Ethidium Bromide

Ethidium bromide 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, MSU Chemical Safety recommends the following disposal procedures for ethidium bromide.

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.  MSU-CS recommends the following:

     Less than 0.1% ethidium bromide:  place in laboratory trash

     More than or equal to 0.1%:  place in biohazard box for incineration.

Ethidium Bromide Solutions

Solutions containing ethidium bromide should be deactivated, 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:

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.

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.

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, MSU-CS 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.  Schleicher and Schuell supply a commercial filter funnel kit that uses a packaged charcoal disk that is graduated for easily tracking the amount of aqueous solution calculated for fixed quantities of ethidium bromide residue.

     Filter the ethidium bromide solution through charcoal filter.

     Pour filtrate down the drain.

     Place charcoal filter in a sealed bag (e.g., zip-lock) and place in biohazardous 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 medical waste for incineration. 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 MSU-Chemical Safety at 994-7803.