Environmental, Health and Safety Services

Disinfectants

What To Consider When 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, The Antimicrobial Spectrum of Disinfectants, for general information on common types of disinfectants used in labs.

(The Center for Food Security and Public Health, Iowa State U.)

Disinfectant Chart

Bleach

  • Bleach is the common, product name often used for this disinfectant. Sodium hypochlorite is the active ingredient in bleach that actually disinfects.
  • Bleach is an effective disinfectant but a poor cleaner. When both cleaning and disinfecting are needed, they must be done in a two-step process, where cleaning with a detergent is performed and allowed to completely dry prior to disinfection with bleach. Bleach is a reactive material that can form toxic compounds when mixed with other cleaning chemicals. Therefore do not mix bleach with a cleaner in an attempt to produce a one-step cleaner/disinfectant.
  • Bleach solutions are inactivated by the presence of organic matter, so physically remove organic material before disinfecting surfaces with bleach.
  • CDC recommendations for contact time: Wait ≥ 10 minutes after application of bleach solution before wiping nonporous surfaces; wait 30 minutes if immersing in bleach solution.
  • Bleach solutions are corrosive to metal surfaces and the skin. When disinfecting metal surfaces with a bleach solution, follow it with a sterile water rinse to avoid corrosion.
  • Contact with bleach can degrade disposable gloves.
  • Never use bleach in the presence of formaldehyde.
  • Never mix bleach with ammonia, as toxic chlorine gas will be released.
  • Bleach disinfectant solutions must be made up fresh weekly, if not daily, as the effectiveness of sodium hypochlorite decreases rapidly with time.
  • Expiration dates of undiluted bleach 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%, sometimes called "Ultra".
Using Bleach as a Disinfectant
Purpose Dilution of Standard Household Bleach
(min. 5.25% sodium hypochlorite)
% Sodium Hypochlorite (NaOCl / ppm) Precautions
Spills of material with large amounts or concentrations of organic matter (e.g., blood), liquid media 1:5 dilution

1 part bleach + 4 parts water or contaminated liquid

(e.g., 20 mls bleach + 80 mls water/media/contaminated liquid)
1% NaOCl

(10,000 ppm)
  • 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.
Surfaces with large amounts or concentrations of organic matter 1:10 dilution

1 part bleach + 9 parts water (e.g., 10 mls bleach + 90 mls water)
.5% NaOCl

(5,000 ppm)
Surfaces with low amounts or concentrations of organic material 1:50 dilution

1 part bleach + 49 parts water (e.g., 2 mls bleach + 98 mls water)
.1% NaOCl

(1000 ppm)
Liquid waste decontamination

(e.g., aspiration flasks, etc.)
1:5 dilution

1 part bleach + 4 parts water or liquid containing biohazardous material
1% NaOCl

(10,000 ppm)

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.
  • A minimum contact time of 10 minutes is necessary for disinfection using alcohols.
  • Air-drying of alcohol on surfaces (vs. wiping surfaces dry) can be practiced, due to the fact that alcohols do not leave residue behind. In many instances, air-drying is the preferred method.
  • Avoid spraying/applying alcohols on surfaces too thinly, resulting in quick evaporation and not enough contact time to achieve disinfection.
  • Frequently spraying disposable gloves with alcohol can degrade gloves and increase their permeability to biological agents.

Importance of Contact Time and Wiping Technique for Surface Disinfection

  • After applying a disinfectant to a surface, it is critical that you wait for the specified contact time to allow the active ingredient(s) in the disinfectant to be effective in killing microorganisms on the surface. Simply applying a greater volume of disinfectant to the surface does not lessen the contact time needed.
  • Wipe a surface in a grid pattern, proceeding in one direction that contacts each sector only once, vs. repeated circular wiping that can re-introduce dust, contaminants, etc. on your newly disinfected surface:

Further Information and Guidance:

BMBL, 5th Ed.