Disinfectants contamination

Phenol coefficient tests were developed in the early 20th century when typhoid fever was a significant public health problem and phenolics were used to disinfect contaminated utensils and other inanimate objects. Details of such tests can be found in earlier editions of this book. However, as non-phenolic disinfectants became more widely available, tests that more closely paralleled the conditions under which disinfectants were being used (e.g. blood spills) and which included a more diverse range of microbial types (e.g. viruses, bacteria, fungi, protozoa) were developed. Evaluation of a disinfectant s efficacy was based on its ability to kill microbes, i.e. its cidal activity, under environmental conditions mimicking as closely as possible real life situations. As an essential component of each test was a final viability assay, removal or neutralization of any residual disinfectant became a significant consideration. 

Cellulose filters have been coated with aramid. Then, the coated filters were then chlorinated in a hypochlorite solution. The chlorinated and unchlorinated filters were checked for their ability to disinfect contaminated water. The chlorinated variant produced a reduction of 10 (5 log [109]) of Escherichia coli and Staphylococcus aureus, which was much higher than that observed on the unchlorinated aramid-coated cellulose filter [110]. 

When removing a syringe and needle from a rubber-stoppered bottle, wrap the needle and stopper in a cotton pledget moistened with the proper disinfectant (209). If there is danger of the disinfectant contaminating sensitive experiments, a sterile dry pledget may be used and discarded immediately into disinfectant solution. 

Sterilize or disinfect contaminated materials (cultures, used glassware, serological discards, etc.) by autoclaving before throwing them away or processing for reuse. Use a germicidal soap and hot water, or an autoclave, as appropriate for the type of analysis involved. All cell culture glassware is to be autoclaved. 

The goal of filtration in the modem municipal treatment plant is a maximum of 0.1 ntu (nephelometric turbidity unit), which ensures a sparkling, clear water (8). Freedom from disease organisms is associated with freedom from turbidity, and complete freedom from taste and odor requites no less than such clarity. The National Interim Primary Drinking Water Regulations (NIPDWR) requite that the maximum contaminant level for turbidity at the point of entry into the distribution system be 1.0 ntu unless it can be shown that levels up to 5 ntu do not interfere with disinfection, interfere with the maintenance of a chlorine residual in the distribution system, nor interfere with bacteriological analyses. 

However, these systems have been shown to be ineffective in either disinfection, algae prevention, or oxidation of swimming-pool contaminants. 

Potable Water Treatment. Treatment of drinking water accounts for about 24% of the total activated carbon used in Hquid-phase apphcations (74). Rivers, lakes, and groundwater from weUs, the most common drinking water sources, are often contaminated with bacteria, vimses, natural vegetation decay products, halogenated materials, and volatile organic compounds. Normal water disinfection and filtration treatment steps remove or destroy the bulk of these materials (75). However, treatment by activated carbon is an important additional step in many plants to remove toxic and other organic materials (76—78) for safety and palatability. 

Povidone—iodine is a brown, water-soluble powder containing approximately 10% iodine. However, the amount of free iodine, which is responsible for the antimicrobial activity, is low in a concentrated solution, but is released as the solution is diluted (41). Concentrated solutions have actually been contaminated with bacteria (42). For use as an antiseptic, povidine—iodine is diluted with water or alcohol to a concentration of 1% iodine. Detergents are added if it is used as a surgical scmb. lodophors are important as broad-spectmm antiseptics for the skin, although they do not have the persistent action of some other antiseptics. They are also used as disinfectants for clinical thermometers that have been used by tuberculous patients, for surface disinfection of tables, etc, and for clean equipment in hospitals, food plants, and dairies, much as chlorine disinfectants are used. 

Available Chlorine Test. The chlorine germicidal equivalent concentration test is a practical-type test. It is called a capacity test. Under practical conditions of use, a container of disinfectant might receive many soiled, contaminated instniments or other items to be disinfected. Eventually, the capacity of the disinfectant to serve its function would be overloaded due to reaction with the accumulated organic matter and organisms. The chlorine germicidal equivalent concentration test compares the load of a culture of bacteria that a concentration of a disinfectant will absorb and still kill bacteria, as compared to standard concentrations of sodium hypochlorite tested similarly. In the test, 10 successive additions of the test culture are added to each of 3 concentrations of the hypochlorite. One min after each addition a sample is transferred to the subculture medium and the next addition is made 1.5 min after the previous one. The disinfectant is then evaluated in a manner similar to the phenol coefficient test. For equivalence, the disinfectant must yield the same number of negative tubes as one of the chlorine standards. 

One of the most widespread methods of water disinfection is it s chlorination. As chloration products ai e toxic, their content is to be controlled. Among them free chlorine and inorganic chloramines ai e predominant in water. Maximum contaminant limit for free chlorine is 0.3 - 0.5 mg/L, for chloramines - 0.8 - 1.2 mg/L. 

Regular cleaning of contamination from, or disinfection of, walls, surfaces etc. 

Modify the environment After cleaning and disinfecting an area that is contaminated by fungal or bacterial growth, control humidity to make conditions inhospitable for regrowth. 

Maximum Residual Disinfectant Level (MRDL) - The highest level of a disinfectant allowed in drinking water. There is convincing evidence that addition of a disinfectant is necessary for control of microbial contaminants. 

Disinfectants Disinfection Byproducts MCLG (mg/L) MCL or TT (mg/L) Potential Health Effects from Ingestion of Water Sources of Contaminant in Drinking Water... 

EPA s surface water treatment rules require systems using surface water or ground water under the direct influence of surface water to (1) disinfect their water, and (2) filter their water or meet criteria for avoiding filtration so that the following contaminants are controlled at the following levels ... 

Coagulation, flocculation, sedimentation, and filtration will remove many contaminants. Perhaps most important is the reduction of turbidity. This treatment yields water of good clarity and enhances disinfection efficiency. If particles are not removed, they harbor bacteria and make fmal disinfection more difficult. 

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