i. Chlorine Compounds (e.g., Household Bleach)

Chlorine compounds are good disinfectants on clean surfaces, but are quickly  inactivated by organic matter, thus, reducing their biocidal activity. They have a broad spectrum of antimicrobial activity and are inexpensive and fast acting. Hypochlorites, the most widely used of the chlorine disinfectants, are available in liquid (e.g., Sodium hypochlorite), household bleach and solid (e.g., calcium hypochlorite, sodium dichloroisocyanurate) forms. Household bleach has an available chlorine content of 5.25%, or 52,500 ppm. For most purposes, a 1:10 dilution of bleach (approximately 0.5% or 5,000 ppm sodium hypochlorite) is recommended in the laboratory. Because of its oxidizing power, diluted bleach loses potency quickly and should be made fresh and used within the same day it is prepared. Bleach should be diluted with cold water in order to prevent breakdown of the disinfectant. The free available chlorine levels of hypochlorite solutions in both opened and closed polyethylene containers are reduced to 40% to 50% of the original concentration over a period of one month at room temperature.

Bleach should be stored between 50 and 70°F. Undiluted household bleach has a shelf life of six months to one year from the date of manufacture, after which it degrades at a rate of 20% each year until totally degraded to salt and water, and a 1:10 bleach solution has a shelf life of 24 hours.

There are two potential occupational exposure hazards when using hypochlorite solutions. The first is the production of the carcinogen bis-chloromethyl ether when hypochlorite solutions come in contact with formaldehyde. The second is the rapid production of chlorine gas when hypochlorite solutions are mixed with an acid. Care must also be exercised in using chlorine–based disinfectants, which can corrode or damage metal, rubber, and other susceptible surfaces. Bleached articles should never be autoclaved without reducing the bleach with sodium thiosulfate or sodium bisulfate.

Chloramine T, which is prepared from sodium hypochlorite and p-toluenesulfonamide, is a more stable, odorless, less corrosive form of chlorine but has decreased biocidal activitiy in comparison to bleach.

ii. Iodophors (e.g. Wescodyne)

Iodophors are used both as antiseptics and disinfectants, typically at a concentration of 25-1600 ppm of titratable iodine: for Wescodyne the recommended final concentration is 75 to 150ppm. Wescodyne, Betadyne, Povidone-Iodine and other iodophors are commercially available Iodine-based disinfectants, which give good control when the manufacturer’s instructions for formulation and application are followed. Iodophors should be diluted in cold water in order to prevent breakdown of the disinfectant.

An iodophor is a combination of iodine and a solubilizing agent or carrier; the resulting complex provides a sustained-release reservoir of iodine and releases small amounts of free iodine in aqueous solution. Antiseptic iodophors are not suitable for use as hard-surface disinfectants because they contain significantly less free iodine than do those formulated as disinfectants.

Alcohols work through the disruption of cellular membranes, solubilization of lipids, and denaturation of proteins by acting directly on S-H functional groups. Ethyl and isopropyl alcohols are the two most widely used alcohols for their biocidal activity. These alcohols are effective against lipid-containing viruses and a broad spectrum of bacterial species, but ineffective against spore-forming bacteria and many non-enveloped viruses. They evaporate rapidly, which makes extended contact times difficult to achieve unless the items are
immersed.

The optimum bactericidal concentration for ethanol and isopropanol is in the range of 70% to 85% by volume. Their cidal activity drops sharply when diluted below 50% concentration. Absolute alcohol is also not very effective. They are used to clean sensitive equipment and are generally regarded as being non-corrosive.

Due to the evaporative nature of the solution, aqueous alcohol is not recommended as the primary disinfectant of spills, especially in areas with significant airflow, such as a Biosafety cabinet. For surface decontamination, a spray, wipe, spray approach is recommended to achieve the desired contact time.

i. Glutaraldehyde

Glutaraldehyde is a colorless liquid and has the sharp, pungent odor typical of all aldehydes,  with an odor threshold of 0.04 parts per million (ppm). It is capable of sterilizing equipment, though to effect sterilization  often requires many hours of exposure. Two percent solutions of glutaraldehyde exhibit very good activity against vegetative  bacteria, spores and viruses. It is ten times more effective than formaldehyde and less toxic. However, it must be limited and controlled because of its toxic properties and hazards. It is important to avoid skin contact with glutaraldehyde as it has been documented to cause  skin sensitization. Glutaraldehyde is also an inhalation hazard. The NIOSH ceiling threshold limit value is 0.2 ppm.

Cidex, a commercially prepared glutaraldehyde disinfectant is used routinely for cold surface sterilization of clinical  instruments. Glutaraldehyde disinfectants should always be used in accordance with the manufacturer’s directions.

ii. Formaldehyde:

Fomaldehyde and its polymerized solid paraformaldehyde have broad-spectrum biocidal activity and are both effective for surface and space decontamination. As a liquid (5% concentration), formaldehyde is an effective liquid decontaminant. Its  biocidal action is through alkylation of carboxyl, hydroxyl and sulfhydryl groups on proteins and the ring nitrogen atoms of  purine bases. Formaldehyde’s drawbacks are reduction in efficacy at refrigeration temperature, its pungent, irritating odor, and several safety concerns. Formaldehyde is presently considered to be a carcinogen or a cancer-suspect agent according to several regulatory agencies. The OSHA 8-hour time-weighted exposure limit is 0.75 ppm.

Quaternary ammonium compounds are generally odorless, colorless, nonirritating, and deodorizing. They also have some detergent action, and they are good disinfectants. However, some quaternary ammonium compounds activity is reduced in the presence of some soaps or soap residues, detergents, acids and heavy organic matter loads. They are generally ineffective against viruses, spores and Mycobacterium tuberculosis. Basically these compounds are not suitable for any type of terminal disinfection. They are typically diluted to 0.1 to 2%.

The mode of action of these compounds is through inactivation of energy producing enzymes, denaturation of essential cell proteins, and disruption of the cell membrane. Many of these compounds are better used in water baths, incubators, and other applications where halide or phenolic residues are not desired.

Phenolics are phenol (carbolaic acid) derivatives and typically used at 1- 5% dilutions. These biocides  act through membrane damage and are effective against enveloped viruses, rickettsiae, fungi and vegetative bacteria. They also retain more activity in the presence of organic material than other disinfectants. Cresols, hexachlorophene, alkyl- and chloro derivatives and diphenyls are more active than phenol itself. Available commercial products include Lysol, Pine-Sol, Amphyl, O-Syl, Tergisyl, Vesphene, and LpH se.