Decontamination is a process of removal, inactivation or destruction, by physical or chemical methods, of pathogenic microorganisms from surfaces or objects to the point where they are no longer capable of transmitting infectious particles, making them safe for handling, use or disposal.
The main objective of the decontamination procedures of materials, objects, instruments, equipment, surfaces, or environments in the biological laboratory is, therefore, to eliminate the possibility of transmission of pathogenic biological agents to a susceptible host, be it research personnel, other people or the environment. This measure acts directly on the first stages of the infection chain, destroying the pathogens, thus avoiding their presence or, depending on the method, limiting their number to levels that do not pose a threat.
- Types of decontamination
- Cleaning
- Disinfection
- Sterilization
- Dry heat or steam sterilization
- Chemical sterilization
- Sterilization by irradiation
- Further information
- Other sources
Types of decontamination
Decontamination can be carried out by cleaning, disinfection or sterilization, depending on the degree of decontamination sought.
To choose the decontamination method, the following aspects must be considered: the use for which the material or object is intended, the composition (resistance to the chosen treatment) and the risk of infection for the person handling it (type of agent and concentration).
It is important that decontamination procedures are clearly defined and defined to avoid human error or lack of proper application. It is highly recommended that all laboratories have a Check-list for manual cleaning and disinfection, defining the “what, who, how and when”, i.e., surfaces or materials to be decontaminated, people responsible for each task, guidelines to be followed and frequency.
The following is a description of the main decontamination methods and their characteristics: general principles, most common uses, agents used, risks and precautions to be taken by workers, etc.
Cleaning
It is the extraction of dirt and infectious focus, by mechanical and chemical action, using soap (or detergent) and water. It is not considered a disinfection method, but in order for the other decontamination methods to be effective, it is essential to first clean the surfaces or objects to be decontaminated.
The main cleaning procedures are:
- Manual cleaning by immersion.
- Manual cleaning without immersion.
- Mechanical cleaning (washing machines).
- Mechanical cleaning (ultrasound).
- Manual cleaning by immersion. It consists of the complete immersion of the objects in the cleaning solution in such a way as to ensure that both the cleaning agent and the cleaning instruments reach the present brutality. To accomplish this, it may be necessary to remove some elements of the object. The actual cleaning with brushes, water jet, etc. should be done below the surface of the cleaning solution. The process is completed with the scouring of the cleaning solution and a complete removal and drying of the rented elements.
- Manual cleaning (without immersion). It consists of the cleaning of the elements that cannot get wet. The process involves cleaning with cloths soaked in the cleaning solution, taking care that the solution does not penetrate the device. The process is completed with the rinsing and drying of the rented elements (manually or in drying chambers).
- Mechanical cleaning (washing machines). One of the most important aspects is the positioning of the devices in such a way as to allow maximum exposure and adequate circulation of water and detergent during the washing cycle, which passes through different stages at different temperatures, including a disinfectant rinse with hot water (minimum 71 °C for 3 minutes) and complete drying of the parts.
- Mechanical cleaning (ultrasound). Ultrasonic cleaning consists of cavitation due to air bubbles formed by the action of high-frequency and high intensity sound waves that break the adherence of dirt on surfaces.
Disinfection
It is the destruction, by chemical or physical methods, of microorganisms, but not of their forms of resistance such as some of the bacterial spores or encysted biological agents. Disinfection is carried out when the cleaning, by itself, does not guarantee the innocuousness in the foreseen use of an element. This is the intermediate level of decontamination, since it allows a decrease in the infectious focus.
The most common disinfection procedures are thermal processes (pasteurization, uperization, etc.), the use of chemical products or radiation (generally with UV light).
The level of disinfection obtained depends on several factors among which the following can be highlighted:
- The quantity and location of microorganisms.
- Resistance of microorganisms to disinfection methods
- The type and quantity of organic and inorganic matter present in the item to be disinfected.
- La temperatura i el temps que es troben exposats els elements contaminats amb el desinfectant.
- The pH of the solution and the hardness of the water used as diluent.
- Its harmfulness to the environment and to workers.
Sterilization
This method is the most exhaustive level of decontamination, consisting of a thermal, chemical or mixed process that destroys all forms of viable microorganisms, including spores, which are the most resistant. Consequently, it is the procedure of choice for all those objects, materials and instruments that will come into intimate contact with a person’s tissues. Likewise, it is the procedure of choice for laboratory material used in microbiology laboratories (pipettes, Petri dishes, culture media, etc.), avoiding contamination and alteration of the tests performed. Finally, it will be the method of decontamination of the waste generated during the activity, whether it is reusable or destined for disposal.
The main sterilization methods are:
Dry heat or steam sterilization
Hot air sterilization is useful for those elements that can withstand the following conditions:
| Temperature | 160-170 °C | 170-180 °C | 180-190 °C |
| Contact time | 120 min | 60 min | 30 min |
It is important to remember that the temperature must be reached throughout the entire delivery and maintained during the contact time for sterilization.
It is a less effective method than steam sterilization, but it is useful for sterilizing non-aqueous liquids (creams, ointments, fats, paraffins, glycerol, etc.) and elements that can be damaged by steam.
The steam sterilisation process is carried out in an autoclave and consists of exposing each element to direct contact with saturated water steam at the required pressure and temperature for the specified time.
| Temperature | 115 °C | 121 °C | 126 °C | 134 °C |
| Minimum contact time | 10 min | 60 min | 30 min | 3 min |
The use of this method is excluded for all materials that do not withstand temperatures between 121 °C and 134 °C.
Workers must wear thermal protection PPE against very hot elements.
Chemical sterilization
Sterilization is achieved by the chemical action of different compounds on microorganisms. These processes are characterized by their development at low temperatures, which makes them suitable for all materials sensitive to heat and steam.
The most frequently used chemical agents are ethylene oxide and hydrogen peroxide (gas-plasma).
Sterilization by irradiation
The disinfecting and sterilizing action of this procedure is directly related to the type of radiation used (penetration, intensity), the dose applied and the time of exposure of the object to the radiation.
Ultraviolet (UV) radiation is the most widely used in biological laboratories, but because of its low penetrating power, its use is limited to non-enveloped microorganisms (viruses, bacteria and fungi).
UV light can have negative aspects, as it can be toxic to people. It also presents penetration limitations on solid or opaque surfaces, as well as in humid environments.
Continuous exposure to this light can cause discolouration and degradation of some materials, especially plastics and textiles.
Its efficiency depends on the type of microorganism and the good condition of the light sources.
Further information
- You can consult the Public Health Agency of Canada’s Pathogen Safety Data Sheets and Risk Assessment-PSDS database of biological agents for various information on the main biological agents that may be present in the work environment; you will find data on their sensitivity to disinfectants.
- Also inAppendix 11. Decontamination and disinfection procedures of the Technical Guide of Biological Agents of the INSST, you can consult information about the most suitable decontamination methods according to the type of biological agent.