Chemical Sterilization is the process of removal of microorganisms by the use of chemical bactericidal agents.
Even if physical methods of sterilization are more appropriate for effective sterilization, it is not always appropriate to use for heat-sensitive materials like plastics, fiber optics, and biological specimens.
Under such conditions, chemical either in liquid or gaseous state can be used for sterilization. However, it is crucial to ensure that the materials undergoing sterilization are compatible with the chemical being used.
Besides, it is important to adopt safety rules in the workplace safety during the use of chemical agents.
The chemical method of sterilization can be categorized as liquid and gaseous sterilization.
Gaseous sterilization involves the process of exposing equipment or devices to different gases in a closed heated or pressurized chamber.
Gaseous sterilization is a more effective technique as gases can pass through a tiny orifice and provide more effective results.
Besides, gases are commonly used along with heat treatment which also facilitates the functioning of the gases.
However, there is an issue of release of some toxic gases during the process which needs to be removed regularly from the system.
The mechanism of action is different for different types of gases.
Some of the common gases used for gaseous sterilization are explained below:
i. Ethylene oxide
Ethylene oxide (EO) gas is a common gas used for chemical treatment applied to sterilize, pasteurize, or disinfect different types of equipment and surfaces because of its wide range of compatibility with different materials.
EO treatment often replaces other sterilization techniques like heat, radiation, and even chemicals in cases where the objects are sensitive to these techniques.
This method is a widespread method used for almost 70% of all sterilizations and around 50% for disposable medical devices.
The mechanism of antimicrobial action of this gas is assumed to be through the alkylation of sulphydryl, amino, hydroxyl, and carboxyl groups on proteins and imino groups of nucleic acids.
EO treatment is usually conducted at the temperature range of 30-60°C for several hours which aids in the activity of the gas.
The efficacy of the gas depends on the concentration of gas available for each article which is greatly assisted by the good penetrating nature of the gas, which diffuses readily into many packaging materials including rubber, plastics, fabric, and paper.
Ethylene oxide kills all known microorganisms, such as bacteria (including spores), viruses, and fungi (including yeasts and molds), and is compatible with almost all materials even when repeatedly applied.
This process, however, is not without drawbacks as the level of gas in the sterilizer goes on decreasing due to absorption, and the treated articles need to undergo a process of desorption to remove the toxic residual wastes.
Organisms are more resistant to ethylene oxide treatment in a dried state, as are those protected from the gas by inclusion in crystalline or dried organic deposits.
Formaldehyde is another important highly reactive gas which is used for sterilization.
This gas is obtained by heating formalin (37%w/v) to a temperature of 70-80°C.
It possesses broad-spectrum biocidal activity and has found application in the sterilization of reusable surgical instruments, specific medical, diagnostic and electrical equipment, and the surface sterilization of powders.
Formaldehyde doesn’t have the same penetrating power of ethylene oxide but works on the same principle of modification of protein and nucleic acid.
As a result of the low penetrating power, its use is often limited to paper and cotton fabrics.
Formaldehyde can generally be detected by smell at concentrations lower than those permitted in the atmosphere and thus can be detected during leakage or other such accidents.
iii. Nitrogen dioxide (NO2)
Nitrogen dioxide is a rapid and effective sterilant that can be used for the removal of common bacteria, fungi, and even spores.
NO2 has a low boiling point (20°C) which allows a high vapor pressure at standard temperature.
This property of NO2 enables the use of the gas at standard temperature and pressure.
The biocidal action of this gas involves the degradation of DNA by the nitration of phosphate backbone, which results in lethal effects on the exposed organism as it absorbs NO2.
An advantage of this gas is that no condensation of the gas occurs on the surface of the devices because of the low level of gas used and the high vapor pressure. This avoids the need for direct aeration after the process of sterilization.
Ozone is a highly reactive industrial gas that is commonly used to sterilize air and water and as a disinfectant for surfaces.
Ozone is a potent oxidizing property that is capable of destroying a wide range of organisms including prions, without the use of hazardous chemicals as ozone is usually generated from medical-grade oxygen.
Similarly, the high reactivity of ozone allows the removal of waste ozone by converting the ozone into oxygen by passing it through a simple catalyst.
However, because ozone is an unstable and reactive gas, it has to be produced on-site, which limits the use of ozone in different settings.
It is also very hazardous and thus only be used at a concentration of 5ppm, which is 160 times less than that of ethylene oxide.