Office of Environmental Health and Safety

Ethidium Bromide

Ethidium bromide (EtBr) is commonly used in molecular biology laboratories.  While it is not regulated as hazardous waste, the mutagenic properties of this substance may present a hazard if it is poured down the drain untreated or placed in the trash.

Based on these considerations, the Office of Environmental Health and Safety (EH&S) recommends the following disposal procedures for ethidium bromide.  

Pure Ethidium Bromide

When purchasing Ethidium Bromide make sure that you purchase the smallest amount possible for your use. Stock quantities of unused Ethidium Bromide should be returned to the supplier if possible. You should also check with other investigators in your area to see if they could use the product. When all other means of distribution have been eliminated then you should call EH&S to pickup the unused product and add it to the RECY-Chem Program.

Electrophoresis Gels

Trace amounts of ethidium bromide in gels should not pose a hazard.  Higher concentrations, e.g., when the color of the gel is dark pink or red, should not be placed in laboratory trash.  EH&S recommends the following:

• Less than 0.1% ethidium bromide:  place in laboratory trash
• More than or equal to 0.1%:  place in biohazard bags and tag for pickup and incineration by Prospective Health.

Ethidium Bromide Solutions

• Aqueous solutions containing less than 10ug/ml EtBr can be released to the sanitary sewer. (Make sure you maintain a drain log).
• Aqueous solutions containing 10ug/ml EtBr or greater: Chemically degrade using the decontamination procedures listed below and dispose tothe sanitary sewer or collect for disposal by EH&S. (Make sure aqueous solutions released to sanitary sewer do not contain heavy metals, organics, cyanides or sulfides.)
• Solvent solutions containing any amount of ethidium bromide should be tagged for pickup by EH&S.
• Ethidium bromide mixed with a radioactive isotope should be picked up by Prospective Health.

All ethidium bromide solutions that are deactivated should be neutralized and poured down the drain with copious amounts of water.  Deactivation may be confirmed using UV light to detect fluorescence.  There are three recognized methods for deactivation:

Ethidium Bromide Deactivation Methods:

Armour Method

This is the simplest method, but is somewhat controversial.  One study found traces of mutagenic reaction mixtures using this method. (Lunn, G. and E. Sansone, Analytical Biochemistry, vol. 162, pp. 453-458, 1987)

• Combine equal amounts of ethidium bromide solution and household bleach.
• Stir constantly for four hours or let sit for 2-3 days.
• Adjust pH to 4-9 with sodium hydroxide.
• Pour down drain with copious amounts of water. (Be sure to note on your drain log)

Lunn and Sansone Method

For each 100 ml of ethidium bromide solution:

• Add 5% hypophosphorus acid.
• Add 12 ml of 0.5 M sodium nitrate.
• Stir briefly and let stand for 20 hours.
• Adjust pH to 4-9 using sodium hydroxide.
• Pour down drain with copious amounts of water. (Be sure to note on your drain log)

Quillardet and Hoffnung Method

This method uses 0.5 M potassium permanganate and 2.5 M hydrochloric acid.  Since chlorine gas may be released in significant concentration, EH&S does not recommend using this method.

Charcoal Filtration

Filtering the aqueous ethidium bromide waste solutions, free of other contaminants, through a bed of activated charcoal is a relatively simple and effective method for removal of ethidium bromide.  The  filtrate may be poured down the drain.   Commercial  filter funnel kits are available that use a packaged charcoal disk that is graduated for easily tracking the amount of aqueous solution calculated for a fixed quantities of ethidium bromide residue.  

• Filter the ethidium bromide solution through charcoal filter.
• Pour filtrate down the drain. (Be sure to note on your drain log)
• Place charcoal filter in a sealed bag (e.g., zip-lock) and place in biohazards waste box for incineration.

Gloves, Equipment and Debris

Gloves, test tubes, paper towels, etc., that are grossly contaminated with ethidium bromide should be placed in biohazard bags and labeled for pickup and incineration by Prospective Health.  Consider deactivating in bleach before disposal if the items are significantly contaminated.

If you have any questions about disposal of ethidium bromide or any other hazardous material, contact EH&S at 328-6166. Information for this web page was provided with permission from the Princeton University Environmental Health and Safety Office.

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