4.11 Disinfection Agents

4.11.1 Choosing A Disinfectant

Choose the most effective disinfectant(s) for your lab based on the following criteria:

• The type of biohazardous materials you are working with (fungal/ bacterial/ vegetative vs. spore formers, etc.) and their risk assessments.
• The degree of contamination you typically encounter.
• Whether organic material is/could be present which reduces effectiveness of some disinfectants.
• How the disinfectant works chemically, and in what quantity and concentration.
• What contact time and temperature is needed for disinfectant to be effective.
• How the disinfectant affects materials, such as corrosiveness, or leaving a residue on surfaces.
• What environmental impact it has, such as toxicity, creating noxious fumes, or being an irritant for the user.
• What sort of shelf life it has.
• How expensive it is.

Labs working with different biohazardous materials may find it necessary to stock several disinfectants to supply effective decontamination for all agents. See the following chart for general information on common types of disinfectants used in labs.

4.11.2 Bleach

Bleach dilutions are inactivated by organic matter and are corrosive to metal surfaces and the skin.

Contact with bleach can degrade disposable gloves.

Never use bleach in the presence of formaldehyde.

Never mix bleach with ammonia or acidic body fluids as toxic chlorine gas will be released.

Bleach disinfectant solutions must be made up fresh weekly as the effectiveness of sodium hypochlorite decreases rapidly with time.

Expiration dates of undiluted bleach and all other disinfectants must always be checked; up-to-date stocks must be maintained in the laboratory.

In the U.S., bleach designated for general purpose or household use was previously formulated between 5.25% and 6% (industrial strength bleaches are often formulated at concentrations greater than 20%). Leading manufacturers such as Clorox are now producing household bleach at 8.25%

Using Bleach as a Disinfectant

Precautions:

• Bleach-based disinfectants can cause skin, eye and lung irritation. Always wear appropriate PPE.
• Skin and eye protection must be worn when handling undiluted bleach solution.
• Make sure you are in a well-ventilated area.
• Bleach is corrosive to metal so all surfaces should be rinsed with water following contact with bleach.

For spills of material with large amounts or concentrations of organic matter (e.g., blood), liquid media:

• Dilution of standard household bleach (min. 5.25% sodium hypochlorite):
  • 1:5 dilution — 1 part bleach + 4 parts water, media, or contaminated liquid (e.g., 20 mls bleach + 80 mls water, media, or contaminated liquid)
• % Sodium Hypochlorite (NaOCl/ppm):
  • 1% NaOCl (10,000 ppm)

For surfaces with large amounts or concentrations of organic matter:

• Dilution of standard household bleach (min. 5.25% sodium hypochlorite):
  • 1:10 dilution — 1 part bleach + 9 parts water (e.g., 10 mls bleach + 90 mls water)
• % Sodium Hypochlorite (NaOCl/ppm):
  • .5% NaOCl (5,000 ppm)

For surfaces with low amounts or concentrations of organic material:

• Dilution of standard household bleach (min. 5.25% sodium hypochlorite):
  • 1:50 dilution — 1 part bleach + 49 parts water (e.g., 2 mls bleach + 98 mls water)
• % Sodium Hypochlorite (NaOCl/ppm):
  • .1% NaOCl (1,000 ppm)

4.11.3 Ethanol/Isopropanol

The disinfecting ability of ethyl alcohol and isopropyl alcohol drops sharply when either is diluted below 50%, or at dilutions higher than 90%. Optimum disinfection occurs at 70% in solution with water. Reason: Alcohol’s mode of action as a disinfectant is protein denaturation, and water supports the denaturing of proteins. Because pure alcohol is very dehydrating to microbial cell walls (which can interfere with protein denaturation) the presence of a certain amount of water in alcohol more readily denatures microbial proteins.

Avoid spraying alcohols on surfaces too thinly, resulting in quick evaporation and not enough contact time to achieve disinfection.

Frequently spraying disposable gloves with alcohol can increase their permeability to biological agents, as well as degrade gloves.