Disinfectants all about
Air disinfectants are typically chemical substances capable of disinfecting microorganisms suspended in the air.
Disinfectants are generally assumed to be limited to use on surfaces, but that is not the case. In 1928, a study found that airborne microorganisms could be killed using mists of dilute bleach. An air disinfectant must be dispersed as either as an aerosol or vapour at a sufficient concentration in the air to cause the number of viable infectious microorganisms to be significantly reduced.
In the 1940s and early 1950s, further studies showed inactivation of diverse bacteria, influenza virus, and Penicillium chrysogenum (previously P. notatum) mould fungus using various glycols, principally propylene glycol and triethylene glycol.
In principle, these chemical substances are ideal air disinfectants because they have both high lethality to microorganisms and low mammalian toxicity.
Although glycols are effective air disinfectants in controlled laboratory environments, it is more difficult to use them effectively in real-world environments because the disinfection of air is sensitive to continuous action. Continuous action in real-world environments with outside air exchanges at door, HVAC, and window interfaces, and in the presence of materials that adsorb and remove glycols from the air, poses engineering challenges that are not critical for surface disinfection.
The engineering challenge associated with creating a sufficient concentration of the glycol vapours in the air have not to date been sufficiently addressed.
Alcohols, usually ethanol or isopropanol, are sometimes used as a disinfectant, but more often as an antiseptic (the distinction being that alcohol tends to be used on living tissue rather than nonliving surfaces). They are non-corrosive, but can be a fire hazard. They also have limited residual activity due to evaporation, which results in brief contact times unless the surface is submerged, and have a limited activity in the presence of organic material.
Alcohols are most effective when combined with purified water to facilitate diffusion through the cell membrane; 100% alcohol typically denatures only external membrane proteins.
A mixture of 70% ethanol or isopropanol diluted in water is effective against a wide spectrum of bacteria, though higher concentrations are often needed to disinfect wet surfaces.
Additionally, high-concentration mixtures (such as 80% ethanol + 5% isopropanol) are required to effectively inactivate lipid-enveloped viruses (such as HIV, hepatitis B, and hepatitis C).
Alcohol is, at best, only partly effective against most non-enveloped viruses (such as hepatitis A), and is not effective against fungal and bacterial spores.
Aldehydes, such as formaldehyde and glutaraldehyde, have a wide microbiocidal activity and are sporocidal and fungicidal. They are partly inactivated by organic matter and have slight residual activity.
Some bacteria have developed resistance to glutaraldehyde, and it has been found that glutaraldehyde can cause asthma and other health hazards; hence ortho-phthalaldehyde is replacing glutaraldehyde.
Oxidizing agents act by oxidizing the cell membrane of microorganisms, which results in a loss of structure and leads to cell lysis and death.
A large number of disinfectants operate in this way. Chlorine and oxygen are strong oxidizers, so their compounds figure heavily here.
Sodium hypochlorite is very commonly used. Common household bleach is a sodium hypochlorite solution and is used in the home to disinfect drains, toilets, and other surfaces.
In more dilute form, it is used in swimming pools, and in still more dilute form, it is used in drinking water. When pools and drinking water are said to be chlorinated, it is actually sodium hypochlorite or a related compound—not pure chlorine—that is being used.
Chlorine partly reacts with proteinaceous liquids such as blood to form non-oxidizing N-chloro compounds, and thus higher concentrations must be used if disinfecting surfaces after blood spills.
Other hypochlorites such as calcium hypochlorite are also used, especially as a swimming pool additive.
Hypochlorites yield an aqueous solution of hypochlorous acid that is the true disinfectant. Hypobromite solutions are also sometimes used.
Chloramine is often used in drinking water treatment.
Chloramine-T is antibacterial even after the chlorine has been spent.
Chlorine dioxide is used as an advanced disinfectant for drinking water to reduce waterborne diseases.
In certain parts of the world, it has largely replaced chlorine because it forms fewer by-products. Sodium chlorite, sodium chlorate, and potassium chlorate are used as precursors for generating chlorine dioxide.
Hydrogen peroxide is used in hospitals to disinfect surfaces and it is used in solution alone or in combination with other chemicals as a high level disinfectant. Hydrogen peroxide vapour is used as a medical sterilant and as room disinfectant. Hydrogen peroxide has the advantage that it decomposes to form oxygen and water thus leaving no long term residues, but hydrogen peroxide as with most other strong oxidants is hazardous, and solutions are a primary irritant. The vapour is hazardous to the respiratory system and eyes and consequently the OSHA permissible exposure limit is 1 ppm (29 CFR 1910.1000 Table Z-1) calculated as an eight hour time weighted average and the NIOSH immediately dangerous to life and health limit is 75 ppm.
Therefore, engineering controls, personal protective equipment, gas monitoring etc. should be employed where high concentrations of hydrogen peroxide are used in the workplace.
Hydrogen peroxide is sometimes mixed with colloidal silver. It is often preferred because it causes far fewer allergic reactions than alternative disinfectants.
Also used in the food packaging industry to disinfect foil containers.
A 3% solution is also used as an antiseptic. However, recent studies have shown hydrogen peroxide to be toxic to growing cells as well as bacteria; its use as an antiseptic is no longer recommended.
VHP is one of the chemicals approved for decontamination of anthrax spores from contaminated buildings, such as occurred during the 2001 anthrax attacks in the U.S.
It has also been shown to be effective in removing exotic animal viruses, such as avian influenza and Newcastle disease from equipment and surfaces.
Accelerated Hydrogen Peroxide
Accelerated Hydrogen Peroxide, also known as AHP, is a globally patented technology for cleaning, disinfection and sterilization. AHP is a synergistic blend of commonly used safe ingredients, that when combined with low levels of hydrogen peroxide, dramatically increase its germicidal potency and cleaning performance.
The inert ingredients, which include surfactants, wetting agents and chelating agents, are listed on the United States Environmental Protection Agency’s (EPA) and Health Canada Inerts lists in addition to the US Food and Drug Administration (FDA) Generally Regarded as Safe (GRAS) List.
The benefits and efficacy of AHP have been validated by third party clinical studies conducted by scientific organizations and third party researchers that are recognized by government regulatory agencies in Canada, the U.S and Europe.
The evidence available suggests that products based on Accelerated Hydrogen Peroxide, apart from being good germicides, are safer for humans and benign to the environment.
Iodine is usually dissolved in an organic solvent or as Lugol’s iodine solution.
It is used in the poultry industry. It is added to the birds’ drinking water.
Although no longer recommended because it increases both scar tissue formation and healing time, tincture of iodine has also been used as an antiseptic for skin cuts and scrapes.
Ozone is a gas that can be added to water for sanitation.
Acidic electrolyzed water is a strong oxidising solution made from the electrolysis of ordinary tap water in the presence of a specific amount of salt, generally sodium chloride.
Anolyte has a typical pH range of 3.5 to 8.5 and an Oxidation-Reduction Potential (ORP) of +600 to +1200 mV. The most powerful anolyte disinfecting solution is that produced at a controlled 5.0 to 6.3 pH where the predominant oxchlorine species is hypochlorous acid.
This environmentally-responsible disinfectant is highly efficacious against bacteria, fungus, mould, spores and other micro-organisms, in very short contact times. It may be applied as liquid, fog or ice.
Peracetic acid is a disinfectant produced by reacting hydrogen peroxide with acetic acid.
It is broadly effective against microorganisms and is not deactivated by catalase and peroxidase, the enzymes that break down hydrogen peroxide.
It also breaks down to food safe and environmentally friendly residues (acetic acid and hydrogen peroxide), and therefore can be used in non-rinse applications. It can be used over a wide temperature range (0-40°C), wide pH range (3.0-7.5), in clean-in-place (CIP) processes, in hard water conditions, and is not affected by protein residues.
Lactic acid is a registered disinfectant. Due to its natural and environmental profile, it has gained importance in the market.
Performic acid is the simplest and most powerful perorganic acid. Formed from the reaction of hydrogen peroxide and formic acid, it reacts more rapidly and powerfully than peracetic acid before breaking down to water and carbon dioxide.
Performic acid is the ultimate environmentally friendly oxidising biocide for all disinfection applications.
Potassium permanganate (KMnO4) is a red crystalline powder that colours everything it touches, through a strong oxidising action. This includes staining “stainless” steel, which somehow limits its use and makes it necessary to use plastic or glass containers.
It is used to disinfect aquariums and is also widely used widely in community swimming pools to disinfect ones feet before entering the pool.
Typically, a large shallow basin of KMnO4/water solution is kept near the pool ladder. Participants are required to step in the basin and then go into the pool.
Additionally, it is widely used to disinfect community water ponds and wells in tropical countries, as well as to disinfect the mouth before pulling out teeth.
It can be applied to wounds in dilute solution.
Potassium peroxymonosulfate, the principal ingredient in Virkon, is a wide-spectrum disinfectant used in laboratories. Virkon kills bacteria, viruses, and fungi. It is used as a 1% solution in water, and keeps for one week once it is made up.
It is expensive, but very effective; its pink colour fades as it is used up so it is possible to see at a glance if it is still fresh.
Phenolics are active ingredients in some household disinfectants. They are also found in some mouthwashes and in disinfectant soap and hand washes.
Phenol is probably the oldest known disinfectant as it was first used by Lister, when it was called carbolic acid.
It is rather corrosive to the skin and sometimes toxic to sensitive people. Impure preparations of phenol were originally made from coal tar, and these contained low concentrations of other aromatic hydrocarbons including benzene, which is an IARC Group 1 carcinogen.
O-Phenylphenol is often used instead of Phenol, since it is somewhat less corrosive.
Chloroxylenol is the principal ingredient in Dettol, a household disinfectant and antiseptic.
Hexachlorophene is a phenolic that was once used as a germicidal additive to some household products but was banned due to suspected harmful effects.
Thymol, derived from the herb thyme, is the active ingredient in the only 100% botanical disinfectant with an EPA registration (#74771-1), Benefect. Registered as “broad spectrum,” or hospital-grade, it is also the only disinfectant with a green certification, Environmental Choice.
Quaternary ammonium compounds
Quaternary ammonium compounds (“quats”), such as benzalkonium chloride, are a large group of related compounds. Some concentrated formulations have been shown to be effective low level disinfectants. Typically quats do NOT exhibit efficacy against difficult to kill non-enveloped viruses such as Norovirus, Rotavirus or Polio. Newer synergous, low alcohol formulations are highly effective broad spectrum disinfectants with quick contact times (3–5 minutes) against bacteria, enveloped viruses, Pathogenic Fungi and Mycobacteria.
Unfortunately, the addition of alcohol or solvents to quat based disinfectant formulas results in the products drying much more quickly on the applied surface which could lead to ineffective or incomplete disinfection.
Quats are biocides which also kill algae and are used as an additive in large-scale industrial water systems to minimize undesired biological growth.
The biguanide polymer polyaminopropyl biguanide is specifically bactericidal at very low concentrations (10 mg/l). It has a unique method of action: the polymer strands are incorporated into the bacterial cell wall, which disrupts the membrane and reduces its permeability, which has a lethal effect to bacteria.
It is also known to bind to bacterial DNA, alter its transcription, and cause lethal DNA damage. It has very low toxicity to higher organisms such as human cells, which have more complex and protective membranes.
High-intensity shortwave ultraviolet light can be used for disinfecting smooth surfaces such as dental tools, but not porous materials that are opaque to the light such as wood or foam. Ultraviolet light fixtures are often present in microbiology labs, and are activated only when there are no occupants in a room (e.g., at night).
Common sodium bicarbonate (NaHCO3) has disinfectant properties.
Measurements of effectiveness
One way to compare disinfectants is to compare how well they do against a known disinfectant and rate them accordingly. Phenol is the standard, and the corresponding rating system is called the “Phenol coefficient”.
The disinfectant to be tested is compared with phenol on a standard microbe (usually Salmonella typhi or Staphylococcus aureus). Disinfectants that are more effective than phenol have a coefficient > 1. Those that are less effective have a coefficient < 1.
A less specific measurement of effectiveness is the EPA classification into high, intermediate or low level of disinfection.
High-level disinfection kills all organisms, except high levels of bacterial spores, and is effected with a chemical germicide cleared for marketing as a sterilant by the FDA.
Intermediate-level disinfection kills mycobacteria, most viruses, and bacteria with a chemical germicide registered as a "tuberculocide" by the EPA.
Low-level disinfection kills some viruses and bacteria with a chemical germicide registered as a hospital disinfectant by the EPA.
So now you know most everything there is to know about cleaning and disinfectants and the combination of both. The million dollar question is: Are you comfortable with the concept that there are so many risks to be familiar with, that you are going to damage the environment, that you will potentially harm people or put their health at risk?