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.