Introduction
10% bleach is recommended for disinfecting laboratory equipment and surfaces. For example, if you suspect nucleic acid (DNA/RNA) contamination of pipettes or surfaces, a 10% bleach solution can be made and sprayed on surfaces for 10 min before removing and following up with 70% ethanol.
Other Common Disinfectant Options Include:
70% isopropyl or ethanol alcohol for non-corrosive and rapid disinfection.
Commercial disinfectants approved for lab use (check manufacturer’s guidelines).
Outline
Various Names for Bleach
Why Bleach is an Effective Disinfectant
How to Prepare 10% Bleach for Disinfection
Why 70% Ethanol is an Effective Disinfectant
Combining Bleach and Ethanol in a Cleaning Regimen
Bleach
Bleach is known by various names depending on its composition, usage, or the context in which it is referred. Here are the common names for bleach:
General Names
Bleach: The most common name used in household and industrial contexts.
Chlorine bleach: Refers specifically to sodium hypochlorite solutions.
Non-chlorine bleach: Used for alternatives like hydrogen peroxide-based bleaches.
Chemical Names
Sodium hypochlorite (NaOCl): The active ingredient in liquid chlorine bleach.
Calcium hypochlorite (Ca(ClO)₂): A solid form of bleach often used in pool sanitization.
Sodium dichloroisocyanurate (NaDCC): A dry, granular form used for disinfection.
Potassium hypochlorite (KOCl): A less common alternative to sodium hypochlorite.
Scientific and Industrial Names
Hypochlorite solution: A generic term for sodium or calcium hypochlorite solutions.
Liquid chlorine: An industrial term for sodium hypochlorite in high concentrations.
Sodium oxychloride: Another term for sodium hypochlorite.
Informal and Regional Names
Liquid bleach: Common term for sodium hypochlorite solutions in many households.
Disinfectant bleach: Refers to bleach solutions marketed for sanitation and cleaning.
Jik® or Powerzone: Popular bleach brand in some African countries.
Why Bleach is an Effective Disinfectant
Bleach is the most widely used disinfectant from the chlorine family. They are typically sold commercially at a concentration that is between 5-8.25%. When preparing bleach, you assume the commercial concentration to be 100% (although it is not) and dilute it 1 in 10.
Bleach is a good choice because it has:
Broad-spectrum efficacy: Bleach is effective against a wide range of microorganisms, including bacteria, viruses, and fungi, which can harbor or transfer nucleic acids.
Readily available: Bleach is inexpensive and easily accessible in most laboratories.
Proven effectiveness: Numerous studies have demonstrated the effectiveness of bleach in decontaminating surfaces and equipment contaminated with nucleic acids.
How to Prepare 10% Sodium Hypochlorite for Disinfection
To prepare a 10% bleach solution, you need the stock sodium hypochlorite solution to be around 5%–6% sodium hypochlorite.
A 10% bleach solution means 10% of the final volume should be the stock bleach (sodium hypochlorite solution) and 90% should be water.
Steps:
Determine the volume of the final solution you need. For example, if you want 100 milliliters (100 mL) of 10% bleach:
Use 10 mL of stock sodium hypochlorite solution.
Add 90 mL of water.
Mix well to ensure the solution is homogeneous.
Considerations
Fresh Preparation: Prepare bleach solutions fresh daily as sodium hypochlorite degrades over time, especially when exposed to light or heat.
Safety: Use gloves and work in a well-ventilated area when preparing and using bleach solutions.
70% Ethanol as a Disinfectant
70% ethanol or isopropyl alcohol is a highly effective disinfectant and can kill a wide range of organisms. However, its efficacy depends on factors such as exposure time, concentration, and the type of microorganism. Here's a breakdown of what 70% alcohol can kill:
Bacteria
Gram-positive bacteria (e.g., Staphylococcus aureus, Streptococcus pneumoniae): Alcohol disrupts their lipid membranes, leading to cell death.
Gram-negative bacteria (e.g., Escherichia coli, Pseudomonas aeruginosa): Alcohol penetrates their thinner peptidoglycan layers effectively.
Mycobacteria (e.g., Mycobacterium tuberculosis): 70% alcohol is effective, but longer contact time is needed due to their waxy cell wall.
Viruses
Enveloped viruses: Alcohol dissolves the lipid envelope, inactivating the virus. Examples include:
Influenza virus
SARS-CoV-2 (the virus causing COVID-19)
HIV
Herpes simplex virus (HSV)
Non-enveloped (naked) viruses: 70% alcohol is less effective or ineffective against non-enveloped viruses, such as:
Norovirus
Hepatitis A virus
Rotavirus
Fungi
Yeasts: Effective against organisms like Candida albicans.
Molds: Alcohol can kill spores of many fungi but may require longer exposure times.
Spores
Bacterial spores (e.g., Clostridium difficile, Bacillus spp.):
Alcohol is generally ineffective against spores because they have tough, resistant structures that alcohol cannot penetrate.
Protozoa
Effective against vegetative forms (active, feeding stage), but not against cysts (dormant, resistant stage). Examples:
Vegetative Giardia lamblia can be killed, but cysts may survive.
Why 70% Alcohol Is Effective
Mechanism of Action:
Alcohol denatures proteins and disrupts lipid membranes.
Optimal Concentration:
70% alcohol is more effective than higher concentrations (e.g., 95%) because water assists in protein denaturation and slows evaporation, allowing better penetration of cell walls.
Organisms That Are Resistant
Endospores (e.g., Clostridium botulinum, Bacillus anthracis).
Non-enveloped viruses (e.g., Norovirus).
Some protozoan cysts.
How to Prepare 70% Ethanol for Disinfection
To prepare a 70% bleach solution, you need the stock ethanol solution to be around 100%.
A 70% ethanol solution means 70% of the final volume should be the stock ethanol and 30% should be water.
Steps:
Determine the volume of the final solution you need. For example, if you want 100 millilitres (100 mL) of 70% bleach:
Use 70 mL of stock ethanol solution.
Add 30 mL of water.
Mix well to ensure the solution is homogeneous.
Considerations
70% ethanol or isopropyl alcohol effectively kills most bacteria, enveloped viruses, yeasts, and molds, but is not effective against bacterial spores, certain non-enveloped viruses, and protozoan cysts. Always use alcohol with adequate exposure time (at least 30 seconds to a few minutes) to maximise its efficacy.
Some cleaning and disinfection protocols use both bleach (sodium hypochlorite) and alcohol (ethanol or isopropanol) in combination or sequentially to maximize microbial elimination.
Combining Bleach and Ethanol in a Cleaning Regimen
First Clean with Bleach (10% dilution)
Kills spores, hardy bacteria, and viruses.
However, bleach leaves residue, which may be corrosive or irritating.
Follow with Alcohol (70%)
Helps remove bleach residue.
Enhances drying and prevents damage to sensitive equipment.
This is because each disinfectant has strengths and limitations, and using both ensures broader-spectrum effectiveness.
NB: Do NOT mix bleach and alcohol directly – this can create toxic chloroform gas, which is highly dangerous.
Conclusion
Use Bleach (10%) when killing all microbes, including spores, is necessary (e.g., spill cleanup, surfaces in biosafety labs).
Use 70% Alcohol for quick disinfection of non-porous surfaces and electronic equipment where bleach may cause damage.
Bibliography
CDC (Centers for Disease Control and Prevention). (2023, November 28). Chemical Disinfectants [Web page]. Retrieved from https://www.cdc.gov/infection-control/hcp/disinfection-sterilization/chemical-disinfectants.html
World Health Organization (WHO). (2014). Infection prevention and control of epidemic- and pandemic-prone acute respiratory infections in health care. Geneva: World Health Organization.
Gallandat, K., Kolus, R. C., Julian, T. R., & Lantagne, D. S. (2020). A systematic review of chlorine-based surface disinfection efficacy to inform recommendations for low-resource outbreak settings. American Journal of Infection Control, 49(1), 90–103.
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