Decontamination of Ethidium Bromide Solution (Solutions containing >0.5mg/ml)

Ethidium Bromide (EtBr) is a powerfull mutagen and is moderatelly toxic. Gloves should be worn when working with solutions that contains this dye. After use, these solution should be decontaminated by one of the methods described below.

Decontamination of Concentrated Solutions of EtBr (Solutions containing >0.5 mg/ml)
Method 1
This method (Lunn and Sansone 1987) reduces the mutagenetic activity of EtBr in the Salmonella/ microsome assay by approximately 200-fold.

1. Add Sufficient water to reduce the concentration of EtBr to <0.5>
2. To the resulting solution, add 0.2 volume of fresh 5% hypophosphorous acid and 0.12 volume of fresh 0.5M sodium nitrite. Mix carefully. Check that the pH of the solution is <3.0.
   
3. After incubation for 24 hours at room temperature, add a large excess of 1M sodium bicarbonate. The solution may now be discarded.

note: Hypophosphorous acid is usually supplied as 50% solution, which is corrosive and should be handled with care. It should be freshly diluted immediatelly before use.
Sodium nitrite solution (0.5M) should be freshly prepared by dissloving 34.5 g of sodium nitrite in water to a final volume of 500 ml.

Method 2
This method (Quillardet and Hofnung 1988) reduces the mutagenenic activity of EtBr in Salmonella/microsome assay by approximately 300-fold. However, there are reports (Lunn and Sansone, 1987) of mutagenic activity in occasional batches of "blanks" treated with decontamination solutions.

1. Add sufficient water to reduce the concentration of ETBr to<0.5>
2. Add 1 volume of 0.5 M KMnO4. Mix carefully, and then add 1 volume of 2.5 N HCl. Mix carefully, and allow the solution to stand at room temperature for several hours. Caution:KMnO4 is irritant and is explosive. Solutions containing KMnO4 should be handled in a chemical hood.
3. Add 1 volume 0f 2.5 N NaOH. Mix carefully, and then discard the solution.