/cm3 after treatment with NaOCl. Both hepatitis B core antigen and deoxyribonucleic acid polymerase activity were significantly reduced after interaction with hypochlorite solutions. These results show that NaOCl destroys hepatitis B antigenicity and virus structures and therefore may be utilized as a disinfectant for the virus.

Hygienic Studies on Drinking Water. I. Disappearance of Residual Chlorine in Water Supply during Storage in Water Tanks

In order to estimate the rate of disappearance of free available chlorine during storage in water tanks, the rate of vaporization of free available chlorine was studied and the rate of the chlorine consumption caused presumably by components in water supply, though the components were unknown, was also investigated. The rate of vaporization was proportional to the air-water interfacial area, but it was independent of the water level and the initial concentration of free available chlorine. A linear relationship exists between the logarithm of the rate of vaporization and the reciprocal of absolute water temperature. The consumption caused by the components in water supply was approximately accounted for the first order reaction. However, the rate constant for consumption varied inversely as the initial concentration of free available chlorine. The constant was not a true one. The apparent rate constant was proportional to the fourth power of water temperatnre. Our proposed model was able to give an adequate explanation of the whole course of the disappearance of free available chlorine during storage in water tanks.

The effects of chlorination of wastewater on fertilization in some marine invertebrates

Unchlorinated domestic sewage was found to be a relatively weak inhibitor of external fertilization in 3 marine invertebrates. Chlorinated sewage was a potent spermicide, active in inhibiting fertilization in concentrations of available chlorine as low as 0.05 ppm. Sodium hypochlorite in seawater duplicated the effect, and excess sodium thiosulfate terminated it. The possibility of chlorine disinfection affecting reproductive success in the vicinity of outfalls is discussed.

Effect of algicidal quaternaries on the germicidal activity of chlorine on swimming pool water.

The Swimming Pool Water Disinfectant Test Method of the Association of Official Analytical Chemists was used to determine the effect of the accepted level of 2 ppm of some commercial quaternary ammonium algicides on the germicidal activity of chlorine. Accurate determinations on the amounts of residual available chlorine in chlorine-quaternary mixtures could not be made by the usual chemical methods. This made it necessary to base all comparisons on the starting concentrations of available chlorine rather than the final concentration as specified in the method employed. No evidence was obtained to support the use of lower concentrations of residual available chlorine for disinfection in the presence of algicidal quaternaries than those commonly recognized as effective by the American Public Health Association. The rate of kill against the gram-positive test organism Streptococcus faecalis was faster in quaternary-chlorine mixtures than in the sodium hypochlorite control solutions. The practical significance of this result in the bench method identified cannot be ascertained in the absence of more sensitive and precise chemical procedures for determining concentrations of residual available chlorine in the presence of quaternaries or in actual swimming pool tests.

Effect of Algicidal Quaternaries on the Germicidal Activity of Chlorine on Swimming Pool Water

The Swimming Pool Water Disinfectant Test Method of the Association of Official Analytical Chemists was used to determine the effect of the accepted level of 2 ppm of some commercial quaternary ammonium algicides on the germicidal activity of chlorine. Accurate determinations on the amounts of residual available chlorine in chlorine-quaternary mixtures could not be made by the usual chemical methods. This made it necessary to base all comparisons on the starting concentrations of available chlorine rather than the final concentration as specified in the method employed. No evidence was obtained to support the use of lower concentrations of residual available chlorine for disinfection in the presence of algicidal quaternaries than those commonly recognized as effective by the American Public Health Association. The rate of kill against the gram-positive test organism Streptococcus faecalis was faster in quaternary-chlorine mixtures than in the sodium hypochlorite control solutions. The practical significance of this result in the bench method identified cannot be ascertained in the absence of more sensitive and precise chemical procedures for determining concentrations of residual available chlorine in the presence of quaternaries or in actual swimming pool tests.

Chlorination in poultry processing

Summary The effect of relatively high concentrations of available chlorine in the tanks used for chilling freshly eviscerated chickens on their shelf‐life at 1° C. and on their appearance, taste and odour has been studied. The nominal initial concentrations of available chlorine that were used were (in p.p.m.): 50, 100, 200, 400, 1000, 2000, 4000 and 8000. The carcasses were immersed in the slush ice for 4 hr. and after this time 20–30 per cent of the initial level, up to 200 p.p.m., was detected as combined chlorine when the contents of the tanks had been stirred between the 2nd and 3rd hr. Under these conditions and with an initial nominal concentration of available chlorine of 200 p.p.m. shelf‐life at 1° C. was extended by about 20 per cent. Panels of observers detected no significant effect on appearance, taste or odour and the results of a small‐scale consumer trial supported these findings. Initial concentrations of available chlorine of 500 p.p.m. and more resulted in tainted carcasses.

Factors Influencing the Effectiveness of Fresh Fish Washing Operations

The effects of ratio of the amount of fish to that of wash water, kinetic energy of impinging water, method of water application and concentration of available chlorine in the wash water on the washing of eviscerated fresh cod of various caught-ages were studied. The studies were designed to provide information of practical value to engineers interested in designing machines to wash slime and bacteria from fish received at filleting plants. A quantitative relation between kinetic energy of impinging wash water and fish to water ratio was established for one practical type of spray washing equipment. Effective spraying was found to be more efficient than fluming or dipping. However, fish dipped several times in water deposited less bacterial load on a clean surface than fish washed effectively on the skin side only by a jet of water. Thus, washing out the body cavity was found to be important. Caught-age was found to influence the results only for washing methods of relatively low effectiveness, namely in fluming and in washing inefficiently with a jet or spray of water. Ineffective spray washing was shown to be associated with waste of equipment and high costs while serving no useful production purpose. Highly effective methods of spray washing fish of all caught-ages were shown to be suitable for efficient application in fish filleting and skinning lines. Free chlorine concentrations as high as 100 ppm in the wash water did not increase washing effectiveness as measured by a bacteriological method.

The Fresh-Water Annelid, Tubifex, as a Pharmacological Test Object

A study of the regeneration of the fresh-water annelid, Tubifex, necessitated an evaluation of the factors conducing to its survival in the laboratory. Other workers, have observed its satisfactory survival in tap-water. Our own experience has shown that it will not survive in the tap-water of New Orleans. The significant differences between the tap-water of New Orleans and the compatible tap-water of other cities appear to be the higher concentration of hydroxyl ion (pH 9-10) and the higher concentration of available chlorine of the water of this city. The chlorine content of New Orleans tap-water is stabilized at a minimum of 0.7 ppm by the addition of ammonium salts. To investigate the influence of the reaction of the medium on the survival of Tubifex, solutions buffered with phosphate to cover the range from pH 6 to pH 8.3 were prepared. In the original solutions where the concentration of phosphate ion was 0.03 M there was no survival. The criterion of toxicity was death of all animals at the end of the arbitrarily chosen period of 18 hours. To ascertain at what concentrations of phosphate ion survival would result, a graded series of concentrations of phosphate ion for separate concentrations of hydroxyl ion from pH 4.6 to pH 8.4 were prepared. It was observed that Tubifex does survive in aqueous media if the phosphate ion concentration is low enough and also that the toxicity of phosphate ion is increased if the hydroxyl ion is increased. The toxicity seems to be a conjunctive result of phosphate ion with hydroxyl ion rather than an intrinsic toxicity of hydroxyl ion. This interpretatioll is strengthened by the survival of Tubifex in aqueous media from which phosphate ion was excluded in the range pH 5.0 to 9.5.