ENVIRONMENTAL HEALTH & SAFETY

Disinfection

Back to Bleach Basics

Due to many EPA registered disinfectants being in high demand, common laboratory disinfectants are unavailable or backordered with long lead times. An effective alternative that kills a wide range of organisms and inactivates viruses that is inexpensive and already readily available in most labs is bleach.

A basic 10% solution of bleach can be made by diluting 1 part bleach with 9 parts water. To be effective, bleach solutions should remain wet on surfaces for at least 10 minutes or follow the contact time recommended by the manufacturer.

When handling bleach, be mindful that:

• Bleach is corrosive on metal surfaces, such as biosafety cabinet work surfaces. To prevent damage, after a sufficient contact time, rinse surfaces with sterile water or ethanol.
• Bleach is irritating to mucous membranes, eyes, and skin. Use appropriate PPE.
• Bleach may damage or discolor clothing and surfaces. Protect clothing and use caution around sensitive equipment.

The available chlorine in bleach rapidly degrades over time, with increased temperatures, and in light; therefore, solutions should be prepared at least weekly and preferably daily. Store bleach solutions in a closed, opaque container at room temperature. Never mix bleach with other chemicals, such as acids or ammonia, which can create hazardous gases.

Disinfection

Consult manufacturer directions to determine the efficacy of the disinfectant against the biohazards in your lab and be sure to allow for sufficient contact time. Some disinfectants appropriate for lab use include: household bleach (5-10% solution), quaternary ammonium compounds, and phenolic compounds.

When choosing a disinfectant consider the following:

• The microorganisms present
• The item to be disinfected or surface(s)
• Corrosivity or hazards associated with the chemicals in the disinfectant
• Ease of use

The Hospital Storeroom stocks a variety of approved disinfectants including bleach, "Cavicide"-a ready to use spray (quaternary ammonium with alcohol) and "Beaucoup"- a concentrated Phenolic.

70% Ethanol

Aqueous alcohol solutions are not appropriate for surface decontamination because of the evaporative nature of the solution; a contact time of ten minutes or more is necessary and not achievable using a 70% (v/v) aqueous solution of ethanol. 70% ethanol can be used to soak small pieces of surgical instruments and for wipe downs following a disinfectant (e.g., 10% bleach) that might leave a corrosive residue.

Difficult organisms

Some agents such as Cryptosporidium, Bacillus spores and prions are very resistant to the usual disinfectants. EHS Biosafety is available to assist you in determining the appropriate disinfectant and provides guidance on use of appropriate disinfection techniques and materials for researchers.

Bacillus spores

Clostridium difficile

Cryptosporidium

Prions, CJD

Summary and Comparison of Liquid Disinfectants

This information was provided to the University of Virginia by: